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Francis Hemeter avatar image
Francis Hemeter asked

Multiplus generator assistant to switch ACOut2 to run a electric hot water system

I have a multiplus 24/3000. 400AH @24V lithium battery bank. I want to heat hot water when on shore power and also when battery is close to full. Heating element 1500W. (it is in a heat exchanger that is heated by bus hot water too). I am looking at powering hot water off multiplus the AC2 circuit. Looking to use the generator assistant to control the AC2 outlet

*)Use ACOut2 relay to start generator


*)’open relay to start generator' - this inverts the logic

(start generator = open relay to turn off ACOut2)


*)’start generator when load higher than 5000 W for 5 seconds’ -and

Open ACOut2 when load higher than 2400W for 10 seconds

Turn off hot water when load higher than 2400W for 10 seconds

'stop generator when load is lower than 1800 W' -

Close ACOut2 when load is lower than 1800W

Turn on the hot water when load is lower than 1800W for 10 seconds


*)’Start generator when DC input voltage is lower than 26.5 volt' -

Open ACOut2 when DC input voltage is lower 26.4

Turn off hot water when voltage is lower than 26.4 will have to experiment with this to get about the SOC I want especially with voltage sag.


*)’stop generator when DC input voltage is higher than 26.61 volt' -

Close ACOut2 when the DC voltage is above 26.61

Heat hot water when the voltage is above 26.61


*)When the generator is started must stay on for a least 10 seconds

When ACOut2 is Open and the hot water system is off must stay off for 5 minutes longer.


*)The generator is not stopped by AC input

I am not sure about this command, I assume it applies to the assistant as a whole, that is not effected by inverted logic with the start/stop, but will allow the assistant to run or remain in its current state even if AC input is active. That is I have shore power.


MultiPlus Quattro Inverter ChargerGeneratorHot Water Diversion
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4 Answers
Guy Stewart (Victron Community Manager) avatar image
Guy Stewart (Victron Community Manager) answered ·

It is always good to test these things. These are my thoughts, they might be wrong.


I disagree with your final point. Once you program an assistant to control ACout2, the normal function of ACin enables ACout2 does not apply anymore.

It is possible to bring this back with another assistant (that is higher in the logic order of the list), or depending on the behaviour you want by using the final configuration setting of the generator assistant.

The generator is stopped when AC1 is available + logic inverted = AC2out relay is closed and water is heating when shore power is available.

This presumes you want to continue heating hot water when shore power is connected, and other conditions are met.


If you want the hot water to immediately heat whenever shore power is connected:

I would add 2 additional programmable relay assistants, one to Use ACout2 relay on when AC input is available for 10 seconds. And the other to Use ACout2 relay off when AC input is not available for 10 seconds.

I would have to think a bit harder about what order they need to go in the logic.

So please test it though, make sure it is behaving like you expect and report back. I still learn something every time I set up a real world assistant application.

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Francis Hemeter avatar image Francis Hemeter commented ·

To be honest I was thinking if *)The generator is not stopped by AC input was needed or if it needed to be inverted so generator is stopped by AC input (making AC2 closed and heating the hot water).

In normal operation I would be ok for the multiplus to charge the battery then start heating water when plugged into shore power I assume on AC2 it will still pass shore power through to AC2 when plugged in before it draws on the battery, the watts used would only apply to inverter load not pass through.


This is a pretty common request or application I know a few people that drive toyota coaster buses converted to motorhomes in Australia with electric/heat exchanger hot water systems with multiples want to know if you can use the AC2 to switch the unit. That's a very small niche and still depend I would not be surprised if it was not more common request.

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Francis Hemeter avatar image
Francis Hemeter answered ·

I have tested it need to work on voltage cut offs due to voltage sag, I added a couple wires down from the battery sense terminal so I hope that will also help with voltage sag and dialling in cut offs.

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daniel1957 avatar image
daniel1957 answered ·

looks like a very complicated way to do a simple function.

If you are using a Victron MPPT solar controller then use its built in programmable relay function.

Best way is to set it for battery float state - the energy dumps into hot water wherever the batteries are floating.

The hysteresis is handled by the "minimum time" period function.

See Victron MPPT Solar Charge Controller manual pages 18 + 19.


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Francis Hemeter avatar image
Francis Hemeter answered ·

I have to be honest the cycling when off grid of the battery kind of annoyed me, especially when I was in hot areas like 45 degree C I really didn't need the hot water, actually I turned it off to use the hot water system like a cold water tank and the tanks under my bus were heated by the road. I found manually cycling the power to the hot water was less demanding on the battery and I did not have to deal with the inverter revving up in the middle of the night to heat water I did not need hot. I didn't plug into shore power for over a year.

When you get the bluetooth models in the future a pre programmed function for this would be useful.

I still have a function programmed for this circuit and that's I am using too much power eg cooking dinner on the induction cooker on 3 (out of 9 settings) I can have the hot water heating too, but if punch the inverter to 9 (2000W technically) the inverter is not going to take to take that and the 1500W heating elements so it cycles the hot water off, until I realise and turn the induction cooker down, I would be burning things at 9 anyways just a quick pre heat of the pan. 18 months now off grid with the magic blue box, happy customer.

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