Dual alternators & Batteries: DC-DC Charger wiring help

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johnm1 asked Nov 3, '21

Dual alternators & Batteries: DC-DC Charger wiring help

I searched the forum and I apologize if I missed the same question(s) ...

I have a truck and 5th wheel RV/camper and I want to be able to charge the RV batteries using the Victron DC-DC charger(s).

The truck has two alternators (125ADC each = 250ADC total) and two batteries. Best I can tell is the batteries are wired in parallel (12VDC) and both are used as starting batteries with no isolation between them. Truck is a 2013 GMC Sierra 2500HD

1. Should I go with one or two of the 12/12-30A units? The DC-DC charger(s) will be mounted in the RV.

2. I assume I should I get the Isolated unit(s)?

3. How do I wire it/them in to the battery(s)? Do I connect both units to one battery or one unit to each battery?

Thanks for any and all help!

charger

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Answer 1 · 2021-11-03T20:53:00Z

kevgermany answered · Nov 03, 2021 at 08:53 PM

First thing you have to do is confirm whether the two truck batteries are series or parallel. And what's connected to each.

What rate do you want to charge the RV batteries?

You're going to be pushing a heavy current at 12V over long cables. They need to be sized properly. And the plug needs to be good quality and up to the current.

Might be an idea to check the wiring setup with GM and if it's non-standard, get an auto electrician to trace it. Much cheaper than doing it wrong and burning things out.

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Answer 2 · 2021-11-05T15:19:16Z

johnm1 answered · Nov 05, 2021 at 03:19 PM

I know the batteries are parallel since it's a stock USA pickup truck (12VDC). What's connected to which battery ... I don't know. Does it really matter?

What do you mean "at what rate to charge the RV batteries"? We have (or will have) 840+ watts of solar on the RV but I'd like to get the "biggest" charge from the truck as possible without hurting the electrical system or putting such a load on the alternators that it kills my fuel economy.

I figured the wire would need to be between 8 to 6 awg (per 30A unit) so I wouldn't loose too much voltage over the distance.

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