casey avatar image
casey asked

Quattro 24/5000/120 with 240V split-phase input

I currently have a Multiplus 24/3000, but am thinking of replacing it with a Quattro 24/5000, both for more output capacity and maybe to handle 100A of charging input from a 240V split-phase (“50A”) outlet. As far as I understand, a single Multiplus can use one of the 50A legs but two configured in split-phase mode would be required to handle both legs.

The PDF manual online claims the 120V Quattro can handle both legs of input but that 240V output is not possible off the inverter. That’s fine with me - I only care about 120V. But can it use both legs for battery charging, or is it just something passed through?

My goal is to charge my batteries using both 50A legs if possible. I only have 120V appliances and would prefer to run single appliances up to 3kW - beyond what a single Multiplus can do. If a Quattro won’t help me, then maybe I need to consider a second Multiplus instead. But with split-phase, I don’t think I’d be able to run anything beyond 2.4kW for long, if I understand correctly. Any advice greatly appreciated!

MultiPlus Quattro Inverter Chargerbattery charging
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1 Answer
Kevin Windrem avatar image
Kevin Windrem answered ·

You have a couple of options:

Since you already have one Multi 3000, your lowest cost and simplest solution would be to add a second Multi 3000/120 to handle the second leg. These would be programmed to operate in split-phase mode and also would also run on two legs of 120/208 using "L2 floating phase". This configuration can probably accommodate 120 volts single phase input feeding both inverters but that needs to be confirmed by someone that knows more than the documentation says about L2 floating phase.

You'd meet your goal of 100 amps of charging current since both Multis would each provide 50 amps of charging current.

You can connect a 230/240 volt Quatro across the two hot legs of a 120/240 volt split phase service. (The second leg goes to the Quatro's neutral and the source's neutral is not connected.) You then create split phase on the output with an autotransformer. The internal ground relay must be disabled and an auto transformer with a controllable ground relay is required. Check the Victron Autotransformer manual for details and schematics. I don't think this confutation would work from two legs of 120/208 3-phase power since the output voltage would track the input and you'd end up with 104 volts on your loads.

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casey avatar image casey commented ·

A significant downside to a second Multiplus is space use. Switching to a Quattro would be more space-efficient. Adding an Autotransformer would also consume an amount of space that I really don’t have to spare. My application is in a camper trailer, where space is limited. I’d rather live with only 50A charging capability if increasing that means adding complexity to the setup.

I also don’t really grasp how to use split-phase power yet so would prefer to keep things single-phase 120V if possible as I understand this well. In a split-phase configuration, wouldn’t each phase need to be wired to different circuits, thus making use of a 3000W 120V appliance impossible?

I may be confused about the available models... this manual ( mentions nothing about charging from 240V, but this manual ( mentions charging from 120V, 208V, and 240V all as possibilities with a single unit. Perhaps there are multiple Quattro 24/5000 models?

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Kevin Windrem avatar image Kevin Windrem casey commented ·

Smaller RVs have 30 amp 120 volt single phase inlets. So you get at most 3600 watts of power for the entire RV. Larger RVs use 50 amp 120/240 volt split phase inlets. Split phase is two 120 volt legs 180 degrees apart so you get 240 volts between the legs. This is what enters most US homes. Total power with this configuration is 12000 watts, 6000 on each leg. Most RVs don't have any 240 volt loads. Everything is 120 volts, connected to one leg or the other -- nothing between the two legs.

Charging current listed in the spec sheets is at the battery voltage, not the incoming AC voltage. The 5000/24 Quatro charges at 120 amps or 2,800 watts which is only 24 amps at 120 volts So if charging is your only reason for upgrading, you can do that even on a 30 amp 120 volt single-phase inlet to the RV. Of course, you can't do much else but the Quatro takes care of that management: less charge current when loads are higher.

You could rewire your RV for a 50 amp 120/240 inlet but only use one leg. This would require a different inlet connector and cord as well as larger wiring inside the RV up to at least the Quatro. Making use of the additional shore current would require upgrading the load distribution panel.

You don't mention the size of your existing battery bank. An increase in inverter probably also means an increase there as well.

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casey avatar image casey Kevin Windrem commented ·

Thanks Kevin,

I am in the process of building a custom camper, which I live in off grid without access to power. I have 1800W of solar, so usually don’t need access to shore power. I am however running some high-load stuff like electric heat, air conditioning, cooktop, water heater, a washing machine, etc. My concern is that with limited solar hours in the winter, along with a high demand for heat, I may end up needing shore power during stretches of overcast weather - if I rent a campsite it will be due to depleted battery, but a full recharge will last me a decent while. So my use case is quite a bit different from most RVs. On the bright side, I have much better insulation so heat & A/C are a lot less intensive than otherwise.

I have already run a 50A inlet and 4-conductor 6 AWG wire under the floor to the generator. Yes, 12kW is way more than I’d ever need, but I figure it’s best to be able to handle as much as possible, or I’d have just run a 15A or 30A inlet. I won’t be able to easily tear up the floor later once I finalize the last few decisions and button it down. However, if it’s just wasted weight that I’ll never benefit from, I’d rather change it out now.

I did not realize that the charger amperage was for DC rather than AC - that definitely changes things. So the Multiplus with a 50A rating and 24V system would mean 1200W so only 10A on the AC side (maybe a little more factoring in loss)? That’s still only using 20A with a Quattro, which is well under 30A, making 50A seem completely useless. If that is the case, it probably makes the most sense for me to change the 6/4 wire to 8/3 and just have a 30A inlet.

I’m not very familiar with large RV’s. Do they rely on external power to run both legs, or run both legs off of a single inverter when not plugged in? It’s funny that they don’t use any 240V - I was contemplating the possibility of using a second Multiplus in split phase configuration and then running more 240V appliances to divide the load between them. My highest load currently is the cooktop, which with both burners on high uses ~25A @ 120V, and alone can overload the Multiplus. I’m not that clear on when higher voltage is necessary/advantageous/safer versus more amperage given the same wattage, though.

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casey avatar image casey Kevin Windrem commented ·

Forgot to mention - the battery bank is currently 400Ah LiFePO4. I am planning to upgrade to 900Ah though.

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Joshua Warren avatar image Joshua Warren casey commented ·

I'm assuming you've done detailed calculations but 1800 watts (nominal) solar is almost certainly not going to be sufficient to run electric HVAC continuously. 900AH might get you through the night depending on outside temperature (it will definitely be inadequate in very cold areas if you intend to run electric heat). If you're really going to be off grid in extreme temperatures you're almost definitely going to need a generator and at that point you may as well switch anything you can over to propane.

As for RVs with a split phase panel, they can be wired so that a single inverter powers both legs when on inverter power (AM Solar has a device called the "Smart Phase Selector," which I believe is just a rewired transfer switch that costs $600, that can be paired with a 120V single-phase inverter to achieve this -- an autotransformer could also achieve a similar outcome but maintain the 240 line-to-line voltage in the panel). I did mine with a pair of Multiplus 3kva/120s, though. But In order to be able to run two air conditioners on 30A/120V input without discharging the batteries I had to wire up a switch that allows me to switch the second air conditioner from L2 to L1. Otherwise, running it results in battery discharge because on single-phase input only the first inverter accepts the grid; the second inverter inverts from the 12V side but of course you're limited to the DC charging capacity of the first inverter (120A at 12V nominal in my case) in order to avoid battery discharge. After conversion losses the result is that you can only pull about 1200 watts on L2 without battery discharge, which is inadequate for an air conditioner.

Some large RVs do have 240V circuits/loads. I installed a 5kw electric heating element into my furnace that I'll use when on 50A 120/240 service to conserve propane. I've heard of some really high-end configurations that have 10kw of electric heating elements. In those rigs, you'll often see a pair of 5k Quattros that are wired to the main panel with 2 AWG to supply a 100A main breaker. The idea here is that at 10kw draw for the electric heat, there's only 2kw remaining on the actual incoming power circuit, so the Quattros provide power assist for any additional demand. Hence the 100A passthrough and main breaker, although the AC input to the inverters can still be done with 6 AWG.

Your cooktop sounds intense. What kind of plug does a 25A cooktop have?

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casey avatar image casey Joshua Warren commented ·

You overrate me - I've done what calculating I can but detailed is not a good word for it - I've been learning a lot as I go!

Propane is a fallback option for heat, and a generator is also a more general fallback option in case I need it, but I'm hoping to avoid using those and am not building in propane lines. I'll have to wait for the winter to see how well it works out, but I have substantial insulation (3.5" of XPS all around), no windows, and a pretty small space (7'x16') to heat which should help considerably. I also don't need that much heat at night at all when sleeping under down comforters and so forth anyways. In addition, I also have external plugs on the trailer to allow plugging in another 1800W of solar, as I may well end up needing to expand the solar input, and there's no way I can fit more than 6 60-cell panels on top of size of trailer I have. The AC/heat pump I have uses 1200W if I recall correctly.

I was thinking from memory that the cooktop ( was 3000W but it's actually only 2700W (22.5A), in any case will make the Multiplus unhappy if I turn both burners all the way up (which realistically I don't ever need to do). It does not come with a plug and is intended to be hardwired, but I was thinking of using a NEMA 5-30 or L5-30 receptacle/plug for it. One motivation to upgrade to a Quattro 5k is to be able to have heat or AC running, and also do other things, like cook a meal, without concern.

Are you able to answer the question I asked Kevin, about whether 50A input wiring would allow any more charging capability than a 30A line? The Quattro is capable of charging at 100A, and if that's at 24V, then that's only 2400W. A 30A input would allow for up to 3600W. Unless I'm missing something, there doesn't seem to be any advantage to me running a 50A input.

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Joshua Warren avatar image Joshua Warren casey commented ·

I would wire it for 50a because on a 30a input if you're running air conditioning and that thermonuclear cooktop you're going to exceed 3600w anyway and will wind up discharging the batteries when you're actually trying to charge them. And in a less extreme scenario a 1200 watt air conditioner load plus 300 watts for the fridge and then another couple hundred watts for other stuff means your rate of battery charging will be limited. You'll have to stay plugged in or run the generator for a lot longer to top off the batteries.

Propane lines are easy to run. I'd run them just for future proofing. If you're building this thing from scratch it's even easier. Adding them later won't be fun.

Definitely sit down and do some serious and conservative calculations under worst case conditions to make sure your solar and battery configuration is going to be adequate. The trailer sounds pretty small and energy efficient so you may be alright.

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casey avatar image casey Joshua Warren commented ·

Thank you for that point about the passthrough current - I had forgotten about that angle. I will keep the 50A inlet since it does offer this advantage.

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solardude avatar image solardude casey commented ·

The Quattro 120/240 in the second link doesn’t exist anymore. If you don’t have space for a second unit or autotransformer, then you are stuck with 120V.

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