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Multiplus inverters setup in split phase to match power input.

I have two multiplus inverters in a mobile set up in split phase that I would like to have match the power input and allow passthrough and assist. There are times when power supplied is from a single phase power source. I do not need 240 volt capabilities. Is it possible for the inverters to see the single phase and fully operate.

MultiPlus Quattro Inverter Charger
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irwinr avatar image

I know I'm late to the party here but I figured i would chime in since I have a very similar setup. I have a motorhome with a 50A shore connection that hooks up to 240v split phase and feeds that to two Victron inverters (5kva Quattros in my case). The Quattro's are configured to run in split phase and my Quattro's are also connected to a 6KW generator which only puts out 120v. (More on that later)

These are tied into a 48v 200 AH Lithium battery (Roughly 10 KWh)

In my case: When I connect to 120v shore power (Such as a TT-30 (30 amp) RV outlet) the adapter that converts from 50 to 30 amp simply connects the one hot leg of the 30 amp outlet to *both* legs of the motorhomes electrical input. When the Quattro's see they are getting a Sine wave that is not as they expect (They expect 180 degrees out of phase, and this gives them 0 degrees out of phase) the "master" inverter connects to the line and the "slave" inverter simply refuses to connect and continues acting as an inverter.

For me this was fine: When connected to a 30 amp outlet the one master Quattro does "pass-thru" on L1 and uses that power to charge the battery, and the "slave" simply draws from the battery to continue powering L2. So you end up still having 240v power available in your RV even when plugged into 120v source. I simply have to dial in the 30 amp shore power limit on the CCGX and everything runs fine.

The only real *problem* was the generator. Sure it could work the same as being plugged into a 30 amp 120v outlet, but a single Quattro can only charge the batteries at about 4kW max (Less when they get warm). Since I have a 6kW generator it's not running most effeciently at the only 3-4kW the single Quattro would draw. In order to address this I added an Autotransformer (Victron offers one but I ended up using the Outback brand) to convert the output of the generator to 240v split phase. Now when i fire up my generator I charge my batteries at the full 6kW available from the genset.

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Nice setup. Do you have 240V circuits on your rig?

If not -- and most RVs today are set up this way -- you can stack the two inverters in parallel and avoid having to buy the autotransformer.

I didn't have 240v circuits originally, but after adding the inverters I have taken advantage of the fact that I *always* have 240v service in the rig to upgrade things like stovetop, water heater, etc. I even added an external NEMA 14-50 for charging our Nissan LEAF that we tow behind the motorhome.

You're right: I could have stacked them in parallel but then we have the opposite problem: If the inverters are configured for parallel operation the "slave" will refuse to accept the L2 power leg when connected to 240v service.


1.) If configured for parallel the inverters work together on 120v but not 240v.

2.) If configured for split phase the inverters work together on 240v but not 120v.

So you have to pick #1 or #2. For me it was easier to go with #2 and add the transformer to step the genset up to 240v.

Regarding adding 240V circuits, awesome. It is nice to be able to do that, if you're up for it. I'm surprised you were able to pull the needed 4-wire runs needed to run most big appliances, however. Did you gut your RV?

Regarding paralleling inverters, I don't think #1 is true if you just parallel them on L1. You just set up your rig to only accept single-phase shore power, any of {15A, 20A, 30A, 50A}. On the output of your paralleled inverters, you put your autotransformer to step up to 240V and make the split phase.

That this is relatively easy to do is why I don't think Victron will bother to make auto-switching a priority -- it's too easy to work around.

Btw, my understanding is that North American marinas also have this identical dualing shore supply issue -- 50A split phase and 30A single phase are both common, just like for us landlubbers. So the market is not that small, I guess. Except most are not going to run stacked inverters in the first place!

To further clarify why I suggest just using L1, basically there is no RV that actually needs the 9.6kW available on a typical 50A/240V shore circuit, because those of us who might actually create those kinds of loads already have large batteries available to peak-shave.

My RV is the most power-hungry one I've seen, and even the 70kWh I can take from a single 30A/120V circuit over the course of 24 hours exceeds the maximum energy I could consume.

The real issue is if you have a very large 240V generator... then, you could run out of headroom on a 120V input for charging. But this is mostly a theoretical problem for 99.9% of RVs.

"basically there is no RV that actually needs the 9.6kW available on a typical 50A/240V"

You haven't seen my rig. I have replaced nearly every propane powered appliance with electric. Electric stove, convection oven, dishwasher, water heater, refrigerator, etc. Add in two roof air units and you can easily hit 10kW. I can easily exceed the 5kW available on a single leg of a 50 amp circuit.

Furthermore: Running on only 1 leg creates a major imbalance on what is supposed to be a fairly balanced circuit. On my previous rig I did exactly what you described: To simplify inverter wiring I only used a single leg of the 50 amp shore power leaving the other unused. The result was I routinely tripped breakers at RV parks by pulling sometimes as little as 28 amps. I also found that the voltage on L1 would drop considerably in such cases (From 125v to under 110v) before the breaker would trip. It was a major hassle and a mistake I decided not to make again.

My rig is more power hungry than yours (I have four roof airs, 10kW of heating elements, 240V appliances, 18kVA of inverters, and a 20kW generator), and an entire day's load even on a warm day is still under 80kWh. That's why I'm confident that it can be done on any RV, as long as the battery is large enough to smooth the demand.

Breakers in RV parks, however, are notoriously weak. They were not designed to be used as on-off switches every day, and they get worn out and the boxes get hot in the sun and these things combine to make them trip early. But even the worst ones I've encountered (also about 28A, but I'd have to check my notes to be sure) still yielded 80kWh per day, which again is plenty with a big battery.



The sag to 110V on one leg is a non-issue in my experience. 8% more current is a rounding error. The issue there is the heat and the worn-out breakers.

A big issue in some RV parks is when 240V is actually 208V because they are running the legs at 120 degrees. Then the pass-through to 240V appliances can become a concern.

I must admit that I'm quite confused now. If you have 240v loads, 18kVA of inverters and a 20 kW generator... What could *possibly* be the advantage of leaving the 2nd leg of 240v service unused, especially when you have 240v loads?!? Sure you can get by with it... But why? Just use both legs. They are there, why not use them? I'm just not understanding why you're pushing so hard for this 1 legged approach.

Especially if you have 240v loads: That means you're taking 1 leg of 120v, sending that to all of your "parallel" inverters, and then using an auto-transformer to step their 120v output to 240v?

Are you also only using 1 leg from your generator? There's no way a 20kW generator is only putting out 120v. That would be nearly 170 amps! What make/model is your generator? I just did a quick search and cannot find any generators that size that are 120v only.

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You could use the same transformer for shorepower I'd think? saves losses from AC-DC-AC conversion (and adds a bit of standby use from the transformer)

In theory: Yes. But the wiring needed to accomplish this gets complicated fast as it would require a transfer switch between the shore power, generator, transformer and slave inverter.

Certainly doable but for me the benefit simply wasn't worth the cost and wiring effort and space that would be lost due to the extra components and wire runs needed. I ended up removing the transfer switch that used to e in the rig to switch between generator and shore power. Now the Quattro's themselves act as that transfer switch. In the space where the old transfer switch used to be is where the autotransformer now lives. There are still losses in the transformer too so if you compare the AC-DC-AC losses with the transformer losses the transformer would only be slightly more efficient.

I am not sure why it has been and continues to be recommended to permanently modify the RV to parallel the inverters. The inverters are smart enough to know when they are 180º out from each other, why can't they just be told to accept that they are on the same phase. It is not uncommon that people bounce between the two situations. But regardless, I still can not understand the reasoning to permanently limit yourself to a single leg of 50 amp service when plugged in unless you were consistently on a single phase output generator over 3000 watts. This is what my CCGX looks like when I am on a 50 amp pedestal. I do not have a large onboard generator so it doesn't matter as much to me in the grand scheme because the way it is now, it all works out for the better. Obviously we are just small fish in the Big Victron pond. But if anyone hears of a hack, please let me know.

irwinr avatar image irwinr Optingoutofnormal ·

I agree with you that the inverters *should* be able to easily switch between split phase and parallel. I argued with Victron engineers for months over this before I finally just settled for the split phase approach.

To be clear though: I never "recommended to permanently modify the RV to parallel the inverters." That's the opposite of what I suggested. My suggestion was that you keep the inverters in split phase (Some call this "serial") rather than parallel. This way you get to use both 50A legs of the 50 amp service.

With this configuration on 30 amp service one inverter will not pass through... But in my experience I haven't really seen this to be a big deal at all. You have full 30 amp service on L1 going to inverter #1, and the 2nd inverter powers leg #2 from DC energy that is provided by the charger from the #1 inverter. You do have some efficiency loss going from AC-DC-AC on inverter #2 but I wouldn't consider it enough to be a major problem.

I did not get the feeling that you were recommending the parallel. I have kept mine in spit phase also as it is more likely that I would be plugged into 50 amp or less than 15 when mooch docking or running off my small generator.

ben avatar image ben ♦ Optingoutofnormal ·

I'm not sure I follow your reasoning vis a vis being "consistently on a single phase output generator over 3000 watts." What does that mean?

I also don't know what could be "permanently modified." Can you clarify?

My experience when running parallel and they are not wired in parallel, they still act in parallel which messes with the GFCIs and causes the chargers to react in unison. So if you have a 2400 watt load on L1, it will cut back the charger on L2 because it thinks the two inverters are carrying the load. So the only way to get them so they work right is to permanently wire them so the outputs are tied together and there is only one hot line in.

So my comment about being on a generator that's single phase and over 3000 watts is that you can not get full use out of the chargers with anything less so there is no use wiring your inverters in parallel to take advantage of it unless you were in that situation on a regular basis. I am full time in my 5th wheel and live off grid most of the time. I spent $48 on campground fees last year and that was for dry camping spots in campgrounds. So I use my inverters mostly off grid with a 600Ah Battle Born Lithium bank and 1400 watts of solar.

I am in progress of installing a similar system to my 50A motorhome, but using 2 48V 3000VA Quattros and have a 7.5 KW Onan - which is wired two hot two neutrals plus one ground through a double pole 35A breaker, originially this went through a transfer swich and I am rewiring to go direct to the inverters AC 1 inputs. As per this discussion this means I only will get 1/2 of the generator output available... I was wondering how you wired up your Outback autotransformer...i.e. did you just wire one of the generator legs and then only connect the transformer output that is now 180 degrees out of phase to the AC 1 input on the second Quattro? I assume this will be limited by the autotransformers neutral phase continuous current limit - about 30A so should be ok for me. Regards Colin

ben avatar image

I believe you can configure both of your MultiPluses in parallel and feed them only L1 when you are on a 50A 240VAC park power pole. Set the shore current limits appropriately, and you can charge and/or pass-through at up to 4800W (80% of 50A at 120VAC) total.

The number of times you would otherwise pass-through more than 4800W (which you can only do with your two Multipluses in split-phase stacking) is very small if you have a typical RV. For those rare times, the power assist can cover your momentary peak load.

Obviously, this configuration works fine for 30A, 20A, and 15A shore supplies as well.

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This is what I believe is happening when in parallel. Because the outputs of the inverters are not wired in parallel, the master is being misled. If both units are powered and charging at the max output and a 1200watt load is applied on L1 (master) it will overcompensate by shutting down both chargers and carries the load until the generator is then reintroduced. If that same load is applied to L2 (slave) it appears the load is not reacted to by the inverters and the load is carried immediately by the generator. The generator output is also not capped at the maximum set on the inverters.

A typical day in the RV can vary based on location but may include running two ac units while doing a load of laundry. Some days it happens while being plugged in to 50amp service in an RV park or a 5500watt onan generator supplying single phase power at 45 amps. It could also be running one ac unit while power is being supplied by a small inverter generator that is putting out 1200-1700 watts depending on elevation. When coupled with a 1400 watt solar supply and 7.9kw of lithium batteries, it can be stretched through the hottest part of the day.

ben avatar image ben ♦ Optingoutofnormal ·

Yes, your loads sound like they will rarely exceed the ~5kW you can draw from one leg of an RV park 50A supply. So you could set your system up as a 120VAC system and be fine.

As could most RVs, in my experience.

ben avatar image ben ♦ Optingoutofnormal ·

Yes, I'm suggesting you wire the outputs of the two inverters to be in parallel. So they are both supplying the same load in-phase.

Then, simply use one leg of the 50A 240V supply delivered to both units.

Optingoutofnormal avatar image

Could they then be calibrated to accept the same sine wave? Because I am mobile my sources of power can change. I am predominantly off grid relying on solar and lithium so split phase does work well for those times. But I would like to maintain passthrough and charging with both units. The outputs are not wired in parallel and would not function correctly if they were and I were to plug into a split phase circuit. Doing a reconfiguration in the inverters would be easy when changing power sources. Rewireing the inverters would not be an option.

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Hi, they would not need calibration to accept the A-C input sine wave.

Note that breaking their link; which is what I’m suggesting; does have some other side effects: you’d need to rewire the lithium protections, and in case you have monitoring like a DMC or CCGX, that will change as well. It’s all possible, but gets a little complicated and not very common.

From Victron we won’t be able to help in all the details with this; best option I can recommend you is to find a trained and experienced installer.

Optingoutofnormal avatar image Optingoutofnormal mvader (Victron Energy) ♦♦ ·

Thank you for your responses. The functionality that I am trying to obtain is actually becoming more common here in the United States with the RV community. There are many of us that are currently living full time in our RVs that bounce between complete off grid situations and partial to full hook up RV parks. Your victron products have become more popular do to the connectivity of a total package. For the most part the dual inverters wired in split phase work for most situations except when the RVs are powered by most onboard single phase generators or connected to 30 amp service. (More)

Does Victron have a list of trained installers that will be able to get the results I am looking for? So far everyone that I have made contact with has said that they have made a request to allow the full functioning of the inverters but that they did not know of a work around other then rewiring the inverters to only give functions in parallel. Because it is still only giving the ability to operate in parallel, it is not a viable solution either. How does the follower know not to turn on the passthrough relay when it is not receiving power 180 out?

Anil Ghatikar avatar image

I think they can be configured as " do not switch as a group" then you may be able to use one of them with the supply.

you will need to use ve bus system configurator.

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I do have them configured in split phase but functionality it not complete. When the inverters test the line voltage and see that the voltage of both L1 and L2 are on the same sine wave, the follower will not allow pass through current or allow the inverte to charge the bank. It will invert full time. I would like the inverters to just match the wave of the input power supplied.

Hi, thats not possible. You have to set the type during configuration, they will not auto-adapt.

One thing you could perhaps do, since you have no 240vac loads, is to split the loads and not pair those two inverters in a system.

Just let each do what it can do, individually.