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MultiPlus 3000 Aux Output programming and Wiring

427 Views 10 Replies 4 Participants Last post by  nebulight
I am looking for help from the Victron experts. I have MultiPlus 3000 and have the AC out 2 going to a 20 amp breaker and feeding a water heater. I would like to have the inverter power the water heater when there is less than 500w of output from the inverter and turn off the water heater when there is more than 500w of load on the inverter. This will let the inverter heat water but stop the inverter from going into overload when another load like the heat pump or microwave are on. The HWT currently has a 2,000w element but it can be changed out easily to lower the wattage. If I can make this load shedding work I would rather leave it so that the water can heat quickly, especially when we are plugged in and have 6,000w available with the power assist.

I have tried to set up an assistant to do this, but I am only seeing AC load as a trigger, not the inverter output. Is this possible? I think I can add another assistant to have the AC out 2 always on when shore power is available to get around it but so far I am having trouble getting it to work. It seems that this question has been asked before in the Victron forums but I am hoping that someone here has actually done it. Is it possible to use the inverter overload warning as a trigger to turn off AUX2 ?


I added a second breaker box to allow for a 30a shore power breaker and to keep the AC out 2 separate.

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This is not something I can answer without some research, but purely from memory

I am not sure if you can trigger on 500W of AC output, but you can setup the inverter to trigger a relay if overloaded. This is typically used to start a generator, but nothing says you cannot use it to turn off a relay that would shut off the water heater.

I am pretty sure you can trigger off inverter output with a GX series device, but I don't see one in your diagram. I think setting up a generator start assistant if the inverter is overloaded will work fine, the inverter can decide when it is overloaded rather than setting a fixed 500W.

I might switch the water heater element to a 1500W anyway as it won't make much difference in usability but can save some stress on your system
 

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I have a Cerbo and I didn't look in the generator start assistant for a way to do it. That's exactly what I was looking for. If something triggers an overload, turn off the relay.

I think the system will be okay, it's spreading the load across 4 batteries so each one is discharging at .15C and less than 1/2 the BMS's rating. I would rather hit it hard while we are driving and heat the water while we have alternator power and save the batteries for running the AC. If for some reason it causes issues it's an easy swap. I had to lower the power in our travel trailer water heater to keep the 30a main breaker from tripping when the AC was running in high temps.

Thanks for the help!
If you ever decide to modify, the isotemp water heaters that heat the water with using engine coolant is the way to go for people that plan to be driving often. I have had two class B RVs (1989 Dodge factory built, 2018 Promaster Self Built) and have had heat exchanger water heaters on both. I will never have an RV with an engine without one.

The electric element on them is only 750W (at least on my model) but if you drive every two days you will never need the electric element anyway because it heats the water to engine temp and keeps it hot for quite a while.

As Nebulight put three assistants may work, I haven't ever set up ones that conflict so I don't know how it behaves when one tells it to turn on the AC2 relay because it is connected to shore power and the other says to turn it off because of >500W load. He might know more than me on this one.
 

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I have the system mocked up in my garage, I'll mess with it and see how it reacts. Stand by.

@jracca I have used water heaters with coolant loops on the boat and they work great but I don't want to have to mess with the PM cooling system if I don't have to. I considered it, but since I am this deep into batteries and inverter I can spare the 2kWh for us to take hot showers. What I don't want is any reason for Ram to deny the warranty. If this was a used van without much powertrain warranty left I would be using the engine to heat the water without a doubt.
I hear that!, It was nerve wracking to splice into my promaster heating loop with 25 miles on the odometer. But Ram sells the kit to do it, so I figured it must be allowable.

I added ball valves right off the T fittings to be able to shut it down in the event of a heater hose puncture, but those hoses are pretty tough.

Of course cutting holes in the roof of a brand new van was also a high stress event. Once the first hole was made it got easier.
 
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