eBike Battery Adventure

[rgsparber]

One of my Lectric XP 1.0 batteries jumped from 10.3 Ampere-Hours to around 5 AH. This tells me one or more cells failed. It is out of warranty, so I took it apart to find the bad cells. Along the way, I learned a few things:

1. After removing all screws, I found it difficult to remove the ends. This was because the manufacturer had injected what looked like black RTV into the ends and then closed up the pack.
2. Carefully (foolishly?), using a hacksaw blade, I was able to cut through the RTV on both ends and remove the battery pack.
3. I counted 27 Samsung 18650 cells.

The nominal voltage of the pack is 48V. Given 3.7V per cell, this comes out to 13 cells in series. If there are two series strings in the pack, I get 26 cells. Each string should have a capacity of 5.2 AH. This implies that one of the strings failed open.

However, an 18650 LiPo cell is rated 2.3 to 3.6 AH. That is far from the needed 5.2 AH.

Does anyone have insights as to what is going on here?

Thanks,

Rick

[ductape]

Regarding the sealant, Permatex makes a product that will dissolve most types of RTV silicone. Part number 80652. I've had some success with it in a similar situation.
I've nothing helpful for the battery issue, though. Kind of stuck on why there is an odd number of cells in that type of circuit.

[rgsparber]

I miscounted the cells! It is 52 cells so 4 strings of 13 cells. Or, it could be 4 cells in parallel and 13 of these clusters in series. I’ve got more disassemble to do before I can tell. The pack is well made and hard to take apart.

Rick

[Frank S]

4 strings of 2.8 to 3.6 Ah cells would make more sense for a 10 Ah pack.

But losing half the Ah sounds like either as you said an open connection, or the battery management chip is bad

[rgsparber]

I hadn’t thought about a bad BMS but that makes sense. All cells measured 4.1V and all connections looked good using my eyes and DVM.

Rick