Re: [EVDL] Alibaba/Aliexpress Lithium

[Dan Baker via EV]

> Hello everyone
> Sorry to dig up an old post but wanted to share some updates.  After some
> time and conversing with a few sellers on Aliexpress, I found a company
> that was responsive and honest to my questions. At the time of looking and
> conversing with these folk, Aliexpress/ GTK had an anniversary sale and I
> was able to get a further 15% off my order.  I ordered in April a 96v
> 100a/h battery, 10 amp charger, and BMS.  The battery and BMS were
> assembled in a nice steel case weighting about 95lbs.  I haven't opened the
> case yet but have been told it is a 26s2p pouch cell configuration.  The
> BMS is a popular one that frequents ebay/amazon etc, has no display but has
> a bluetooth interface.  The app is quite good, I can see all 26 pairs of
> batteries status, 6 points of temperature, a/h draw, lifetime a/h that has
> come out of pack.  All in, it cost me about 2050 US to get it to my
> doorstep. Shipping and customs was paid for by the seller.  It took about
> 45 days for it to get here, although I was told it would only take 15-20.
> They spent almost 4 weeks before they shipped, and claimed because of the
> sale they were very backlogged.  This made me very nervous at the time.  I
> did however manage to have payment through paypal, which provided some
> comfort over Aliexpress' unknown to me pay system.   At the time, I debated
> building my own pack with Tesla packs as there were some packs on ebay that
> were close in price.  Unfortunately where I really wanted 96v I would have
> needed 4 packs which was far more capacity than I needed.  I also read that
> the Tesla bus bars could be cut to make it 48v instead of 24v per pack but
> really didn't want to get into that risk.   The pack I purchased
> surprisingly has almost the same watt/kg as a Tesla S/X pack, although the
> C rating is much lower.
> So how does it all work?  Very well, I am both very happy and surprised at
> the improvement it has brought to my boat.  With doubling my pack voltage,
> I was able to discard a chain gear setup to make my prop go fast enough.
> This has significantly reduced noise and vibration.  As well, with twice
> the voltage my amps have dropped and my temperatures across all components
> have as well.   With the chain system gone, I also had enough room to
> finally employ a water cooling system on my Mars ME-1003, a copper coil
> wrapped around the motor running off a small bilge pump in the outboard
> leg.  My temps there are about half what they were before with an auxiliary
> fan.  Switching 460lbs of lead acid for 95lbs has made a significant
> difference in range, speed and efficiency. I have been running the boat the
> last 6 weeks and cautiously testing it.  I expected about a 1.8x range
> improvement, however it is closer to 2.5x.  I have gone 3 loops on my lake
> on one charge and still had 23% SOC left.  In the past, measurements of
> power at a outlet showed about 5.6 KW to refuel a lap of the lake (about 3
> miles), now it is taking on average  3.7.  The boat is faster with the same
> power applied - 96v 50 amps is 3-4km faster than the old leads at 48v 100
> amps.
> I would say the only fault I found so far with my Aliexpress purchase was
> the standard cord that came with the charger.  It was was too thin for the
> charger on hi-mode, got very warm.  I replaced it with a heavier cord, no
> issues since.
>
>  If anyone has any questions I would be happy to answer them.  Thank you
> all on the EVDL that helped!
>
> http://www.evalbum.com/4767
>
> Cheers
> Dan
>
> On Mon, Mar 18, 2019 at 2:00 PM Dan Baker  wrote:
>
>> Thanks Paul.   Yeah not quite the same but somewhat similar.  I'm
>> assuming that the Alibaba battery would have a higher finishing voltage
>> ~108 volts vs the Tesla pack which would be 24s or 100.8.  I should also be
>> able to push a lot more amps out of a Tesla pack if required down the
>> road.  I like the fact that the Tesla pack is likely much more configurable
>> as the voltage/ amperage is what I use for BMS/ cell layout but also dont
>> like it for the same reason lol.  I can be great to dangerous in my
>> projects.  It's down to the unknown turn-key solution vs DIY. using known
>> good (but used) products ,
>>
>> On Mon, Mar 18, 2019 at 12:39 PM paul dove  wrote:
>>
>>> Well, I am not sure you are comparing apples to apples. All Lithium Ion
>>> batteries are not equal in power density or energy density.
>>>
>>> A Tesla model S battery cell goes up to 4.2 volts.
>>> 2modules x 4.2V x 444cells x 2.8Ah = 10.4kW
>>> So 2 x modules of 6s74p (444 cells) =10.4kWh
>>>
>>> While your 96v100ah pack on Aliexpress may be Lithium Iron Phosphate
>>> 96 x 100 = 9.6Kw and may have lower discharge rates.
>>>
>>> On Monday, March 18, 2019, 7:19:01 AM CDT, Dan Baker via EV <
>>> ev@lists.evdl.org> wrote:
>>>
>>>
>>> Thank you everyone for the great response so far.  I am still
>>> communicating
>>> with a few Aliexpress sellers although it has been quite frustrating.  So
>>> far no

Re: [EVDL] Alibaba/Aliexpress Lithium

[Dan Baker via EV]

Thanks Paul.   Yeah not quite the same but somewhat similar.  I'm assuming
that the Alibaba battery would have a higher finishing voltage ~108 volts
vs the Tesla pack which would be 24s or 100.8.  I should also be able to
push a lot more amps out of a Tesla pack if required down the road.  I like
the fact that the Tesla pack is likely much more configurable as the
voltage/ amperage is what I use for BMS/ cell layout but also dont like it
for the same reason lol.  I can be great to dangerous in my projects.  It's
down to the unknown turn-key solution vs DIY. using known good (but used)
products ,

On Mon, Mar 18, 2019 at 12:39 PM paul dove  wrote:

> Well, I am not sure you are comparing apples to apples. All Lithium Ion
> batteries are not equal in power density or energy density.
>
> A Tesla model S battery cell goes up to 4.2 volts.
> 2modules x 4.2V x 444cells x 2.8Ah = 10.4kW
> So 2 x modules of 6s74p (444 cells) =10.4kWh
>
> While your 96v100ah pack on Aliexpress may be Lithium Iron Phosphate
> 96 x 100 = 9.6Kw and may have lower discharge rates.
>
> On Monday, March 18, 2019, 7:19:01 AM CDT, Dan Baker via EV <
> ev@lists.evdl.org> wrote:
>
>
> Thank you everyone for the great response so far.  I am still communicating
> with a few Aliexpress sellers although it has been quite frustrating.  So
> far none have been able to give me any documentation on these packs- cell
> type and count, string info, bms used, etc.  I have been able to weed a few
> out by reviews and overzealous claims.  Product weight seems to be a tell
> tale as well, how can a pack weight half as much as other packs and have
> the same claimed a/h rating?
>
> After some more digging this weekend I have found a Canadian seller of used
> Tesla packs.  I think I can get 2 x modules of 6s74p (444 cells) from a low
> mileage 2015 P85D for around the same price as a 96v100ah pack on
> Aliexpress.  I would still have to buy a BMS and likely a charger.  I have
> saw some articles on cutting the bus bars and turning it them into 12s37p
> packs so I could get 2 x 48v packs and 96 volts total so I can eliminate my
> noisy gear set.  I could also buy 4 packs but that would be way more pack
> that I need at this time.  Anyone ever hack a Tesla pack to make it 48
> volts?
>
> Cheers
> Dan
>
> On Sun, Mar 17, 2019 at 6:20 AM Steve Heath via EV 
> wrote:
>
> > Michael:  totally agree. At the cell level you are right and in the end
> > the user has to take responsibility. The challenge facing people that a
> > single Liion cell is not going to cut it so they have to be assembled
> > into packs and that is where the differences start coming out. What
> > follows is that cell level properties do not automatically
> > follow/scale/apply to the battery pack.
> >
> > At the cell level Liion shows virtually zero  Peukerts effect. At the
> > pack level with a BMS, it will. The cause is very different though.
> >
> > At the cell level, 0%age discharge is not damaging. At the pack level,
> > cells can go out of balance and potentially short out. BMS will prevent
> > the 0%age from being reached as part of the system level management
> > strategy.
> >
> > At the cell level, there is nothing stopping Liion cells from being
> > connected in parallel or series. At the pack level, parallel operation
> > is not a problem but in series, the BMS can fail.
> >
> > At the cell level, you can extract all the capacity. At the pack level,
> > this is difficult with the BMS applied. So if 100aH is the minimum
> > needed in reality, a bigger capacity battery is needed.
> >
> > I think the problem is that we have become so used to treating cells
> > like lego that it is easy to forget about the care and management side
> > of Liion. Equally it can be very confusing when cell level and system
> > level data/behaviour is compared because they can be almost
> > contradictory which makes it very confusing to people trying to
> > understand what is going on.
> >
> >
> >
> > On 17/03/2019 04:10, Michael Ross via EV wrote:
> > > Steve, the ratings are per cell. WHat else is there to do?  No
> management
> > > is needed as with a pack. Measuring the capacity of a cell is pretty
> > > straightforward. It is up to the user to determine the needed capacity
> > of a
> > > pack and how to take care of it.
> > >
> > > On Sat, Mar 16, 2019 at 6:31 PM Steve Heath via EV 
> > > wrote:
> > >
> > >> There are lies, damn lies and battery AH data.
> > >>
> > >> Yes you are right in that even with a "100aH Liion battery" I would
> > >> derate it by 80% or so because of the BMS and so on.
> > >> The problem with many Ah figures is that you do not know how they were
> > >> measured. Is this with or without the BMS?
> > >>
> > >> Most companies take the aH from each cell in the series string and add
> > >> them up. Some pluck a figure out of the air!
> > >>
> > >> 80% of the manufacturer figure is a good place to start but that might
> > >> be a tad high in my experience with those size of currents.

Re: [EVDL] Alibaba/Aliexpress Lithium

[paul dove via EV]

 Well, I am not sure you are comparing apples to apples. All Lithium Ion 
batteries are not equal in power density or energy density.
A Tesla model S battery cell goes up to 4.2 volts. 
2modules x 4.2V x 444cells x 2.8Ah = 10.4kW
So 2 x modules of 6s74p (444 cells) =10.4kWh
While your 96v100ah pack on Aliexpress may be Lithium Iron Phosphate 
96 x 100 = 9.6Kw and may have lower discharge rates.

On Monday, March 18, 2019, 7:19:01 AM CDT, Dan Baker via EV 
 wrote:  
 
 Thank you everyone for the great response so far.  I am still communicating
with a few Aliexpress sellers although it has been quite frustrating.  So
far none have been able to give me any documentation on these packs- cell
type and count, string info, bms used, etc.  I have been able to weed a few
out by reviews and overzealous claims.  Product weight seems to be a tell
tale as well, how can a pack weight half as much as other packs and have
the same claimed a/h rating?

After some more digging this weekend I have found a Canadian seller of used
Tesla packs.  I think I can get 2 x modules of 6s74p (444 cells) from a low
mileage 2015 P85D for around the same price as a 96v100ah pack on
Aliexpress.  I would still have to buy a BMS and likely a charger.  I have
saw some articles on cutting the bus bars and turning it them into 12s37p
packs so I could get 2 x 48v packs and 96 volts total so I can eliminate my
noisy gear set.  I could also buy 4 packs but that would be way more pack
that I need at this time.  Anyone ever hack a Tesla pack to make it 48
volts?

Cheers
Dan

On Sun, Mar 17, 2019 at 6:20 AM Steve Heath via EV 
wrote:

> Michael:  totally agree. At the cell level you are right and in the end
> the user has to take responsibility. The challenge facing people that a
> single Liion cell is not going to cut it so they have to be assembled
> into packs and that is where the differences start coming out. What
> follows is that cell level properties do not automatically
> follow/scale/apply to the battery pack.
>
> At the cell level Liion shows virtually zero  Peukerts effect. At the
> pack level with a BMS, it will. The cause is very different though.
>
> At the cell level, 0%age discharge is not damaging. At the pack level,
> cells can go out of balance and potentially short out. BMS will prevent
> the 0%age from being reached as part of the system level management
> strategy.
>
> At the cell level, there is nothing stopping Liion cells from being
> connected in parallel or series. At the pack level, parallel operation
> is not a problem but in series, the BMS can fail.
>
> At the cell level, you can extract all the capacity. At the pack level,
> this is difficult with the BMS applied. So if 100aH is the minimum
> needed in reality, a bigger capacity battery is needed.
>
> I think the problem is that we have become so used to treating cells
> like lego that it is easy to forget about the care and management side
> of Liion. Equally it can be very confusing when cell level and system
> level data/behaviour is compared because they can be almost
> contradictory which makes it very confusing to people trying to
> understand what is going on.
>
>
>
> On 17/03/2019 04:10, Michael Ross via EV wrote:
> > Steve, the ratings are per cell. WHat else is there to do?  No management
> > is needed as with a pack. Measuring the capacity of a cell is pretty
> > straightforward. It is up to the user to determine the needed capacity
> of a
> > pack and how to take care of it.
> >
> > On Sat, Mar 16, 2019 at 6:31 PM Steve Heath via EV 
> > wrote:
> >
> >> There are lies, damn lies and battery AH data.
> >>
> >> Yes you are right in that even with a "100aH Liion battery" I would
> >> derate it by 80% or so because of the BMS and so on.
> >> The problem with many Ah figures is that you do not know how they were
> >> measured. Is this with or without the BMS?
> >>
> >> Most companies take the aH from each cell in the series string and add
> >> them up. Some pluck a figure out of the air!
> >>
> >> 80% of the manufacturer figure is a good place to start but that might
> >> be a tad high in my experience with those size of currents.
> >>
> >> Steve
> >>
> >>
> >> On 16/03/2019 21:51, Dan Baker via EV wrote:
> >>> Wow, lots of learning here.  So with Lithium, a safe BMS cut-off
> >> typically
> >>> kicks around when there is less than 20% remaining? So the a/h ratings
> >>> typically (and when truthfully) displayed are actually 20% less?  100
> a/h
> >>> battery is typically only 80 a/h?  This is fine as I know you can't get
> >>> 100% of out lead either.  I looked up my SBS-170f lead's datasheet, to
> >> take
> >>> the cells to 1.80VPc (half discharged I believe) will happen with 116
> >> amps
> >>> for 1 hour.  This is recommended bottom voltage and I typically see
> that
> >>> with my boat as the draw is pretty constant when cruising.  To take the
> >>> leads all the way to near complete discharge (damaging but not
> >> exploding) -
> >>> 1.60 Vpc the amps 

Re: [EVDL] Alibaba/Aliexpress Lithium

[Dan Baker via EV]

Thank you everyone for the great response so far.  I am still communicating
with a few Aliexpress sellers although it has been quite frustrating.  So
far none have been able to give me any documentation on these packs- cell
type and count, string info, bms used, etc.  I have been able to weed a few
out by reviews and overzealous claims.  Product weight seems to be a tell
tale as well, how can a pack weight half as much as other packs and have
the same claimed a/h rating?

After some more digging this weekend I have found a Canadian seller of used
Tesla packs.  I think I can get 2 x modules of 6s74p (444 cells) from a low
mileage 2015 P85D for around the same price as a 96v100ah pack on
Aliexpress.  I would still have to buy a BMS and likely a charger.  I have
saw some articles on cutting the bus bars and turning it them into 12s37p
packs so I could get 2 x 48v packs and 96 volts total so I can eliminate my
noisy gear set.  I could also buy 4 packs but that would be way more pack
that I need at this time.  Anyone ever hack a Tesla pack to make it 48
volts?

Cheers
Dan

On Sun, Mar 17, 2019 at 6:20 AM Steve Heath via EV 
wrote:

> Michael:  totally agree. At the cell level you are right and in the end
> the user has to take responsibility. The challenge facing people that a
> single Liion cell is not going to cut it so they have to be assembled
> into packs and that is where the differences start coming out. What
> follows is that cell level properties do not automatically
> follow/scale/apply to the battery pack.
>
> At the cell level Liion shows virtually zero  Peukerts effect. At the
> pack level with a BMS, it will. The cause is very different though.
>
> At the cell level, 0%age discharge is not damaging. At the pack level,
> cells can go out of balance and potentially short out. BMS will prevent
> the 0%age from being reached as part of the system level management
> strategy.
>
> At the cell level, there is nothing stopping Liion cells from being
> connected in parallel or series. At the pack level, parallel operation
> is not a problem but in series, the BMS can fail.
>
> At the cell level, you can extract all the capacity. At the pack level,
> this is difficult with the BMS applied. So if 100aH is the minimum
> needed in reality, a bigger capacity battery is needed.
>
> I think the problem is that we have become so used to treating cells
> like lego that it is easy to forget about the care and management side
> of Liion. Equally it can be very confusing when cell level and system
> level data/behaviour is compared because they can be almost
> contradictory which makes it very confusing to people trying to
> understand what is going on.
>
>
>
> On 17/03/2019 04:10, Michael Ross via EV wrote:
> > Steve, the ratings are per cell. WHat else is there to do?  No management
> > is needed as with a pack. Measuring the capacity of a cell is pretty
> > straightforward. It is up to the user to determine the needed capacity
> of a
> > pack and how to take care of it.
> >
> > On Sat, Mar 16, 2019 at 6:31 PM Steve Heath via EV 
> > wrote:
> >
> >> There are lies, damn lies and battery AH data.
> >>
> >> Yes you are right in that even with a "100aH Liion battery" I would
> >> derate it by 80% or so because of the BMS and so on.
> >> The problem with many Ah figures is that you do not know how they were
> >> measured. Is this with or without the BMS?
> >>
> >> Most companies take the aH from each cell in the series string and add
> >> them up. Some pluck a figure out of the air!
> >>
> >> 80% of the manufacturer figure is a good place to start but that might
> >> be a tad high in my experience with those size of currents.
> >>
> >> Steve
> >>
> >>
> >> On 16/03/2019 21:51, Dan Baker via EV wrote:
> >>> Wow, lots of learning here.  So with Lithium, a safe BMS cut-off
> >> typically
> >>> kicks around when there is less than 20% remaining? So the a/h ratings
> >>> typically (and when truthfully) displayed are actually 20% less?  100
> a/h
> >>> battery is typically only 80 a/h?  This is fine as I know you can't get
> >>> 100% of out lead either.  I looked up my SBS-170f lead's datasheet, to
> >> take
> >>> the cells to 1.80VPc (half discharged I believe) will happen with 116
> >> amps
> >>> for 1 hour.  This is recommended bottom voltage and I typically see
> that
> >>> with my boat as the draw is pretty constant when cruising.  To take the
> >>> leads all the way to near complete discharge (damaging but not
> >> exploding) -
> >>> 1.60 Vpc the amps for one hour is 125 amps so not much more.  So with a
> >> 200
> >>> ah pack I can expect about 1.6 hours of run time at 100 amps?   In
> >> reality
> >>> I think I can probably get closer to 2 hours if I keep the speed the
> same
> >>> and reduce the amps as the weight loss will dramatically reduce water
> >>> drag.
> >>>
> >>> On Sat, Mar 16, 2019 at 6:08 PM Bill Dube via EV 
> >> wrote:
>  No Paul, Lee is indeed referring to the rate of discharge chart,
>  howev

Re: [EVDL] Alibaba/Aliexpress Lithium

[Steve Heath via EV]

Michael:  totally agree. At the cell level you are right and in the end 
the user has to take responsibility. The challenge facing people that a 
single Liion cell is not going to cut it so they have to be assembled 
into packs and that is where the differences start coming out. What 
follows is that cell level properties do not automatically 
follow/scale/apply to the battery pack.


At the cell level Liion shows virtually zero  Peukerts effect. At the 
pack level with a BMS, it will. The cause is very different though.


At the cell level, 0%age discharge is not damaging. At the pack level, 
cells can go out of balance and potentially short out. BMS will prevent 
the 0%age from being reached as part of the system level management 
strategy.


At the cell level, there is nothing stopping Liion cells from being 
connected in parallel or series. At the pack level, parallel operation 
is not a problem but in series, the BMS can fail.


At the cell level, you can extract all the capacity. At the pack level, 
this is difficult with the BMS applied. So if 100aH is the minimum 
needed in reality, a bigger capacity battery is needed.


I think the problem is that we have become so used to treating cells 
like lego that it is easy to forget about the care and management side 
of Liion. Equally it can be very confusing when cell level and system 
level data/behaviour is compared because they can be almost 
contradictory which makes it very confusing to people trying to 
understand what is going on.




On 17/03/2019 04:10, Michael Ross via EV wrote:

Steve, the ratings are per cell. WHat else is there to do?  No management
is needed as with a pack. Measuring the capacity of a cell is pretty
straightforward. It is up to the user to determine the needed capacity of a
pack and how to take care of it.

On Sat, Mar 16, 2019 at 6:31 PM Steve Heath via EV 
wrote:


There are lies, damn lies and battery AH data.

Yes you are right in that even with a "100aH Liion battery" I would
derate it by 80% or so because of the BMS and so on.
The problem with many Ah figures is that you do not know how they were
measured. Is this with or without the BMS?

Most companies take the aH from each cell in the series string and add
them up. Some pluck a figure out of the air!

80% of the manufacturer figure is a good place to start but that might
be a tad high in my experience with those size of currents.

Steve


On 16/03/2019 21:51, Dan Baker via EV wrote:

Wow, lots of learning here.  So with Lithium, a safe BMS cut-off

typically

kicks around when there is less than 20% remaining? So the a/h ratings
typically (and when truthfully) displayed are actually 20% less?  100 a/h
battery is typically only 80 a/h?  This is fine as I know you can't get
100% of out lead either.  I looked up my SBS-170f lead's datasheet, to

take

the cells to 1.80VPc (half discharged I believe) will happen with 116

amps

for 1 hour.  This is recommended bottom voltage and I typically see that
with my boat as the draw is pretty constant when cruising.  To take the
leads all the way to near complete discharge (damaging but not

exploding) -

1.60 Vpc the amps for one hour is 125 amps so not much more.  So with a

200

ah pack I can expect about 1.6 hours of run time at 100 amps?   In

reality

I think I can probably get closer to 2 hours if I keep the speed the same
and reduce the amps as the weight loss will dramatically reduce water
drag.

On Sat, Mar 16, 2019 at 6:08 PM Bill Dube via EV 

wrote:

No Paul, Lee is indeed referring to the rate of discharge chart,
however, he has chosen the cut-off to be _*3 volts*_, rather than the
customary cut-off of_*2.5 volts*_. (No one uses a cut-off of 3 volts,
that I am aware of. All the charts note that 2.5v cut-off is the
standard for comparison. If we picked 3.5 volts as the cut-off, we would
get a huge spread in the apparent capacity, but that would be silly.)

You are correct that the 12 minute discharge (0.2C rate), the 0.5C rate,
and the 1C rate all show the same capacity, 3.25 mA-hr. While the 2 hour
discharge (2C rate) shows a slightly elevated capacity of  3.350 mA.

   I suspect that the faster rates had some unavoidable internal
heating, (even though the case temperature was held at a constant 25
degrees Celsius,) which tends to decrease the internal resistance, and
tends to raise the terminal voltage under load, especially when the
impedance rises near the end. Thus, the apparent capacity shift is quite
likely due to increased internal temperature rather than ion diffusion.

   Lead acid curves would have shown a much greater sensitivity to

the

discharge rate. Much greater. As I said earlier, the ions can diffuse
perhaps 100 times more quickly in Li-Ion cells than in lead-acid cells,
which makes the Puekert exponent very close to unity in Li_ion. Puekert
is not really useful in Li_ion because the diffusion is so fast in

Li-Ion.

Bill D.


On 3/17/2019 12:40 AM, paul dove via EV wrote:

That’s not wha

Re: [EVDL] Alibaba/Aliexpress Lithium

[Michael Ross via EV]

Steve, the ratings are per cell. WHat else is there to do?  No management
is needed as with a pack. Measuring the capacity of a cell is pretty
straightforward. It is up to the user to determine the needed capacity of a
pack and how to take care of it.

On Sat, Mar 16, 2019 at 6:31 PM Steve Heath via EV 
wrote:

> There are lies, damn lies and battery AH data.
>
> Yes you are right in that even with a "100aH Liion battery" I would
> derate it by 80% or so because of the BMS and so on.
> The problem with many Ah figures is that you do not know how they were
> measured. Is this with or without the BMS?
>
> Most companies take the aH from each cell in the series string and add
> them up. Some pluck a figure out of the air!
>
> 80% of the manufacturer figure is a good place to start but that might
> be a tad high in my experience with those size of currents.
>
> Steve
>
>
> On 16/03/2019 21:51, Dan Baker via EV wrote:
> > Wow, lots of learning here.  So with Lithium, a safe BMS cut-off
> typically
> > kicks around when there is less than 20% remaining? So the a/h ratings
> > typically (and when truthfully) displayed are actually 20% less?  100 a/h
> > battery is typically only 80 a/h?  This is fine as I know you can't get
> > 100% of out lead either.  I looked up my SBS-170f lead's datasheet, to
> take
> > the cells to 1.80VPc (half discharged I believe) will happen with 116
> amps
> > for 1 hour.  This is recommended bottom voltage and I typically see that
> > with my boat as the draw is pretty constant when cruising.  To take the
> > leads all the way to near complete discharge (damaging but not
> exploding) -
> > 1.60 Vpc the amps for one hour is 125 amps so not much more.  So with a
> 200
> > ah pack I can expect about 1.6 hours of run time at 100 amps?   In
> reality
> > I think I can probably get closer to 2 hours if I keep the speed the same
> > and reduce the amps as the weight loss will dramatically reduce water
> > drag.
> >
> > On Sat, Mar 16, 2019 at 6:08 PM Bill Dube via EV 
> wrote:
> >
> >> No Paul, Lee is indeed referring to the rate of discharge chart,
> >> however, he has chosen the cut-off to be _*3 volts*_, rather than the
> >> customary cut-off of_*2.5 volts*_. (No one uses a cut-off of 3 volts,
> >> that I am aware of. All the charts note that 2.5v cut-off is the
> >> standard for comparison. If we picked 3.5 volts as the cut-off, we would
> >> get a huge spread in the apparent capacity, but that would be silly.)
> >>
> >> You are correct that the 12 minute discharge (0.2C rate), the 0.5C rate,
> >> and the 1C rate all show the same capacity, 3.25 mA-hr. While the 2 hour
> >> discharge (2C rate) shows a slightly elevated capacity of  3.350 mA.
> >>
> >>   I suspect that the faster rates had some unavoidable internal
> >> heating, (even though the case temperature was held at a constant 25
> >> degrees Celsius,) which tends to decrease the internal resistance, and
> >> tends to raise the terminal voltage under load, especially when the
> >> impedance rises near the end. Thus, the apparent capacity shift is quite
> >> likely due to increased internal temperature rather than ion diffusion.
> >>
> >>   Lead acid curves would have shown a much greater sensitivity to
> the
> >> discharge rate. Much greater. As I said earlier, the ions can diffuse
> >> perhaps 100 times more quickly in Li-Ion cells than in lead-acid cells,
> >> which makes the Puekert exponent very close to unity in Li_ion. Puekert
> >> is not really useful in Li_ion because the diffusion is so fast in
> Li-Ion.
> >>
> >> Bill D.
> >>
> >>
> >> On 3/17/2019 12:40 AM, paul dove via EV wrote:
> >>> That’s not what the spec sheet says. You are reading the graph for
> >> temperature variations. There is almost no difference due to discharge
> >> rates. 2C is 3250 and 0.5C is 3350 according to your spec sheet.
> >>> And lead acid batteries have a Puekert coefficient as low as 1.08.
> >>>
> >>> Sent from my iPhone
> >>>
>  On Mar 15, 2019, at 9:14 AM, Steve Heath via EV 
> >> wrote:
>  Peukert's law is not an actual law but an empirical formula that is
> >> based on actual physical measurements. It gives an approximate estimate
> of
> >> how much capacity can be obtained. The way that it is used is that the
> >> capacity is measured at different discharge rates to give a co-efficient
> >> that can then be applied to other batteries.  This is where the
> difficulty
> >> lies. The coefficient is taken by measurement and providing another
> battery
> >> is the same then the coefficient is applicable. If not and it isn't.
>  The key point is that the discharge curves for li ion batteries do
> vary
> >> significantly depending on the load in real life according to the
> >> manufacturer data.  At the 0% soc end point, the capacities are the same
> >> (give or take). This is why the Peukerts coefficient is close to 1
> rather
> >> than 1.2 or higher for a lead acid battery. Hence the comment that it is
> >> not applicable.

Re: [EVDL] Alibaba/Aliexpress Lithium

[Michael Ross via EV]

Dan Baker,

There is nothing wrong with taking a Li ion cell down to 0%SOC (which is
not a great idea with PbSO4). The problem is when you have a multitude of
them there is some variation between them. Over time, they get misaligned
in terms of capacity. There are cell balancing routines to help even them
out. You want them aligned at the low end of SOC so that they all come down
to the same level near but not at 0%SOC. If you don't and one goes to 0% an
you keep discharging the pack that low cell can reverse and short out.

That short circuit can cause damage. You don't want to risk heat and its
bad effects, nor do you want to hurt other costly cells in the pack. Smart
pack manufacturers like Tesla have a fusible link in series with every
cell, even if there are 7000 of them, then if a cell shorts it just blows
its fuse and is no longer in the pack functionally.

So you only get the top 50% soc WITH PbSO4, but with Li ion you get the top
80%, or 90% of capacity, whatever you can successfully manage.

Cell management is a very important piece of the puzzle for anyone using
batteries for a vehicle whether DIY or OEM, lead or lithium.

You said:
"100 a/h battery is typically only 80 a/h?"

No cell manufacturer is being disingenuous telling you the full capacity of
the cells.  It is up to the application and the designer to determine how,
and how much of that capacity can be used.


On Sat, Mar 16, 2019 at 8:20 PM Dan Baker via EV  wrote:

> Wow, lots of learning here.  So with Lithium, a safe BMS cut-off typically
> kicks around when there is less than 20% remaining? So the a/h ratings
> typically (and when truthfully) displayed are actually 20% less?  100 a/h
> battery is typically only 80 a/h?  This is fine as I know you can't get
> 100% of out lead either.  I looked up my SBS-170f lead's datasheet, to take
> the cells to 1.80VPc (half discharged I believe) will happen with 116 amps
> for 1 hour.  This is recommended bottom voltage and I typically see that
> with my boat as the draw is pretty constant when cruising.  To take the
> leads all the way to near complete discharge (damaging but not exploding) -
> 1.60 Vpc the amps for one hour is 125 amps so not much more.  So with a 200
> ah pack I can expect about 1.6 hours of run time at 100 amps?   In reality
> I think I can probably get closer to 2 hours if I keep the speed the same
> and reduce the amps as the weight loss will dramatically reduce water
> drag.
>
> On Sat, Mar 16, 2019 at 6:08 PM Bill Dube via EV 
> wrote:
>
> > No Paul, Lee is indeed referring to the rate of discharge chart,
> > however, he has chosen the cut-off to be _*3 volts*_, rather than the
> > customary cut-off of_*2.5 volts*_. (No one uses a cut-off of 3 volts,
> > that I am aware of. All the charts note that 2.5v cut-off is the
> > standard for comparison. If we picked 3.5 volts as the cut-off, we would
> > get a huge spread in the apparent capacity, but that would be silly.)
> >
> > You are correct that the 12 minute discharge (0.2C rate), the 0.5C rate,
> > and the 1C rate all show the same capacity, 3.25 mA-hr. While the 2 hour
> > discharge (2C rate) shows a slightly elevated capacity of  3.350 mA.
> >
> >  I suspect that the faster rates had some unavoidable internal
> > heating, (even though the case temperature was held at a constant 25
> > degrees Celsius,) which tends to decrease the internal resistance, and
> > tends to raise the terminal voltage under load, especially when the
> > impedance rises near the end. Thus, the apparent capacity shift is quite
> > likely due to increased internal temperature rather than ion diffusion.
> >
> >  Lead acid curves would have shown a much greater sensitivity to the
> > discharge rate. Much greater. As I said earlier, the ions can diffuse
> > perhaps 100 times more quickly in Li-Ion cells than in lead-acid cells,
> > which makes the Puekert exponent very close to unity in Li_ion. Puekert
> > is not really useful in Li_ion because the diffusion is so fast in
> Li-Ion.
> >
> > Bill D.
> >
> >
> > On 3/17/2019 12:40 AM, paul dove via EV wrote:
> > > That’s not what the spec sheet says. You are reading the graph for
> > temperature variations. There is almost no difference due to discharge
> > rates. 2C is 3250 and 0.5C is 3350 according to your spec sheet.
> > >
> > > And lead acid batteries have a Puekert coefficient as low as 1.08.
> > >
> > > Sent from my iPhone
> > >
> > >> On Mar 15, 2019, at 9:14 AM, Steve Heath via EV 
> > wrote:
> > >>
> > >> Peukert's law is not an actual law but an empirical formula that is
> > based on actual physical measurements. It gives an approximate estimate
> of
> > how much capacity can be obtained. The way that it is used is that the
> > capacity is measured at different discharge rates to give a co-efficient
> > that can then be applied to other batteries.  This is where the
> difficulty
> > lies. The coefficient is taken by measurement and providing another
> battery
> > is the same then t

Re: [EVDL] Alibaba/Aliexpress Lithium

[Steve Heath via EV]

There are lies, damn lies and battery AH data.

Yes you are right in that even with a "100aH Liion battery" I would 
derate it by 80% or so because of the BMS and so on.
The problem with many Ah figures is that you do not know how they were 
measured. Is this with or without the BMS?


Most companies take the aH from each cell in the series string and add 
them up. Some pluck a figure out of the air!


80% of the manufacturer figure is a good place to start but that might 
be a tad high in my experience with those size of currents.


Steve


On 16/03/2019 21:51, Dan Baker via EV wrote:

Wow, lots of learning here.  So with Lithium, a safe BMS cut-off typically
kicks around when there is less than 20% remaining? So the a/h ratings
typically (and when truthfully) displayed are actually 20% less?  100 a/h
battery is typically only 80 a/h?  This is fine as I know you can't get
100% of out lead either.  I looked up my SBS-170f lead's datasheet, to take
the cells to 1.80VPc (half discharged I believe) will happen with 116 amps
for 1 hour.  This is recommended bottom voltage and I typically see that
with my boat as the draw is pretty constant when cruising.  To take the
leads all the way to near complete discharge (damaging but not exploding) -
1.60 Vpc the amps for one hour is 125 amps so not much more.  So with a 200
ah pack I can expect about 1.6 hours of run time at 100 amps?   In reality
I think I can probably get closer to 2 hours if I keep the speed the same
and reduce the amps as the weight loss will dramatically reduce water
drag.

On Sat, Mar 16, 2019 at 6:08 PM Bill Dube via EV  wrote:


No Paul, Lee is indeed referring to the rate of discharge chart,
however, he has chosen the cut-off to be _*3 volts*_, rather than the
customary cut-off of_*2.5 volts*_. (No one uses a cut-off of 3 volts,
that I am aware of. All the charts note that 2.5v cut-off is the
standard for comparison. If we picked 3.5 volts as the cut-off, we would
get a huge spread in the apparent capacity, but that would be silly.)

You are correct that the 12 minute discharge (0.2C rate), the 0.5C rate,
and the 1C rate all show the same capacity, 3.25 mA-hr. While the 2 hour
discharge (2C rate) shows a slightly elevated capacity of  3.350 mA.

  I suspect that the faster rates had some unavoidable internal
heating, (even though the case temperature was held at a constant 25
degrees Celsius,) which tends to decrease the internal resistance, and
tends to raise the terminal voltage under load, especially when the
impedance rises near the end. Thus, the apparent capacity shift is quite
likely due to increased internal temperature rather than ion diffusion.

  Lead acid curves would have shown a much greater sensitivity to the
discharge rate. Much greater. As I said earlier, the ions can diffuse
perhaps 100 times more quickly in Li-Ion cells than in lead-acid cells,
which makes the Puekert exponent very close to unity in Li_ion. Puekert
is not really useful in Li_ion because the diffusion is so fast in Li-Ion.

Bill D.


On 3/17/2019 12:40 AM, paul dove via EV wrote:

That’s not what the spec sheet says. You are reading the graph for

temperature variations. There is almost no difference due to discharge
rates. 2C is 3250 and 0.5C is 3350 according to your spec sheet.

And lead acid batteries have a Puekert coefficient as low as 1.08.

Sent from my iPhone


On Mar 15, 2019, at 9:14 AM, Steve Heath via EV 

wrote:

Peukert's law is not an actual law but an empirical formula that is

based on actual physical measurements. It gives an approximate estimate of
how much capacity can be obtained. The way that it is used is that the
capacity is measured at different discharge rates to give a co-efficient
that can then be applied to other batteries.  This is where the difficulty
lies. The coefficient is taken by measurement and providing another battery
is the same then the coefficient is applicable. If not and it isn't.

The key point is that the discharge curves for li ion batteries do vary

significantly depending on the load in real life according to the
manufacturer data.  At the 0% soc end point, the capacities are the same
(give or take). This is why the Peukerts coefficient is close to 1 rather
than 1.2 or higher for a lead acid battery. Hence the comment that it is
not applicable. It is there but very small to be accurate.  However at a
typical self preservation point e.g   cutoff voltage used by BMS, the
capacities are different. As a result, there is a "Peukerts" effect where
the amount of capacity that can be obtained is different depending on the
discharge current. It is not the same Peukerts effect but the end result is
the same. Discharge more, less capacity...

The data sheet for a Panasonic 18650 shows this effect very well (

https://www.batteryspace.com/prod-specs/NCR18650B.pdf ) where a cut off
voltage of 3v gives a capacity of 2400mAh at 2c and 3300 mAh  at 0.2C .  At
the 0% soc point they all come out at 3300 and 3400. So d

Re: [EVDL] Alibaba/Aliexpress Lithium

[Steve Heath via EV]

Thanks Paul. I thought it was a simple misunderstanding.

On 16/03/2019 21:07, Bill Dube via EV wrote:
No Paul, Lee is indeed referring to the rate of discharge chart, 
however, he has chosen the cut-off to be _*3 volts*_, rather than the 
customary cut-off of_*2.5 volts*_. (No one uses a cut-off of 3 volts, 
that I am aware of. All the charts note that 2.5v cut-off is the 
standard for comparison. If we picked 3.5 volts as the cut-off, we 
would get a huge spread in the apparent capacity, but that would be 
silly.)
It's Steve actually but no offence taken. I selected 3 v as it has a 
nice horizontal line  with which to visually drop the perpendiculars. 
And yes 3v is a bit high for a cut off voltage. The BMS I use is set at 
2.85v but some will go lower or higher. The actual voltage will depend 
on the battery cutoff voltage itself which does vary from manufacturer 
to manufacturer. Some quote2.5v but others higher like 2.8 or 2.9. The 
end result is that the more current you discharge at the less capacity 
you will get. The BMS needs to be set at a high enough point to stop 
discharge to 0% but low enough to get a reasonable capacity.


You are correct that the 12 minute discharge (0.2C rate), the 0.5C 
rate, and the 1C rate all show the same capacity, 3.25 mA-hr. While 
the 2 hour discharge (2C rate) shows a slightly elevated capacity of  
3.350 mA.


    I suspect that the faster rates had some unavoidable internal 
heating, (even though the case temperature was held at a constant 25 
degrees Celsius,) which tends to decrease the internal resistance, and 
tends to raise the terminal voltage under load, especially when the 
impedance rises near the end. Thus, the apparent capacity shift is 
quite likely due to increased internal temperature rather than ion 
diffusion.


    Lead acid curves would have shown a much greater sensitivity to 
the discharge rate. Much greater. As I said earlier, the ions can 
diffuse perhaps 100 times more quickly in Li-Ion cells than in 
lead-acid cells, which makes the Puekert exponent very close to unity 
in Li_ion. Puekert is not really useful in Li_ion because the 
diffusion is so fast in Li-Ion.


To be honest Peukert is not a law but an empirical formula that is 
specific to the battery type and conditions which makes its use not very 
accurate at all. It does describe an effect (but not explains why it 
happens) and the coefficient gives an indication of the depth or 
severity of the effect. Yes you can do the calculations to as many 
decimal points as you want but the error still might be +/- 20% or more!







On 3/17/2019 12:40 AM, paul dove via EV wrote:
That’s not what the spec sheet says. You are reading the graph for 
temperature variations. There is almost no difference due to 
discharge rates. 2C is 3250 and 0.5C is 3350 according to your spec 
sheet.


And lead acid batteries have a Puekert coefficient as low as 1.08.

Sent from my iPhone

On Mar 15, 2019, at 9:14 AM, Steve Heath via EV  
wrote:


Peukert's law is not an actual law but an empirical formula that is 
based on actual physical measurements. It gives an approximate 
estimate of how much capacity can be obtained. The way that it is 
used is that the capacity is measured at different discharge rates 
to give a co-efficient that can then be applied to other batteries.  
This is where the difficulty lies. The coefficient is taken by 
measurement and providing another battery is the same then the 
coefficient is applicable. If not and it isn't.


The key point is that the discharge curves for li ion batteries do 
vary significantly depending on the load in real life according to 
the manufacturer data.  At the 0% soc end point, the capacities are 
the same (give or take). This is why the Peukerts coefficient is 
close to 1 rather than 1.2 or higher for a lead acid battery. Hence 
the comment that it is not applicable. It is there but very small to 
be accurate. However at a typical self preservation point e.g   
cutoff voltage used by BMS, the capacities are different. As a 
result, there is a "Peukerts" effect where the amount of capacity 
that can be obtained is different depending on the discharge 
current. It is not the same Peukerts effect but the end result is 
the same. Discharge more, less capacity...


The data sheet for a Panasonic 18650 shows this effect very well ( 
https://www.batteryspace.com/prod-specs/NCR18650B.pdf ) where a cut 
off voltage of 3v gives a capacity of 2400mAh at 2c and 3300 mAh  at 
0.2C .  At the 0% soc point they all come out at 3300 and 3400. So 
discharging to 0% soc, the discharge current is more or less 
irrelevant. Interestingly these results are taken at constant cell 
temperature where any overheating advantage is not applicable. 
Without seeing the complete paper that was referred to, it is 
difficult to know if any comparison with manufacturer data was made 
or whether tests were done at constant temperature and what the 
results were.


Discharging to a lo

Re: [EVDL] Alibaba/Aliexpress Lithium

[Dan Baker via EV]

Wow, lots of learning here.  So with Lithium, a safe BMS cut-off typically
kicks around when there is less than 20% remaining? So the a/h ratings
typically (and when truthfully) displayed are actually 20% less?  100 a/h
battery is typically only 80 a/h?  This is fine as I know you can't get
100% of out lead either.  I looked up my SBS-170f lead's datasheet, to take
the cells to 1.80VPc (half discharged I believe) will happen with 116 amps
for 1 hour.  This is recommended bottom voltage and I typically see that
with my boat as the draw is pretty constant when cruising.  To take the
leads all the way to near complete discharge (damaging but not exploding) -
1.60 Vpc the amps for one hour is 125 amps so not much more.  So with a 200
ah pack I can expect about 1.6 hours of run time at 100 amps?   In reality
I think I can probably get closer to 2 hours if I keep the speed the same
and reduce the amps as the weight loss will dramatically reduce water
drag.

On Sat, Mar 16, 2019 at 6:08 PM Bill Dube via EV  wrote:

> No Paul, Lee is indeed referring to the rate of discharge chart,
> however, he has chosen the cut-off to be _*3 volts*_, rather than the
> customary cut-off of_*2.5 volts*_. (No one uses a cut-off of 3 volts,
> that I am aware of. All the charts note that 2.5v cut-off is the
> standard for comparison. If we picked 3.5 volts as the cut-off, we would
> get a huge spread in the apparent capacity, but that would be silly.)
>
> You are correct that the 12 minute discharge (0.2C rate), the 0.5C rate,
> and the 1C rate all show the same capacity, 3.25 mA-hr. While the 2 hour
> discharge (2C rate) shows a slightly elevated capacity of  3.350 mA.
>
>  I suspect that the faster rates had some unavoidable internal
> heating, (even though the case temperature was held at a constant 25
> degrees Celsius,) which tends to decrease the internal resistance, and
> tends to raise the terminal voltage under load, especially when the
> impedance rises near the end. Thus, the apparent capacity shift is quite
> likely due to increased internal temperature rather than ion diffusion.
>
>  Lead acid curves would have shown a much greater sensitivity to the
> discharge rate. Much greater. As I said earlier, the ions can diffuse
> perhaps 100 times more quickly in Li-Ion cells than in lead-acid cells,
> which makes the Puekert exponent very close to unity in Li_ion. Puekert
> is not really useful in Li_ion because the diffusion is so fast in Li-Ion.
>
> Bill D.
>
>
> On 3/17/2019 12:40 AM, paul dove via EV wrote:
> > That’s not what the spec sheet says. You are reading the graph for
> temperature variations. There is almost no difference due to discharge
> rates. 2C is 3250 and 0.5C is 3350 according to your spec sheet.
> >
> > And lead acid batteries have a Puekert coefficient as low as 1.08.
> >
> > Sent from my iPhone
> >
> >> On Mar 15, 2019, at 9:14 AM, Steve Heath via EV 
> wrote:
> >>
> >> Peukert's law is not an actual law but an empirical formula that is
> based on actual physical measurements. It gives an approximate estimate of
> how much capacity can be obtained. The way that it is used is that the
> capacity is measured at different discharge rates to give a co-efficient
> that can then be applied to other batteries.  This is where the difficulty
> lies. The coefficient is taken by measurement and providing another battery
> is the same then the coefficient is applicable. If not and it isn't.
> >>
> >> The key point is that the discharge curves for li ion batteries do vary
> significantly depending on the load in real life according to the
> manufacturer data.  At the 0% soc end point, the capacities are the same
> (give or take). This is why the Peukerts coefficient is close to 1 rather
> than 1.2 or higher for a lead acid battery. Hence the comment that it is
> not applicable. It is there but very small to be accurate.  However at a
> typical self preservation point e.g   cutoff voltage used by BMS, the
> capacities are different. As a result, there is a "Peukerts" effect where
> the amount of capacity that can be obtained is different depending on the
> discharge current. It is not the same Peukerts effect but the end result is
> the same. Discharge more, less capacity...
> >>
> >> The data sheet for a Panasonic 18650 shows this effect very well (
> https://www.batteryspace.com/prod-specs/NCR18650B.pdf ) where a cut off
> voltage of 3v gives a capacity of 2400mAh at 2c and 3300 mAh  at 0.2C .  At
> the 0% soc point they all come out at 3300 and 3400. So discharging to 0%
> soc, the discharge current is more or less irrelevant. Interestingly these
> results are taken at constant cell temperature where any overheating
> advantage is not applicable. Without seeing the complete paper that was
> referred to, it is difficult to know if any comparison with manufacturer
> data was made or whether tests were done at constant temperature and what
> the results were.
> >>
> >> Discharging to a lower 15-20% level to

Re: [EVDL] Alibaba/Aliexpress Lithium

[Bill Dube via EV]

No Paul, Lee is indeed referring to the rate of discharge chart, 
however, he has chosen the cut-off to be _*3 volts*_, rather than the 
customary cut-off of_*2.5 volts*_. (No one uses a cut-off of 3 volts, 
that I am aware of. All the charts note that 2.5v cut-off is the 
standard for comparison. If we picked 3.5 volts as the cut-off, we would 
get a huge spread in the apparent capacity, but that would be silly.)


You are correct that the 12 minute discharge (0.2C rate), the 0.5C rate, 
and the 1C rate all show the same capacity, 3.25 mA-hr. While the 2 hour 
discharge (2C rate) shows a slightly elevated capacity of  3.350 mA.


    I suspect that the faster rates had some unavoidable internal 
heating, (even though the case temperature was held at a constant 25 
degrees Celsius,) which tends to decrease the internal resistance, and 
tends to raise the terminal voltage under load, especially when the 
impedance rises near the end. Thus, the apparent capacity shift is quite 
likely due to increased internal temperature rather than ion diffusion.


    Lead acid curves would have shown a much greater sensitivity to the 
discharge rate. Much greater. As I said earlier, the ions can diffuse 
perhaps 100 times more quickly in Li-Ion cells than in lead-acid cells, 
which makes the Puekert exponent very close to unity in Li_ion. Puekert 
is not really useful in Li_ion because the diffusion is so fast in Li-Ion.


Bill D.


On 3/17/2019 12:40 AM, paul dove via EV wrote:

That’s not what the spec sheet says. You are reading the graph for temperature 
variations. There is almost no difference due to discharge rates. 2C is 3250 
and 0.5C is 3350 according to your spec sheet.

And lead acid batteries have a Puekert coefficient as low as 1.08.

Sent from my iPhone


On Mar 15, 2019, at 9:14 AM, Steve Heath via EV  wrote:

Peukert's law is not an actual law but an empirical formula that is based on 
actual physical measurements. It gives an approximate estimate of how much 
capacity can be obtained. The way that it is used is that the capacity is 
measured at different discharge rates to give a co-efficient that can then be 
applied to other batteries.  This is where the difficulty lies. The coefficient 
is taken by measurement and providing another battery is the same then the 
coefficient is applicable. If not and it isn't.

The key point is that the discharge curves for li ion batteries do vary significantly 
depending on the load in real life according to the manufacturer data.  At the 0% soc end 
point, the capacities are the same (give or take). This is why the Peukerts coefficient 
is close to 1 rather than 1.2 or higher for a lead acid battery. Hence the comment that 
it is not applicable. It is there but very small to be accurate.  However at a typical 
self preservation point e.g   cutoff voltage used by BMS, the capacities are different. 
As a result, there is a "Peukerts" effect where the amount of capacity that can 
be obtained is different depending on the discharge current. It is not the same Peukerts 
effect but the end result is the same. Discharge more, less capacity...

The data sheet for a Panasonic 18650 shows this effect very well ( 
https://www.batteryspace.com/prod-specs/NCR18650B.pdf ) where a cut off voltage 
of 3v gives a capacity of 2400mAh at 2c and 3300 mAh  at 0.2C .  At the 0% soc 
point they all come out at 3300 and 3400. So discharging to 0% soc, the 
discharge current is more or less irrelevant. Interestingly these results are 
taken at constant cell temperature where any overheating advantage is not 
applicable. Without seeing the complete paper that was referred to, it is 
difficult to know if any comparison with manufacturer data was made or whether 
tests were done at constant temperature and what the results were.

Discharging to a lower 15-20% level to protect the battery, there is a big 
difference. If you want to get the best capacity out of a li ion battery with a 
BMS, either reduce the discharge rate or change the BMS to accept a lower 
cutoff voltage and risk battery damage.



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Re: [EVDL] Alibaba/Aliexpress Lithium

[Steve Heath via EV]

I wasn't and I think you misread what I said. I was referring to the 
bottom right graph entitled discharge characteristic.   I actually said 
that at 0%soc that the capacities were similar. However in real life 
there will be a bms system that will prevent reaching that level and it 
does this by creating an artificial cutoff voltage where the batteries 
are disconnected if the voltage goes below this.  To see what the 
capacity actually is now, draw a horizontal line at the 3 volt level (or 
whatever BMS cutoff voltage you are using) and drop a perpendicular down 
where the discharge curves intersect. You will then get the different 
capacities I was referring to.  I actually said that at the 0% soc level 
that the capacities are similar, but that because the BMS never allows 
the voltage to get that low and that they cutoff at a higher voltage 
e.g  3v or thereabouts, you get reduced capacity.


Yes there are so types that can get as low as 1.08 but generally the 
batteries have a constant of 1.2 or higher. I did use the word typically.


BTW I did find that paper 
(https://www.slideshare.net/componer/a-critical-review-of-using-the-peukert-equation-for-determining-the-remaining-capacity-of-lead-acid-and-lithium-ion-batteries) 
and they tested the batteries down to their cutoff voltage so it was not 
surprising that the capacities are similar with the different discharge 
rates. However they did say that they suspected that if the li ion 
battery had been kept at the same temperature as the low discharge i.e. 
keep it at 25C instead of 50C, they expected the capacity for the higher 
discharge to be less. This then raises the question of if it is good for 
cycle life etc to allow this. If cooling is then used, a capacity 
reduction when discharging heavier is to be expected.



On 16/03/2019 11:40, paul dove via EV wrote:

That’s not what the spec sheet says. You are reading the graph for temperature 
variations. There is almost no difference due to discharge rates. 2C is 3250 
and 0.5C is 3350 according to your spec sheet.

And lead acid batteries have a Puekert coefficient as low as 1.08.

Sent from my iPhone


On Mar 15, 2019, at 9:14 AM, Steve Heath via EV  wrote:

Peukert's law is not an actual law but an empirical formula that is based on 
actual physical measurements. It gives an approximate estimate of how much 
capacity can be obtained. The way that it is used is that the capacity is 
measured at different discharge rates to give a co-efficient that can then be 
applied to other batteries.  This is where the difficulty lies. The coefficient 
is taken by measurement and providing another battery is the same then the 
coefficient is applicable. If not and it isn't.

The key point is that the discharge curves for li ion batteries do vary significantly 
depending on the load in real life according to the manufacturer data.  At the 0% soc end 
point, the capacities are the same (give or take). This is why the Peukerts coefficient 
is close to 1 rather than 1.2 or higher for a lead acid battery. Hence the comment that 
it is not applicable. It is there but very small to be accurate.  However at a typical 
self preservation point e.g   cutoff voltage used by BMS, the capacities are different. 
As a result, there is a "Peukerts" effect where the amount of capacity that can 
be obtained is different depending on the discharge current. It is not the same Peukerts 
effect but the end result is the same. Discharge more, less capacity...

The data sheet for a Panasonic 18650 shows this effect very well ( 
https://www.batteryspace.com/prod-specs/NCR18650B.pdf ) where a cut off voltage 
of 3v gives a capacity of 2400mAh at 2c and 3300 mAh  at 0.2C .  At the 0% soc 
point they all come out at 3300 and 3400. So discharging to 0% soc, the 
discharge current is more or less irrelevant. Interestingly these results are 
taken at constant cell temperature where any overheating advantage is not 
applicable. Without seeing the complete paper that was referred to, it is 
difficult to know if any comparison with manufacturer data was made or whether 
tests were done at constant temperature and what the results were.

Discharging to a lower 15-20% level to protect the battery, there is a big 
difference. If you want to get the best capacity out of a li ion battery with a 
BMS, either reduce the discharge rate or change the BMS to accept a lower 
cutoff voltage and risk battery damage.



On 15/03/2019 10:20, paul dove via EV wrote:
Peukert's law was developed for Lead-Acid batteries, and works well in that 
application.

It does not necessarily apply to other battery chemistries, especially 
Lithium-Ion batteries. Lithium-Ion batteries tend to self-heat during rapid 
discharge, and the Nernst Equation predicts battery voltage will increase with 
temperature. Thus, the effect of increased resistance is offset by the 
self-heating effect. This advantage of Lithium-Ion batteries is a well-known 
advertised feature. In a resea

Re: [EVDL] Alibaba/Aliexpress Lithium

[Michael Ross via EV]

Discharging to 0%SOC is not a realistic condition for Li ion cells in a
large pack, and I am not aware that PbSO4 are taken below 50% fro greatest
life (though I don;t know the why and wherefores of this). With Li ion you
get more usable capacity  - down to 15% or 20%SOC. Not going to 0% is about
not pushing individual low capacity cells around the bend and turning them
into a short in the pack.  An important consideration for EV manufacturers
is getting cells that are very consistent in their performance.  This
allows them to safely push the cutoff voltage lower. I understand that
Tesla packs call ~80% to be 100%, and ~20% to be 0% to ensure the range
does not drop in anything close to the near term of the pack.

Taking a Li ion cell to 0%SOC is not an issue because at that condition the
electrodes and electrolytes are not reactive at all; but, when near
100%SOC, coupled with excessive heat, this causes the very reactive de-
lithiated positive electrode to damage the electrolyte.

So a small appliance with only a few  Li ion cells, going very close to
0%SOC, is not as likely to be troubling. Cooking them in a cheap charger
that get hot and stays hot at fully charged, is a good way to ruin cells.

The cell chemistry has a lot to do with the ability to withstand high SOC.
LiFePO is particularly susceptible to damage at lower temperatures (even as
low as 95°F) with 100%SOC is going to cause trouble. Whereas the better
chemistries and with judicious use of additives to hold off damage to the
cells can handle higher temps. Managing the pack to not actually go close
to 100%SOC also speeds up charging.  They nave really float charge them, so
you average a higher C during a "full" charge.

It is fortunate that driving after a full charge quickly brings the SOC
down away from the reactive 100% SOC state. It is always best to store Li
ion cells at something less than 100%SOC. I have heard 80% suggested as a
good SOC for storage.

On Sat, Mar 16, 2019 at 2:20 PM paul dove via EV  wrote:

> That’s not what the spec sheet says. You are reading the graph for
> temperature variations. There is almost no difference due to discharge
> rates. 2C is 3250 and 0.5C is 3350 according to your spec sheet.
>
> And lead acid batteries have a Puekert coefficient as low as 1.08.
>
> Sent from my iPhone
>
> > On Mar 15, 2019, at 9:14 AM, Steve Heath via EV 
> wrote:
> >
> > Peukert's law is not an actual law but an empirical formula that is
> based on actual physical measurements. It gives an approximate estimate of
> how much capacity can be obtained. The way that it is used is that the
> capacity is measured at different discharge rates to give a co-efficient
> that can then be applied to other batteries.  This is where the difficulty
> lies. The coefficient is taken by measurement and providing another battery
> is the same then the coefficient is applicable. If not and it isn't.
> >
> > The key point is that the discharge curves for li ion batteries do vary
> significantly depending on the load in real life according to the
> manufacturer data.  At the 0% soc end point, the capacities are the same
> (give or take). This is why the Peukerts coefficient is close to 1 rather
> than 1.2 or higher for a lead acid battery. Hence the comment that it is
> not applicable. It is there but very small to be accurate.  However at a
> typical self preservation point e.g   cutoff voltage used by BMS, the
> capacities are different. As a result, there is a "Peukerts" effect where
> the amount of capacity that can be obtained is different depending on the
> discharge current. It is not the same Peukerts effect but the end result is
> the same. Discharge more, less capacity...
> >
> > The data sheet for a Panasonic 18650 shows this effect very well (
> https://www.batteryspace.com/prod-specs/NCR18650B.pdf ) where a cut off
> voltage of 3v gives a capacity of 2400mAh at 2c and 3300 mAh  at 0.2C .  At
> the 0% soc point they all come out at 3300 and 3400. So discharging to 0%
> soc, the discharge current is more or less irrelevant. Interestingly these
> results are taken at constant cell temperature where any overheating
> advantage is not applicable. Without seeing the complete paper that was
> referred to, it is difficult to know if any comparison with manufacturer
> data was made or whether tests were done at constant temperature and what
> the results were.
> >
> > Discharging to a lower 15-20% level to protect the battery, there is a
> big difference. If you want to get the best capacity out of a li ion
> battery with a BMS, either reduce the discharge rate or change the BMS to
> accept a lower cutoff voltage and risk battery damage.
> >
> > SNIP

-- 
Michael E. Ross
(919) 585-6737 Land
(919) 901-2805 Cell and Text
(919) 576-0824  Tablet,
Google Phone and Text





Virus-free.
www.avg.com

Re: [EVDL] Alibaba/Aliexpress Lithium

[paul dove via EV]

That’s not what the spec sheet says. You are reading the graph for temperature 
variations. There is almost no difference due to discharge rates. 2C is 3250 
and 0.5C is 3350 according to your spec sheet.

And lead acid batteries have a Puekert coefficient as low as 1.08.

Sent from my iPhone

> On Mar 15, 2019, at 9:14 AM, Steve Heath via EV  wrote:
> 
> Peukert's law is not an actual law but an empirical formula that is based on 
> actual physical measurements. It gives an approximate estimate of how much 
> capacity can be obtained. The way that it is used is that the capacity is 
> measured at different discharge rates to give a co-efficient that can then be 
> applied to other batteries.  This is where the difficulty lies. The 
> coefficient is taken by measurement and providing another battery is the same 
> then the coefficient is applicable. If not and it isn't.
> 
> The key point is that the discharge curves for li ion batteries do vary 
> significantly depending on the load in real life according to the 
> manufacturer data.  At the 0% soc end point, the capacities are the same 
> (give or take). This is why the Peukerts coefficient is close to 1 rather 
> than 1.2 or higher for a lead acid battery. Hence the comment that it is not 
> applicable. It is there but very small to be accurate.  However at a typical 
> self preservation point e.g   cutoff voltage used by BMS, the capacities are 
> different. As a result, there is a "Peukerts" effect where the amount of 
> capacity that can be obtained is different depending on the discharge 
> current. It is not the same Peukerts effect but the end result is the same. 
> Discharge more, less capacity...
> 
> The data sheet for a Panasonic 18650 shows this effect very well ( 
> https://www.batteryspace.com/prod-specs/NCR18650B.pdf ) where a cut off 
> voltage of 3v gives a capacity of 2400mAh at 2c and 3300 mAh  at 0.2C .  At 
> the 0% soc point they all come out at 3300 and 3400. So discharging to 0% 
> soc, the discharge current is more or less irrelevant. Interestingly these 
> results are taken at constant cell temperature where any overheating 
> advantage is not applicable. Without seeing the complete paper that was 
> referred to, it is difficult to know if any comparison with manufacturer data 
> was made or whether tests were done at constant temperature and what the 
> results were.
> 
> Discharging to a lower 15-20% level to protect the battery, there is a big 
> difference. If you want to get the best capacity out of a li ion battery with 
> a BMS, either reduce the discharge rate or change the BMS to accept a lower 
> cutoff voltage and risk battery damage.
> 
> 
>> On 15/03/2019 10:20, paul dove via EV wrote:
>> Peukert's law was developed for Lead-Acid batteries, and works well in that 
>> application.
>> 
>> It does not necessarily apply to other battery chemistries, especially 
>> Lithium-Ion batteries. Lithium-Ion batteries tend to self-heat during rapid 
>> discharge, and the Nernst Equation predicts battery voltage will increase 
>> with temperature. Thus, the effect of increased resistance is offset by the 
>> self-heating effect. This advantage of Lithium-Ion batteries is a well-known 
>> advertised feature. In a research paper, a 50Ah lithium-ion battery tested 
>> was found to give about the same capacity at 5A and 50A; this was attributed 
>> to possible Peukert loss in capacity being countered by the increase in 
>> capacity due to the 30◦C temperature rise due to self-heating, with the 
>> conclusion that the Peukert equation is not applicable.
>> 
>> https://www.google.com/amp/s/www.researchgate.net/publication/245106038_A_critical_review_of_using_the_Peukert_equation_for_determining_the_remaining_capacity_of_lead-acid_and_lithium-ion_batteries/amp
>> 
>> Sent from my iPhone
>> 
>>> On Mar 14, 2019, at 10:19 PM, Lee Hart via EV  wrote:
>>> 
>>> Michael Ross via EV wrote:
 I am not sure about previous discussions and you may know this: Peukert's
 Law is not applicable to Li ion cells in any way. It only relates to lead
 acid cells.
>>> I agree with the rest of what you said, but not with this. Peukert's law 
>>> says nothing about the chemistry involved; it applies to *all* types of 
>>> batteries and all chemistries.
>>> 
>>> Peukert's equation applies to any battery or cell that has internal 
>>> resistance, and that has a minimum "cutoff" voltage below which it is 
>>> harmed. It simply states that the higher the load current, the lower the 
>>> apparent amphour capacity. High currents cause a larger voltage drop, so 
>>> you reach the "cutoff" voltage before the cell is truly dead.
>>> 
>>> The amphours are not "missing"; you just can't get them without reducing 
>>> the load current, or pulling its voltage below the safe minimum. If you're 
>>> willing to shorten the life of the cell, you can still get it.
>>> 
>>> Peukert matters more for lead-acids because they typically have a higher 
>>> internal resistanc

Re: [EVDL] Alibaba/Aliexpress Lithium

[Dan Baker via EV]

Thanks for the info Jay.  I have been looking but no luck yet with any used
car part dealers locally. The area I live in (Nova Scotia) doesn't have a
lot of EVs on the roads so not much to be expected at the wreckers.
Getting used cells from afar would be costly if not impossible to ship,
think it would be cheaper & easier to ship loose hand grenades lol.

On Fri, Mar 15, 2019 at 11:39 AM Jay Summet via EV 
wrote:

> You can certainly get used Leaf packs in the $2500-$4000 range from auto
> dismantlers / wrecking yards. They have 48 8v modules in the 40-60 AH
> range depending upon age, so you can use them in 8 parallel 6 series to
> get a 48volt (50.4 volt max) pack with 320+ AH of capacity.
>
> Plus you don't need to bother with liquid cooling connections...(which
> may be a plus or minus depending upon how hard you are hitting them...)
>
> Jay
>
> On 3/15/19 9:20 AM, Dan Baker via EV wrote:
> > Wow lots of great info.  So I guess the counteraction of temp rise &
> > voltage compensates for any losses from Peukert's equation in Lithium
> under
> > normal operating conditions.  I suspect the equation is still applicable
> to
> > Lithium but at much higher draws, far past the C rating i.e. the battery
> > will eventually lose more energy to heating than it can compensate with
> > voltage rise.  Of course that heat will destroy the battery so staying
> > inside the C rating will avoid damage and Peukert effect?  As suggested I
> > have decided to do as close to real world loads and will do as close to
> the
> > amperage my boat typically draws, 100amps @ 48v.  Where as I may be
> testing
> > with a smaller set of battery (don't want to order the whole lot and get
> > 100% ripped off if they are garbage) I may reduce the load to what it
> would
> > see with a full pack and not exceed the stated C rating (if I go with 2 x
> > 48v 100ah packs, each pack would only see a 50 amp draw)
> >
> > The concern on Alibaba battery quality had me double think this yesterday
> > and I dug through the web trying to find a reasonably priced alternative.
> > There is an aftermarket GM parts company called GMpartsdepot Canada, they
> > sell a refurbished 2013 volt pack online for 2400 dollars CAD.  It didn't
> > say anything about a core return so I inquired to confirm.   Apparently
> it
> > didn't matter, they won't sell it to me without going through a dealer,
> > bummer.
> >
> > On Fri, Mar 15, 2019 at 9:56 AM paul dove via EV 
> wrote:
> >
> >> Peukert's law was developed for Lead-Acid batteries, and works well in
> >> that application.
> >>
> >> It does not necessarily apply to other battery chemistries, especially
> >> Lithium-Ion batteries. Lithium-Ion batteries tend to self-heat during
> rapid
> >> discharge, and the Nernst Equation predicts battery voltage will
> increase
> >> with temperature. Thus, the effect of increased resistance is offset by
> the
> >> self-heating effect. This advantage of Lithium-Ion batteries is a
> >> well-known advertised feature. In a research paper, a 50Ah lithium-ion
> >> battery tested was found to give about the same capacity at 5A and 50A;
> >> this was attributed to possible Peukert loss in capacity being
> countered by
> >> the increase in capacity due to the 30◦C temperature rise due to
> >> self-heating, with the conclusion that the Peukert equation is not
> >> applicable.
> >>
> >>
> >>
> https://www.google.com/amp/s/www.researchgate.net/publication/245106038_A_critical_review_of_using_the_Peukert_equation_for_determining_the_remaining_capacity_of_lead-acid_and_lithium-ion_batteries/amp
> >>
> >> Sent from my iPhone
> >>
> >>> On Mar 14, 2019, at 10:19 PM, Lee Hart via EV 
> wrote:
> >>>
> >>> Michael Ross via EV wrote:
>  I am not sure about previous discussions and you may know this:
> >> Peukert's
>  Law is not applicable to Li ion cells in any way. It only relates to
> >> lead
>  acid cells.
> >>>
> >>> I agree with the rest of what you said, but not with this. Peukert's
> law
> >> says nothing about the chemistry involved; it applies to *all* types of
> >> batteries and all chemistries.
> >>>
> >>> Peukert's equation applies to any battery or cell that has internal
> >> resistance, and that has a minimum "cutoff" voltage below which it is
> >> harmed. It simply states that the higher the load current, the lower the
> >> apparent amphour capacity. High currents cause a larger voltage drop, so
> >> you reach the "cutoff" voltage before the cell is truly dead.
> >>>
> >>> The amphours are not "missing"; you just can't get them without
> reducing
> >> the load current, or pulling its voltage below the safe minimum. If
> you're
> >> willing to shorten the life of the cell, you can still get it.
> >>>
> >>> Peukert matters more for lead-acids because they typically have a
> higher
> >> internal resistance. In particular, lead-acid internal resistance goes
> up a
> >> lot as the cell approaches dead. Most other chemistries do not have this
> >> large change in internal

Re: [EVDL] Alibaba/Aliexpress Lithium

[Jay Summet via EV]

You can certainly get used Leaf packs in the $2500-$4000 range from auto 
dismantlers / wrecking yards. They have 48 8v modules in the 40-60 AH 
range depending upon age, so you can use them in 8 parallel 6 series to 
get a 48volt (50.4 volt max) pack with 320+ AH of capacity.


Plus you don't need to bother with liquid cooling connections...(which 
may be a plus or minus depending upon how hard you are hitting them...)


Jay

On 3/15/19 9:20 AM, Dan Baker via EV wrote:

Wow lots of great info.  So I guess the counteraction of temp rise &
voltage compensates for any losses from Peukert's equation in Lithium under
normal operating conditions.  I suspect the equation is still applicable to
Lithium but at much higher draws, far past the C rating i.e. the battery
will eventually lose more energy to heating than it can compensate with
voltage rise.  Of course that heat will destroy the battery so staying
inside the C rating will avoid damage and Peukert effect?  As suggested I
have decided to do as close to real world loads and will do as close to the
amperage my boat typically draws, 100amps @ 48v.  Where as I may be testing
with a smaller set of battery (don't want to order the whole lot and get
100% ripped off if they are garbage) I may reduce the load to what it would
see with a full pack and not exceed the stated C rating (if I go with 2 x
48v 100ah packs, each pack would only see a 50 amp draw)

The concern on Alibaba battery quality had me double think this yesterday
and I dug through the web trying to find a reasonably priced alternative.
There is an aftermarket GM parts company called GMpartsdepot Canada, they
sell a refurbished 2013 volt pack online for 2400 dollars CAD.  It didn't
say anything about a core return so I inquired to confirm.   Apparently it
didn't matter, they won't sell it to me without going through a dealer,
bummer.

On Fri, Mar 15, 2019 at 9:56 AM paul dove via EV  wrote:


Peukert's law was developed for Lead-Acid batteries, and works well in
that application.

It does not necessarily apply to other battery chemistries, especially
Lithium-Ion batteries. Lithium-Ion batteries tend to self-heat during rapid
discharge, and the Nernst Equation predicts battery voltage will increase
with temperature. Thus, the effect of increased resistance is offset by the
self-heating effect. This advantage of Lithium-Ion batteries is a
well-known advertised feature. In a research paper, a 50Ah lithium-ion
battery tested was found to give about the same capacity at 5A and 50A;
this was attributed to possible Peukert loss in capacity being countered by
the increase in capacity due to the 30◦C temperature rise due to
self-heating, with the conclusion that the Peukert equation is not
applicable.


https://www.google.com/amp/s/www.researchgate.net/publication/245106038_A_critical_review_of_using_the_Peukert_equation_for_determining_the_remaining_capacity_of_lead-acid_and_lithium-ion_batteries/amp

Sent from my iPhone


On Mar 14, 2019, at 10:19 PM, Lee Hart via EV  wrote:

Michael Ross via EV wrote:

I am not sure about previous discussions and you may know this:

Peukert's

Law is not applicable to Li ion cells in any way. It only relates to

lead

acid cells.


I agree with the rest of what you said, but not with this. Peukert's law

says nothing about the chemistry involved; it applies to *all* types of
batteries and all chemistries.


Peukert's equation applies to any battery or cell that has internal

resistance, and that has a minimum "cutoff" voltage below which it is
harmed. It simply states that the higher the load current, the lower the
apparent amphour capacity. High currents cause a larger voltage drop, so
you reach the "cutoff" voltage before the cell is truly dead.


The amphours are not "missing"; you just can't get them without reducing

the load current, or pulling its voltage below the safe minimum. If you're
willing to shorten the life of the cell, you can still get it.


Peukert matters more for lead-acids because they typically have a higher

internal resistance. In particular, lead-acid internal resistance goes up a
lot as the cell approaches dead. Most other chemistries do not have this
large change in internal resistance as a function of state of charge.


--
Any intelligent fool can make things bigger, more complex, and more
violent. It takes a touch of genius, and a lot of courage, to move
in the opposite direction. -- Albert Einstein
--
Lee Hart, 814 8th Ave N, Sartell MN 56377, www.sunrise-ev.com
___
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Re: [EVDL] Alibaba/Aliexpress Lithium

[Steve Heath via EV]

Peukert's law is not an actual law but an empirical formula that is 
based on actual physical measurements. It gives an approximate estimate 
of how much capacity can be obtained. The way that it is used is that 
the capacity is measured at different discharge rates to give a 
co-efficient that can then be applied to other batteries.  This is where 
the difficulty lies. The coefficient is taken by measurement and 
providing another battery is the same then the coefficient is 
applicable. If not and it isn't.


The key point is that the discharge curves for li ion batteries do vary 
significantly depending on the load in real life according to the 
manufacturer data.  At the 0% soc end point, the capacities are the same 
(give or take). This is why the Peukerts coefficient is close to 1 
rather than 1.2 or higher for a lead acid battery. Hence the comment 
that it is not applicable. It is there but very small to be accurate.  
However at a typical self preservation point e.g   cutoff voltage used 
by BMS, the capacities are different. As a result, there is a "Peukerts" 
effect where the amount of capacity that can be obtained is different 
depending on the discharge current. It is not the same Peukerts effect 
but the end result is the same. Discharge more, less capacity...


The data sheet for a Panasonic 18650 shows this effect very well ( 
https://www.batteryspace.com/prod-specs/NCR18650B.pdf ) where a cut off 
voltage of 3v gives a capacity of 2400mAh at 2c and 3300 mAh  at 0.2C .  
At the 0% soc point they all come out at 3300 and 3400. So discharging 
to 0% soc, the discharge current is more or less irrelevant. 
Interestingly these results are taken at constant cell temperature where 
any overheating advantage is not applicable. Without seeing the complete 
paper that was referred to, it is difficult to know if any comparison 
with manufacturer data was made or whether tests were done at constant 
temperature and what the results were.


Discharging to a lower 15-20% level to protect the battery, there is a 
big difference. If you want to get the best capacity out of a li ion 
battery with a BMS, either reduce the discharge rate or change the BMS 
to accept a lower cutoff voltage and risk battery damage.



On 15/03/2019 10:20, paul dove via EV wrote:

Peukert's law was developed for Lead-Acid batteries, and works well in that 
application.

It does not necessarily apply to other battery chemistries, especially 
Lithium-Ion batteries. Lithium-Ion batteries tend to self-heat during rapid 
discharge, and the Nernst Equation predicts battery voltage will increase with 
temperature. Thus, the effect of increased resistance is offset by the 
self-heating effect. This advantage of Lithium-Ion batteries is a well-known 
advertised feature. In a research paper, a 50Ah lithium-ion battery tested was 
found to give about the same capacity at 5A and 50A; this was attributed to 
possible Peukert loss in capacity being countered by the increase in capacity 
due to the 30◦C temperature rise due to self-heating, with the conclusion that 
the Peukert equation is not applicable.

https://www.google.com/amp/s/www.researchgate.net/publication/245106038_A_critical_review_of_using_the_Peukert_equation_for_determining_the_remaining_capacity_of_lead-acid_and_lithium-ion_batteries/amp

Sent from my iPhone


On Mar 14, 2019, at 10:19 PM, Lee Hart via EV  wrote:

Michael Ross via EV wrote:

I am not sure about previous discussions and you may know this: Peukert's
Law is not applicable to Li ion cells in any way. It only relates to lead
acid cells.

I agree with the rest of what you said, but not with this. Peukert's law says 
nothing about the chemistry involved; it applies to *all* types of batteries 
and all chemistries.

Peukert's equation applies to any battery or cell that has internal resistance, and that has a 
minimum "cutoff" voltage below which it is harmed. It simply states that the higher the 
load current, the lower the apparent amphour capacity. High currents cause a larger voltage drop, 
so you reach the "cutoff" voltage before the cell is truly dead.

The amphours are not "missing"; you just can't get them without reducing the 
load current, or pulling its voltage below the safe minimum. If you're willing to shorten 
the life of the cell, you can still get it.

Peukert matters more for lead-acids because they typically have a higher 
internal resistance. In particular, lead-acid internal resistance goes up a lot 
as the cell approaches dead. Most other chemistries do not have this large 
change in internal resistance as a function of state of charge.

--
Any intelligent fool can make things bigger, more complex, and more
violent. It takes a touch of genius, and a lot of courage, to move
in the opposite direction. -- Albert Einstein
--
Lee Hart, 814 8th Ave N, Sartell MN 56377, www.sunrise-ev.com
___
UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub
http://lists.ev

Re: [EVDL] Alibaba/Aliexpress Lithium

[Dan Baker via EV]

Wow lots of great info.  So I guess the counteraction of temp rise &
voltage compensates for any losses from Peukert's equation in Lithium under
normal operating conditions.  I suspect the equation is still applicable to
Lithium but at much higher draws, far past the C rating i.e. the battery
will eventually lose more energy to heating than it can compensate with
voltage rise.  Of course that heat will destroy the battery so staying
inside the C rating will avoid damage and Peukert effect?  As suggested I
have decided to do as close to real world loads and will do as close to the
amperage my boat typically draws, 100amps @ 48v.  Where as I may be testing
with a smaller set of battery (don't want to order the whole lot and get
100% ripped off if they are garbage) I may reduce the load to what it would
see with a full pack and not exceed the stated C rating (if I go with 2 x
48v 100ah packs, each pack would only see a 50 amp draw)

The concern on Alibaba battery quality had me double think this yesterday
and I dug through the web trying to find a reasonably priced alternative.
There is an aftermarket GM parts company called GMpartsdepot Canada, they
sell a refurbished 2013 volt pack online for 2400 dollars CAD.  It didn't
say anything about a core return so I inquired to confirm.   Apparently it
didn't matter, they won't sell it to me without going through a dealer,
bummer.

On Fri, Mar 15, 2019 at 9:56 AM paul dove via EV  wrote:

> Peukert's law was developed for Lead-Acid batteries, and works well in
> that application.
>
> It does not necessarily apply to other battery chemistries, especially
> Lithium-Ion batteries. Lithium-Ion batteries tend to self-heat during rapid
> discharge, and the Nernst Equation predicts battery voltage will increase
> with temperature. Thus, the effect of increased resistance is offset by the
> self-heating effect. This advantage of Lithium-Ion batteries is a
> well-known advertised feature. In a research paper, a 50Ah lithium-ion
> battery tested was found to give about the same capacity at 5A and 50A;
> this was attributed to possible Peukert loss in capacity being countered by
> the increase in capacity due to the 30◦C temperature rise due to
> self-heating, with the conclusion that the Peukert equation is not
> applicable.
>
>
> https://www.google.com/amp/s/www.researchgate.net/publication/245106038_A_critical_review_of_using_the_Peukert_equation_for_determining_the_remaining_capacity_of_lead-acid_and_lithium-ion_batteries/amp
>
> Sent from my iPhone
>
> > On Mar 14, 2019, at 10:19 PM, Lee Hart via EV  wrote:
> >
> > Michael Ross via EV wrote:
> >> I am not sure about previous discussions and you may know this:
> Peukert's
> >> Law is not applicable to Li ion cells in any way. It only relates to
> lead
> >> acid cells.
> >
> > I agree with the rest of what you said, but not with this. Peukert's law
> says nothing about the chemistry involved; it applies to *all* types of
> batteries and all chemistries.
> >
> > Peukert's equation applies to any battery or cell that has internal
> resistance, and that has a minimum "cutoff" voltage below which it is
> harmed. It simply states that the higher the load current, the lower the
> apparent amphour capacity. High currents cause a larger voltage drop, so
> you reach the "cutoff" voltage before the cell is truly dead.
> >
> > The amphours are not "missing"; you just can't get them without reducing
> the load current, or pulling its voltage below the safe minimum. If you're
> willing to shorten the life of the cell, you can still get it.
> >
> > Peukert matters more for lead-acids because they typically have a higher
> internal resistance. In particular, lead-acid internal resistance goes up a
> lot as the cell approaches dead. Most other chemistries do not have this
> large change in internal resistance as a function of state of charge.
> >
> > --
> > Any intelligent fool can make things bigger, more complex, and more
> > violent. It takes a touch of genius, and a lot of courage, to move
> > in the opposite direction. -- Albert Einstein
> > --
> > Lee Hart, 814 8th Ave N, Sartell MN 56377, www.sunrise-ev.com
> > ___
> > UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub
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> http://groups.yahoo.com/group/NEDRA)
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Re: [EVDL] Alibaba/Aliexpress Lithium

[paul dove via EV]

Peukert's law was developed for Lead-Acid batteries, and works well in that 
application. 

It does not necessarily apply to other battery chemistries, especially 
Lithium-Ion batteries. Lithium-Ion batteries tend to self-heat during rapid 
discharge, and the Nernst Equation predicts battery voltage will increase with 
temperature. Thus, the effect of increased resistance is offset by the 
self-heating effect. This advantage of Lithium-Ion batteries is a well-known 
advertised feature. In a research paper, a 50Ah lithium-ion battery tested was 
found to give about the same capacity at 5A and 50A; this was attributed to 
possible Peukert loss in capacity being countered by the increase in capacity 
due to the 30◦C temperature rise due to self-heating, with the conclusion that 
the Peukert equation is not applicable.

https://www.google.com/amp/s/www.researchgate.net/publication/245106038_A_critical_review_of_using_the_Peukert_equation_for_determining_the_remaining_capacity_of_lead-acid_and_lithium-ion_batteries/amp

Sent from my iPhone

> On Mar 14, 2019, at 10:19 PM, Lee Hart via EV  wrote:
> 
> Michael Ross via EV wrote:
>> I am not sure about previous discussions and you may know this: Peukert's
>> Law is not applicable to Li ion cells in any way. It only relates to lead
>> acid cells.
> 
> I agree with the rest of what you said, but not with this. Peukert's law says 
> nothing about the chemistry involved; it applies to *all* types of batteries 
> and all chemistries.
> 
> Peukert's equation applies to any battery or cell that has internal 
> resistance, and that has a minimum "cutoff" voltage below which it is harmed. 
> It simply states that the higher the load current, the lower the apparent 
> amphour capacity. High currents cause a larger voltage drop, so you reach the 
> "cutoff" voltage before the cell is truly dead.
> 
> The amphours are not "missing"; you just can't get them without reducing the 
> load current, or pulling its voltage below the safe minimum. If you're 
> willing to shorten the life of the cell, you can still get it.
> 
> Peukert matters more for lead-acids because they typically have a higher 
> internal resistance. In particular, lead-acid internal resistance goes up a 
> lot as the cell approaches dead. Most other chemistries do not have this 
> large change in internal resistance as a function of state of charge.
> 
> -- 
> Any intelligent fool can make things bigger, more complex, and more
> violent. It takes a touch of genius, and a lot of courage, to move
> in the opposite direction. -- Albert Einstein
> --
> Lee Hart, 814 8th Ave N, Sartell MN 56377, www.sunrise-ev.com
> ___
> UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub
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Re: [EVDL] Alibaba/Aliexpress Lithium

[Lee Hart via EV]

Michael Ross via EV wrote:

I am not sure about previous discussions and you may know this: Peukert's
Law is not applicable to Li ion cells in any way. It only relates to lead
acid cells.


I agree with the rest of what you said, but not with this. Peukert's law 
says nothing about the chemistry involved; it applies to *all* types of 
batteries and all chemistries.


Peukert's equation applies to any battery or cell that has internal 
resistance, and that has a minimum "cutoff" voltage below which it is 
harmed. It simply states that the higher the load current, the lower the 
apparent amphour capacity. High currents cause a larger voltage drop, so 
you reach the "cutoff" voltage before the cell is truly dead.


The amphours are not "missing"; you just can't get them without reducing 
the load current, or pulling its voltage below the safe minimum. If 
you're willing to shorten the life of the cell, you can still get it.


Peukert matters more for lead-acids because they typically have a higher 
internal resistance. In particular, lead-acid internal resistance goes 
up a lot as the cell approaches dead. Most other chemistries do not have 
this large change in internal resistance as a function of state of charge.


--
Any intelligent fool can make things bigger, more complex, and more
violent. It takes a touch of genius, and a lot of courage, to move
in the opposite direction. -- Albert Einstein
--
Lee Hart, 814 8th Ave N, Sartell MN 56377, www.sunrise-ev.com
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Re: [EVDL] Alibaba/Aliexpress Lithium

[Michael Ross via EV]

If you want to see whether a cell will last a long time you have to test it
in damaging conditions - full charge and high temps.

Cycling does nothing useful beyond allowing the cell to spend more time a
conditions that are not damaging at all. That's not really useful, but is
is what you will get from most low cost purveyors. When I tried to survey
vendors I got nowhere even finding out the test conditions.

If you could get tests that actually stress the cells you still have to
make comparisons between various cells to see if they are consistent in
withstanding the difficult conditions, or a particular brand or design is
better than another.

Your best bet is to go with a vendor and manufacturer that has a good
reputation, and that is likely not a low cost solution.

I am not sure about previous discussions and you may know this: Peukert's
Law is not applicable to Li ion cells in any way. It only relates to lead
acid cells.

If you nave not listened to lectures by Jeff Dahn you should to understand
how Li ion cells are damaged.
http://tinyurl.com/y395ahod
This 2013 lecture is worth spending time with on what causes Li ion cells
to die:
https://www.youtube.com/watch?v=pxP0Cu00sZs

On Thu, Mar 14, 2019 at 6:20 AM Dan Baker via EV  wrote:

> I have been communicating with a couple sellers now on Aliexpress.  Prices
> seem quite varied and reviews are mixed on these batteries.  I suspect
> there isn't a lot of standards or testing on actual claimed capacities.  I
> would like to try a 12v pack or 2 before buying more and perform some tests
> to verify capacity.  Has anyone done this testing before?  I assume the ah
> rating is based on a 1amp draw for x amount of claimed hours.  So would I
> hook up a 12 watt load (LED bulbs?) and watch pack voltage till it drops
> till below 12v?  Or would I measure it till the BMS protection cuts in -
> (9-10v?).  Some reviewers have found packs listed at 100ah capacity to
> actually have only 30ah cells inside, lots of misinformation.
>
> Thank you,
> Dan
>
> On Tue, Mar 12, 2019 at 1:01 PM Jay Summet via EV 
> wrote:
>
> >
> >
> > On 3/12/19 9:59 AM, Dan Baker via EV wrote:
> >
> > > If I don't charge with my Sevcons and use the included individual 12v
> > > chargers, would there still be worry of connecting too many in series?
> > Is
> > > it charging,discharging or both the issue when connecting in series?
> >
> > That depends entirely upon the battery model/manufacturer and the specs
> > for that specific battery.  If there is an issue, it would most likely
> > be an issue for both charging and discharging.
> >
> > The thing to watch out for is if the batteries have a MOSFET (solid
> > state switch) that is used to disconnect the battery when charging (done
> > charging, voltage too high) or when discharging (voltage too low).  In
> > many cases, the MOSFETS are not rated for super high voltages. It may be
> > twice the working voltage or much higher (24,36 or perhaps 60 volt
> > rated).  If your series pack goes above the MOSFET rating, it is likely
> > to fail spectacularly (short closed in the worst case) when it is asked
> > to disconnect the battery.
> >
> > If the batteries use relays or contractors, they may or may not be rated
> > for higher series voltages, you need to verify.
> >
> > In short, the electronics that are making these batteries "drop in
> > replacements" for a 12 volt battery are designed to work at that voltage
> > level...with perhaps  a 2x or 4x safety factor (24 to 48 volts), but the
> > system was not designed for high voltage (72-144 or higher) to be seen
> > by the battery.
> >
> > The BattleBorn batteries for example use 60V electronics, and are rated
> > to be used in series up to a 48 volt system (They were designed this way
> > to be a drop in replacement for 12, 24, 36 and 48 volt solar power
> > systemsbut many "auto starter" or RV replacement batteries gave no
> > thought about using more than one in series, or if they did, it was only
> > up to a 24 or 48 volt level.)
> >
> > Jay
> >
> > ___
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(919) 585-6737 Land
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Re: [EVDL] Alibaba/Aliexpress Lithium

[paul dove via EV]

Rated Capacity” is defined in the UN Model Regulations as follows: Rated 
capacity means the capacity, in ampere-hours, of a cell or battery as measured 
by subjecting it to a load, temperature and voltage cut-off point specified by 
the manufacturer.

You need to know how the manufacturer tested them and use the same process to 
see if they do as claimed.

Sent from my iPhone

> On Mar 13, 2019, at 3:45 PM, Jay Summet via EV  wrote:
> 
> I think it would be better to measure at a higher amp rating if possible. 
> (Make your test go faster, and more accurately model the true draw on the 
> battery under load).
> 
> How many amps will the batteries see under your particular usage scenario? If 
> you can replicate that same amp draw (either with lots of lights, a big 
> resistor in a bucket of water or whatever) it would probably be the best 
> test for your situation.  (Plus, if the amp draw is higher, the precision of 
> the amp meter would matter less)
> 
> Jay
> 
>> On 3/13/19 3:38 PM, Dan Baker via EV wrote:
>> Thanks guys- never thought of this, I have a similar unit in my boat
>> already.  I typically use it just for monitoring amp output and volts.  I
>> have two throttles on my boat, a spring loaded Curtis-PB6 which I use for
>> docking/ maneuvering and a 5k knob style pot that I switch over for
>> cruise control, set the pot for desired amps/speed off of the gauge.  I'm
>> not sure if it will accurately pick up a small 1 amp load as it is rated
>> for up to 400 amps.  Anyone share what they used for a test load- a
>> resister or a bulb?  I assuming around 1 amp (12 watts) will be closest to
>> measuring true a/h readings.  Given that these lithiums only charge to 12.6
>> volts means my cut-off voltage will likely be closer to the stated BMS
>> cut-off, somewhere between 9-10 volts or when the voltage starts sharply
>> falling off?
>> On Wed, Mar 13, 2019 at 3:23 PM John Lussmyer via EV 
>> wrote:
>>> On Wed Mar 13 11:06:36 PDT 2019 ev@lists.evdl.org said:
 Yep Totally agree. I use several of these to monitor voltages and
 currents in my DIY EV. Nice thing about them is that they work both ways
 and will take into account regen and charging as well as discharge. I
 found them to be as accurate as shunt based meters at a similar price
 range BTW.
>>> 
>>> I use this one:
>>> 
>>> https://www.amazon.com/Programmable-Digital-meter-battery-monitoring/dp/B0043BDFYA/ref=sr_1_1
>>> 
>>> has 2 relay outputs, counts AH in both directions, uses a shunt for
>>> currents over 5A.
>>> I've found it to be pretty accurate.
>>> 
>>> 
>>> --
>>> 
>>> Try my Sensible Email package!
>>> https://sourceforge.net/projects/sensibleemail/
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>>> http://groups.yahoo.com/group/NEDRA)
>>> 
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Re: [EVDL] Alibaba/Aliexpress Lithium

[EVDL Administrator via EV]

To verify the factory AH rating you would measure at the same rate the 
factory does. That's probably the 20 hour rate (C20; that is, current at 
which they'll be flat in 20 hours).  

But you really don't (or shouldn't) care what the C20 capacity is.  All that 
matters is how many AH (or WH) they'll deliver at the current your vehicle 
actually requires.  

I'm far from a lithium expert, but as I understand it, generally lithium 
batteries' capacity holds up better at higher currents, compared to lead 
batteries'.  But IIRC you're looking at cheapies, so who knows.

BTW, watch out for recycled (used) cells in those cheap batteries.  As 
anyone who does business in China regularly will tell you, it's still mostly 
true that anything-goes-profit-above-all unrestricted capitalism and 
stifling authoritarianism pick each others' fleas there.  Many Chinese 
businesses will cut any and every corner to sell cheaply with the highest 
possible profit.  Especially with no US quality control, there's no telling 
what you'll get.  You might get lucky.  You might waste your money.

You don't always get what you pay for, but you very seldom get what you 
DON'T pay for, and that goes triple for shady direct-import ¢r@p from China.

Good luck.

David Roden - Akron, Ohio, USA
EVDL Administrator

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Re: [EVDL] Alibaba/Aliexpress Lithium

[Jay Summet via EV]

Also keep in mind that Lithium batteries, are not usually subject to 
Peukert's law.  (Capacity loss due to high discharge rates is balanced 
by voltage gain due to self heating.)


Jay

On 3/13/19 4:38 PM, Dan Baker wrote:
Good points Jay.  I'm concerned with Peukert's law but if I could 
perform under similar loads it would mean more to me and less to stated 
ah.  Both would be ideal I guess- one for me and one for the evdl list.  
But maybe I'm the last guy here running lead so results given back 
wouldn't be of much value here lol.


Thanks
Dan

On Wed, Mar 13, 2019 at 4:46 PM Jay Summet via EV > wrote:


I think it would be better to measure at a higher amp rating if
possible. (Make your test go faster, and more accurately model the true
draw on the battery under load).

How many amps will the batteries see under your particular usage
scenario? If you can replicate that same amp draw (either with lots of
lights, a big resistor in a bucket of water or whatever) it would
probably be the best test for your situation.  (Plus, if the amp
draw is
higher, the precision of the amp meter would matter less)

Jay

On 3/13/19 3:38 PM, Dan Baker via EV wrote:
 > Thanks guys- never thought of this, I have a similar unit in my boat
 > already.  I typically use it just for monitoring amp output and
volts.  I
 > have two throttles on my boat, a spring loaded Curtis-PB6 which I
use for
 > docking/ maneuvering and a 5k knob style pot that I switch over for
 > cruise control, set the pot for desired amps/speed off of the
gauge.  I'm
 > not sure if it will accurately pick up a small 1 amp load as it
is rated
 > for up to 400 amps.  Anyone share what they used for a test load- a
 > resister or a bulb?  I assuming around 1 amp (12 watts) will be
closest to
 > measuring true a/h readings.  Given that these lithiums only
charge to 12.6
 > volts means my cut-off voltage will likely be closer to the
stated BMS
 > cut-off, somewhere between 9-10 volts or when the voltage starts
sharply
 > falling off?
 >
 > On Wed, Mar 13, 2019 at 3:23 PM John Lussmyer via EV
mailto:ev@lists.evdl.org>>
 > wrote:
 >
 >> On Wed Mar 13 11:06:36 PDT 2019 ev@lists.evdl.org
 said:
 >>> Yep Totally agree. I use several of these to monitor voltages and
 >>> currents in my DIY EV. Nice thing about them is that they work
both ways
 >>> and will take into account regen and charging as well as
discharge. I
 >>> found them to be as accurate as shunt based meters at a similar
price
 >>> range BTW.
 >>
 >> I use this one:
 >>
 >>

https://www.amazon.com/Programmable-Digital-meter-battery-monitoring/dp/B0043BDFYA/ref=sr_1_1
 >>
 >> has 2 relay outputs, counts AH in both directions, uses a shunt for
 >> currents over 5A.
 >> I've found it to be pretty accurate.
 >>
 >>
 >> --
 >>
 >> Try my Sensible Email package!
 >> https://sourceforge.net/projects/sensibleemail/
 >> ___
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 >> http://groups.yahoo.com/group/NEDRA)
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Re: [EVDL] Alibaba/Aliexpress Lithium

[Dan Baker via EV]

Good points Jay.  I'm concerned with Peukert's law but if I could perform
under similar loads it would mean more to me and less to stated ah.  Both
would be ideal I guess- one for me and one for the evdl list.  But maybe
I'm the last guy here running lead so results given back wouldn't be of
much value here lol.

Thanks
Dan

On Wed, Mar 13, 2019 at 4:46 PM Jay Summet via EV  wrote:

> I think it would be better to measure at a higher amp rating if
> possible. (Make your test go faster, and more accurately model the true
> draw on the battery under load).
>
> How many amps will the batteries see under your particular usage
> scenario? If you can replicate that same amp draw (either with lots of
> lights, a big resistor in a bucket of water or whatever) it would
> probably be the best test for your situation.  (Plus, if the amp draw is
> higher, the precision of the amp meter would matter less)
>
> Jay
>
> On 3/13/19 3:38 PM, Dan Baker via EV wrote:
> > Thanks guys- never thought of this, I have a similar unit in my boat
> > already.  I typically use it just for monitoring amp output and volts.  I
> > have two throttles on my boat, a spring loaded Curtis-PB6 which I use for
> > docking/ maneuvering and a 5k knob style pot that I switch over for
> > cruise control, set the pot for desired amps/speed off of the gauge.  I'm
> > not sure if it will accurately pick up a small 1 amp load as it is rated
> > for up to 400 amps.  Anyone share what they used for a test load- a
> > resister or a bulb?  I assuming around 1 amp (12 watts) will be closest
> to
> > measuring true a/h readings.  Given that these lithiums only charge to
> 12.6
> > volts means my cut-off voltage will likely be closer to the stated BMS
> > cut-off, somewhere between 9-10 volts or when the voltage starts sharply
> > falling off?
> >
> > On Wed, Mar 13, 2019 at 3:23 PM John Lussmyer via EV 
> > wrote:
> >
> >> On Wed Mar 13 11:06:36 PDT 2019 ev@lists.evdl.org said:
> >>> Yep Totally agree. I use several of these to monitor voltages and
> >>> currents in my DIY EV. Nice thing about them is that they work both
> ways
> >>> and will take into account regen and charging as well as discharge. I
> >>> found them to be as accurate as shunt based meters at a similar price
> >>> range BTW.
> >>
> >> I use this one:
> >>
> >>
> https://www.amazon.com/Programmable-Digital-meter-battery-monitoring/dp/B0043BDFYA/ref=sr_1_1
> >>
> >> has 2 relay outputs, counts AH in both directions, uses a shunt for
> >> currents over 5A.
> >> I've found it to be pretty accurate.
> >>
> >>
> >> --
> >>
> >> Try my Sensible Email package!
> >> https://sourceforge.net/projects/sensibleemail/
> >> ___
> >> UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub
> >> http://lists.evdl.org/listinfo.cgi/ev-evdl.org
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> >> http://groups.yahoo.com/group/NEDRA)
> >>
> >>
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Re: [EVDL] Alibaba/Aliexpress Lithium

[Jay Summet via EV]

I think it would be better to measure at a higher amp rating if 
possible. (Make your test go faster, and more accurately model the true 
draw on the battery under load).


How many amps will the batteries see under your particular usage 
scenario? If you can replicate that same amp draw (either with lots of 
lights, a big resistor in a bucket of water or whatever) it would 
probably be the best test for your situation.  (Plus, if the amp draw is 
higher, the precision of the amp meter would matter less)


Jay

On 3/13/19 3:38 PM, Dan Baker via EV wrote:

Thanks guys- never thought of this, I have a similar unit in my boat
already.  I typically use it just for monitoring amp output and volts.  I
have two throttles on my boat, a spring loaded Curtis-PB6 which I use for
docking/ maneuvering and a 5k knob style pot that I switch over for
cruise control, set the pot for desired amps/speed off of the gauge.  I'm
not sure if it will accurately pick up a small 1 amp load as it is rated
for up to 400 amps.  Anyone share what they used for a test load- a
resister or a bulb?  I assuming around 1 amp (12 watts) will be closest to
measuring true a/h readings.  Given that these lithiums only charge to 12.6
volts means my cut-off voltage will likely be closer to the stated BMS
cut-off, somewhere between 9-10 volts or when the voltage starts sharply
falling off?

On Wed, Mar 13, 2019 at 3:23 PM John Lussmyer via EV 
wrote:


On Wed Mar 13 11:06:36 PDT 2019 ev@lists.evdl.org said:

Yep Totally agree. I use several of these to monitor voltages and
currents in my DIY EV. Nice thing about them is that they work both ways
and will take into account regen and charging as well as discharge. I
found them to be as accurate as shunt based meters at a similar price
range BTW.


I use this one:

https://www.amazon.com/Programmable-Digital-meter-battery-monitoring/dp/B0043BDFYA/ref=sr_1_1

has 2 relay outputs, counts AH in both directions, uses a shunt for
currents over 5A.
I've found it to be pretty accurate.


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Re: [EVDL] Alibaba/Aliexpress Lithium

[Dan Baker via EV]

Thanks guys- never thought of this, I have a similar unit in my boat
already.  I typically use it just for monitoring amp output and volts.  I
have two throttles on my boat, a spring loaded Curtis-PB6 which I use for
docking/ maneuvering and a 5k knob style pot that I switch over for
cruise control, set the pot for desired amps/speed off of the gauge.  I'm
not sure if it will accurately pick up a small 1 amp load as it is rated
for up to 400 amps.  Anyone share what they used for a test load- a
resister or a bulb?  I assuming around 1 amp (12 watts) will be closest to
measuring true a/h readings.  Given that these lithiums only charge to 12.6
volts means my cut-off voltage will likely be closer to the stated BMS
cut-off, somewhere between 9-10 volts or when the voltage starts sharply
falling off?

On Wed, Mar 13, 2019 at 3:23 PM John Lussmyer via EV 
wrote:

> On Wed Mar 13 11:06:36 PDT 2019 ev@lists.evdl.org said:
> >Yep Totally agree. I use several of these to monitor voltages and
> >currents in my DIY EV. Nice thing about them is that they work both ways
> >and will take into account regen and charging as well as discharge. I
> >found them to be as accurate as shunt based meters at a similar price
> >range BTW.
>
> I use this one:
>
> https://www.amazon.com/Programmable-Digital-meter-battery-monitoring/dp/B0043BDFYA/ref=sr_1_1
>
> has 2 relay outputs, counts AH in both directions, uses a shunt for
> currents over 5A.
> I've found it to be pretty accurate.
>
>
> --
>
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> https://sourceforge.net/projects/sensibleemail/
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Re: [EVDL] Alibaba/Aliexpress Lithium

[John Lussmyer via EV]

On Wed Mar 13 11:06:36 PDT 2019 ev@lists.evdl.org said:
>Yep Totally agree. I use several of these to monitor voltages and
>currents in my DIY EV. Nice thing about them is that they work both ways
>and will take into account regen and charging as well as discharge. I
>found them to be as accurate as shunt based meters at a similar price
>range BTW.

I use this one:
https://www.amazon.com/Programmable-Digital-meter-battery-monitoring/dp/B0043BDFYA/ref=sr_1_1

has 2 relay outputs, counts AH in both directions, uses a shunt for currents 
over 5A.
I've found it to be pretty accurate.


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Re: [EVDL] Alibaba/Aliexpress Lithium

[Steve Heath via EV]

Yep Totally agree. I use several of these to monitor voltages and 
currents in my DIY EV. Nice thing about them is that they work both ways 
and will take into account regen and charging as well as discharge. I 
found them to be as accurate as shunt based meters at a similar price 
range BTW.



Steve

On 13/03/2019 17:39, Jay Summet via EV wrote:
I would recommend buying an inexpensive amp hour / voltage / watt hour 
meter and using that to monitor the battery. (The one I use records 
the data it has logged when power is removed, so that when you apply 
power again the AH counter keeps the last reading.  You can also buy 
them with relay outputs that allow you to program a "low voltage 
disconnect" to act like a very basic BMS protection circuit...but the 
low voltages is based off of the entrie pack, not the individual 
cells)


This is the one I used on my last project:
https://www.amazon.com/gp/product/B07B4CWKRJ/ref=ppx_yo_dt_b_asin_title_o06_s00?ie=UTF8&psc=1 



(It does not have relay outputs, but does support up to 200AH with 
it's current sensor...which was important for my project).


You may wish to choose one with a 100 AH or lower current sensor if 
you will be testing at lower currents, as the accuracy of the current 
sensors is usually a percentage of their max rating. (Also note that a 
shunt based current sensor is more accurate than these magnetic 
sensors that you put the wire through, but if you are trying to get a 
very accurate measure you probably are not buying $30 meters.)


Jay

On 3/13/19 10:21 AM, Dan Baker via EV wrote:
I have been communicating with a couple sellers now on Aliexpress.  
Prices

seem quite varied and reviews are mixed on these batteries.  I suspect
there isn't a lot of standards or testing on actual claimed 
capacities.  I
would like to try a 12v pack or 2 before buying more and perform some 
tests
to verify capacity.  Has anyone done this testing before?  I assume 
the ah

rating is based on a 1amp draw for x amount of claimed hours. So would I
hook up a 12 watt load (LED bulbs?) and watch pack voltage till it drops
till below 12v?  Or would I measure it till the BMS protection cuts in -
(9-10v?).  Some reviewers have found packs listed at 100ah capacity to
actually have only 30ah cells inside, lots of misinformation.

Thank you,
Dan

On Tue, Mar 12, 2019 at 1:01 PM Jay Summet via EV  
wrote:





On 3/12/19 9:59 AM, Dan Baker via EV wrote:


If I don't charge with my Sevcons and use the included individual 12v
chargers, would there still be worry of connecting too many in series?

Is

it charging,discharging or both the issue when connecting in series?


That depends entirely upon the battery model/manufacturer and the specs
for that specific battery.  If there is an issue, it would most likely
be an issue for both charging and discharging.

The thing to watch out for is if the batteries have a MOSFET (solid
state switch) that is used to disconnect the battery when charging 
(done

charging, voltage too high) or when discharging (voltage too low).  In
many cases, the MOSFETS are not rated for super high voltages. It 
may be

twice the working voltage or much higher (24,36 or perhaps 60 volt
rated).  If your series pack goes above the MOSFET rating, it is likely
to fail spectacularly (short closed in the worst case) when it is asked
to disconnect the battery.

If the batteries use relays or contractors, they may or may not be 
rated

for higher series voltages, you need to verify.

In short, the electronics that are making these batteries "drop in
replacements" for a 12 volt battery are designed to work at that 
voltage
level...with perhaps  a 2x or 4x safety factor (24 to 48 volts), but 
the

system was not designed for high voltage (72-144 or higher) to be seen
by the battery.

The BattleBorn batteries for example use 60V electronics, and are rated
to be used in series up to a 48 volt system (They were designed this 
way

to be a drop in replacement for 12, 24, 36 and 48 volt solar power
systemsbut many "auto starter" or RV replacement batteries gave no
thought about using more than one in series, or if they did, it was 
only

up to a 24 or 48 volt level.)

Jay

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Re: [EVDL] Alibaba/Aliexpress Lithium

[Jay Summet via EV]

I would recommend buying an inexpensive amp hour / voltage / watt hour 
meter and using that to monitor the battery. (The one I use records the 
data it has logged when power is removed, so that when you apply power 
again the AH counter keeps the last reading.  You can also buy them with 
relay outputs that allow you to program a "low voltage disconnect" to 
act like a very basic BMS protection circuit...but the low voltages is 
based off of the entrie pack, not the individual cells)


This is the one I used on my last project:
https://www.amazon.com/gp/product/B07B4CWKRJ/ref=ppx_yo_dt_b_asin_title_o06_s00?ie=UTF8&psc=1

(It does not have relay outputs, but does support up to 200AH with it's 
current sensor...which was important for my project).


You may wish to choose one with a 100 AH or lower current sensor if you 
will be testing at lower currents, as the accuracy of the current 
sensors is usually a percentage of their max rating. (Also note that a 
shunt based current sensor is more accurate than these magnetic sensors 
that you put the wire through, but if you are trying to get a very 
accurate measure you probably are not buying $30 meters.)


Jay

On 3/13/19 10:21 AM, Dan Baker via EV wrote:

I have been communicating with a couple sellers now on Aliexpress.  Prices
seem quite varied and reviews are mixed on these batteries.  I suspect
there isn't a lot of standards or testing on actual claimed capacities.  I
would like to try a 12v pack or 2 before buying more and perform some tests
to verify capacity.  Has anyone done this testing before?  I assume the ah
rating is based on a 1amp draw for x amount of claimed hours.  So would I
hook up a 12 watt load (LED bulbs?) and watch pack voltage till it drops
till below 12v?  Or would I measure it till the BMS protection cuts in -
(9-10v?).  Some reviewers have found packs listed at 100ah capacity to
actually have only 30ah cells inside, lots of misinformation.

Thank you,
Dan

On Tue, Mar 12, 2019 at 1:01 PM Jay Summet via EV  wrote:




On 3/12/19 9:59 AM, Dan Baker via EV wrote:


If I don't charge with my Sevcons and use the included individual 12v
chargers, would there still be worry of connecting too many in series?

Is

it charging,discharging or both the issue when connecting in series?


That depends entirely upon the battery model/manufacturer and the specs
for that specific battery.  If there is an issue, it would most likely
be an issue for both charging and discharging.

The thing to watch out for is if the batteries have a MOSFET (solid
state switch) that is used to disconnect the battery when charging (done
charging, voltage too high) or when discharging (voltage too low).  In
many cases, the MOSFETS are not rated for super high voltages. It may be
twice the working voltage or much higher (24,36 or perhaps 60 volt
rated).  If your series pack goes above the MOSFET rating, it is likely
to fail spectacularly (short closed in the worst case) when it is asked
to disconnect the battery.

If the batteries use relays or contractors, they may or may not be rated
for higher series voltages, you need to verify.

In short, the electronics that are making these batteries "drop in
replacements" for a 12 volt battery are designed to work at that voltage
level...with perhaps  a 2x or 4x safety factor (24 to 48 volts), but the
system was not designed for high voltage (72-144 or higher) to be seen
by the battery.

The BattleBorn batteries for example use 60V electronics, and are rated
to be used in series up to a 48 volt system (They were designed this way
to be a drop in replacement for 12, 24, 36 and 48 volt solar power
systemsbut many "auto starter" or RV replacement batteries gave no
thought about using more than one in series, or if they did, it was only
up to a 24 or 48 volt level.)

Jay

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Re: [EVDL] Alibaba/Aliexpress Lithium

[Dan Baker via EV]

I have been communicating with a couple sellers now on Aliexpress.  Prices
seem quite varied and reviews are mixed on these batteries.  I suspect
there isn't a lot of standards or testing on actual claimed capacities.  I
would like to try a 12v pack or 2 before buying more and perform some tests
to verify capacity.  Has anyone done this testing before?  I assume the ah
rating is based on a 1amp draw for x amount of claimed hours.  So would I
hook up a 12 watt load (LED bulbs?) and watch pack voltage till it drops
till below 12v?  Or would I measure it till the BMS protection cuts in -
(9-10v?).  Some reviewers have found packs listed at 100ah capacity to
actually have only 30ah cells inside, lots of misinformation.

Thank you,
Dan

On Tue, Mar 12, 2019 at 1:01 PM Jay Summet via EV  wrote:

>
>
> On 3/12/19 9:59 AM, Dan Baker via EV wrote:
>
> > If I don't charge with my Sevcons and use the included individual 12v
> > chargers, would there still be worry of connecting too many in series?
> Is
> > it charging,discharging or both the issue when connecting in series?
>
> That depends entirely upon the battery model/manufacturer and the specs
> for that specific battery.  If there is an issue, it would most likely
> be an issue for both charging and discharging.
>
> The thing to watch out for is if the batteries have a MOSFET (solid
> state switch) that is used to disconnect the battery when charging (done
> charging, voltage too high) or when discharging (voltage too low).  In
> many cases, the MOSFETS are not rated for super high voltages. It may be
> twice the working voltage or much higher (24,36 or perhaps 60 volt
> rated).  If your series pack goes above the MOSFET rating, it is likely
> to fail spectacularly (short closed in the worst case) when it is asked
> to disconnect the battery.
>
> If the batteries use relays or contractors, they may or may not be rated
> for higher series voltages, you need to verify.
>
> In short, the electronics that are making these batteries "drop in
> replacements" for a 12 volt battery are designed to work at that voltage
> level...with perhaps  a 2x or 4x safety factor (24 to 48 volts), but the
> system was not designed for high voltage (72-144 or higher) to be seen
> by the battery.
>
> The BattleBorn batteries for example use 60V electronics, and are rated
> to be used in series up to a 48 volt system (They were designed this way
> to be a drop in replacement for 12, 24, 36 and 48 volt solar power
> systemsbut many "auto starter" or RV replacement batteries gave no
> thought about using more than one in series, or if they did, it was only
> up to a 24 or 48 volt level.)
>
> Jay
>
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Re: [EVDL] Alibaba/Aliexpress Lithium

[paul dove via EV]

Contrary to popular belief charging a Lithium Ion battery as little to do with 
the voltage of the charger.

Charging Lithium Ion batteries is a procedure when one holds the current 
constant until a voltage is reached and then holding the voltage constant 
letting current drop to a current cutoff value. 

You can use any voltage over the max voltage of the cell while in constant 
current mode. 

Any charger or power supply can do this the part it may not do is the constant 
voltage phase of the charge. 

You could just skip the constant voltage phase and shutoff the charger when the 
voltage is reached. You will be over 90% charged at this point especially if 
you are using a low current.



Sent from my iPhone

> On Mar 12, 2019, at 9:59 AM, Dan Baker via EV  wrote:
> 
> Thank you again for the great info Jay.  Fire is never a good thing with
> any vehicle and fires on boats are much worse than land vehicles, you
> likely won't drown or your car wont sink if it catches fire.  Perhaps I can
> install a trapdoor below my batts and eject them like a warp core on a Star
> trek episode in a worse case scenario lol.   I do carry an extinguisher at
> all times as per safe boating regulations, mine is 2x the min. size
> required just in case.  I see a lot of these lithium batteries come with
> chargers that are only 2 pin so I suspect they are a fixed top voltage and
> an internal BMS to limit?   My Sevcons are isolated I know that, what I
> don't know is if the top voltage can be changed.  They have an interface on
> them which allows some settings but I could not find any documentation
> online about them, Sevcon's website has nothing on them, may have to give
> them a call.   I got them on a ebay deal clear out at a really good price.
> If I don't charge with my Sevcons and use the included individual 12v
> chargers, would there still be worry of connecting too many in series?  Is
> it charging,discharging or both the issue when connecting in series?
> 
> Cheers
> Dan
> 
>> On Mon, Mar 11, 2019 at 9:18 PM Jay Summet via EV  wrote:
>> 
>> 
>> 
>>> On 3/11/19 7:40 PM, Dan Baker via EV wrote:
>>> 
>>> I have two really nice 17amp 48v Sevcon lead acid chargers,  would I be
>>> able to use them with these Lithium packs (connected to match 48v of
>> batts
>>> of course)?
>>> 
>> 
>> You can certainly hook up a Lead Acid battery charger to a Lithium
>> battery bank, and it will charge the cells as long as it's voltage is
>> above the battery bank voltage. Doing so is probably not safe however.
>> 
>> The trick is stopping the charge right when the cells are full, but not
>> overcharging them.  If you overcharge a flooded Lead Acid battery, it
>> bubbles a bit of Hydrogen out and the next time you top it up with
>> distilled water everything is good. (This is how they equalize all the
>> cells in a Lead Acid battery...they overcharge them all until they all
>> bubble)
>> 
>> If you did the same to a lithium ion battery, it may burst into flames
>> very energetically, so your charger must be able to detect the voltage
>> level of every cell and stop charging the pack as soon as any cell
>> reaches it's "maximum" voltage.
>> 
>> Typically a "12 volt" charger will go up to 14.6 volts for a while to
>> equalize all six of the 2 volt cells in a lead acid battery, and then
>> drop down to 13.6 volts to maintain (float) the charge.)  In the same
>> way, a "48 volt" charger may actually go up to 58.4 volts.
>> 
>> 
>> You need to make sure that your "48 volt" lithium ion batteries can
>> safely be charged up to 58.4 volts (and that there is some way to make
>> sure that none of the cells are out of balance, because if even one cell
>> is too high, it may burst into flamesigniting other cells.)
>> 
>> So, if you have a BMS that can turn a relay to turn off your
>> chargers...you probably could use those chargers to charge your
>> batteries safely. As long as the relay/bms worked every time.
>> 
>> Typically, a charger dedicated for LiIon batteries allows you to program
>> a specific stopping voltage (or comes pre-programmed for the appropriate
>> voltage of your pack.) They sometimes also have other safety features
>> such as automatically stopping after a set time limit, or a set number
>> of amp hours, or watt hours have been delivered, even if the voltage
>> hasn't reached the stopping point. They also usually have some way to
>> interact with a BMS (or a built in BMS) that allows them to stop
>> charging if any single cell within the pack goes above the max voltage
>> per cell.
>> 
>> Jay
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Re: [EVDL] Alibaba/Aliexpress Lithium

[Jay Summet via EV]

On 3/12/19 9:59 AM, Dan Baker via EV wrote:


If I don't charge with my Sevcons and use the included individual 12v
chargers, would there still be worry of connecting too many in series?  Is
it charging,discharging or both the issue when connecting in series?


That depends entirely upon the battery model/manufacturer and the specs 
for that specific battery.  If there is an issue, it would most likely 
be an issue for both charging and discharging.


The thing to watch out for is if the batteries have a MOSFET (solid 
state switch) that is used to disconnect the battery when charging (done 
charging, voltage too high) or when discharging (voltage too low).  In 
many cases, the MOSFETS are not rated for super high voltages. It may be 
twice the working voltage or much higher (24,36 or perhaps 60 volt 
rated).  If your series pack goes above the MOSFET rating, it is likely 
to fail spectacularly (short closed in the worst case) when it is asked 
to disconnect the battery.


If the batteries use relays or contractors, they may or may not be rated 
for higher series voltages, you need to verify.


In short, the electronics that are making these batteries "drop in 
replacements" for a 12 volt battery are designed to work at that voltage 
level...with perhaps  a 2x or 4x safety factor (24 to 48 volts), but the 
system was not designed for high voltage (72-144 or higher) to be seen 
by the battery.


The BattleBorn batteries for example use 60V electronics, and are rated 
to be used in series up to a 48 volt system (They were designed this way 
to be a drop in replacement for 12, 24, 36 and 48 volt solar power 
systemsbut many "auto starter" or RV replacement batteries gave no 
thought about using more than one in series, or if they did, it was only 
up to a 24 or 48 volt level.)


Jay

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Re: [EVDL] Alibaba/Aliexpress Lithium

[Dan Baker via EV]

Thank you again for the great info Jay.  Fire is never a good thing with
any vehicle and fires on boats are much worse than land vehicles, you
likely won't drown or your car wont sink if it catches fire.  Perhaps I can
install a trapdoor below my batts and eject them like a warp core on a Star
trek episode in a worse case scenario lol.   I do carry an extinguisher at
all times as per safe boating regulations, mine is 2x the min. size
required just in case.  I see a lot of these lithium batteries come with
chargers that are only 2 pin so I suspect they are a fixed top voltage and
an internal BMS to limit?   My Sevcons are isolated I know that, what I
don't know is if the top voltage can be changed.  They have an interface on
them which allows some settings but I could not find any documentation
online about them, Sevcon's website has nothing on them, may have to give
them a call.   I got them on a ebay deal clear out at a really good price.
If I don't charge with my Sevcons and use the included individual 12v
chargers, would there still be worry of connecting too many in series?  Is
it charging,discharging or both the issue when connecting in series?

Cheers
Dan

On Mon, Mar 11, 2019 at 9:18 PM Jay Summet via EV  wrote:

>
>
> On 3/11/19 7:40 PM, Dan Baker via EV wrote:
> >
> > I have two really nice 17amp 48v Sevcon lead acid chargers,  would I be
> > able to use them with these Lithium packs (connected to match 48v of
> batts
> > of course)?
> >
>
> You can certainly hook up a Lead Acid battery charger to a Lithium
> battery bank, and it will charge the cells as long as it's voltage is
> above the battery bank voltage. Doing so is probably not safe however.
>
> The trick is stopping the charge right when the cells are full, but not
> overcharging them.  If you overcharge a flooded Lead Acid battery, it
> bubbles a bit of Hydrogen out and the next time you top it up with
> distilled water everything is good. (This is how they equalize all the
> cells in a Lead Acid battery...they overcharge them all until they all
> bubble)
>
> If you did the same to a lithium ion battery, it may burst into flames
> very energetically, so your charger must be able to detect the voltage
> level of every cell and stop charging the pack as soon as any cell
> reaches it's "maximum" voltage.
>
> Typically a "12 volt" charger will go up to 14.6 volts for a while to
> equalize all six of the 2 volt cells in a lead acid battery, and then
> drop down to 13.6 volts to maintain (float) the charge.)  In the same
> way, a "48 volt" charger may actually go up to 58.4 volts.
>
>
> You need to make sure that your "48 volt" lithium ion batteries can
> safely be charged up to 58.4 volts (and that there is some way to make
> sure that none of the cells are out of balance, because if even one cell
> is too high, it may burst into flamesigniting other cells.)
>
> So, if you have a BMS that can turn a relay to turn off your
> chargers...you probably could use those chargers to charge your
> batteries safely. As long as the relay/bms worked every time.
>
> Typically, a charger dedicated for LiIon batteries allows you to program
> a specific stopping voltage (or comes pre-programmed for the appropriate
> voltage of your pack.) They sometimes also have other safety features
> such as automatically stopping after a set time limit, or a set number
> of amp hours, or watt hours have been delivered, even if the voltage
> hasn't reached the stopping point. They also usually have some way to
> interact with a BMS (or a built in BMS) that allows them to stop
> charging if any single cell within the pack goes above the max voltage
> per cell.
>
> Jay
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Re: [EVDL] Alibaba/Aliexpress Lithium

[Jay Summet via EV]

On 3/11/19 7:40 PM, Dan Baker via EV wrote:


I have two really nice 17amp 48v Sevcon lead acid chargers,  would I be
able to use them with these Lithium packs (connected to match 48v of batts
of course)?



You can certainly hook up a Lead Acid battery charger to a Lithium 
battery bank, and it will charge the cells as long as it's voltage is 
above the battery bank voltage. Doing so is probably not safe however.


The trick is stopping the charge right when the cells are full, but not 
overcharging them.  If you overcharge a flooded Lead Acid battery, it 
bubbles a bit of Hydrogen out and the next time you top it up with 
distilled water everything is good. (This is how they equalize all the 
cells in a Lead Acid battery...they overcharge them all until they all 
bubble)


If you did the same to a lithium ion battery, it may burst into flames 
very energetically, so your charger must be able to detect the voltage 
level of every cell and stop charging the pack as soon as any cell 
reaches it's "maximum" voltage.


Typically a "12 volt" charger will go up to 14.6 volts for a while to 
equalize all six of the 2 volt cells in a lead acid battery, and then 
drop down to 13.6 volts to maintain (float) the charge.)  In the same 
way, a "48 volt" charger may actually go up to 58.4 volts.



You need to make sure that your "48 volt" lithium ion batteries can 
safely be charged up to 58.4 volts (and that there is some way to make 
sure that none of the cells are out of balance, because if even one cell 
is too high, it may burst into flamesigniting other cells.)


So, if you have a BMS that can turn a relay to turn off your 
chargers...you probably could use those chargers to charge your 
batteries safely. As long as the relay/bms worked every time.


Typically, a charger dedicated for LiIon batteries allows you to program 
a specific stopping voltage (or comes pre-programmed for the appropriate 
voltage of your pack.) They sometimes also have other safety features 
such as automatically stopping after a set time limit, or a set number 
of amp hours, or watt hours have been delivered, even if the voltage 
hasn't reached the stopping point. They also usually have some way to 
interact with a BMS (or a built in BMS) that allows them to stop 
charging if any single cell within the pack goes above the max voltage 
per cell.


Jay
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Re: [EVDL] Alibaba/Aliexpress Lithium

[Jay Summet via EV]

On 3/11/19 4:49 PM, Lawrence Rhodes via EV wrote:
If the problem is charging, charging using multiple chargers will work. 


Just make sure that the chargers are isolated if you are using them on 
different parts of the same pack without breaking the pack up into 
sections with a physical disconnect.


Jay
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Re: [EVDL] Alibaba/Aliexpress Lithium

[Dan Baker via EV]

Thank you everyone for the response so far, lots of information to
consider as usual. I currently running my boat at 48 volts but considering
running at 96 to reduce amperage, heat and a not so silent gear set.
Interesting on the 12v voltage limits Jay.  4 packs of 12v 100ah currently
look to be cheaper than a single 48v 100ah pack, likely due to the
popularity of 12v over 48v I suspect.  I currently use 4 x 12v 170ah
datacenter batts so I would likely have to run 8 x12v or 2 x 48 to keep
range up but more importantly the max discharge rate per cell in check.
These packs don't look to have much design around cooling.  It looks like
either 2 x 48 or 8 x 12 weight about the same, around 110lbs, which would
reduce weight by more than 360lbs over my leads  .

I have two really nice 17amp 48v Sevcon lead acid chargers,  would I be
able to use them with these Lithium packs (connected to match 48v of batts
of course)?

Cheers
Dan

On Mon, Mar 11, 2019 at 7:10 PM Lawrence Rhodes via EV 
wrote:

> If the problem is charging, charging using multiple chargers will work.
> If the problem is in discharge I don't know a solution.  Batteries in my
> scooter still at a proper voltage after charging.  I have only done a
> couple trips.  Nice not to see the voltage drop until a hill.  Lawrence
> Rhodes
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Re: [EVDL] Alibaba/Aliexpress Lithium

[Lawrence Rhodes via EV]

If the problem is charging, charging using multiple chargers will work.  If the 
problem is in discharge I don't know a solution.  Batteries in my scooter still 
at a proper voltage after charging.  I have only done a couple trips.  Nice not 
to see the voltage drop until a hill.  Lawrence Rhodes
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Re: [EVDL] Alibaba/Aliexpress Lithium packs

[Willie via EV]

On 3/11/19 8:29 AM, Dan Baker via EV wrote:

Hello EVDL members

I'm looking at replacing the lead pack on my pontoon boat this year with a


A very interesting discussion.

I have had very good luck using 36v hoverboard batteries in 36v golf 
carts.  Massively paralleled, maybe as many as 40 HB batteries which are 
supposed to be 10S2P.  About 5 HB batteries seem sufficient to run a 
golf cart; the larger number I use for range.  Using standard 42v 
lithium chargers.


I started a 48v golf cart project using ~48v Volt modules.  I had not 
settled on a good charging solution at the time I put the project aside; 
no OTS chargers to match the Volt voltage seem available.


I believe it is Lawrence here that put some 12v Valences in a scooter. 
Maybe 2S for 24v.  I hope he keeps us apprised of successes and 
failures.  The 12v lead replacement batteries are attractive mainly 
because they can supposedly be charged with lead chargers and are 
supposedly "bullet proof" in dealing with over demand and over charging.


If the price is low enough, I, personally, am willing to try something 
that may not work.  I've bought some stuff through AliExpress and have 
been generally satisfied.


I encourage Dan to continue to post on his project.

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Re: [EVDL] Alibaba/Aliexpress Lithium packs

[Jay Summet via EV]

On 3/11/19 9:29 AM, Dan Baker via EV wrote:

I see on Aliexpress that they have 12v and
48v 100ah packs with built in BMS that look be the best prices I've seen.
One issue with using multiple 12v or 48V drop in replacement batteries 
in an EV is that the BMS system may ONLY work at a maximum of 12 or 48 
volts. (e.g. if you put multiple in series, to get a total pack voltage 
of 120-144 volts (or more), the mosfets, etc used in the BMS to 
disconnect the individual batteries in a low-power or over-charge 
scenario may fail (spectacularly).


For example, the BattleBorn 12 volt battery specifically say that you 
can ONLY put them in series up to 48 volts (I expect they are using 60 
volt rated mosfets).


This depends entirely upon the BMS/battery construction (some of them 
just have a balancing BMS which is isolated, and does not even try to 
disconnect the battery from the rest of the system in an over or under 
voltage type of situation...these guys are actually safer to put in 
series...


Jay
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Re: [EVDL] Alibaba/Aliexpress Lithium packs

[Michael Ross via EV]

My experience (limited and dated to be sure) is you get what you pay for.
In particular, a cheaper pack with a no name source, the cells may not be
well matched in capacity and the BMS may be total crap. I tried to carry on
conversations with a couple suppliers at this tier and found that they knew
almost nothing about the cells they used, or how to test them to see if
they had any quality and consistency. They offered graphs and specs that
made no sense at all. Axes not labeled, missing information, etc. I believe
they were running long tests at levels that would never damage or detect a
defective cell, but they had a lot of repititions so it sounded OK. If you
don't know much about the cells in your packs, then you can't set up the
battery management so it does a good job.

Its a jungle out there.

On Mon, Mar 11, 2019, 9:35 AM Dan Baker via EV  wrote:

> Hello EVDL members
>
> I'm looking at replacing the lead pack on my pontoon boat this year with a
> much lighter lithium solution.  I see on Aliexpress that they have 12v and
> 48v 100ah packs with built in BMS that look be the best prices I've seen.
>  These are brands I have not heard before (GTK/Demuda, etc) The area I live
> in doesn't have a lot of EVs so finding used cells for DIY is quite
> sparse.  Anyone have any experience with purchasing packs from Aliexpress,
> are they any good?
>
> Thank you
> Dan
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[EVDL] Alibaba/Aliexpress Lithium packs

[Dan Baker via EV]

Hello EVDL members

I'm looking at replacing the lead pack on my pontoon boat this year with a
much lighter lithium solution.  I see on Aliexpress that they have 12v and
48v 100ah packs with built in BMS that look be the best prices I've seen.
 These are brands I have not heard before (GTK/Demuda, etc) The area I live
in doesn't have a lot of EVs so finding used cells for DIY is quite
sparse.  Anyone have any experience with purchasing packs from Aliexpress,
are they any good?

Thank you
Dan
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