liam-hogan avatar image

Using Cerbo GX and Multiplus to control dump load

Victron AC System.png

Hi everyone,

I have a question about using my Cerbo GX and Multiplus II together.

I want to heat a 240v water heater as either a dump load (when battery SOC is high) OR when shore power is available to the Multiplus.

This is simple enough with just the dump load setup - I can use the relay in the Cerbo to trigger at a certain SOC to a second relay to power the heater.

What I am wondering is whether it is electrically possible to combine the 2 AC outputs of the Multiplus so that the heater is ALSO powered when shore power is available - as the second AC out on the Multiplus is active only in this case. Maybe there is another way of doing this (like if the Cerbo logic could control the relay based on AC availability too).

I have attached a simplified diagram of what I propose.

Are the 2 AC outputs perfectly synchronous?

Thanks for any advice


MPPT ControllersMultiplus-IIcerbo gxac out 2
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1 Answer
Vance Mitchell avatar image
Vance Mitchell answered ·

Using assistants would be the easiest way.

There have been a few examples on here of people doing similar.

Multiplus generator assistant This is one that I found that should give you a good starting point.

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Thanks for the quick answer, Vance.

I wasn't aware yet of the 'assistants' programming feature - but setting up the system this way seems more elegant than trying to make it work in the physical domain (combining AC and relays like in my diagram).

Only thing is that it seems you can not program in for a specific battery state of charge, just voltage (which is not the most accurate option when using lithium).

My idea now is to use the Cerbo relay to trigger at a specific SOC, run that into the multiplus aux input, and then apply the state of that to an assistant? Would this work to your knowledge?

If the cerbo reads the SOC from the batteries or a BMV/Smartshunt then it can be used with SOC rather than voltage. If you search this forum for Dump Assistant or water heater assistant you should be able to find an example where someone has done exactly what you require.

I can't remember which post it was but I set up a similar assistant by following what I found on here. Unfortunately I am not sure where exactly I found the information.