One P group out of balance

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So, I was riding today, with about 20% Battert left, suddenly I got a cutout while driving, metr recorded UNDERVOLTAGE error and my VX1 lost connection with ESC, so my first thought was that DieBieMS did a cell under voltage cutoff… But I was puzzled since battery was not empty…

Got home connected DieBie and as you can see first P group is significantly lower voltage then the rest of the pack…

So, how do you approach this issue in a best possible way? I guess one of the cells is dead or not soldered…

@pjotr47 Any helpful tips? Remember this pack?

BTW its 12s7p pack, that has maybe 15 cycles in total with 30Q cells… Never had an issue before. DieBie is set to charge to 4.1V Max…

Thanks in advance

DieBie
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You may have damage to one or all of the cells (it got too hot, manufacturing error, it shorted). For now you can probably charge the one parallel pack on its own with an external li-ion charger and see if it happens again

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I’ve opened the pack, all welds are good, so that’s not an issue, also all the hotglue looks intact, so i dont thing there was any substantial heat, nothing looks odd…

Anyways Ill charge that group to the voltage of the rest of the cells, then charge the whole pack to the 4.1 and leave it overnight to balance out…

If this happens again I guess only solution is to disassemble that parallel group and check cell by cell in my LitoKala charger…

4

Well, well…

I’ve got that group to a same voltage as the rest, the strange thing is that now as the whole pack is charging that same group starts to lag behind the rest in charging…

I am charging with 9A, none of the cells in that group is hot, so what could be a problem here, it looks like a defective cell or something else?

DieBie2
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Oof something is very wrong…either something really wrong with a cell or the BMS

Just let it sit for 2 hours and watch the voltage every 15 minutes, see if its draining at all

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Sure, I don’t think it’s the BMS siNe it’s doing nothing while charging the whole pack until it starts to balance.

Now it is started to balance Cells, nothing to do except to wait…

I’ll send an update soon.

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That is awfully strange. Often a dead cell in a P group means that group discharges faster but also charges faster (lower capacity in that group)… The fact it keeps sagging behind even during charging… maybe a short in one of the cells??

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check the series connection on that p group, maybe something happened there? also the balance lead

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Feel free to send me a private message if you have extra questions @EreTroN

I am always happy to check it by myself.

I would suggest to charger now the whole pack to 4.1v/cel and then charge the cell with the lower voltage. Then do a discharge test again and let me know what voltage each cell has.

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Well, eventually it did balance out… Since I am in a lockdown until tuesday, Ill leave it on connectedd to BMS to see if it will drain out…

DieBie3
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What. Ya’ll done on tuesday?

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Here we have lockdowns mon-fri form 17h-05h, and 24hrs during weekends…

But this weekend since its ester they’ve put us on 24hrs lockdown from Friday until Tuesday.

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Wuuuut? What country is this if you don’t mind sharing?

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Serbia.

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Thanks for the reply…

Actually the first P group is losing voltage with and without connected to BMS, so BMS is out of question… Its not losing Voltage fast, but its definitely draining (voltage difference between highV and LowV in a pack has doubled overnight. It has to be something with cells… The only solution I see is to disassemble that P group and check cell by cell…

Is it possible that 1 bad cell is draining the whole group? Anyone had similar experience?

Thanks

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Did you find the problem?

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Ive tested all the cells individually, all were good, so I’ve velded them back together, from that time all is good.

So I have no idea what was going on… It seems all good now…

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Dat sum weird shit.