The best way to combine batteries

[cholmes100]

Hi everyone, anyone know of the best way to combine batteries in a solar system? I have an RV with panels (2 x 160 w) through an MPPT controller It charges two 6v AGM that are supplying the 1800 w inverter/charger. I also have two 12v batteries that are running the "house" (12v lights,pump etc) and no way to charge them unless I run the gen. I know I could buy another panel but I would like to use what I have. Can I use a battery combiner? I can't seem to get a straight answer. from what I read there can't be a load on the additional battery bank, of which of course there would be. Another thought would be an isolator but I'm thinking the batteries would charge at different rates. Any other suggestions?

[Sunking]

What are you not using a electronic battery isolator to use the engine alternator to charge the batteries? If you had that you would not need any solar to begin with.

In an RV the batteries are so abused and used infrequently, you can get away with mixing the batteries. Otherwise you will need two isolated systems.

[cholmes100]

So running a diesel truck to charge batteries sort of defeats the purpose of solar doesn't it? That would be great, just let that 5.9 Cummins sit and idle for 4-5 hours charging batteries, everyone would appreciate that. I am not sure what infrequently means? every day? as long as they are charged properly then the usage matters not. I am referring to the RV only, not the start battery, It is a fifth wheel not a motor home.

[Sunking]

So running a diesel truck to charge batteries sort of defeats the purpose of solar doesn't it?

No difference, your alternator is more than large enough to do both the starting battery and a truck load of house batteries. Your alternator can do more charging in 1-hour than your panels can do in 3 days. All the solar really does in your application is cost money and keeps the batteries charged when parked in storage. You can keep the panels for show and tell for the kids and make everyone think you are Cool and Green. I won't tell anyone and blow your cover that you spent money needlessly.

However you can use them to charge both house batteries if you wish, but I would just get an electronic Isolator and call it good. A quality unit of 100 amps wil cost you less than $100 and run circles around your solar. They even make them with more than 1-Port. 1 input from the Alternator and up to 3 isolated output ports for 3 sets of house batteries.

[cholmes100]

OK, not helpful. Not sure why you are on a solar forum but anyway, Not sure either how I would accomplish the charge part, big giant booster cables? That sounds safe, get my girlfriend or one of the kids to do that when I'm not around. They can crawl in the basement of the RV full of batteries with bare wires and vice grip them maybe. Or you thinking it will charge all those batteries through that little tiny wire in the light cord?

[Sunking]

I am dead serious and giving you the best advice you will ever get. Build and design these things for a living. Here is an example of of a real RV system. No one will give you any better advice or go to the lengths I will to help you. Look in the Stickies, I own most of them.

[PNW_Steve]

OK, not helpful. Not sure why you are on a solar forum but anyway, Not sure either how I would accomplish the charge part, big giant booster cables? That sounds safe, get my girlfriend or one of the kids to do that when I'm not around. They can crawl in the basement of the RV full of batteries with bare wires and vice grip them maybe. Or you thinking it will charge all those batteries through that little tiny wire in the light cord?

I fought with the same issue trying to come up with a practical solution for charging the house batteries from the truck charging system.

I got discouraged trying to come up with a workable setup for the connection to the 5th wheel. Between that, the materials cost and the fact that the we disconnect the truck whenever we park, I decided that it was not worth it.

[Mike90250]

If your panel output voltage is about 20V. you can use a PWM controller and the mornigstar sunsaver dual charge controller
https://www.morningstarcorp.com/products/sunsaver-duo/

If your panels produce more than 25Vmp, you need to use a MPPT controller, and I don't know of any with dual outputs

[Guest]

To join batteries in parallel, use a jumper wire to connect both the positive terminals, and another jumper wire to connect both the negative terminals of both batteries to each other.

[Mike90250]

To join batteries in parallel, use a jumper wire to connect both the positive terminals, and another jumper wire to connect both the negative terminals of both batteries to each other.

Welcome Mr Obvious.....

[PNW_Steve]

OP,

if I am understanding correctly, you have two sets of "house" batteries. One running the 12 volt loads and one dedicated to the inverter. Is that correct?

You could run an isolator between the two sets of house batteries. Not ideal but I understand that running a charging circuit from the truck presents significant challenges.

[PNW_Steve]

Just "what if'ing".....

if you were to run an isolator from the truck what wire size and what kind of connectors would you use at the connection to the 5th wheel ?

The battery isolators that I was looking at were rated 140-160amps.

The wire run on mine would be about 55' (each conductor).

my wire size calculator chokes and tells me that I need something larger than 00.

Perhaps 110' of 2/0 would do the job?

Edit: I found a connector that may work : https://powerwerx.com/anderson-sb-co...s-sb350-350amp

i missed these when I looked before.