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Myles Best avatar image
Myles Best asked

Cerbo GX Setting Amperage Limit based on Generator

Howdy- I'm setting up an RV install with 2x Multiplus, a Cerbo, pre-existing automatic transfer switch (ATS), and pre-existing 220V Onan genset. Okay- so the transfer switch takes shore (50A service) and generator haven't tested which it favors. So my thoughts are ATS L1 going to one multiplus and ATS L2 going to the other multiplus. What I'm confused about here is if I can setup decently smart amperage limits based on the input. Eg, can I say that for shore I'm at the house and hooked up to a 15 or 20A, but if the generator is on use all the available 45 amps. I know that since the ATS is out of the CAN system (is there any integrated ATS?) it won't know which source is active. But my thought is if the system is kicking the generator on itself, that it would set it to 45A. After the generator goes off, set it back to previous amperage. Is this something that the Cerbo can do or something that I might want to write an MQTT script for? Though- if I recall correctly, since the gen is 5.5KW with 2 lines, the input amperage should be ~22.5 which is close enough to the 20A in this example and on a 50A service or 30A service switching to the genset doesn't make sense. So I'm probably just over thinking this 15/20A service situation but am curious if others have answers.

cerbo gxGenerator
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4 Answers
Matthias Lange - DE avatar image
Matthias Lange - DE answered ·

If you can add an additional relay to the ATS or to the generator input you could use the "Input current limit control" assistant to lower the input current limit if the generator is running.

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Kevin Windrem avatar image
Kevin Windrem answered ·

This comes up a lot. The Multiplus has no way of knowing whether the AC source is grid or generator so it can't switch current limits. A GX device (Cerbo) does not provide any help there except that you could as you say use MQTT, or other mechanisms to set the input current limit parameter when switching between grid and generator.

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derrick thomas avatar image derrick thomas commented ·
Kevin first I want to say I am really impressed with the work you do for this community, you are a valuable asset.


I admit right off I know just enough about programming to know I don't know anything at all. That being said, if the digital input on the cerbo is being used to sense the generator run state would it be possible to (upon activation of the input) first read the existing input current limit variable and store it to be used later, then set the variable to a user predefined value for generator input current limit. Then when the digital input changes state indicating that the generator is no longer running, reset the input current limit variable back to the previously set value?

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Kevin Windrem avatar image Kevin Windrem derrick thomas commented ·
Yes, this is certainly possible.


Using the generator running input may not be the best as the generator could be running and not supplying load such as during a test run, warm up or cool down.


The proper way to do this is to use another digital input fed by the AC transfer switch. Then code in a constantly running service could change the input current limit between values for grid and generator.

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derrick thomas avatar image derrick thomas Kevin Windrem commented ·
Being that there are 2 digital inputs on the cerbo this would be acceptable. Would it be possible to program it in such a way that when the generator shuts down the input current limit setting reverts to not a preset limit, but whatever the user had previously set in the gui?


Is this something you might consider doing for a future update to guimods? Or maybe a standalone mod?

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Kevin Windrem avatar image Kevin Windrem derrick thomas commented ·
I was kind of hoping Victron would take on the project.

To do this right a digital input would need to hook into the AC input selection logic (AC 1 in AC 2 in) so that an external transfer switch would act like the internal one in Quattros.

While this is possible, it's really messy and I'm not inclined to dig into it.

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derrick thomas avatar image derrick thomas Kevin Windrem commented ·

Fair enough, I appreciate your responses. Would it be possible to do something like this with node red (when relay2 is active via generator ac output node red flow sets current to "whatever" and when relay2 opens node red sets current limit to "whatever2") but still be able to retain the remote override feature where the user can set the input current limit via the touch screen when the generator is off? Or would this cause a conflict between the node red flow control and the gx remote override?


Of coarse if there was a simple way to change the current limit settings called out by node red via the touch screen that would be easy.

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Kevin Windrem avatar image Kevin Windrem derrick thomas commented ·
The GUI does provide a way to change the current limit. The Mobile Overview in the stock GUI has a spinner at the bottom left to change the current limit. GuiMods adds a details page to the AC input tile in the flow and mobile overview pages. From there you can select one of 4 user defined current limit presets or adjust the current limit manually 1 amp at a time.


I know little about node red but would assume it could change the current limit parameter, but here is just one. So it would have to remember what it was then set it back.

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Myles Best avatar image
Myles Best answered ·

For any future folks. This was my solution using an LCI Gateway (common in American RVs) and MQTT: https://github.com/TheEmpty/generator-manager


For anyone technical, should be easy enough to switch the generator start/stop to a trait and have the config setup the instance so that it supports using the Victron relays or any other item. But since the Onan generators don't like the built-in relay it was easier to run it this way for me.

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derrick thomas avatar image
derrick thomas answered ·

I ended up using node red and a digital input triggered from the ats to switch between shore and generator current limits.

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