Badly swollen LifePo4 5ah cell

[Encebras]

Hello: please confirm my existence...!

I have a 48 v 20 AH lifePo4 ping-battery (pouch prismatic) that has a badly swollen cell in one of the groups. It heats up under charging, and seems to have impacted the surrounding cells. The group heats up during charging, and looses charge almost immediately after disconnecting the charger. One neighbouring group will charge up, but discharge by itself in about 30 mins.

So, when carging, 14 of the 16 BMS leds ligth up, while two stay unlit. It is obvious that there are som degraded cells involved and should be replaced. So please bear with me  for posting these questions - I am new to this...!

1: Can I continue to use the battery with two malfunctioning groups until new cells arrive? This could take up to two months to reach Norway...). I use my bike for commuting, and do not need more than about 7 AH between every charge.

2: If 4 out of 8 cells are degraded in two groups, is it feasible to combine the 8 good cells in a group and use the battery "as is" with only 15 out of 16 groups intact? Again, temporarily until I get a hold of replacement cells.

3: Each group in the battery consists of 8 x 3,2V 5ah signalab prismatic pouch cells. It seems to be hard to get these cells nowadays as most similar cells are 10 or 20 AH. Can I replace one group of 8 x 5ah cells with 2 x 20 AH cells? Or 4 x 10 AH cells?


4: Would any one happen to know someone with a bad battery who is willing to sell a group or two...?

Cheers everyone!
Erik

[Bikemad]

Hi Erik andto the forum.

1: I would not recommend using the battery as it is with the ballooned cells as the heat build up (during charging and discharging) may cause problems.

Contrary to popular belief, LiFePO₄ batteries can actually catch fire while being charged, resulting in intense heat and a lot of fire damage:


More details can be found here for those who are interested.

This is definitely not what you would want to happen to a known faulty pack being charged indoors.

2: I don't know if the BMS will still function with only 15 groups of cells.

3: Placing new cells in series with the old degraded cells will result in a battery that could take a long time to balance the cells and would place a lot of load onto the BMS as it tries to balance all the new and old cells.

Replacing all 64 of the 5Ah cells with 16 x 20Ah cells (or 32 x 10Ah cells) would be a more sensible option, as this would give you a completely new LiFePO₄ battery but would retain the old BMS and Charger etc.

Alan
 

[Encebras]

Thank you for your quick answer!

I will start by trying to build one functioning group and run the charger to see how the BMS reacts to one missing group.

Erik