BMS Bypass
- Thread starter furcifer
- Start date
docw009
1 MW
My common port BMS only have P- and B- . No C-. Isn't that the point of a common port? They charge thru the discharge connector. I still put a charge connector in parallel with the discharge port. MAybe I don't follow your question,
I recently had to bypass a new BMS that I had installed on a used Uber ebike battery I bought for 40 bucks. The cells were down around 2.90V and the BMS wouldn't allow a charge. I unplugged the balance cable and put a charger directly across the cells until the cells got to about 3.3V. Then I reconnected the balance cable, and now the BMS allows a charge. Shouldn't have to do this again.
I recently had to bypass a new BMS that I had installed on a used Uber ebike battery I bought for 40 bucks. The cells were down around 2.90V and the BMS wouldn't allow a charge. I unplugged the balance cable and put a charger directly across the cells until the cells got to about 3.3V. Then I reconnected the balance cable, and now the BMS allows a charge. Shouldn't have to do this again.
docw009 said:
You know I looked at some many diagrams and boards I'm not sure if this one has a P- or a C-. Either way you have a B-, which connects to the battery and another (-) terminal on a common port BMS. I was thinking the BMS should still balance even if you don't go through it.
I ended up adding a second charge port going through the board just to be safe.
E-HP said:furcifer said:
Per this diagram, if it's common port, then it seems like P+ and B- is all you need
Yah that's what I was thinking. So long as you don't quick charge at 20 or 30A the BMS should still balance the cells well enough. I just wasn't sure if the BMS had to be "activated" by grounding the P- (or C- if that's how it's labelled on the board). Likewise, I'm not sure what the upper limit on charging is. I mean I wouldn't want to charge at 30A without going through the BMS. If one of the cells got to 4.3V it would be difficult to bleed off that much current through a 24AWG balance wire. 2A seems reasonable but 5A might be pushing it.
Like I mentioned, I added a charge port and will just use that. The nice thing about a charge port is it gives you an accessory connection. But I had to tear the battery apart again to do it and I don't have an infinite supply of shrink wrap.
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