AT with 240V Quattro or Split Phase with Do not Switch as group

DIY
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Greetings:

I potentially found my answer to this question on the old community site, but I don’t think I understand it, and am looking for some additional clarification.

Original Question: Split Phase dual Multiplus with generator - VictronEnergy

In his answer, @kwindrem said:

> 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.

This makes sense to me, if my input was always 120v from shore power, but depending on what type of input I have, I could have :
1 phase : 15 Amps @ 115V,
1 phase : 30A@120V
2 phase: 50A@120V

I have an ATS in the RV that selects between shore and generator, and the generator produces two phases of 120V, one at 30 A, one at 20 A, with unknown phase relationship.

Following Kevin’s suggestion, I can put an AT between the ATS and the inverter(s), but it’s not clear to me if it can handle / auto switch between 1 phase at 120 or 2 phases @ 120, or true 240 to make a true 240 V output…

I think I could solve the problem by:
- Remove the existing ATS and inserting a couple of Q2 -120V in parallel or
- keep the ATS, and insert a couple of split phase MP2-120V
The problem with either of these solutions is that I need more inverter power than the 120V./24VDC products provide. Temperature de-rated at 65 Celsius I need 4kW@120 on phase 1, and 3 kW@120 on Phase 2 of the inverter solution. So, that means moving to parallel 5 kW units on phase 1. Hence why I was trying to go 240V. This is an RV solution, and space and weight are important.

A third solution is 48V system to get more inverter capacity, but I’ve been advised not to use 48V for RVs (safety), and I’m not having a lot of luck finding 48V batteries built for the vibe/shock of RVs. I know I could do series connections of 24V, but when combined with the safety concerns, I didn’t look too hard at a series solution.

So, the questions:
Q1: Is there a mode with the AT can autoswitch between 1 phi @ 120, 2 phi @ 120, true 240 inputs and create / pass through 240V out?
Q2: In the original posting shaneyake asked about using a 3 position, 3 pole switch… My google fu has failed me, and I’ve not found something like this that can handle 50A of current without going to some big grid-grade massive device for many $k. Does anyone know of something RV appropriate?
Q3: Is there another way to approach this problem / solution?

Thank you all.

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A single 240 volt Quattro will not produce split phase power without an auto transformer on its output.

The 120x2 products have only a single inverter but will feed both output leges IN PHASE when running on inverter. With AC input, the inverter is in the first leg with the second leg is only a pass-thru.

You need to determine the phase relationship between the two outputs of the generator. If they are in phase, another transformer may be able to produce split-phase power to feed a pair of inverter/chargers. It is odd the two outputs have different current ratings but this can probably be managed.

I don’t think 48 volts in inherently less safe than a 12 or 24 volt system as long as everything is fused properly.

A solution to handle your three input scenarios might be to find an isolation transformer with two independent 120 volt input windings and a center tapped 120/240 volt output winding. Then a switch could handle the transition between the three configurations regardless of the phase relationship of the two generator outputs.

Some split phase RV shore power is actually two legs of 120/208 3-phase power. If this is the case, then a single input transformer can’t be used. If the input is taken from the two hot legs, the voltage at the output would be 104/208. If the neutral is incorporated, the two legs are 120 degrees apart (not 180) and would fight each other in trying (and failing) to produce two legs 180 degrees apart.

So the best solution might be to have two 120 volt to 120 volt ISOLATION transformers for the input and switch them appropriately for each power source. The result would be output power of 120/240 or 120/208. As long as you have no 240 volt loads, this should work.

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Kevin:
Thanks very much. I need to do some more thinking.