Bad Battery?

[Vanc3ur]

Hi All

I have a 20S12P battery using Samsung 35E together with an Ant bms (Controller is capped at 90 Amps).

When the battery is fully charged there are no problems. But when the battery gets down to about 74-76V the LVC cuts off power. I can see from the bms, that it is always cell 1 that drops to around 0.2 - 0.5 volt. After 2-5 minutes cell 1 recovers to the same level as all the other cells again. Then I can drive a couple of minutes or until I accelerate hard and the same thing happens again. Apart from this scenario the battery is always balances at 0.001 - 0.003 volt.

First I thought the bms was at fault (bms is outside the pack). But then I managed to use a voltmeter when the above scenario happened. From the battery's balance wires I could measure the same voltage drop from cell 1.

I am thinking cell 1 needs to be replaced, but as this would be a pain in the a**, I wanted to hear if anyone has any other idea or test to perform to know for certain?
If cell 1 is bad should it also not be bad when fully charged?, and not just when getting down in the 74-76V range.

Any reply is appreciated.

 

[999zip999]

So you have access to cells ? Can you give us state of charge.
1. 3.95v
2. 4.18v
3. 4.19v

20. Xxx volt
Voltage of charger. Xxx
Voltage of battery. Xxx
If fully charged and all cells 4.18- 4.20. V 83.5 - 84 volts or so and balance.
You can put a load on the battery an old heated or 1,500 watt hair drawer and see how fast cells drop or just #1 drops off. As lost of capacity. Dead cells ? Bad parelle connections ?
You'll get more help here soon.

 

[goatman]

12p at 90amps is about 7.5amps/cell look at the 35e discharge chart from lygte

how many amps do you use?
if your running upto 90 amps then your going to sag into the lvc
if you look at the picture
7amps sags to 3.4v at about 1.5ah. 12px1.5= 18ah
is the problem that youre not getting the 40ah range that you were expecting ???