Help with BMS wiring

Hi !

I’m modding a Onewheel+ by replacing the internal battery and BMS.
The new BMS will be used for charge only.
Power ON/OFF is handled with a loop key on battery-.

Now when I plug the balance wires on the BMS, my onewheel powers up (I can connect to the board from the bluetooth app).

I figured that if I setup a loop key on battery+ instead of battery-, I don’t have this problem anymore.
But why is the charge circuit powering up the onewheel ?

I have limited electronics knowledge so I’m concerned that if I ride like this, the high amps load might go through the BMS balance wires, which would blow off the wires.

Hope someone can help,
Thank you :slight_smile:

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-B goes to battery main negative.
Charge + to battery main positive
Charge - to bms C-
Charge + to battery main positive
Discharge + to battery main positive
Discharge - to battery main negative.
The balance wires are soldered the same
That’s a usual bypass
Take into consideration that if you plugged the balance wires without B- soldered to battery main negative there’s a big chance to have fried the bms


Why would the BMS have fried with balance wires only ?

B- is the communication between bms and battery. If you hang that phone…shorts are to come…
Check your bms diagram and the seller’s instructions. Depending on the bms architecture it is fried or not.
Check smells or burnt traces. If they didn’t happen maybe yer lucky.

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From the instructions, it says that I have to first connect the B-, then the balance wires, but I think the BMS is fine.

What do you think about the diagram ? Do you think the wiring are OK ?

Is B- on main negative? It is not…
Read what I wrote and think about it.
I have made made how to videos at YouTube.
It’s plenty of them actually.
Do your homework or build a bomb.
Your choice.
Battery building is not rocket science but deserves some respect.
Gather the knowledge and then go for it

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Actually I’ve spent months gathering information about battery building and I’m pretty familiar with the basics now.

The charge port is connected to the main battery. So if I connect the BMS B- to the charge port-, that’s the same thing right ?

Could work depending on how the solders are done. B- is a critical part of the bms so I’d make a solid solder on main negative.

I can’t solder directly to the battery unfortunately. But I’ve tested like this and it seems works.

My main concern is about the BMS which switches ON the board.
Does it seem normal to you ?

It’s not optimal but if it works…
Turning on the thing is not normal. I know nothing about one wheels tho.

Hi, guys, am new to BMS wiring. I want make a top mounted battery connected in parallel to an enclosure battery. My first battery is a 20S8P and the top mounted one is a 20S4P. Instead of using two different BMS, I was thinking about slightly cutting each wire exposing the copper and soldering a second wire to connect it to the first P groupe of the top mounted battery and doing the same for all P groups effectively making a 20S 12P wired to one BMS. Is this approche to BMS wiring feasible ?