Re: [EVDL] plusing charger controller / no bms

[Paul Compton via EV]

Any charger has internal sensing of its output voltage. This is nearly
always in the form of a resistor divider network.

If you place an additional resistor in parallel with one of the
sensing resistors, you can influence the voltage that the charger
'sees'. Raise the apparent voltage high enough and the charger will
reduce its current output to practically zero.

If the additional resistor is in the form of an opto-isolator, or
opto-isolator+resistor then you now have externaal control that can
connect to a BMS.

This is exacty what Cedric Lynch did on his ultra efficient enclosed
feet forward motorcycle. The Zivan NG3 was hacked and interfaced to
his cell protection boards. Each board could shunt a small amount of
current, but if the voltage across the shunt resistor was high enough,
it would turn on an opto-isolator and limit the output of the charger.

On Fri, 22 Mar 2019 at 06:41, Lee Hart via EV  wrote:
>
> ken via EV wrote:
> >> My charger is set to be the right voltage but the old cells being 22 in
> >> series string they need to equalized out at the top/end of the charge.
> >> this requires some battery baby sitting,
> >>
> >> if your cells are staying very well balanced then your voltage cut off
> >> method/gadjet may be good.
> >>
> >> your ebay gadget coud also be be good for those wanting to do a lower
> >> state of  charge, like turn the voltage down   5 volts for a 10% lower top
> >> charge.
> >>
> >> I have 2 ev scooters with  22 and 24 lfp cells.
>
> This is a harder problem than you might think. Mistakes can lead to
> expensive failures, and even fires! I have several concerns in this
> discussion:
>
> - Lack of knowledge about the cells being charged:
> - Don't know their actual state of balance.
> - Don't know the right voltage to charge them to.
>
> - Lack of information on exactly what the charger is doing:
> - What voltage and current does it actually charge to?
> - What exactly makes it decide the battery is full?
> - And, does it really shut off, or keep on "float" charging?
>
> - Human nature: People who are inexperienced tend to:
> - Guess.
> - Ignore the problem.
> - Seek bad advice (that tells them what they want to hear).
> - Then go with the cheapest solution.
>
> So, my advice is to learn all you can! Get data sheets for the batteries
> and charger in question. If you can't, make measurements for yourself
> (don't rely on assumptions, or bogus experts on the internet. or
> marketing claims from unknown suppliers).
>
> If you go without a BMS, understand that any minor failure is likely to
> escalate into a *major* failure before you notice it! It's like deciding
> you don't need any expensive fuses or circuit breakers in your house
> wiring; just wire everything directly to the incoming power. Cheap!
> Easy! And it works fine, until the first time anything anywhere happens
> to fail shorted. Then it burns your house down.
>
> Now, on the subject of a voltage-sensing controller: This is a simple
> method of shutting off a "dumb" charger for a lead-acid pack. That's
> because voltage is a reasonable indication of state of charge for
> lead-acid. Also, overcharging an old or damaged string of lead-acid
> batteries may cause early cell failures; but they are not likely to be
> spectacular disasters.
>
> For charging lithiums, you really need to know the voltage *and* current
> *and* time to turn off the charger. Voltage alone is not enough.
>
> The normal approach is to have a charger that is smart enough to shut
> off when the voltage and current and time are all "right". It won't
> charge to an excessive voltage; and it will turn itself off if the
> current stays too high for too long (an indication that something is
> wrong). A good charger will also have some form of temperature sensing,
> as the correct conditions are temperature-dependent.
>
> But if the charger is only sensing total voltage, it won't know if just
> one cell fails in the pack. That one cell could go seriously
> over-voltage, or fail shorted. In either case, this can lead to a fire.
> That's why you normally have a BMS. It senses each cell, and can stop
> the charger if something goes wrong.
>
> If you are a cheapskate, and don't believe in BMS, then at the very
> least I would suggest something like my Batt-Bridge
> . It will at least warn
> you that something is wrong *before* the disaster. You can also use the
> light from the Batt-Bridge LEDs to control a relay to shut down the
> charger (if charging) or motor controller (if driving).
>
> --
> 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: 

Re: [EVDL] plusing charger controller / no bms

[EVDL Administrator via EV]

This is kind of long (I tend to run on, sorry).  Please bear with me and 
I'll eventually come to the point.

I'm sort of the electronics equivalent of a shadetree mechanic.  I've hacked 
(in the good sense) electronics since I was a teenager.  ICs weren't really 
available to hobbyists then.  My early tinkering was with tubes, germanium 
semiconductors, and eventually silicon semiconductors. 

You young whippersnappers don't know what you've missed, not getting to play 
with 6SL7 and 6V6 tubes, inefficient selenium rectifiers, and 800 volt B+ 
supplies (yeah, I got zapped a few times).

So even though I'm a EE dropout, I have a lot of years of messing around 
with electronics and, with a little research and luck, making things work.

I'm glad to say that despite doing some moderately stupid things, I've never 
started any fires.  I want to keep it that way, which is the reason that 
when I started using lithium batteries for a few tasks, I did NOT try to 
hack up my own lithium batteries.  

Instead, I did my homework, researching who made reliable batteries with 
charging systems.  Then I bought them.  

Yes, they cost me more than buying bare cells on Ebay and tacking them 
together -- quite a bit more.  They cost me more than Aliexpress junk.  But 
they worked right out of the shipping box, delivering their rated capacity 
and then some. 

And they STILL work.  The batteries I bought from Li Ping in early 2012 are 
still producing over 90% of their rated capacity.  

You'll find lots of lithium hackers in Youtube channels, forums, and social 
media, who swear that they don't need no steenkin' BMSes.  You'll even find 
some who claim that BMSes *cause* fires.  You can identify these folks by 
their frequent use of the phrase "bottom balancing."

With all due respect, and at the risk of offending someone, I suggest that 
you not listen to them.

Your mobile phone has smart charging and discharging control.  (The charger 
IS the BMS because phones need only one lithium cell.)  Every laptop and 
tablet has a smart BMS and charging/discharging control.  Every good lithium 
power tool and home appliance has them.  Every production EV has them.  

With some notable exceptions (*cough* cheap Chinese hoverboards *cough*), 
these are lithium battery systems designed by experienced engineers.  Some 
engineers are better than others, and some bean counters managing them are 
more ethical than others, but by and large you can reasonably expect that 
you can leave a lithium-powered commercial product charging on your kitchen 
counter and it won't burst into flames.  That's because it has appropriate 
charging / discharging control.

There are people on the EVDL who have the engineering chops to design a 
lithium battery system that maximizes the life of the cells and prevents 
such disasters as fires and explosions.  However, I'm not one of them.  With 
all due respect, from what you've posted here, I don't think you are either.

In fact, one of the EV conversion pioneers that I greatly respect, Bob 
Batson of EV America, didn't try to design his own lithium battery system 
either.  He referred his customers who wanted lithium to companies with more 
experience with it.  More recently he's taken on an experienced supply 
partner for lithium.  He wisely knew and knows his own limitations.

http://evamerica.com/flux.html

I'm not recommending Bob's batteries.  I can't, since I haven't used them.  
I'm just pointing out that designing a safe and long-lived lithium battery 
for an EV is not a trivial project.  It's not (IMO) a good one for EV 
hackers like me.  

I strongly suggest that instead of jumping in feet first and maybe having to 
jump out and run really fast on singed feet, you keep using lead for a 
while.  Save up your pennies until you can afford to buy a well designed 
integrated lithium battery SYSTEM (cells, BMS, charger).

It might be boring, but it will help avoid the kind of excitement that you 
probably don't want.

David Roden - Akron, Ohio, USA
EVDL Administrator

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Re: [EVDL] plusing charger controller / no bms

[paul dove via EV]

Doesn't somebody have to die for a Darwin award?
 

On Friday, March 22, 2019, 11:44:25 AM CDT, Lee Hart via EV 
 wrote:  
 
 Dan Baker via EV wrote:
> Thanks guys for the information. Ken and I are reaching out for help so
> don't spank us yet for putting in something dangerous lol.

Hi guys,

I'm not trying to "spank" anyone. Just get them to look before they leap!

Did you ever have a (usually teenage) friend say, "Hold my beer and 
watch this..." What followed was one of those disasterous "Darwin award" 
moments that you can only laugh about years later.

I've *been* one of those "teenagers" myself. I've done some amazingly 
stupid things out of ignorance, or just to "see what happens if..." So 
some of the things in this discussion set off alarm bells.

> In my case, where I plan to use a BMS but want to reuse a lead charger,
> a BMS and voltage cut-off so the charger doesn't just send amps to the
> shunts when all cells reach full charge is a bad idea?

It is a bad idea. It only works if

- You KNOW the voltage and current that the charger actually delivers 
when the BMS tries to shunt current around a cell.

- You KNOW the BMS can safely shunt the charger's current at that time.

- You KNOW that something will turn the charger off before it sits too 
long under these conditions.

You will have to test this for yourself. Do not trust the charger or BMS 
manufacturer's marketing claims. They will say anything to "make the 
sale", and will not accept *any* responsibility if things go wrong!

> Without a CAN bus, how does the charger know when to turn off?

Exactly! A lead-acid charger may *never* turn off. Many simply stay on 
"forever", on the assumption that a lead-acid battery won't be harmed 
(too much) by being left on a "float" charge forever.

> Does it need to turn off?

Yes! This is intolerable for lithiums. You have to be SURE the charger 
turns off, or the cells will get charged to death.

> Most of the pre-built packs for sale I have seen only employ 2 wires
> (sometimes a third for temp) to the battery which say they have an on-board 
> BMS.

The cheapest (and so most common) scheme is no BMS at all. They depend 
on the cells being matched well enough that you won't need a BMS until 
they age a bit and start to drift apart.

The second-cheapest scheme (which covers alomst everything else) is 
something equivalent to a zener diode across each cell. When it reaches 
some voltage, it shunts the charging current away from the cell.

This only works if the charger is delivering a current that is *lower* 
than the shunt can safely handle. Most shunts are tiny; they can only 
bypass maybe 100 milliamps of current.

If the shunts can't handle the charger's current, they burn up or fail. 
Then you have no protection. The next thing to fail is the cell (perhaps 
spectacularly).

Even if the shunt can handle the charging current, it is converting it 
to heat. This heat is dumped into the battery box. Having large numbers 
of shunts all producing heat for long periods is a bad thing, as heat 
kills lithium cells. That's why you must *know* that the charger will 
shut down in some relatively short time period.

> I know in lead charging, the amperage draw slowly drops to near 0 as
> the pack reaches full charge.

Yes, if all the cells are good. If a cell is bad, or the pack is hot, or 
old, the current does not drop off at full charge. Lead-acids can "take 
it" for a while (this is how you equalize them).

> With Lithium and a BMS, when the cells reach full charge
> (determined by the BMS) and the BMS shunts the load, is that load
> significant?  I have looked at a few BMS boards so far, none seem to have a
> relay or signal that controls the charger power so I'm assuming a fully
> shunted BMS isnt that much of a load.

If the BMS is any good, it will have an output that either tells a 
"smart" charger to shut off, or can control a relay to force a "dumb" 
charger to shut off.

Assuming your BMS has such an output, you also want to be sure it is 
"fail safe". That is, if the BMS fails, it STOPS the charger. Too many 
cheap ones can fail "on".

-- 
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] plusing charger controller / no bms

[Lee Hart via EV]

Dan Baker via EV wrote:

Thanks guys for the information. Ken and I are reaching out for help so
don't spank us yet for putting in something dangerous lol.


Hi guys,

I'm not trying to "spank" anyone. Just get them to look before they leap!

Did you ever have a (usually teenage) friend say, "Hold my beer and 
watch this..." What followed was one of those disasterous "Darwin award" 
moments that you can only laugh about years later.


I've *been* one of those "teenagers" myself. I've done some amazingly 
stupid things out of ignorance, or just to "see what happens if..." So 
some of the things in this discussion set off alarm bells.



In my case, where I plan to use a BMS but want to reuse a lead charger,
a BMS and voltage cut-off so the charger doesn't just send amps to the
shunts when all cells reach full charge is a bad idea?


It is a bad idea. It only works if

- You KNOW the voltage and current that the charger actually delivers 
when the BMS tries to shunt current around a cell.


- You KNOW the BMS can safely shunt the charger's current at that time.

- You KNOW that something will turn the charger off before it sits too 
long under these conditions.


You will have to test this for yourself. Do not trust the charger or BMS 
manufacturer's marketing claims. They will say anything to "make the 
sale", and will not accept *any* responsibility if things go wrong!



Without a CAN bus, how does the charger know when to turn off?


Exactly! A lead-acid charger may *never* turn off. Many simply stay on 
"forever", on the assumption that a lead-acid battery won't be harmed 
(too much) by being left on a "float" charge forever.



Does it need to turn off?


Yes! This is intolerable for lithiums. You have to be SURE the charger 
turns off, or the cells will get charged to death.



Most of the pre-built packs for sale I have seen only employ 2 wires
(sometimes a third for temp) to the battery which say they have an on-board BMS.


The cheapest (and so most common) scheme is no BMS at all. They depend 
on the cells being matched well enough that you won't need a BMS until 
they age a bit and start to drift apart.


The second-cheapest scheme (which covers alomst everything else) is 
something equivalent to a zener diode across each cell. When it reaches 
some voltage, it shunts the charging current away from the cell.


This only works if the charger is delivering a current that is *lower* 
than the shunt can safely handle. Most shunts are tiny; they can only 
bypass maybe 100 milliamps of current.


If the shunts can't handle the charger's current, they burn up or fail. 
Then you have no protection. The next thing to fail is the cell (perhaps 
spectacularly).


Even if the shunt can handle the charging current, it is converting it 
to heat. This heat is dumped into the battery box. Having large numbers 
of shunts all producing heat for long periods is a bad thing, as heat 
kills lithium cells. That's why you must *know* that the charger will 
shut down in some relatively short time period.



I know in lead charging, the amperage draw slowly drops to near 0 as
the pack reaches full charge.


Yes, if all the cells are good. If a cell is bad, or the pack is hot, or 
old, the current does not drop off at full charge. Lead-acids can "take 
it" for a while (this is how you equalize them).



With Lithium and a BMS, when the cells reach full charge
(determined by the BMS) and the BMS shunts the load, is that load
significant?  I have looked at a few BMS boards so far, none seem to have a
relay or signal that controls the charger power so I'm assuming a fully
shunted BMS isnt that much of a load.


If the BMS is any good, it will have an output that either tells a 
"smart" charger to shut off, or can control a relay to force a "dumb" 
charger to shut off.


Assuming your BMS has such an output, you also want to be sure it is 
"fail safe". That is, if the BMS fails, it STOPS the charger. Too many 
cheap ones can fail "on".


--
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] plusing charger controller / no bms

[Dan Baker via EV]

Thanks guys for the information. Ken and I are reaching out for help so
don't spank us yet for putting in something dangerous lol.   In my case,
where I plan to use a BMS but want to reuse a lead charger, a BMS and
voltage cut-off so the charger doesn't just send amps to the shunts when
all cells reach full charge is a bad idea?  Without a CAN bus, how does the
charger know when to turn off?  Does it need to turn off?  Most of the
pre-built packs for sale I have seen only employ 2 wires (sometimes a third
for temp) to the battery which say they have an on-board BMS.  I know in
lead charging, the amperage draw slowly drops to near 0 as the pack reaches
full charge.  With Lithium and a BMS, when the cells reach full charge
(determined by the BMS) and the BMS shunts the load, is that load
significant?  I have looked at a few BMS boards so far, none seem to have a
relay or signal that controls the charger power so I'm assuming a fully
shunted BMS isnt that much of a load.

Thanks again
Dan

On Fri, Mar 22, 2019 at 8:45 AM Steve Heath via EV 
wrote:

> Wise words indeed. The price of a BMS is so cheap these days that it is
> almost inconceivable not to fit one.
>
> Steve
>
> On 22/03/2019 06:42, Lee Hart via EV wrote:
> > ken via EV wrote:
> >>> My charger is set to be the right voltage but the old cells being 22 in
> >>> series string they need to equalized out at the top/end of the charge.
> >>> this requires some battery baby sitting,
> >>>
> >>> if your cells are staying very well balanced then your voltage cut off
> >>> method/gadjet may be good.
> >>>
> >>> your ebay gadget coud also be be good for those wanting to do a lower
> >>> state of  charge, like turn the voltage down   5 volts for a 10%
> >>> lower top
> >>> charge.
> >>>
> >>> I have 2 ev scooters with  22 and 24 lfp cells.
> >
> > This is a harder problem than you might think. Mistakes can lead to
> > expensive failures, and even fires! I have several concerns in this
> > discussion:
> >
> > - Lack of knowledge about the cells being charged:
> > - Don't know their actual state of balance.
> > - Don't know the right voltage to charge them to.
> >
> > - Lack of information on exactly what the charger is doing:
> > - What voltage and current does it actually charge to?
> > - What exactly makes it decide the battery is full?
> > - And, does it really shut off, or keep on "float" charging?
> >
> > - Human nature: People who are inexperienced tend to:
> > - Guess.
> > - Ignore the problem.
> > - Seek bad advice (that tells them what they want to hear).
> > - Then go with the cheapest solution.
> >
> > So, my advice is to learn all you can! Get data sheets for the
> > batteries and charger in question. If you can't, make measurements for
> > yourself (don't rely on assumptions, or bogus experts on the internet.
> > or marketing claims from unknown suppliers).
> >
> > If you go without a BMS, understand that any minor failure is likely
> > to escalate into a *major* failure before you notice it! It's like
> > deciding you don't need any expensive fuses or circuit breakers in
> > your house wiring; just wire everything directly to the incoming
> > power. Cheap! Easy! And it works fine, until the first time anything
> > anywhere happens to fail shorted. Then it burns your house down.
> >
> > Now, on the subject of a voltage-sensing controller: This is a simple
> > method of shutting off a "dumb" charger for a lead-acid pack. That's
> > because voltage is a reasonable indication of state of charge for
> > lead-acid. Also, overcharging an old or damaged string of lead-acid
> > batteries may cause early cell failures; but they are not likely to be
> > spectacular disasters.
> >
> > For charging lithiums, you really need to know the voltage *and*
> > current *and* time to turn off the charger. Voltage alone is not enough.
> >
> > The normal approach is to have a charger that is smart enough to shut
> > off when the voltage and current and time are all "right". It won't
> > charge to an excessive voltage; and it will turn itself off if the
> > current stays too high for too long (an indication that something is
> > wrong). A good charger will also have some form of temperature
> > sensing, as the correct conditions are temperature-dependent.
> >
> > But if the charger is only sensing total voltage, it won't know if
> > just one cell fails in the pack. That one cell could go seriously
> > over-voltage, or fail shorted. In either case, this can lead to a
> > fire. That's why you normally have a BMS. It senses each cell, and can
> > stop the charger if something goes wrong.
> >
> > If you are a cheapskate, and don't believe in BMS, then at the very
> > least I would suggest something like my Batt-Bridge
> > . It will at least warn
> > you that something is wrong *before* the disaster. You can also use
> > the light from the Batt-Bridge LEDs to control a relay to shut down
> > the 

Re: [EVDL] plusing charger controller / no bms

[Steve Heath via EV]

Wise words indeed. The price of a BMS is so cheap these days that it is 
almost inconceivable not to fit one.


Steve

On 22/03/2019 06:42, Lee Hart via EV wrote:

ken via EV wrote:

My charger is set to be the right voltage but the old cells being 22 in
series string they need to equalized out at the top/end of the charge.
this requires some battery baby sitting,

if your cells are staying very well balanced then your voltage cut off
method/gadjet may be good.

your ebay gadget coud also be be good for those wanting to do a lower
state of  charge, like turn the voltage down   5 volts for a 10% 
lower top

charge.

I have 2 ev scooters with  22 and 24 lfp cells.


This is a harder problem than you might think. Mistakes can lead to 
expensive failures, and even fires! I have several concerns in this 
discussion:


- Lack of knowledge about the cells being charged:
- Don't know their actual state of balance.
- Don't know the right voltage to charge them to.

- Lack of information on exactly what the charger is doing:
- What voltage and current does it actually charge to?
- What exactly makes it decide the battery is full?
- And, does it really shut off, or keep on "float" charging?

- Human nature: People who are inexperienced tend to:
- Guess.
- Ignore the problem.
- Seek bad advice (that tells them what they want to hear).
- Then go with the cheapest solution.

So, my advice is to learn all you can! Get data sheets for the 
batteries and charger in question. If you can't, make measurements for 
yourself (don't rely on assumptions, or bogus experts on the internet. 
or marketing claims from unknown suppliers).


If you go without a BMS, understand that any minor failure is likely 
to escalate into a *major* failure before you notice it! It's like 
deciding you don't need any expensive fuses or circuit breakers in 
your house wiring; just wire everything directly to the incoming 
power. Cheap! Easy! And it works fine, until the first time anything 
anywhere happens to fail shorted. Then it burns your house down.


Now, on the subject of a voltage-sensing controller: This is a simple 
method of shutting off a "dumb" charger for a lead-acid pack. That's 
because voltage is a reasonable indication of state of charge for 
lead-acid. Also, overcharging an old or damaged string of lead-acid 
batteries may cause early cell failures; but they are not likely to be 
spectacular disasters.


For charging lithiums, you really need to know the voltage *and* 
current *and* time to turn off the charger. Voltage alone is not enough.


The normal approach is to have a charger that is smart enough to shut 
off when the voltage and current and time are all "right". It won't 
charge to an excessive voltage; and it will turn itself off if the 
current stays too high for too long (an indication that something is 
wrong). A good charger will also have some form of temperature 
sensing, as the correct conditions are temperature-dependent.


But if the charger is only sensing total voltage, it won't know if 
just one cell fails in the pack. That one cell could go seriously 
over-voltage, or fail shorted. In either case, this can lead to a 
fire. That's why you normally have a BMS. It senses each cell, and can 
stop the charger if something goes wrong.


If you are a cheapskate, and don't believe in BMS, then at the very 
least I would suggest something like my Batt-Bridge 
. It will at least warn 
you that something is wrong *before* the disaster. You can also use 
the light from the Batt-Bridge LEDs to control a relay to shut down 
the charger (if charging) or motor controller (if driving).



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Re: [EVDL] plusing charger controller / no bms

[Lee Hart via EV]

ken via EV wrote:

My charger is set to be the right voltage but the old cells being 22 in
series string they need to equalized out at the top/end of the charge.
this requires some battery baby sitting,

if your cells are staying very well balanced then your voltage cut off
method/gadjet may be good.

your ebay gadget coud also be be good for those wanting to do a lower
state of  charge, like turn the voltage down   5 volts for a 10% lower top
charge.

I have 2 ev scooters with  22 and 24 lfp cells.


This is a harder problem than you might think. Mistakes can lead to 
expensive failures, and even fires! I have several concerns in this 
discussion:


- Lack of knowledge about the cells being charged:
- Don't know their actual state of balance.
- Don't know the right voltage to charge them to.

- Lack of information on exactly what the charger is doing:
- What voltage and current does it actually charge to?
- What exactly makes it decide the battery is full?
- And, does it really shut off, or keep on "float" charging?

- Human nature: People who are inexperienced tend to:
- Guess.
- Ignore the problem.
- Seek bad advice (that tells them what they want to hear).
- Then go with the cheapest solution.

So, my advice is to learn all you can! Get data sheets for the batteries 
and charger in question. If you can't, make measurements for yourself 
(don't rely on assumptions, or bogus experts on the internet. or 
marketing claims from unknown suppliers).


If you go without a BMS, understand that any minor failure is likely to 
escalate into a *major* failure before you notice it! It's like deciding 
you don't need any expensive fuses or circuit breakers in your house 
wiring; just wire everything directly to the incoming power. Cheap! 
Easy! And it works fine, until the first time anything anywhere happens 
to fail shorted. Then it burns your house down.


Now, on the subject of a voltage-sensing controller: This is a simple 
method of shutting off a "dumb" charger for a lead-acid pack. That's 
because voltage is a reasonable indication of state of charge for 
lead-acid. Also, overcharging an old or damaged string of lead-acid 
batteries may cause early cell failures; but they are not likely to be 
spectacular disasters.


For charging lithiums, you really need to know the voltage *and* current 
*and* time to turn off the charger. Voltage alone is not enough.


The normal approach is to have a charger that is smart enough to shut 
off when the voltage and current and time are all "right". It won't 
charge to an excessive voltage; and it will turn itself off if the 
current stays too high for too long (an indication that something is 
wrong). A good charger will also have some form of temperature sensing, 
as the correct conditions are temperature-dependent.


But if the charger is only sensing total voltage, it won't know if just 
one cell fails in the pack. That one cell could go seriously 
over-voltage, or fail shorted. In either case, this can lead to a fire. 
That's why you normally have a BMS. It senses each cell, and can stop 
the charger if something goes wrong.


If you are a cheapskate, and don't believe in BMS, then at the very 
least I would suggest something like my Batt-Bridge 
. It will at least warn 
you that something is wrong *before* the disaster. You can also use the 
light from the Batt-Bridge LEDs to control a relay to shut down the 
charger (if charging) or motor controller (if driving).


--
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] plusing charger controller / no bms

[Dan Baker via EV]

This might be what we are looking for?

https://www.ebay.com/itm/Voltage-Detection-Relay-Switch-Control-Module-Digital-LED-Display-DC-12V-E2O2/392218823066?hash=item5b5210499a:g:cRkAAOSw-yJcQVCH

On Tue, Mar 19, 2019 at 3:14 PM ken via EV  wrote:

>I understand with a BMS that as per
> > cell voltage is reached shunts/resisters are used, what happens when the
> > pack is fully charged without a smart signal to the charger?  Do the
> > shunts just continue to work absorbing charge/ generating heat?
>
> My charger is set to be the right voltage but the old cells being 22 in
> series string they need to equalized out at the top/end of the charge.
> this requires some battery baby sitting,
>
> if your cells are staying very well balanced then your voltage cut off
> method/gadjet  may  be good .
>
> your ebay gadget coud also be be good for those wanting to do a lower
> state of  charge, like turn the voltage down   5 volts for a 10% lower top
> charge.
>
> I have 2 ev scooters with  22 and 24 lfp cells.
>
> wheres the voltage cut off gagaet on ebay??
>
>
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Re: [EVDL] plusing charger controller / no bms

[ken via EV]

   I understand with a BMS that as per
> cell voltage is reached shunts/resisters are used, what happens when the
> pack is fully charged without a smart signal to the charger?  Do the
> shunts just continue to work absorbing charge/ generating heat?

My charger is set to be the right voltage but the old cells being 22 in
series string they need to equalized out at the top/end of the charge.
this requires some battery baby sitting,

if your cells are staying very well balanced then your voltage cut off
method/gadjet  may  be good .

your ebay gadget coud also be be good for those wanting to do a lower
state of  charge, like turn the voltage down   5 volts for a 10% lower top
charge.

I have 2 ev scooters with  22 and 24 lfp cells.

wheres the voltage cut off gagaet on ebay??


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Re: [EVDL] plusing charger controller

[Dan Baker via EV]

I think Ken and I are looking for the same thing (I hope).  I'm looking to
use "dumb" (non CAN Bus) chargers with a cell pack with a BMS (or in Ken's
case maybe no BMS).  In my case the chargers I have are designed for lead
acid so they have a higher finishing voltage than acceptable for the pack.
Basically employ a circuit that measures voltage and turns a relay on & off
as needed, cycle as necessary or timed. I think these would be much similar
to those ebay programmable digital thermostats with relay, except with
voltage instead.  As the pack reaches top charge, the relay would see the
high voltage and open a relay, likely connected to the AC side of the
charger and turn it off.   I understand with a BMS that as per cell voltage
is reached shunts/resisters are used, what happens when the pack is fully
charged without a smart signal to the charger?  Do the shunts just continue
to work absorbing charge/ generating heat?

On Mon, Mar 18, 2019 at 6:22 PM EVDL Administrator via EV 
wrote:

> On 18 Mar 2019 at 14:04, ken via EV wrote:
>
> > there must be some kind of modaul that you'd input  on seconds / off
> seconds,
> >  then it would run a relay to controll charger on/off  or program an
> > ?adrainal?  the little computer.
>
> You're talking about charging, yes?  I can't understand why you want to do
> this.  I don't see the advantage.  What am I missing?
>
> David Roden - Akron, Ohio, USA
> EVDL Administrator
>
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Re: [EVDL] plusing charger controller

[EVDL Administrator via EV]

On 18 Mar 2019 at 14:04, ken via EV wrote:

> there must be some kind of modaul that you'd input  on seconds / off seconds,
>  then it would run a relay to controll charger on/off  or program an
> ?adrainal?  the little computer.

You're talking about charging, yes?  I can't understand why you want to do 
this.  I don't see the advantage.  What am I missing?

David Roden - Akron, Ohio, USA
EVDL Administrator

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Re: [EVDL] plusing charger controller

[EVDL Administrator via EV]

On 18 Mar 2019 at 13:52, ken via EV wrote:

> i guess i could charging voltage but with current lower than
> shunts. 

Is there a typo in this?  I have no idea what it's supposed to mean.

> 
> where which item  would dc to dc control the amperage  down to 500ma and
> 72 volts ?

Same here.  

I can't tell what you're asking.  

If you want people to help you with these questions, may I suggest that you 
please slow down when you type, and proofread and correct before you send 
the message?   Thanks.

David Roden - Akron, Ohio, USA
EVDL Administrator

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Re: [EVDL] plusing charger controller/ ebay Digital Display Time Delay Relay Timing Timer

[ken via EV]

 
https://www.ebay.com/p/1500w-0-999h-Digital-Display-Time-Delay-Relay-Timing-Timer-Cycling-Module-DC-12v/16027066160?_trksid=p2047675.l2644


theses come in many variations.  some go from  few seconds to 999 hours
with delay also.

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Re: [EVDL] plusing charger controller

[ken via EV]

On Sun, March 17, 2019 6:09 pm, Dan Baker via EV wrote:
> Great question Ken, want the same answer!  I have 2 nice Sevcon Lead acid
>  chargers that I would like to re-purpose for charging Lithium.  End
> voltages would likely be too high, I am planning on running a BMS. But
> when max voltage is obtained I take it the BMS should start taking the
> load instead?  Would keep the cells in check but then the BMS eats lots of

there must be some kind of modaul that you'd input  on seconds / off seconds,
 then it would run a relay to controll charger on/off  or program an
?adrainal?  the little computer.

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Re: [EVDL] plusing charger controller

[ken via EV]

On Mon, March 18, 2019 3:45 am, Steve Heath via EV wrote:
> Alternatively get a dc-dc converter from ebay and use that as the front
> end. Your existing charger is the input and then set the output current and


both packs I have have shunts on each cell, but the bms is not sensing
properly, so i guess i could charging voltage but with current lower than
shunts. it would be slow but non damaging.

where which item  would dc to dc control the amperage  down to 500ma and
72 volts ?

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Re: [EVDL] plusing charger controller

[Steve Heath via EV]

Alternatively get a dc-dc converter from ebay and use that as the front 
end. Your existing charger is the input and then set the output current 
and voltage to match the battery pack.

Used that to charge a 72volt pack from a 48v charger.


Steve

On 18/03/2019 06:20, EVDL Administrator via EV wrote:

On 17 Mar 2019 at 16:39, ken via EV wrote:


I like to see some kind of a charger timer that could control the input
to the charger as on/off

This is pretty much what a cycle dropping charge controller does.  It's a
relatively simple (crude) method.

The charger is designed to produce a voltage higher than the battery's fully
charged (on charge) voltage.  The controller monitors the voltage, and shuts
off the charger when it rises above some threshold (typically 2.35 to 2.45
volts per cell).  With the charger off, the battery voltage then falls until
it crosses some lower threshold (hysteresis), and the charger turns on
again.  This cycle repeats, usually for hours.  As the battery works its way
through its absorption phase, gradually the on time becomes shorter and the
off time longer.  This effectively tapers the average current as the battery
reaches full.

Normally the switching is done at the charger output, but I've seen one
oddball charger where the charger INPUT (tansformer primary) was switched on
and off.

David Roden - Akron, Ohio, USA
EVDL Administrator

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Re: [EVDL] plusing charger controller

[EVDL Administrator via EV]

On 17 Mar 2019 at 16:39, ken via EV wrote:

> I like to see some kind of a charger timer that could control the input
> to the charger as on/off 

This is pretty much what a cycle dropping charge controller does.  It's a 
relatively simple (crude) method.

The charger is designed to produce a voltage higher than the battery's fully 
charged (on charge) voltage.  The controller monitors the voltage, and shuts 
off the charger when it rises above some threshold (typically 2.35 to 2.45 
volts per cell).  With the charger off, the battery voltage then falls until 
it crosses some lower threshold (hysteresis), and the charger turns on 
again.  This cycle repeats, usually for hours.  As the battery works its way 
through its absorption phase, gradually the on time becomes shorter and the 
off time longer.  This effectively tapers the average current as the battery 
reaches full.  

Normally the switching is done at the charger output, but I've seen one 
oddball charger where the charger INPUT (tansformer primary) was switched on 
and off.

David Roden - Akron, Ohio, USA
EVDL Administrator

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Re: [EVDL] plusing charger controller

[paul dove via EV]

What would that accomplish?

Sent from my iPhone

> On Mar 17, 2019, at 4:39 PM, ken via EV  wrote:
> 
> From thoese of us with no bms HVC cut off, or top end shunts, or fragel
> charging circuts or time of day..  I like to see some kind of a charger
> timer that could control the input to the charger as on/offbut like
> for varibale timing like1 min on /  10 mins off  continusly maybe
> some kind of adrilal program or settable timing modual .
> 
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Re: [EVDL] plusing charger controller

[Dan Baker via EV]

Great question Ken, want the same answer!  I have 2 nice Sevcon Lead acid
chargers that I would like to re-purpose for charging Lithium.  End
voltages would likely be too high, I am planning on running a BMS. But when
max voltage is obtained I take it the BMS should start taking the load
instead?  Would keep the cells in check but then the BMS eats lots of watts
and generates heat?

On Sun, Mar 17, 2019 at 6:39 PM ken via EV  wrote:

>  From thoese of us with no bms HVC cut off, or top end shunts, or fragel
> charging circuts or time of day..  I like to see some kind of a charger
> timer that could control the input to the charger as on/offbut like
> for varibale timing like1 min on /  10 mins off  continusly maybe
> some kind of adrilal program or settable timing modual .
>
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[EVDL] plusing charger controller

[ken via EV]

 From thoese of us with no bms HVC cut off, or top end shunts, or fragel
charging circuts or time of day..  I like to see some kind of a charger
timer that could control the input to the charger as on/offbut like
for varibale timing like1 min on /  10 mins off  continusly maybe
some kind of adrilal program or settable timing modual .

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