Solar panel earth point?

The positive is regulated is most solar. Most mppt regulators have the solar in Neg and the battery Neg directly connected internally

RMD, that only applies to regulators like the Plasmatronics, Steca and many of the cheap evilbay models that were designed for positive earth systems. The communications systems were the first to use solar systems and they are all positive earth systems (your telephones work off 50 V pos earth.) If you are wiring in one of the above regulators in negative earth systems you have to be careful how you wire them in. You have to decide which part of the system you wish to earth, you have to decide whether you want the battery terminal, load terminal or solar panel negative earthed, you can not earth more than one of them.

Sometimes this is not as easy as it sounds, the Projecta solar controllers are an example, they are positive earth which if only a regulator is not such a big deal, but in this case they also have an inbuilt BMS which for it to work correctly means all accessories must be have their negatives only connected to the solar controllers load negative terminal so that the controller can monitor current drawn by the loads as well as current into and out of the battery. This also means the negative battery terminal can't be grounded else the controller will not see the current they are drawing.

Sounds strange why not just monitor current in and out of the battery you ask, well actually it works very well you can see what current the solar panels are generating, how much is flowing in and out of the battery as well as monitor the actual current being drawn by the loads, and by a simple press of a button you can turn the power off to all accessories. All in all very comprehensive, only issue is the battery negative terminal and solar panels negatives must be isolated from the van chassis for all this to work, which they are.

The problem is if you connect the van to the car and try to charge the van batteries either directly off the alternator or via a DCDC charger where the negative passes straight through as you then have the vans battery negative terminal grounded to the cars chassis, which of course then grounds the van chassis via the tow hitch or chains etc.

With these units you would need a fully floating earth system for them to work correctly if direct charging off the vehicle is to be used.

Thanks for that. I will add that one to my list of controllers not to recommend. Collyn Rivers had several articles in the CMCA magazine about problems whit these pos earth regulators incorrectly wired by people including licensed electricians. Switched on people can work around their difficulties but they are a big headache for lesser people to install.

Relay neg is not as important so any neg will do