What is going on here? 72V?

[LarsNiko]

The case says 72V but the inside shows 11S + 13S packs. What is the possible chemistry here? I was hoping I could replace the cells with 18650's but i guess that will be a problem, at least if I would use the same BMS? Some of the cells are swollen and in the 13S pack all cells are below 1V.

https://imgshare.io/image/N5jNCx
https://imgshare.io/image/N5WzQg

 

[serious_sam]

The case says 72V but the inside shows 11S + 13S packs. What is the possible chemistry here?

I think the "13S" is a red herring. The end pad has been (mostly) clipped off.

Based on the number of balance leads (11+13), i'd say that it's 10S+12S=22S.

And the part number is "PX-LFP...", which suggests LFP chemistry.

And 22x3.3V=72.6V (LFP is 3.3V nominal).

That would be my guess.

 

[john61ct]

Nominal for LFP is much more often cited as 3.2Vpc rather than 3.3V.

Nominal is supposed to be the 50% SoC at rest "midpoint".

Do not allow to go below 3.0V at rest

Charge to around 3.45V, maybe 3.50V if at a low C-rate.

Never mind what the data sheet says, those are extreme min/max, stresspoints not working voltages.

Multiply by 22 or 23 depending on how many in series to get pack level.

But that pack is shot, dead, BMS likely not re-usable either, especially not for 3.6-3.7V chemistries.

 

[999zip999]

How old is the battery ? How big ah ?

 

[LarsNiko]

Thanks guys!

Pack is 6,5Ah each, 2 packs.

 

[John in CR]

The cells are LiFePo4 cells. The 2 sub packs are in series for 24s which is essentially a 72V nominal battery.