Sharing 24v bus with 2 inverters -- questions about shore power

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Evan Something asked Jun 5, '23

Sharing 24v bus with 2 inverters -- questions about shore power

So, I'd like to build an RV setup with two inverters:

24v batteries
multiplus-ii 24/3000
phoenix 1200va

I have a couple questions about my options. First, the reason for 2 inverters is that the lower power Phoenix 1200VA would have a minisplit and a small refrigerator plugged into it, which I understand do best on LF inverters like the phoenix. The minisplit should average around 500w and the fridge around 100w. The multiplus-ii will power the rest of my RV electronics, be it computers, TVs, chargers, blenders, toasters, etc (not all at once, just to give an idea).

Obviously when plugged into shore, the Power Control will feed shore to my appliances and any remaining to the 24v bus, and I'm curious if that could pose any problems for the Phoenix inverter / my batteries (beyond a small loss/waste from conversion AC to DC to AC)?

Also, I'm curious if there is any device that can switch the power for the Minisplit to come from the MP-ii when it is plugged in, but otherwise to come from the Phx?

I have included a basic diagram of the basic setup:

And then if there is some kind of device, like a transformer or smart relay or something, I imagine it would look like this?:

I know there is some sort of programmable relay function on the mp-ii, but I don't know if that could apply here.

Much thanks!

(PS, I am looking to wire in a Progress Dynamic PD55K004 AC Panel, which shows that it can wire in each 120v AC main separately, but I haven't purchased it yet. If this is useful for my scenario.)

wiring Relay transfer switch

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Answer 1 · 2023-06-05T04:44:27Z

kevgermany answered · Jun 05, 2023 at 04:44 AM

Power assist supplements inadequate AC in from the batteries. If the batteries are suitably sized for the phoenix and the multiplus no issues.

I don't understand the reasoning for phoenix plus multi. Multi will feed direct AC in to the minisplit.

Only advantage of the Phoenix is that as it's a smaller inverter, lower losses than the multi. But it looks as if the multi will be on permanently, so yo will have losses from both and higher overall.

But if the minisplit is connected to the multi, transfer from AC in to battery is automatic. In your proposed setup, the minisplit will be powered by the batteries, which will be fed from AC when available, so little difference except the losses from AC to DC to AC.

Maybe think about just a multi, possibly a larger one if total load is an issue, but it doesn't seem to be.

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Evan Something commented · Jun 05, 2023 at 04:34 PM

the reason was because I determined the multi wouldn't be enough inverted power for my needs, and the next step up (QUATTRO-II 24/5000) was over 1000$ more, whereas the phoenix was only 390$.... although maybe I should have just ponied up. I also convinced myself that have two inverters, just in case of a failure, would be of benefit (but that's a likely rare scenario).

And yeah, i guess it is just "Power Control" that does the splitting of incoming shore to loads and then extra to batteries, (and "Power Assist" that will backfill power needs from the batteries). I edited my post for clarification on that.

So my second question about any devices still stands;

but it sounds like "the minisplit will be powered by the batteries, which will be fed from AC when available, so little difference except the losses from AC to DC to AC." answers that I will be fine with the proposed basic setup.

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