Multi battery system with chassis ground(overkill bms)

[bgflyguy]

I'm installing a solar setup in my camper van. Everything is currently running off the starter battery setup, and there appears to be some stuff grounded to the chassis. I'm adding a LifePo4 battery that will only be charged by solar initially, and will be separate from the starter battery. I was trying to hook some stuff up to the new battery, but I'm finding a bunch of the grounds are connected. I think this is because of some of the stuff being grounded to the chassis at the outlet, or chained to other grounds?

I'm using the xiaoxiang(overkill) bms, which is negative controlled(?) In order for the BMS to work, I would need the grounds to be completely isolated, correct? What if something bridges grounds via the chassis? What are the consequences?

I'm trying to think about a common ground system with separate positives, but I don't see the BMS working correctly? But maybe it would? I guess I don't know batteries that well.

 

[bgflyguy]

The more I think about, the more I think it should work fine. So i'm going this route with testing.

It's a small load right now, if the bms looks off, I'll go back to the drawing board.

 

[Zil]

Just think of the BMS as the negative battery post. Any negative that returns to the LiFePo needs to go through the BMS. Even if it by way of the chassis.

 

[chevymike]

Just like Zil said, once you install the BMS to your pack, thing of the common wires as the negative battery post. You can see my setup. The lid has a positive and negative connection, just like a battery would. Inside the C- wires (black) are hooked to that. The blue wires are connected to the actual negative batter terminal.

 

[HRTKD]

A common chassis ground isn't a problem. Where you run into issues are when the positive side of the circuit is common to both batteries.

 

[bgflyguy]

So far everything is testing okay. No ground issues. The BMS is tracking pretty much what I estimated the load should be.