Weird BMS Voltage

I’ve Been Riding my board reliably for a few months, but when on a ride the other afternoon, my board completely shut down. I restarted the board and it worked completely fine on the way home. However, the day after that, my board shut down and wouldn’t turn on… When I tried to power back on, the battery meter went from 4% to 0% slowly. However, when I tried to power it back on after the the fifth time, with my board upside down, my board shut on, and went back to 74%. But shortly after, my board shut down again, doing the same thing…

I went to go open up my board, and I measures the battery pack’s voltage, 47.2V, okay. Then I went go go measure the B- port on my bms, and that, too, read 47.2V. But, when I went to the P- port, the voltage read 3.3V… I’m thinking the bms has a problem, but I cannot flip the BMS upside down due to how its secured to the enclosure. But, if I have to, I will take the BMS out. Do you guys think the BMS is toast? Or should I take the BMS out and see if anything is burnt, because from the top (Heatsink side), It looks okay. Any advice is greatly appreciated! :slight_smile:

What battery and what BMS are you using? I’d start with looking for cold/loose soldering joints.

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I agree. Sounds like a loose connection. Especially considering the upside down board “test”. Check solder joints in xt60/90 if you are using them. Check at the bms connection too.

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I’m using 2x 8000Mah Lipo batteries in series. I do agree that a cold/loose solder could be the issue, but when I measured the B- (input) terminal and the positive end of my battery, I got a voltage reading of around 47V, but when I measured the P- (Output) terminal of my bms, it read about 3V. So I think the issure is between the B- terminal and the P- terminal, and the BMS is right in between those… I am going to go re solder the B- and P- connections later today and see if that solves the issue, if not, I’ll take out the bms to inspect it. I have a 80Amp Bestech BMS. (Not Bypassed)

I assume its the one with the build in switch so you need to turn on the board in order to see the voltages in the P-.

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Ah you are right, the more you know… I’ll turn on the board next time and measure the voltage :sweat_smile:

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Alright I fixed it, for now… I found out that when I put pressure on the bms wires, which were on top of the bms, my board would cut power.

I moved the bms wires because they were right on the bms and I think that the sharp solder joints from the bms were puncturing the wires.

So I just moved and re arranged the order of the wires in my enclosure and boom its fixed I guess. :joy:

I’ll update this thread if the issue comes back tho, thanks for the help!

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