Grounding solar controller

Question

I am wiring up the solar system in my van and I need help with claryfing some things up.

I have a Phocos CA08-2.2 controller and in the manual one can read:

Be aware that the positive terminals of the controller are connected internally and therefore have the same electrical potential. If any grounding is required, always do this on the positive wire.

Right, but there is a remark later on that actually corresponds to my situation:

If the device is used in a vehicle which has the battery negative on the chassis, loads connected to the regulator must not have an electric connection t the car body. Otherwise the Low Voltage Disconnect function and the electronic fuse function of the controller are short circuited.

So clearly I am missing something because it sounds contradictory to me. In the very first paragraph it says that "any grounding should be done on the positive wire" but later on it says "if you have your battery grounded on the negative side, then...". How should I understand this?

I figured the following circuit and after reading the manual about grounding the positive, I got my concern.

(I skipped the controller loads that are not grounded, and solar connectors in the solar controller for the clarity.)

So all in all - I have my 12V battery connected to my van chassis. Is it safe to connect the solar controller such that the controller negative connector will be grounded because the battery is grounded on the negative?

Answer 1

I agree with you, there seems to be a bit of confusion.

But I think what they mean is, that in the case where the batter "-" terminal is connected to the chassis, thus grounded, then this should be the only point of grounding in the system.

That means the solar panel and the load(s) you have on the controller are not allowed to have electrical contact with the chassis, with neither of their two terminals.

So the conclusion is: I think you can indeed use the circuit you have in mind, with the battery negative connector grounded, but with the condition that the neither the panel nor the loads are grounded (have electrical contact with the car chassis).

Answer 2

I've been confused over this until recently (I hope). Many solar controllers have positive ground; meaning that the solar panel + and the battery + and the contollers's load terminal + are all connected in common. The term ground in this case is the zero reference voltage. These connections are isolated from the vehicle chassis. So, in this case, for example, you would not connect the solar panel Negative (-) to the chassis.

Confusingly, the same term "ground" applies to the vehicle return path. So, loads connected to the vehicle battery and the house/aux battery are wired normally - a 12v fridge, for example. The negative is "grounded" to the chassis because that is the return "wire" for the circuit.

When you wire your solar controller, follow the connection instructions and don't be tripped up by the confusing use of the word "ground."