kempza avatar image
kempza asked

Multiplus II - Transfer switch operation


I'm planning to install a 3kVA Multiplus II with some solar PV running ESS and want to better understand how the system will work when grid power is available.

  1. I have been advised that the max power that can be supplied to the backup loads on AC1 is 2400W even when the grid is available. Is that correct? My understanding of this scenario is that the limiting factor is the 32A transfer switch which would imply a 7680VA limit when running 240V?
  2. How are high startup loads on AC1 handled when grid is available? We have a water pump I would like to have on the backup circuit - the inverter and batteries could take the full startup load - but I would prefer that the initial high current be pulled from the grid when available to reduce wear on the inverter and batteries. Is that possible?
  3. Does the Multiplus combine the output from the inverter and grid to power the backup loads or does it switch distinctly between the two? For example, if I had a 4000W load on AC1 would this all be supplied from the grid, or would the inverter provide the first 2400W and balance of 1600W would come from the grid?


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nigelfxs avatar image nigelfxs commented ·

Hi Kempza

I also have the Multiplus-II so can hopefully answer your questions ;-)

1. This is correct. The max continuous power that can be supplied to backup loads is 3000VA (reactive loads) or 2400W (resistive loads). This assumes that your Multiplus-II has proper ventilation and that the internal fans can keep it cool. The Multiplus-II has a larger "peak power" when supplying loads above 2400W/3000VA for a short-duration. This is useful for situations such as motors starting up etc.

The limiting factor, in most cases, is probably the Multiplus-II. An external Miniature Circuit Breaker (MCB) is needed to protect the wiring to the Multiplus-II from extreme events, so should not be a limitation to normal operation.

2. The Multiplus-II , when configured with typical ESS settings, will always pull the first 2400W from the battery to power essential loads (AC-OUT1) and non-essential loads (AC-IN or AC-OUT2). This assumes that the battery well charged etc. If the loads require more than 2400W then the excess power is drawn from the Grid. So the answer to your question is no - it is not possible to get this initial power from the grid, but I doubt that it will have any problem delivering short bursts of power when starting your pump (it is designed to work at 2400W, assuming suitable cooling) .

3. In your example, 2400W will come from the inverter/battery and 1600W will come from the Grid.

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kempza avatar image kempza nigelfxs commented ·

Thanks NigelFXS, thanks for the explanation. I just want to confirm this - will I be able to run a 7000W load through AC1 when the grid is available?

We want to have the plug points running the kettle, microwave, hair dryer etc on the critical circuit and will only run one at a time when there is a grid failure. I just don't want to have that limitation in day to day use when the grid is available.

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boekel avatar image boekel ♦ kempza commented ·

That is correct, the inverter's power is added to the grid power.

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kempza avatar image kempza boekel ♦ commented ·

Thanks, much appreciated

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2 Answers
JohnC avatar image
JohnC answered ·

In a simple installation you could look upon it as a UPS. The grid will have priority, passing through and charging batts too, up to the 32A ac input limit. If grid fails it can invert 2400W (temp rated, etc) to running loads, so can't manage 32A ac.

Typically, loads on terminal AC OUT 1 would be essential loads and setup so 2400W would be adequate. Non-essential loads (in a gridout) would be wired to AC OUT 2, and wouldn't be supported by the inverter.

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kempza avatar image
kempza answered ·

Thanks @JohnC I didn't mention that this will be running as part of an ESS setup with PV. Hope will that affect it?

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JohnC avatar image JohnC ♦ commented ·

Yeh, I did say a 'simple' system, just for a start point, ha..

There's all sorts of things can be done with ESS, assistants, DVCC, etc. The design essence remains though - tis for you and/or your installer to work out how to achieve your aims. Whatever they are..

Ideally, rely on your supplier/installer, or be prepared to put in a lotta time researching the prolific data available. Sizing your boxes-o-blue is most important too, and I guess that's what you're doing now before you commit.

Keep researching and asking til you're sure. For good answers, make your questions as specific as you can - the full monty..

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Related Resources

MultiPlus-II Product page 

MultiPlus-II Manual

MultiPlus-II 230V Datasheet 

VE.Bus Error codes

Additional resources still need to be added for this topic