What could be the cause of a tripping bms

C

CanadianKid

1 mW
Joined
Sep 10, 2019
Messages
15
Recently individually charged my 20s12p pack with a ISDT q6 to SoC 100%

c1 4.19
2=4.19
3=4.20
4=4.21
5=4.19
6=4.20
7=4.19
8=4.20
9=4.22
10=4.19
11=4.20
12=4.19
13=4.18
14=4.21
15=4.22
16=4.23
17=4.23
18=4.25
19=4.22
20=4.19

The bms trips everytime i put high load over 35AMPS

PS.
Cell*6 was at 0.31v when taking balance back
cell*9was 1.81
cell*11 was 1.45

What could be the culprit here is one of my recently brought back to.life cell wich is odly at 4.2 volt could trip the LVC?? when drawing currwnt on a ebike the voltage sags from 84volt to 82~~ ish volts

Cell 6 wich was at 0.31v took about 12 hours to charge at 3 amps

others took 9 hours
 
pack is new bought it last year and during storage the cels sagged to said voltage. About 20 full cycle MAX
 
Sounds like the BMS is hitting it's current limit, or at least what it thinks is it's current limit. What's it supposed to be rated for?

It's possible that it has multiple current sensing shunts and one (or more) of them has a bad connection to the PCB, which would cause the overcurrent to be tripped at a lower than expected current.
 
its supossed to be a 25-50 but had the same bms before changing it and never had a problem tripping under load
 
It's also possible that one of the cell groups that went dead is actually toast. It might be able to hold full voltage when you charge it but it sags below LVC under load due to high internal resistance.
 
dustNbone said:
Sounds like the BMS is hitting it's current limit, or at least what it thinks is it's current limit. What's it supposed to be rated for?

It's possible that it has multiple current sensing shunts and one (or more) of them has a bad connection to the PCB, which would cause the overcurrent to be tripped at a lower than expected current.
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One cell was at 0.31 volt when charging it but now it keeps it charge and voltage. Could it be this one that hits LVC at like 3 volt ?
 
dustNbone said:
It's also possible that one of the cell groups that went dead is actually toast. It might be able to hold full voltage when you charge it but it sags below LVC under load due to high internal resistance.
Click to expand...
High internal resistance means longer to charge ?
 
dustNbone said:
It's also possible that one of the cell groups that went dead is actually toast. It might be able to hold full voltage when you charge it but it sags below LVC under load due to high internal resistance.
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Would bypassing the bms for discharge fix this problem or i should remove the toasted serie to make a 19s instead of 20
 
Well, it could mean that as well but in this context it means that it can't deliver it's rated current anymore, because there's too much resistance through the cell. It's a sign of physical damage to the internal components of the cell.

Resistance also means heat, so attempting to pull high current through will make the cells hot, possibly dangerously hot if you push them hard enough.
 
dustNbone said:
Well, it could mean that as well but in this context it means that it can't deliver it's rated current anymore, because there's too much resistance through the cell. It's a sign of physical damage to the internal components of the cell.

Resistance also means heat, so attempting to pull high current through will make the cells hot, possibly dangerously hot if you push them hard enough.
Click to expand...

So basically i should just isolate the bad group of cells. What is a good way to monitor voltage under load .. i cant see the sag on my voltmeter but i guess if i monitored the voltage of that said cell under load i could
 
What would be the best course of action here , Monitor voltage of cells or check for bms integrity .. Pack is 20s 35AH i just cant trash it
 
You're going to need to get rid of those bad cells somehow. Depending how the packs put together, and since the remaining cell groups are relatively unused it's probably worth replacing them.

I'd do all 3 groups that went low just to be sure you're going to have a reliable pack that stays reasonably balanced.

The ones that went totally dead are a fairly serious fire hazard, the others probably less of a hazard and more of a nuisance as they're going to have far less capacity now which will cause them to hit LVC before the rest of the pack, reducing it's effective capacity significantly.
 
As stated above, sounds like you have damaged cells that sag under load, causing a LVC condition. Also as stated, they are a fire hazard. Somehow you abused your battery and now it has problems. You could replace the cells that went under 2.75v or better yet, get a new battery and retire the damaged battery.
 
e-beach said:
As stated above, sounds like you have damaged cells that sag under load, causing a LVC condition. Also as stated, they are a fire hazard. Somehow you abused your battery and now it has problems. You could replace the cells that went under 2.75v or better yet, get a new battery and retire the damaged battery.
Click to expand...
is there any way i could check for that sag?
 
CanadianKid said:
Cell*6 was at 0.31v when taking balance back
cell*9was 1.81
cell*11 was 1.45
Click to expand...
Those cells are physically damaged inside, and unsafe to use (anything that goes below 2v you shouldn't ever recharge, remove all three of those cell groups, all cells in those groups, and discard them, and replace them with new cells.

It doesn't matter what they charge up to--they're damaged and a fire risk, as well as being unable to operate like they were before being damaged.
 
CanadianKid said:
is there any way i could check for that sag?
Click to expand...

If you have a meter that is connected to all the cells in you battery pack you could meter all the cells under load. Like going up a steep hill. CellLog's used to be around and people used to use them. Or if you get an iMax b6 or other lipo charger you can test cells with the discharge function. It won't be a fast test but it will be thorough However, AmberWolf is right. Pull all the cells that were under 2v (I personally would say under 2.75v) and put a resister to them until they drain to something around 0v and then discard them.
 
First wild guess - somebody fed the BMS some really good LSD?

Second wild guess - you live in Canada, and the battery was stored in extreme cold?

As repeatedly stated, those extremely low cells constitute a severe risk and should be replaced. That vehicle should not be anywhere within 50 feet of flammable materials. Your battery is a serious danger to you and any innocent bystanders or property owners in the area.

Continuing to use and charge those cells is criminally negligent. That means you would be not just financially liable for any and all damages but would also face jail time.

Solve the problem, replace the cells.
 
AngryBob said:
First wild guess - somebody fed the BMS some really good LSD?

Second wild guess - you live in Canada, and the battery was stored in extreme cold?

As repeatedly stated, those extremely low cells constitute a severe risk and should be replaced. That vehicle should not be anywhere within 50 feet of flammable materials. Your battery is a serious danger to you and any innocent bystanders or property owners in the area.

Continuing to use and charge those cells is criminally negligent. That means you would be not just financially liable for any and all damages but would also face jail time.

Solve the problem, replace the cells.
Click to expand...
I own a few batteries 20s 12p, 20s 15p, 20s6p. 17s 1p, 22s 6p , thats not a problem. Wont be using it as its useless im just exploring my possibilities here. As to say its is dangerous to have it in my possesion is a bit over the top. It wont burst in flame spontaneously by sitting on my shelf.

Battery was stored above 1C and never charged during the winter so not extreme cold
 
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