Advice Needed: Switching from 3-Phase to Single-Phase Setup

DIY
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Hello everyone,

I’m currently running a 3-phase Victron setup and I’m considering switching to a single-phase configuration to better suit my household energy needs. I’d really appreciate your input on whether this change is technically feasible and what the best configuration might be.

Current system:

  • 3x Victron MultiPlus 48/5000
  • 16 kWp solar
  • 20 kWh battery storage
  • RS 450/200
  • Victron busbar with Smart BMS

This setup has been operational since late last summer. During this time, I’ve also been renovating the house—including the electrical system—and I’ll soon be installing a new distribution board. This board can be configured for either single-phase or three-phase (my grid connection is 3x20A), so I need to make a final decision soon.

The challenge:
Load balancing has proven difficult. While the base load is relatively even across the phases, high-demand scenarios—such as using the oven with light house loads, running the induction cooktop while the EV is charging, or operating the dishwasher and washing machine at the same time—frequently trigger overload warnings on one phase, while the other two remain underutilized.

I currently don’t have any 400V appliances, and while a 3-phase EV charger might be something for the future, it’s far from certain.

Over the past winter, I managed fine by grid-charging the batteries at 3A for 2–3 hours per day. At the moment, I use the “Ignore AC Input” setting, and I’ve configured the generator contact to trigger grid charging when the battery SoC drops below 15%.

Possible new configurations:

Option 1:
Parallel two MultiPlus units for general household use and dedicate the third to EV charging.

  • Peak load has reached 32A only once (for less than 10 minutes), with typical peaks around 24–26A.
  • Two units in parallel (10 kVA total) should comfortably handle normal household demand.
  • The third unit would be used exclusively for EV charging, only switching on when needed.

I’m not entirely sure if this configuration is possible or advisable with Victron hardware.

Option 2:
Use one MultiPlus most of the time, with a second in search mode to assist when needed.

  • During the night and when we’re away, household power demand is under 500W—often for 16+ hours per day.
  • One unit could handle these low loads on its own.
  • A second unit could be placed in search mode and configured (possibly via an assistant) to wake up and assist during higher loads.
  • The third unit would remain dedicated to EV charging, as in Option 1.

Questions:

  • Are either (or both) of these configurations technically possible using Victron equipment?
  • If yes, could anyone point me to documentation, configuration guides, or examples to help set this up?

Thank you very much in advance for your time and advice!

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Hi isnt it more a load spreading problem in your distribution board? Since its one phase overloading, i would stick to 3 phase, so the system can be controlled with one GX

If you split it up in 3 separate phases you will need 3 gx and 3 batterys (if you want to run it correctly)

Is 3 extra mp2 5k in 3x2 parallel an option, if the current mp2 5ks are not too old ( you would need more battery also for that)

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I didn’t realize I’d need one GX device per MultiPlus II—definitely a bummer.

Sure, adding 3 more MultiPlus units would solve the power limitations, but honestly, this system is already quite expensive. I’d much rather spend that kind of money (around €2500) on additional battery storage. Plus, let’s not forget the physical space they’d take up—something the “boss at home” strongly objects to. :sweat_smile:

As for better load distribution, I’ve been working on it slowly since September. The truth is, it’s not that easy. Ideally, I’d need to run dedicated circuits: one cable just for the oven, one for the dishwasher, etc. I already have a dedicated line for the induction cooktop. But even with that, I still end up with “forbidden combinations” of appliances. It’s hard to explain, but after months of tweaking, I can confidently say that 5 kVA is just not enough.

Take the oven—it pulls 3000W on its own, leaving very little headroom for anything else.

In winter, on sunny days, I want to charge the EV right after it gets home to make the most of direct solar input (instead of draining the batteries). That’s another 2500W out of my 4000W budget… and that often overlaps with dinner prep time. So yeah, charging the car and cooking dinner at the same time gets tricky.

And honestly, I’m getting tired of my wife having to ask me if she can start the washing machine or dishwasher. I want our energy system to be invisible—something that just works, without us having to think about it all the time.

This really is a power availability problem. Sure, 3x 15kVA inverters would fix everything :grinning_face_with_smiling_eyes: — but let’s be real, budgets aren’t unlimited.

That’s why I still believe Option 2 is the best solution for me:

  • One inverter handles the base load (which is fine 70%+ of the time),
  • A second one kicks in when needed for peaks.

Basically, I want to put all the power into one “bucket” and draw from there as needed. I could maybe even get by with just 2x MP2 units—if I exclude the car, or shift its charging to night-time (which I’d rather avoid due to the noise the MP2 makes at night).

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You could also split heavy loads to ac in side, i have that too

Our whole house is on 3phase 3k multiplus 2, with 3x25A grid
but the oven en electric cooking is on ac in side,

rest on ac out (dish washer, washing machine, dryer, microwave, qooker, airco)

I never have any issues or need to account loads, but i dont have an ev (yet) however
I did the tweaking too when setting up this system, but i do have separate lines for most appliences

See my profile for a link to my topic

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Unfortunatelly for the case, I only have AC-IN 4 months per year.
I’m disconnected from the grid since 26 February.

My goal is being off-grid.

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If you parallel the units you need only 1 gx device. As you suggest 2 X 5kva units will take care of most loads. I run 2 mp parallel and they take care of all house loads. Good to have 1 as a back-up as you are offgrid. Don’t worry about search mode, stand-by usage isn’t that big in relation to your battery size.

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Thanks Bart.
I already paralelled 2 units since half May or so. It 2x MP2 in paralel has been wonderfully enough.
I will probably put the third also, Since I already have it. Then it will be even less effort on each one. I just need to go buy a few more meters of 95mm² wire, I used the third set on the MPPT.

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Or you could use a kVAr generator to balance the phases.

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I thought of it at the time, but why spend one or 2 thousand euros more and get to find space for it, if just some rewiring can do the thing? I already have the material. I had to try it.
other than some annoying problem I’m facing here It’s working very well. I already tried to load it up all I could, and without the car, it’s more than enough. Also I don’t charge the car and turn the oven on; even if I do, Victron’s EVCS will lower the charging to a low enough level and I can still use everything.
And I still have the third MP2, so, the parallel setup is a good enough solution. I have still both clamps on AC out and once in a while I have a look at it. They are dead balanced :slight_smile:

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Did you already use the ESS-assistant in 3-fa

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se configuration. And then you have to switch on “Fase compensation”. and also: “power assistent”
In that case , he uses automatically al three inverters to divide the peaks over the 3 fases, by using the grid as a buffer. But the grid does not see that as usage, it remains 0…
This is really the force of the victron system!
This works perfect, peak power until 10Kw are no problem!
Joost from belgium

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You cant use ESS off grid unfortunatly…

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I tried for a day or two. The problem of ESS is that it can’t keep the grid at zero.

A pity that I already did the physical change to parallel, and actually I’m very happy with it.
If I would had still it in 3 phase I would for sure try that.

Amazing that the digital meter keeps it balanced.

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If ESS was good at keeping it at zero, I would be on grid.

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Yes, ESS will always need grid to balance, so cant run off grid and will always take some power from grid

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Sorry, I didn’t read that you are most of the time offgrid. Maybe you don’t have so much at my answer, goodluck!!

Maybe you van connect the third inverter as a generator ? Andy from offgridgarage has made a video about it:

Joost from Belgium

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My original idea was the same as Andy and I had it for some days, but in the end, the second inverters frequently sent alarm because the second inverter wasn’t fast enough to pick up the loads. The power assist would bridge it but I was sick of seeing the alarms. Tried the parallel and I’m very happy with it. 2x5000 are enough for my usage. I’ll wire the third one, eventually, this summer…

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If your peak loads are during sunny time, you could rewire or add some panels to PV inverters e.g. Fronius or even cheap Hoymiles.

The PV inverters will offload the MP2 and be more efficient.

While offgrid throttling is done by frequency shifting. All PV inverters (shall) support this.

I have 7kWp on Hoymiles HM and HMS, 3x MP2 5K and one MPPT 150/45 with 1,5 kWp for black start.

Though one HMS-2000-4T could add 2kW peak power while 100% sun. The HMS have 1-phase AC trunks.

The MP2 5K inverts most efficient at 1kW at around 84%. The HMS have >95%.