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exmoso asked

Split Phase dual Multiplus with generator

Hi all,

I could use a little help planning my setup. I have a pretty standard US configuration in my RV 120v/240v split phase. My mini split AC is 240v so I need 240v. I have a 12.5kw Onan that says 120v/240v 1 phase *picture attached*. I would like to put in an inverter system but I'm pretty confused about what functionality is possible.

Ideally I would like everything to passthrough the inverters. Generator, 50A 240v split phase shore power, 30A-15A 120v single phase all passing through the inverters so I can utilize the charger and power assist features of the multiplus's.

My current understanding is that I will need 2 Multi's and 2 autotransformers. One autoT to balance the genset and one to balance the inverters but I'm not sure exactly how to hook them up. Where my understanding really stops is at the single phase input. How do I add the ability to charge from 120v hookups without a separate bank of chargers?


Thanks for any help!

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1 Answer
Kevin Windrem avatar image
Kevin Windrem answered ·

Victron has a new product aimed at this RV setup. It's the Multiplus-II 12/3000/120-50 2x120. 3000 VA 12 volt battery connection. It's a single inverter/charger core with switching to support 120v or 240v shore power.

With 120/240 volt shore power, the inverter sits on the L1 leg and offers power assist. The L2 leg passes through to the loads but there is no power assist.

With 120 volt shore power, the inverter and both legs of the load panel are switched to the L1 shore power leg.

When inverting, both legs of the load panel are fed from the inverter.

If you can live with the 3000 VA limit from the inverter, it's really the best way to go.

If you need more inverter power, then using a pair of Multis (or Quatros) in a split-phase configuration would be needed. This works great except when presented with 120 volt single phase shore power. You need a transformer ahead of the Multis to create 120/240 volt split-phase power from the single 120 volt shore power leg.

Balancing power between the two legs gets more complicated. It might be best in this case to use one large Quatro with 240 volt AC in/out. You'd need a transformer to make 240 volts from a single phase shore power. A second transformer on the output to take 240 volts from the inverter to make 120/240 split-phase for the load panel.

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shaneyake avatar image shaneyake commented ·

One thing to note about the Multiplus-II 12/3000/120-50 2x120 is that it can not create 240v when running off battery. No shore or Generator. Just want that to be clear.

I would also recommend that if you can go 48V, I would do that.

Also the Multiplus-ii 240V series is cheaper and more compact than the quattro. Except does not have dual input so would need a change over switch for genny vs shore.

My prefered setup is a 240V inverter with Autotransformer on the output.
If you want to be able to take in 120V shore power then will need a second transformer.

But as Kevin said, small probably get a Multiplus-II 2x120.
If you want I bigger system I would go 48V and Multiplus-II 240V 5kw, 8kw or 10kw.

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exmoso avatar image exmoso commented ·

Unfortunately the 2x120 won't work for a few reasons. It doesn't produce 240 on battery power, Thanks shaneyake. Also 12volt is ridiculous lol. I have taken a little time to research this a bit.

Tell me if this line of thinking is wrong. Two 24v-3000kw Multis in a split phase configuration with the "switch as group" option selected will work flawlessly with a 120/240 split phase input and a 120/240v genset. The issue arises when trying to hook up to 120v single phase. Could we not simply have a 3 position switch at the input side of the multis? With one position for the genset, one for the 120/240 shore power, and the final one for a 32A auto transformer set the input 120v single phase and output 120/240v.

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shaneyake avatar image shaneyake exmoso commented ·
Yes, you could just have a 3 position 3-pole switch that switches the inputs, I would also include a breaker that you switch off first and then change positions and then turn on.


You would only need a step-up transformer, which may be cheaper to get than an autotransformer. Depending on the size you want.

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exmoso avatar image exmoso shaneyake commented ·
Awesome!


Just to be thorough, the multis require a line and neutral. The auto transformer will transform 120v line/neutral into 120v/240v split phase line/neutral/line. Where 120v is present at either line and neutral and both lines produce 240v. Is this correct?

Again for the sake of completeness, theoretically the max legitimate 120v shore power hookup would be a 30A. So a 32A AutoT would be sufficient if its only intended use is to transform 30A 120v to 120v/240v split?

Also would Step-up transformer do all of that? If so which one specifically? I'm not to familiar with brands and such.

One last thing, If I wanted to replace this fuel hog of a generator with something smaller. Say a 5000w 120v. Could I get a larger autotransformer or step-up transformer and put an automatic transfer switch on the input to select between the smaller generator and 120v shore power?

Thanks again for the help! You Rock!

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shaneyake avatar image shaneyake exmoso commented ·

The Multi's don't require an input neutral when in split phase and can accept 240V without a center tap. However I forgot that this won't provide a neutral to your loads.
So you are correct, you will need an autotransformer.

All Victron Auto transformer are limited to 28A of continuous use in this config as that current will pass through the Neural winding.

I would look for smaller 240V generator and then have it feed the input of the autotransformer if the Generator can not output split-phase.

You could then switch between 120V shore or 240V genny with a change over switch into the transformer.

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exmoso avatar image exmoso shaneyake commented ·
There has to be something out there that can transform 120v single phase to 120v/240v split phase at around 50Amps. Right?


What are all the people with 120v generators doing?


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vick-da-aerbus avatar image vick-da-aerbus commented ·

I have 50amp shore power service with 120V on each leg. Works well with ATS and Multiplus II 3000W 2x120V.

Problem I have is a Generac 7500W single phase 120/240 volt generator. The ATS makes the switch, but the multiplus doesn't accept the connection. I have UPS selected. I tried weak AC.

Do I have to rewire the generator for 120v only?

Does the Multi not recognize the 25A per leg as valid input to connect?

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