36V 10S2P pack not charging - bad cells or BMS?

[lineslim]

Its the BMS. I just had to take apart and replace that EXACT BMS in an identical 36V hoverboard battery.

I ran the hoverboard until the battery was 37V (a long time, still did not display low battery) but it would not charge so its likely the same problem with BMS.
The cells from the computer pack was marked ICR18650-30B. Samsung SD1 2E63. Measured all the cells again:
1)3.7 (new)
2)3.4
3)4.0
4)4.0
5)3.7 (new)
6)3,7 (new)
7)3.8
8)3.7
9)3.9
10)3.9
The hoverboard is marked 36V/700W. What specifications should I be looking for if I were to buy a new BMS from ebay or similar? Approximately how much would the cheapeast one I could get away with be? I looking at european sellers to avoid import duties/tax etc. I guess I could leave everything attached to the old board and just connect the new bms to all the cell groups and +/- to the motor/logic board?

 

[docw009]

Lineslim, you have the pack where the BMS acts like a frame, with the upper and lower cells soldered to it.You can't find that style as a stand alone BMS. Maybe give up on the BMS idea unless you can manage to cut/dremel all the traces that go to the sense circuits on the original BMS. Then you could use the old card as a frame.

With packs that use a small BMS card, you can replace them. My packs didn't have balance circuits on the BMS. DIdn't matter because they don't use the charge port. So no overcharge protection. No balancing. That's why a few probably got unbalanced, were plugged into an out-of-tolerance charger and caught fire. I did replace one BMS on my packs. It cost about $12 and wasn't hard. Also wired in a little 5mm socket for charging.

I noted that your pack shows the XT60 connected to the -C pin, which is usually what they label the charge port. That would suggest you have no under voltage protection, as that's usually in the discharge port circuit? Just musing.

 

[e-beach]

As suspected the computer cells are not a high discharge cell. They are only rated to 2C when the original cells are rated to 5C.
Here is a snip of the datasheet specs.



What that means is if the motor is drawing more then about 6 amps your computer cells will be heavily stressed and could over heat. Personally I wouldn't run that board much with your current battery configuration. As for a cheap 10s BMS, a cheap one would only cost about $10.00 USA on eBay. However, you shouldn't get one until you decided on the new cells you are going to use. The cells and the BMS need to be matched.

 

[lineslim]

Thanks guys,
The option that maks most sense is ofcourse to buy that replacement pack from the supplier of the hoverboard for $53US, altough it is not as fun as repairing things yourself ..Especially if it could overheat as you say because of the computer cells (altough I doubt it would draw 6 amps at the speed used when me and the kids play with it ).

Using the old board as a frame after cutting connections with the rest of the board wouldnt be an issue, is only about 3 points on group 9&10 to detach and resolder in order to reach all those parts that need to be "dremmel treated".

Cheapest BMS from a european seller I found:
https://www.ebay.com/itm/10S-36V-Li-ion-Lithium-Cell-40A-18650-Battery-Protection-BMS-PCB-Board/183478560647?hash=item2ab82ca787:g:VWsAAOSwfjVbvQob

Otherwise at least I concuded the board works and learnt a lot about lithium batteries