Multiple Neg. MPPT cables on same Neg. Bus?

[FoxenTec]

I would like to use my solar panel to essentially feed two MPPT Controllers (only one active at a time), each with their own set of batteries wired in parallel. Truck Camper has batteries in the shell and we also have batteries in the trailer we tow.

In order to do this, I have the pos. from the solar panel connected to a Blue Sea 3 Position Switch. One side connected to the Solar Panel for input, one side facing the tow vehicles MPPT Controller and one side facing the MPPT Controller located in the trailer I am towing. (long story but I could not install solar panels on the trailer)

I was thinking this will work since only ONE MPPT will receive solar power at a time. The switch will either be OFF, MPPT-1 or MPPT-2.

The question I have is can I tie all the NEG. cables down to a common negative bus as shown in my diagram. Essentially the Solar Panel Neg., MPPT-1 Neg. and the MPPT-2 Neg. will all be on the same bus.

(on a side note, the batteries in the shell of the tow vehicle are not chassis grounded but the batteries in the trailer are grounded to the trailer chassis)

 

[Vic Harder]

Jon, instead of a three way switch, why not use a ACR to charge both as needed?

 

[FoxenTec]

I reviewed the Blue Sea ACR. It "sounds" like they are used for two sets of batteries but in a starting battery/house battery setup.

My batteries are completely separate from my truck starting battery. The batteries in my shell are smaller AGM batteries (2 x 35ah) and the batteries in the trailer are 2 x 105ah AGM batteries The smaller ACR I looked at is 1/0 AWG and I am using 10 gauge from my solar panels to the MPPT Controllers. Quite a difference in wire gauge.

I will look at the ACR but the setup I am not familiar with and as a dumb low voltage tech, it might be above my paygrade.

 

[Vic Harder]

ah, no alternator... no need for the ACR. Another brain fart. Sorry.

 

[ntsqd]

If the trailer batteries are connected to the trailer frame, then when coupled to the TR they are (tenuously) connected to the TR's frame. I say "tenuously" because of all of the trouble this assumed ground gives in trailer lights. Not to mention that some trailer lighting sockets & plugs can either or both have short jumpers to their respective frames as their grounding.

That said, I do not believe that this is a problem. It is not a circuit until the loop is closed.

A VSR/ACR won't care what the charge source is, it only will care if the charging voltage is above the threshold or not. It will favor charging one bank before charging the other, but given enough time it will charge both. Which bank is favored depends on how it is wired.

But, to answer the original question, I do not think that tying all of the grounds together will pose any problem at all.