TranZX 36V 10Ah battery BMS trouble (?)

[cdriko]

hello
I have a eBike with a tranzx electric assistance with a 36V 10Ah battery. It doesn't work
while opening it to prepare to replace the elements, I see a thing that make me think about a BMS trouble :
After charging (charger disconnected) the tension betwen B+ and B- is 41V but the tension beetwenn B+ and P- (wich is connected to the plug to the controler) is ~ 3,7V

41V seems says to me that the battery pack is OK
but P- off make me suppose that maybe the mosfet of the BMS is trouble.
what do you think of that ?

 

[Manny]

you want to check the cell voltages. if the pack is 41V than the cells should be all be 4,1V.

 

[cdriko]

ok thanks I understand. mesures done :
1 : 4,75
2 : 4,69
3 : 4,68
4 : 4,64
5 : 4,67
6 : 3,30
7 : 3,20
8 : 3,43
9 : 4,50
10: 3,36

So it confirm two things : the BMS do the job, and some cells are gone (6,7,8,10) note that the others are near overcharged not ?

The pack is in fact made of 40 cells CGR18650CG MH12210 (lithium ion 2250mAh) the total made 9Ah
Is it lithium ion despite the box inscription "10Ah Lithium Polymer".... ok I'm not so sad.

Now my hesitation is : changing only the low voltage cells or the entire pack (the battery is from 2011)
If I change the pack I envisage to use real LiPo cells like this : https://fr.aliexpress.com/item/10pc...-lifepo4-10ah-For-power-tool/32550460167.html does the original BMS will work despite differences of charging and discharging voltage difference?

 

[fechter]

Yikes! the high cells are dangerously high. Around the voltage where they can catch fire.

Anyway, you can be sure that those are fully charged. You can attempt to charge the low ones and bring them up to 4.2v and see how it goes. Either your BMS drained some of the cell groups or you have some bad cells. I use a bench supply as a single cell charger for manually balancing packs. If you manage to get all the cells up to 4.2v, let it sit overnight and measure again to see if they are being drained.

BMS can fail in a way that drains certain cells or you could have cells with high self-discharge rates.

 

[kdog]

that battery is toast. The bms has killed it. Chuck it. I wouldn't trust it ever again. Groups 1,2,3,4,5&9 are way too high and destroyed. You could potentially salvage the other groups for lights etc.
don't even think about buying new cells and putting the same bms on it. It'll likely kill them as well.
Start again

 

[amberwolf]

I'd agree with that.


But before you do, check the battery in the multimeter, because a bad battery there can cause voltage readings that are way off.