Is it possible for the Multipus II 5KVA to handle a 4500w electric water heater?

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jeromep asked Mar 5, '24

Is it possible for the Multipus II 5KVA to handle a 4500w electric water heater?

Can the Multiplus II 5KVA handle a 4500 watt electric water heater (Richmond 50 gal)?

My water heater has 2 4500 watt heating elements which I can disconnect one element.

The Multi II will be passing ac current to the Victron 120/220v autotransformer so I am able to run my 8amp 220v well pump. The transformer will be connected to my house service panel, (grid will be turned off)

The water heater will only be used to heat up enough water 100f degrees for my 10 minute shower then turned off for rest of the day. While the water heater is on, the well pump will be turned off as well as all the other circuits.

I don't have any of the solar components yet, I would like to go with the Multi II 5KVA but it's rated for only 4000 watts, 5000KVA x .8=4000 watts. I would also have two SOK 48V, 100AMH batteries.

Running 2 Multiplus 3KVA (4800 watts) will be beyond my budget but may be mangable if I were to delay the solar install.

Multiplus-II

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Answer 1 · 2024-03-05T23:07:31Z

Al answered · Mar 05 at 11:07 PM

No.

As you say, the 5k is rated 4000W continuous at 25°C, so a 4500W load for an hour or two to heat water won't work.

You'll also need more than a single 100Ah battery, as it'll only last for just over an hour pulling close to 1C, so not an ideal setup.

Get yourself a 3000W immersion element instead and you'll have a better chance of making it work.

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Answer 2 · 2024-03-05T23:54:46Z

ejrossouw answered · Mar 05 at 11:54 PM

@JeromeP The MP-II 8kVA 6400W would be another option to keep things easy and simple compared to a parallel setup. It may be worth stretching the budget.

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Answer 3 · 2024-03-06T04:42:31Z

kevgermany answered · Mar 06 at 04:42 AM

It might as a single load. Water heater loads are resistive, not inductive, so you can work from the VA figure. And then you have an excess of 500VA. Question with that is how long before it de-rates the output due to heat in the Multiplus.

What may also help is reducing the output voltage. Grid voltage is nominal and as long as you stay within normal range, everything will work safely but the heater will draw less current. E.g. in England voltage is nominally 240V. Electrical kit runs fine at 220V. Same will apply running a 120V nominal at 110V. That's close to a 10% voltage and power reduction.

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Al commented · Mar 07 at 01:00 PM

Being a pedant.. sorry, the UK harmonised from 240V to 230V with the EU years ago.

"In the UK, the declared voltage and tolerance for an electricity supply is 230 volts -6%, +10%. This gives an allowed voltage range of 216.2 volts to 253.0 volts."

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Answer 4 · 2024-03-06T15:23:36Z

jeromep answered · Mar 06 at 03:23 PM

Would using the Power Assist on the Multipus II be of any benefit to bring the ac output wattage up to 4500 while on the 3500 watt gas generator?

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Answer 5 · 2024-03-06T15:42:42Z

Jason - UK answered · Mar 06 at 03:42 PM

@JeromeP I've run my MPII 5kva unit flat out for 2 hours. I managed to maintain about 4.4kW for about an hour before it started dropping to 4kW, then by the end of the 2 hours I was down to 3.6kW. That was with a power factor of about 0.9. When I added 3No small fans to the top of the MPII unit, I was able to maintain over 4kW for the whole 2 hour period.

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Answer 6 · 2024-03-06T17:09:25Z

jeromep answered · Mar 06 at 05:09 PM

That's quite impressive, a bit taxing on the unit. Was this done without Power Assist if applicable?

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Jason - UK commented · Mar 06 at 05:30 PM

@JeromeP I should have noted that's in ESS mode, grid connected. Off-grid, the unit will behave differently but then off-grid, the MPII controls the voltage so with a resistive load, you might be able to run it at a lower voltage to reduce the work on the MPII unit but then the resistive load gets less amps. Might be worth testing your proposed set up with different voltages. My grid is at 243v.

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Answer 7 · 2024-03-06T17:40:25Z

jeromep answered · Mar 06 at 05:40 PM

Thanks. That would be a good option for the water heater but I don't want to risk lowering the ac limit, there is a good chance I may forget to set it up again to 120 volts to run my electronics, unless I'm missing something here.

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