[dog_house]

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.

 

[dog_house]

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

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!

 

[dog_house]

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.

 

[dog_house]

You will have to have two assistants: one to turn the relay on when loads are below 500w as AC2 Out is always off by default and one to turn the relay off at loads OVER 500w:

View attachment 93244
View attachment 93245

You can set the time offset to whatever you works. You should have something built it so it's not fluctuating on and off rapidly based on your loads.

Also a third may be needed if you plan to use shore power as well to force the AC2 Out relay when shore is available. I've never tested this though as I rarely am on shore power:

View attachment 93246

You can try this order:

View attachment 93247

This worked like a champ with a minor adjustment. The Relay OFF assistant needed to be increased by the amount of the load so that it does not cycle over and over. I could have set it to 2500w but instead I set it to turn the ACOut 2 OFF when the overload pre-alarm LED comes on and that seems to work well. Adding the AC1 trigger to turn it ON when we were plugged in was the ticket.

The inverter seems happy running a 1500w resistive load (oil filled space heater) and the heat pump at the same time so I think the idea of lowering the wattage of the HWT is the right way to go. I am going to swap the 2000w element out for 1125w one and 90% of the time the assistant won't be needed. I doubt the extra 30 minutes it will take to recover will ever really matter.

Thanks again!