Bms killed my pack?

Hey guys,

I have a 10s4p pack I built myself using lg hg2 cells and a bestech d140 10s discharge only bms.

The pack used copper buss bar and each cell was fused.

While assembling. I accidentally let my 12th bms wire short to something. It seemed to still work but stupid me didn’t check voltages of each parallel pack the next day. I’m certain it was wired up correctly other than that mishap. The resistor on the bms got a little brown on the conformal coating from the heat but looked ok otherwise.

I went for a ride last night and noticed I only had 37 volts even though I just charged it. I tried to charge again and it cut off at 37. So I tore the pack down and found the pack attached to the 12th bms wire at 0 volts.

Has anyone else experienced this? I’m currently rebuilding the pack. I had 5 spare batteries from the same lot and the pack only has two charge cycles on it.

Did your 12th balance lead burn out during the short?

You just gave me a headache. Thats why I don’t mess with shit I don’t master. Playing the little electrician fellow role leads to this kind of mess (in my personal opinion), thats why I let the masters do this type of job. You avoid a lot of troubles. There are plenty of battery professionals here @barajabali, @psychotiller, etc.

These batteries are basically ticking bombs on wheels. :grimacing:

I disagree how does one learn if they don’t do it them self and learn from their own mistakes, yes it can be expensive but the knowlege you gain is invaluable


Haha. I won’t take offense because you don’t know my background. But ok. I’m an automation technician/electrician. I repair circuits, drives, motors etc every day. It was literally my last solder joint to be made and I got careless. I really don’t think the pack is dangerous. The bms (kinda) did it’s job and stopped the charging when the other 9 groups got to 4.2 volts. So the only cells affected have already been removed and replaced

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I don’t think the balance lead burnt out. It seems like it broke the bms itself to make the 12th group just constantly discharge

Non intended (no offense). Oh, you are a professional in the field. I take back my words. Speaking more for people like me.:metal::slightly_smiling_face:

Okay, probably a burned resistor then… What’s the voltage of the whole pack if you measure it before the bms ?

What do you mean before the bms? Currently the bms is removed as it’s suspect (probably bad)

37.58 at the xt90 plug right now measured on a fluke 179. My tenth group has been siliconed together and wrapped in fish paper. I’m going to manually balance the whole pack until I can get a new bms


Ah the bit darker spot on the PCB might indicate that that component is defective. That might also lead to the leakage current that drained that paralel group.

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