Battery keeps cutting out


1 µW
Mar 13, 2022
Hello you guy, need some help on my diy battery. I have a Dengfu e10 frame and battery. Decided to build an extra battery with a case bought from AliExpress.

So I 1:1 copied the original and installed the bms. Some how the bike did not power on after putting the battery in. Ther was enough voltage etc on the pins of the battery. So I could not find the issue. After a couple of months I decided to find the issue. It appear I switched the balancing wires from the 12th and 13th cell. Now the 13th cell is below the voltage of the other cells (3,4 instead of 4,15). After modifying the wire i decided to fully charge it and put in the bike. Now after a couple of miles it shuts down at about 76%.

What could be the problem? My guess was that the cell would get charged after the wires were properly connected.
The pack was put out of balance and the low cell is shutting it down early. In theory, the BMS would re-balance the pack, but that much imbalance would take an extremely long time to correct. You should manually charge just the low cell group to bring it up to what the others are. This should improve things a lot.
Use a thrift store cell phone charger and baby sit it, they're usually 5v but pop the low one up to the rest and see what happens. Remember to get the resting voltage, if you measure the voltage right when you done charging, its higher, let it sit for a few minutes and the voltage comes down a bit. The hard part is attaching the snipped off connector wire to the tabs. I used electrical tape and a wood workers clamp that had foam ends, worked good to charge 1s when all I had was bulk chargers. I dont have to tell you to be extra careful checking polarity before attachment.
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If the balance wires were swapped, there's a good chance one or both balancer channels on the BMS that were swapped were destroyed, so they can't balance the groups they're attached to anymore.

So your low group(s) aren't charging up, and so your pack never fully charges, and can't provide you with any more than the capacity you see (because that's all the low group has in it).

In this event, it's lucky that the BMS can even still work on those channels enough to sense the low group and stop discharge, instead of overdischarging and reversing that low group. ;)