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the-doon avatar image
the-doon asked

Cerbo relay control by SOC and voltage

Hi, would it be possible to add extra features to the relay settings menu of the Cerbo to include the option to switch the relays using SOC and voltage options? I’d like to use the higher end of the charge voltage to switch on a battery cell balancer on one relay and SOC to switch on a hot water element (dump load) using the other relay. Is this something that can be added to the next firmware update?

cerbo gx
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2 Answers
Guy Stewart (Victron Community Manager) avatar image
Guy Stewart (Victron Community Manager) answered ·

Hi @The Doon,

This is already currently possible if you set the relay control to generator start stop mode, and can then be set in the generator start stop conditions menu.


cleanshot-2024-04-24-at-123030.jpg



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the-doon avatar image the-doon commented ·
Thanks Guy. I tried that but the settings only allow you to use voltage the other way around. Start at a lower voltage and stop at a higher voltage. I want to start at a higher voltage and stop at a lower voltage. I suppose I could program it so the relay is powered 99% of the time and turns off to activate the balancers but it seems a bit backwards to me.
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the-doon avatar image the-doon the-doon commented ·

img-6834.pngIf the rules were modified slightly to allow whatever voltage or SOC value the generator start/stop option would work. As it is now I’m unable to set the values I want and see this if I try.img-6833.pngImage Caption

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Guy Stewart (Victron Community Manager) avatar image Guy Stewart (Victron Community Manager) ♦♦ the-doon commented ·

Hi @The Doon

My relay control logic is a little bit rusty, but can't you do that by just inverting the state of the relay by using the normally closed instead normally open contacts.


Normally Closed

Start at low (opening)

End at high (closing)


10V = open

14.4V = close


Normally Open

Start at low (close)

End at high (open)


10V = close

14.4V = open


Functionally the same as:


Normally open

Start at high (close)

End at low (open)


Low voltage 10V = open

High voltage 14.4V = close


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the-doon avatar image the-doon Guy Stewart (Victron Community Manager) ♦♦ commented ·
Thanks Guy, would you have any concerns having the coil of the relay powered for 23 hours per day?
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Guy Stewart (Victron Community Manager) avatar image Guy Stewart (Victron Community Manager) ♦♦ the-doon commented ·

I have never heard any advice to the contrary.

The warnings about the relays are more to make sure they are aren't actually switching any more current or voltage than is required to drive a larger contactor that actually handles the load, or even better activate a voltage free contact detection.

Continuous activation (and using either of the positions) is intended use.

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luphi avatar image
luphi answered ·

You can also use the relay of a Multi

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the-doon avatar image the-doon commented ·
Thanks but I want 2 relays and the multi is off most of the time so I don’t believe the relays works in the off state.
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luphi avatar image luphi the-doon commented ·
If the Multi is off by the Cerbo and not by it's physical switch, it's relay will still work.



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the-doon avatar image the-doon luphi commented ·

I do use a remote switch but this actually might work for the HWS as I can leave the inverter on when hot water is required. Gives me something to think about. Thanks.

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