Lipo fire - Accidentally charged 14S with BMS @ 84V - should BMS have prevented this?

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Koalemos   1 mW

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Lipo fire - Accidentally charged 14S with BMS @ 84V - should BMS have prevented this?

Post by Koalemos » Jan 29 2018 12:10pm

Obviously this was a (very stupid) mistake on my part.
I should have had implemented better controls to not use the wrong charger.
I have used color coded plugs to prevent this in the past...

However, this time I had a programmable charger that I had used at 58.8V all summer.
I reprogrammed it to 84V for another pack.
Inadvertently used it back on my 14S /58.8V pack and... puff! - a few hours later I had a fireball.

Questions: I'm surprised the the BMS did not cutoff charging once a cell hit 4.2V - what could have caused this overcharging?
Perhaps the FETs were not rated for higher voltages?

Should mention that I had two 14S packs/BMS plugged in parallel while charging - note that I've bulked charged BMS's in parallel for years (at proper voltage) with no issue.

I'd like to hear your thoughts.

PS. No one was hurt - just significant property damage.

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fechter   100 GW

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Re: Lipo fire - Accidentally charged 14S with BMS @ 84V - should BMS have prevented this?

Post by fechter » Jan 29 2018 12:23pm

I guess that is one possibility. Fist cell reaches HVC, the charge FET switches off, and immediately blows and becomes shorted. But the charge control FETs are usually rated for the pack voltage, and when it goes open during charge, it will only see the difference between the charger and pack. I think the BMS should have prevented this if it was working properly.

If the BMS isn't burnt beyond recognition, it should be possible to test for at least some failure modes.

It sounds like nobody was injured and your house wasn't destroyed. That's very fortunate.
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Re: Lipo fire - Accidentally charged 14S with BMS @ 84V - should BMS have prevented this?

Post by 999zip999 » Jan 29 2018 8:51pm

Sorry to hear your lost. I had one bad fire. And the next thing are looters. For some reason looters follow a disaster. Sorry state of man.

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Re: Lipo fire - Accidentally charged 14S with BMS @ 84V - should BMS have prevented this?

Post by jonyjoe303 » Jan 29 2018 9:25pm

The bms when it triggers it doesnt completely turn off the pack it just suppose to not to let any more amps in. The charger will continue to read a battery voltage, it will be a lower voltage. With the right charger it wont go higher than its rating but since you had higher rating charger, it was trying to forcibly keep charging it. As long as the charger sees a low battery it will keep trying to charge it.

I see this all the time when I'm charging my 4s battery with my solar controller, even though I set it to max out at 14.6 volts, when the bms trips the solar controller trys to keep charging it at up to 24 volts, I burn out many fans because of this. Hit your bms with high enough volts and amps and it will short something out.

One thing I do now is use a overvoltage relay to disconnect the battery when the voltage reaches a certain level, its a deadman switch in case the bms fails. You can find them on ebay for less than 6 dollars, I got it connected to a larger automotive relay.

The only safe way to charge lithiums is with a balance charger, all other methods rely on the bms and that can fail. This relay for instance, even with the wrong charger as soon as the pack voltage climb to 58 volts or what you set it too it would trip the relay and stop all power going to the pack. Its cheap insurance and very easy to connect.
a overvoltage relay.jpg
a overvoltage relay.jpg (39.26 KiB) Viewed 2049 times

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Re: Lipo fire - Accidentally charged 14S with BMS @ 84V - should BMS have prevented this?

Post by dogman dan » Jan 30 2018 8:33am

Ouch!

I hope the fire did not leave you nowhere to live.

I've been wanting a satiator, for that ability to charge any voltage, but on the other hand sticking to one voltage for everything in the garage starts making even more sense.

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Re: Lipo fire - Accidentally charged 14S with BMS @ 84V - should BMS have prevented this?

Post by spinningmagnets » Jan 30 2018 9:16am

I'd even go so far as to change the plugs on chargers of the the odd voltage. Not so much for me, but family members might just plug the charger in (how hard can that be?) when I'm not there.

I have three ebike batteries, and three chargers, all the same voltage...

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Re: Lipo fire - Accidentally charged 14S with BMS @ 84V - should BMS have prevented this?

Post by Koalemos » Jan 30 2018 9:27am

spinningmagnets wrote:
Jan 30 2018 9:16am
I'd even go so far as to change the plugs on chargers of the the odd voltage. Not so much for me, but family members might just plug the charger in (how hard can that be?) when I'm not there.

I have three ebike batteries, and three chargers, all the same voltage...
I was using 2.5mm plug with color coding for 13S vs 14S and xt60 only for 20S, but got lazy and started charging 14S with xt60 as well...lesson learned.

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Re: Lipo fire - Accidentally charged 14S with BMS @ 84V - should BMS have prevented this?

Post by Koalemos » Jan 30 2018 9:30am

dogman dan wrote:
Jan 30 2018 8:33am
Ouch!

I hope the fire did not leave you nowhere to live.

I've been wanting a satiator, for that ability to charge any voltage, but on the other hand sticking to one voltage for everything in the garage starts making even more sense.
It will take a few weeks before I can move back in the house. Lots of electrical damage. Not as bad as your house Dogman, but it was close. I caught it just in time...luckily the basement door was closed and had a sweap making it pretty airtight - otherwise I'd be completely homeless.

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Re: Lipo fire - Accidentally charged 14S with BMS @ 84V - should BMS have prevented this?

Post by Koalemos » Jan 30 2018 9:31am

jonyjoe303 wrote:
Jan 29 2018 9:25pm
One thing I do now is use a overvoltage relay to disconnect the battery when the voltage reaches a certain level, its a deadman switch in case the bms fails. You can find them on ebay for less than 6 dollars, I got it connected to a larger automotive relay.

The only safe way to charge lithiums is with a balance charger, all other methods rely on the bms and that can fail. This relay for instance, even with the wrong charger as soon as the pack voltage climb to 58 volts or what you set it too it would trip the relay and stop all power going to the pack. Its cheap insurance and very easy to connect.
a overvoltage relay.jpg
Thanks for the suggestion. I will look into those.

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Re: Lipo fire - Accidentally charged 14S with BMS @ 84V - should BMS have prevented this?

Post by Koalemos » Jan 30 2018 9:35am

jonyjoe303 wrote:
Jan 29 2018 9:25pm
The bms when it triggers it doesnt completely turn off the pack it just suppose to not to let any more amps in. The charger will continue to read a battery voltage, it will be a lower voltage. With the right charger it wont go higher than its rating but since you had higher rating charger, it was trying to forcibly keep charging it. As long as the charger sees a low battery it will keep trying to charge it.

I see this all the time when I'm charging my 4s battery with my solar controller, even though I set it to max out at 14.6 volts, when the bms trips the solar controller trys to keep charging it at up to 24 volts, I burn out many fans because of this. Hit your bms with high enough volts and amps and it will short something out.
I wonder if the BMS did open the circuit, but maybe the FETs could not handle to the high voltage difference and current, overheated and caused the fire as opposed to the cells overcharging?

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Re: Lipo fire - Accidentally charged 14S with BMS @ 84V - should BMS have prevented this?

Post by Koalemos » Jan 30 2018 9:35am

fechter wrote:
Jan 29 2018 12:23pm
If the BMS isn't burnt beyond recognition, it should be possible to test for at least some failure modes.
Unfortunately it is...

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Re: Lipo fire - Accidentally charged 14S with BMS @ 84V - should BMS have prevented this?

Post by Jon NCal » Jan 30 2018 9:54am

what type of charger was it? My hobby charger has cut offs for amount of ah or time. Maybe we should be using smarter chargers?

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Re: Lipo fire - Accidentally charged 14S with BMS @ 84V - should BMS have prevented this?

Post by 999zip999 » Jan 30 2018 4:12pm

Was it a bms fire or a battery cell fire ?

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Re: Lipo fire - Accidentally charged 14S with BMS @ 84V - should BMS have prevented this?

Post by vex_zg » Jan 30 2018 7:17pm

I've tested my Besttech BMS and it allowed my pack to go overvoltage, to 4.25-4.3V per cell (this was for a short while, I ended this manually and I don't know when it would have stopped)

I can't tell exactly why but the BMS might be counting on bleeding resistors to relieve some voltage (which they can't with their only 100-200mA discharge per cell group), and it might be only looking at total voltage not go too high but then still allow some cell groups to go too high.

that said, I never charge any lithium cells unsupervised (i.e. sleeping, out of house, out of sight)

When I charge my pack I don't trust the BMS or the charger enough to trust them with my life&property, so near the end of the charge I am checking it often with (similar to) cellog plugged in balance port.

If you think about it - when charging - you are entrusting a lot of your safety&property to BMS and Charger, and if they don't terminate correctly, there can easily be a fire.

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Re: Lipo fire - Accidentally charged 14S with BMS @ 84V - should BMS have prevented this?

Post by fechter » Jan 31 2018 9:28am

Many BMS circuits have a high cutoff of 4.3v but balance to 4.2v. Under high rate charge, you get some "reverse sag" so the HVC has to be a little high but still in the safe range. The specifications for the BMS generally show the voltage cutoff points.

If the pack was reaching full, normally the charge current would start to taper down but since the charger voltage was set wrong, it would be still going at maximum current as the cells reached full. I think this is what causes a problem.
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Re: Lipo fire - Accidentally charged 14S with BMS @ 84V - should BMS have prevented this?

Post by Koalemos » Jan 31 2018 2:37pm

999zip999 wrote:
Jan 30 2018 4:12pm
Was it a bms fire or a battery cell fire ?
That's sorta of what I'm trying to figure out. No way of telling from what is left.

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Re: Lipo fire - Accidentally charged 14S with BMS @ 84V - should BMS have prevented this?

Post by Koalemos » Jan 31 2018 2:40pm

fechter wrote:
Jan 31 2018 9:28am
Many BMS circuits have a high cutoff of 4.3v but balance to 4.2v. Under high rate charge, you get some "reverse sag" so the HVC has to be a little high but still in the safe range. The specifications for the BMS generally show the voltage cutoff points.

If the pack was reaching full, normally the charge current would start to taper down but since the charger voltage was set wrong, it would be still going at maximum current as the cells reached full. I think this is what causes a problem.
I agree that's likely the cause, but still you'd think the BMS would open the circuit at HVC and prevent cells from going above 4.3V

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Re: Lipo fire - Accidentally charged 14S with BMS @ 84V - should BMS have prevented this?

Post by fechter » Jan 31 2018 2:53pm

What was the pack capacity?

What was the charger current?

Just trying to estimate the C rate.
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Re: Lipo fire - Accidentally charged 14S with BMS @ 84V - should BMS have prevented this?

Post by Koalemos » Jan 31 2018 3:08pm

fechter wrote:
Jan 31 2018 2:53pm
What was the pack capacity?

What was the charger current?

Just trying to estimate the C rate.
Sure.
14S multistar with 10ah per BMS.
Charger was at 84V and ~2Amps.
When I plugged it in, it was at ~58V...I just wanted to top if off/balance the pack... :roll:

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Re: Lipo fire - Accidentally charged 14S with BMS @ 84V - should BMS have prevented this?

Post by Punx0r » Feb 01 2018 4:06am

The BMS should have disconnected the charger when the first cell hit HVC and bled down the high cell(s) as per it's normal balancing mode. That's what mine did. I think there was something wrong with yours, or it failed through excessive voltage, unfortunately.

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Re: Lipo fire - Accidentally charged 14S with BMS @ 84V - should BMS have prevented this?

Post by dogman dan » Feb 01 2018 8:17am

Much like my fire in some ways. What I did should not have flamed, but it did. Your mistake should have been stopped by a functioning bms.

I also had to wonder if my bms had stopped working right months ago or not. Unbalanced pack charging funny, it should not have charged any cell high enough even at the proper 54.6v if the bms worked. Should have just undercharged it when one cell group got full enough to shut it all off.

But from the ashes, can't tell anything.

Shit happens despite doing things right, which is why I'm now preaching at least charge em outside. Not because it so damn likely to catch fire. Really, its not.

Because its such a damn big fire if it should happen.

Its like the difference between a firecracker( your cell phone) and a stick of dynamite ( your 1000 wh or larger pack)

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Re: Lipo fire - Accidentally charged 14S with BMS @ 84V - should BMS have prevented this?

Post by Koalemos » Feb 01 2018 8:31am

dogman dan wrote:
Feb 01 2018 8:17am
Much like my fire in some ways. What I did should not have flamed, but it did. Your mistake should have been stopped by a functioning bms.

I also had to wonder if my bms had stopped working right months ago or not. Unbalanced pack charging funny, it should not have charged any cell high enough even at the proper 54.6v if the bms worked. Should have just undercharged it when one cell group got full enough to shut it all off.

But from the ashes, can't tell anything.

Shit happens despite doing things right, which is why I'm now preaching at least charge em outside. Not because it so damn likely to catch fire. Really, its not.

Because its such a damn big fire if it should happen.

Its like the difference between a firecracker( your cell phone) and a stick of dynamite ( your 1000 wh or larger pack)
Yeah I charge outside in the summer, but it's too cold to do that in the winter where I live.
For a while I was charging in double metal garbage can, but after a few years of no issue I got a bit complacent and charged them just outside of it. In this case I think the cans would have significantly controlled the damage...
I'm going to have to find a better winter solution...

Side question. they say not to charge below freezing...so how do electric car manufacturer (and owners) get away with charging outdoors?

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Re: Lipo fire - Accidentally charged 14S with BMS @ 84V - should BMS have prevented this?

Post by fechter » Feb 01 2018 9:06am

Koalemos wrote:
Jan 31 2018 3:08pm
Sure.
14S multistar with 10ah per BMS.
Charger was at 84V and ~2Amps.
When I plugged it in, it was at ~58V...I just wanted to top if off/balance the pack... :roll:
0.2C is a pretty conservative rate. Combined with cold temps, heating should not have been an issue.
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