I want to charge in-house battery (Fiat Ducato) from the motorhome solar system. I presume I can use a diode to do this? Can you please advise and what size diode would be necessary. Thank you.

  • If I were you, I would check out a "split-charge" relay to do this.
    – Solar Mike
    Feb 22 '19 at 10:24
  • Is this question better suited to Electronics.SE?
    – GdD
    Feb 22 '19 at 12:50
  • 1
    @GdD It probably is, but they have a habit of migrating anything even remotely related to vehicles to us anyway...
    – Nick C
    Feb 22 '19 at 14:28
  • @GdD vehicle electrical issues can confuse some “ordinary” electricians - having worked on and sorted their cars in the past - discussing the issues with them was always interesting...
    – Solar Mike
    Feb 22 '19 at 15:22

As Solar Mike says, you need to look at split-charge relay systems for this - these are specially designed to protect both batteries by only connecting them when the inputs are operating and the voltages are appropriate, so that you don't end up draining the vehicle battery when using the domestic one or vice-versa.

To use both the solar system and the engine's alternator to charge both batteries may require a more complex relay system - I think it's more usual to use the alternator with a split-charge system to charge both batteries, then have the solar system connected to just the leisure battery (usually through the charge controller). I'm sure there are combined systems available to do both however.

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