Sorry about that.
It’s a brand-new motorhome, model year 2026.
There’s a silver braided steel strap on the starter’s negative terminal. It goes to the body (which is supposed to be a painted car — shame on me). The Orion’s GND is connected there too.
As I understand it, a #common# ground should be enough, right?
The 300A busbar doesn’t seem to be connected to the bodywork. It’s a bit difficult to tell from schematics spread over several pages. Does that mean the auxiliary battery system isn’t electrically connected to the bodywork? If so, the Orion can’t charge the system at its output. The two potentials could also drift apart as a result.
Have you tried testing the booster without it being connected to the Cerbo yet?
The 6 mm² cable to the solar charge controllers is missing a fuse at the busbar end.
That was the crucial clue. Thanks so much. I’ve now connected the negative from the starter battery to the leisure battery’s negative busbar.
From the negative busbar to the DC-DC. Everything works now.
Just odd that it had apparently already been running like that for 3.5 months beforehand. But hopefully that’s sorted now.
That’s true. To be honest, I don’t understand it either.
Thanks again.