Power 12v with bus battery while driving and with solar battery when stopped.

[peaceofanotherkind]

Hey folks! This is probably an easy question, but I keep second guessing myself. I’m running additional 12v outlets and I want them to be powered by the bus battery while driving, then switch to using the solar batteries when the bus is off.

I have an isolator that will allow the solar batteries to be charged by the alternator while the bus is moving, so I thought that could help. I was going to attach the fuse box to the Coach Battery (where the solar batteries are connected) so that they’ll only draw power from the alternator if the bus is running. But if I do that it’ll also be connected to the solar batteries while the bus is running. I don’t know how intuitive it is, whether it would default to the alternator or just use the solar batteries the whole time.

I hope this makes sense.

Looking at the pic, the 2 awg red wire going up is connected to the bus battery. The one going down is connected to the solar battery.

[john61ct]

Two separate issues.

Loads that are required for, part of driving should get powered off the starter / engine circuit directly by the alternator.

Nothing is coming out of the Starter **battery**, that is used only for cranking the motor.

All House / auxiliary loads get powered off the House bank, at all times.

Now, if you are also sending enough current from the alternator while driving, the House bank will not be drawn down either but being charged.

You just need to make sure the House loads cannot pull from the Starter circuit when the alternator (and other Sources) are inactive.

[peaceofanotherkind]

I used words interchangeably.

I have an isolator to ensure that the solar batteries are not drawing from the bus battery while the bus is off.

In the picture, there are two wires attached to “batt coach”. One is to the solar batteries and the other is to the fuse box I’m installing.

My question is if the 12v outlets will pull from the solar batteries while the bus is running if they’re connected this way.

[john61ct]

No idea about that device, but get a DMM and learn how to use it, absolutely essential to check your system for proper functioning.

Hate to quote a Nazi but

“One good test is worth a thousand expert opinions.”

― Wernher Von Braun

[Doktari]

With the engine running the load (fuse block) will be connected to both the “bus” battery and the “solar” battery as long as the bus battery voltage is above the cutout voltage. If the load drags down the voltage to the cutout voltage the bus battery will be disconnected from the load so only the solar battery can be drained. May be wrong but that’s how I understand it to work.

[john61ct]

Originally Posted by Doktari

If the load drags down the voltage to the cutout voltage the bus battery will be disconnected from the load so only the solar battery can be drained

Should be,

if the circuit voltage drops below the setpoint **for whatever reason**, Starter circuit gets isolated from House circuit.

Ideally sensing voltage levels from either side, so it closes again when it comes back up from any source, i.e. the two circuits get re-combined

[sepudo]

I wanted essentially the same objective and then I found a DC to dc charger with mppt from renogy. I bought it, haven't installed but I believe it will work plus help keep my starter battery healthy via solar as well