mworl avatar image
mworl asked

Autotransformer>Multiplus 48-220v>Autotransformer mobile setup for split phase?

I am designing the electrical setup for a full time custom RV. It has a 48v battery bank, solar panels, and will see 110v shore power (15amp-30amp plus 50amp split phase). There will be no propane appliances so having 220v available for AC, water heating, and stove would be ideal. It would also be nice to be able to make use of both legs of a 50 amp split phase hook up in a balanced and simple way. I have 2 paralleled honda 2000w generators mounted on a vehicle that will be just plugged in to the shore power when used.

The best solution I have been able to figure out (excluding dual Quattros because that's out of my price range) is to use the less expensive 220v Multiplus 48v/5000 with Autotransformers on both ends. This allows me to use the 220v from a split phase input or step up any 110v input, then step down the passthrough and inverter output to 110v as needed.

Any thoughts about this setup? Will I have excessive losses due to the two transformers?

Otherwise I would just get the Quatro48v/5000/110v and have to live without 220v or making use of both legs of split phase 50amp shore power. Side question, could I connect the two legs of the split phase to the two Quattro inputs and use them both? Im thinking probably not..


MultiPlus Quattro Inverter Charger
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2 Answers
ben avatar image
ben answered ·

You won't have excessive losses, but I think you will find that you lose more than you gain by going the 240V route, overall.

The first thing to note is that the Victron autotransformers are rated only for 28A continuous on the 120V tap (or 32A for 30 minutes). So you would be capped at 3360VA maximum right off the bat, for long loads like charging.

If you haven't selected appliances yet, you would probably end up in a better place with just 120V ones and no transformers, as long as you're going to typically find yourself limited to the 5kVA cap in the first place.

(If you really want to power a big 240V appliance for something like heating when on a 50A shore supply, you could just wire that circuit separately at the shore connection, and put your inverter downstream. But, then you wouldn't have the use of that heater when you're anywhere else... which might actually be okay, since it's really inefficient to be heating off your battery anyway. You should be switching to another heating method then, probably.)

For your side question: no, the relay(s) inside the Quattro switch in only zero or one of the two inputs at any point.

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mworl avatar image mworl commented ·

Thanks for your reply. The 28 amp limit is not a problem because the highest amp 110v shore connections I will see is 30 amp, when a 50 amp connection is available I will use both legs for 220v (over 10k VA) and bypass the first autotransformer. My 110v needs will always be well below 28 amps if using 220v for heating/cooling.

I have a large solar panel set up of 1710 nominal watts.

One of the primary reasons I would love 220v is for a dual zone minisplit AC/heat pump unit. Only single zone units are available in 110v. The unit I am looking at has a nominal max draw of 17 amps for 30k BTU of cooling capacity. It is far more efficient than rv rooftop units. On a hot sunny day I should be able to stay cool and keep batteries charged with even just a 15 amp 110v shore line supplementing the solar power.

The other reason is for an effective on demand water heater. The 110v units just dont cut it and not having a tank to keep hot should be more efficient as well as much more convenient. This will be a full time home for a family of 4 and will be mobile so convenience as well as adaptability to any available power source is important.

You are right though that I will be limited on heating when away from a 30amp or 50amp shore line, especially at night. We don't like the cold anyways as natives of the SW US so we will most likely avoid staying in cold climates during winter. Perhaps a small wood furnace may be nice to have.

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ben avatar image ben ♦ mworl commented ·

Ah, I see, you'll just bypass the input side's transformer when you're on a 240V grid. Makes sense!

The multi-zone split minis are a great idea.

I think your design will work fine. I haven't priced it out to see how it compares with a split-phase (2x3KVA) setup. Did you make that comparison? It might give you what you want in a more "traditional" design with the added bonus of some redundancy.

How are you charging when you're off the grid, aside from solar? How big is your battery bank?

It would be quite unusual to try to do primary heating off the battery. You may not be able to get warm on the coldest nights, although you could always just pretend your camping and get out the sleeping bags, I suppose!

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mworl avatar image mworl ben ♦ commented ·

The dual inverters is a bit more expensive because the Multiplus 110v models are only available for 12v and 24v batteries so I would need to use Quattro's.

I have 12kwh of batteries (8x6v) with room in the battery compartment to double that in the future if I decide to.

Off grid charging will be by a pair of honda eu2200 inverter generators paralleled, plugged in to the shore power cable. That will be able to max out the 28amp capacity of the Autotransformer.

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ben avatar image ben ♦ mworl commented ·

Got it. Sounds like a neat build! Good luck!

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mrt avatar image
mrt answered ·

I have to ask … Why exclude the option of the vastly more efficient propane for heating and cooking? Exclude these items from your electrical system and your flexibility is much improved …

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mworl avatar image mworl commented ·

It's going to be a full time home and I would rather not have to deal with swapping cylinders. We have 1710 watts of solar panels to install as well.

Either way AC will need to be electric of course and I would like to use a 2 zone minisplit heat pump which are only available in 220v. Far more efficient than roof top AC units.

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