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How can I use Victron Cerbo GX Relay to Activate Heat Pad in Green House

Dear Community,

I am using a Cerbo GX + Ruvvi Temp Sensors in a Greenhouse. When Temperature falls below a certain point, I want the relay to close, and the heat pads to activate. When the temperature exceeds a certain point, I want the relay to open, and power to the heat pads to disconnect.

I have built the setup, and it's running, but I believe the configuration on the Cerbo GX, and relay control is designed to operate for cooling principles NOT heating. I believe the program is directional, and the user would benefit from being able to determine the direction that the program operates. One should be able to determine if the activation value or de-activation value triggers the relay based on direction.

Below is my current setup, 'Activate' at 11 degrees, and 'de-activate' at 17 degrees, yet its currently 8 degrees outside and the condition is 'active'.

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Its active because at some point in the day, the temperature exceeded 11 degrees, so the relay activated, yet even though its fallen below 11 degrees it remains active. It would only shut off if the temperature exceeded 17 degrees.

How can I set it up, so that if the temperature falls below a certain point the relay is activated, (as I think the relay works only when the temperature EXCEEDS a certain value.

It's designed for a hot cabinet, activate when temperature is 30 degrees, de-activate when temperature is 20 degrees as an example.

I believe the activation direction is the limiting factor, since once temperature exceeds 17 degrees the relay would deactivate. Yet if it falls below 11 degrees It won't activate, only once it INCREASES past 11 degrees.

A link to the setup is here, in-case you wanted to have a look. https://vrm.victronenergy.com/installation/213577/share/7a0c99c7

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I am using Carbon heat pads, which are incredibly low energy, but will give enough heat to the plant pots to improve growing conditions.

Let me know if you have a better way of programming this.

Thank you


cerbo gxRelay
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Alistair Warburton avatar image Alistair Warburton commented ·
I cant comment on what should be happening but if as you say the system expects the deactivate temperature to be lower than the activate temperature, to work, then you can still wire it that way...

Currently your relay turns the pad on, warming things up. if you use the normally closed contact instead activating the relay will turn the pad off, cooling things down.

If in fact the system can only be configured to activate cooling then swapping the setpoints over, along with the wiring, should do what you need.

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Alexandra avatar image
Alexandra answered ·

@Next Day Solar

It is very simple logic. In your case has two triggers.

Since the system has not reached the deactivate point it will remain on.

You would need to set the second condition if you want it off under 11°C.

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matt09 avatar image
matt09 answered ·

@Next Day Solar

I'm interested in the carbon heat pads you that you are using. Do you have a link/brand etc? I'm wanting to do something similar with my greenhouse, but have been put off by the potential power drain overnight...

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next-day-solar avatar image next-day-solar commented ·

Hi, I actually used a thermal camera to see how they worked, and turns out they were rather rubbish. I have a new set arriving. If you want to see what I did, I made a short video here : https://youtu.be/DriK95uA3cA

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nickdb avatar image
nickdb answered ·

Personally I would use a Sonoff smart relay (or similar) and have it activated by Node Red on the GX.

Requires some minor integration.

They have 4 port relays, so you can pretty much automate a few things as well as use it's native smart automation - like sunrise/sunset timers etc.

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next-day-solar avatar image
next-day-solar answered ·

Thank you, I know little of 'Node Red' on the GX, how do I go about getting familiar with it ?

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Alexandra avatar image Alexandra ♦ commented ·
There is a series on you tube, just search victron node red.

Then the node red channel has a ton of short tutorials for the beginner.

So pretty easy to get going.


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next-day-solar avatar image
next-day-solar answered ·

After a few weeks of testing, I have finally realised how the system correctly works. Its not overly intuitive in my view, and seems work in the reverse way you'd expect.

For a heating system :

Activation value = when temperature falls below this figure, turn on. I had an activation figure of 4 degrees, so whenever the greenhouse fell below 4 degrees it would activate the heater. When temperature exceeds activation (4 degrees) figure nothing happens, until of course the temperature reaches de-activation value.

Deactivation value = when temperature exceeds this figure, turn off. When temperature falls below this figure nothing happens. So when my greenhouse reached 20 degrees the heater turned off. And remained off until it dropped below the activation value figure and it was re-started.

My summary would be that for a HEATING system, your deactivation value is the temperature you want the heating system to turn off at, and your activation value is the temperature you want the system to try and maintain, so whenever it falls below activation temperature the system activates.

Initially I had it setup incorrectly as my activation temperature was far too low, meaning if the de-activation temperature was reached, the system would stay off until such time as the temperature dropped very low to achieve the activation temperature.

If you want to view the results yourself you can here : https://vrm.victronenergy.com/installation/213577/share/7a0c99c7

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Related Resources

Additional resources still need to be added for this topic

Cerbo GX product page

GX family product range

Cerbo GX & GX Touch datasheet

Cerbo GX Manual

Venus root access document