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Godoh
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Joined: 26/09/2020
Location: Australia
Posts: 678

Posted: 06:16am 08 Jul 2026

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I am setting up a dual battery system on our solar.
I have a switch that I can switch manually between banks but am wondering if anyone has a simple way to charge both banks while they remain isolated from each other.

I have seen commercial battery isolators but the diagrams show a separate alternator input into the isolator and then FETS to feed the power to both banks

I can't easily isolate the solar inputs from the main battery as I also backfeed through two GTI inverters as well.

I am under the weather a bit with RSV at the moment and my brain is fuzzy and not working too well.

I have two Kilovacs that I can use, but am wondering about using a diode or a FET. To keep the batteries isolated.

Ideally I want both banks to be charged and to be able to switch between banks manually when the weather is not so good for solar inputs.

Cheers
Pete

Solar Mike
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Joined: 08/02/2015
Location: New Zealand
Posts: 1228

Posted: 11:52am 08 Jul 2026

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Do you want to have one bank connected to your inverter on load, with the other connected to your PV; then flip them over when the 2nd bank is fully charged.

Perhaps a simple drawing is in order to visualize requirement.

Cheers
Mike

Godoh
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Joined: 26/09/2020
Location: Australia
Posts: 678

Posted: 09:54pm 08 Jul 2026

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HI Mike, I would like both banks to be charging off the solar all the time if possible.
And to only draw from one bank at a time

If I were to use a diode to isolate one bank from the other so they could both be charged at the same time, then when I switched to the other bank of batteries I would need to switch the diode over too. Of course there are diode losses to take into account too, so that is not optimal.

As the batteries are different ages I don't want to permanently parallel them up.

Other than that I will just manually switch them over when I want to swap banks

Pete

Godoh
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Joined: 26/09/2020
Location: Australia
Posts: 678

Posted: 09:59pm 08 Jul 2026

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Mike another thing that I thought of is.

Using a relay to switch the Kilovacs to change banks when a voltage set point is reached.

But there the relay would have to have a time delay so that the MPPT regulators don't get disconnected from the batteries at any time. They don't like having no battery to look at.

Pete

Solar Mike
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Joined: 08/02/2015
Location: New Zealand
Posts: 1228

Posted: 11:32pm 08 Jul 2026

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You could place a separate PV charger on each battery bank, they would share the common PV array output, this would allow isolation between the two battery banks with no isolation diodes that would otherwise cause massive voltage drops and heating. Not sure how their MPPT logic would current share under low sun conditions.

The Kilovacs then switch your inverter to either bank via a manual 2 position switch, or a voltage sensing relay across each bank.

Unless each bank had vastly differing voltage set points, I would just parallel them together via large fuse + isolator on each bank.

Mike

Godoh
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Joined: 26/09/2020
Location: Australia
Posts: 678

Posted: 01:43am 09 Jul 2026

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Thanks Mike, that has given me some stuff to work on.
At the moment both my partner and I are unwell with RSV, So the brain isn't working too well.
I appreciate your input
Thanks
Pete

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