Replacing 3 wire BMS with 2 wire BMS

[supergadgetman]

Hello All,

Hoping to get some guidance with my BMS replacement. I have a 72v 35ah BtrPower battery pack that has a bad BMS. The battery is configured with separate charge and discharge leads. I contacted the company and they sent a new BMS but it's only a 2 wire and the old one had a 3 wire setup. I had C- P- B- on the old BMS and the new one has only B- and C-.

As it stands I have no where to connect the negative discharge lead (P-) on the new BMS. Could I solder the negative charge and discharge leads (P- & C-) together onto the C- spot on the new BMS? Will that have any ill effects on HVC or LVC? I could attempt to make the battery a 2 wire setup and have charge and discharge through the same leads, but I don't know if the battery is wired that way and I really don't want to risk frying anything. I've tried to contact the seller but they are not responding likely due to the Chinese New Year.
Any help would be greatly appreciated.

Please see attached photo for reference.

Cheers!

 

[LewTwo]

Wish I could find one of those for my LiFePO4 pack. It allows for the use of a bidirectional power meter.
I have a couple of diagrams for similar 'common wire' two lead BMSs that I have saved to help with my senility.
Perhaps this will help.

 

[supergadgetman]

Thank you for your reply and diagram.

Would I need to rearrange the balance wires in order to to use the 2 wire BMS? I was hoping to avoid that. The new BMS has a different size clips for the balance wires but the seller did include a harness that retrofits the existing balance wires to the new BMS's clips so in that regard it's plug and play. I don't think I would need to rearrange the balance wires in the pack since he did send me that harness so the existing clips will fit. I was more wondering if I can use the new 2 wire (B- C-) BMS on my 3 wire battery (C- P- B-) and if so, what's the wire placement. I'd like to keep this pack a separate charge/discharge port, unless it's impossible to do with a 2 wire BMS.

Thanks!