> 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
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
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
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
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
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
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
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
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%
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.
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
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
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
>
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
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
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
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
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
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
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
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
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)
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
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
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
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
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
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 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
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
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
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
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
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
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
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
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
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
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
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
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,
41 matches
Mail list logo
