Would it be possible to control the power to Open EVSE with a simple relay

I Would like to control the mains supply to the charge point with a relay switched from a program (I have not written yet)
Is That possible or would it cause damage to the charge point?

I have a program I wrote that monitors my Solar Panel export, how much is being diverted to a Hot water Tank and how much is being exported to the grid.
I was Thinking I might be able to write code that would just use a simple relay to switch to charging the EV whenever there was any substantial export.

It seems a very simple way to control the Open EVSE and I’m hoping that it might work…

I have a mk2Router as well but am thinking that I wouldn’t be able to switch the output from that from the hot water tank to the Car because of the output from the Mk2 being more ‘Pulsed’ IFYSWIM

Thanks for any advice



This would not be a good way to do it and would need a relay that could handle 40A sustained for safety.
As answered in your other thread the best way would be by MQTT, if your program could output this.


I looked at the cct diagram on the wiki about multiple outputs and there are two contactors/relay switches in that. isn’t that the same.
Sorry for my ignorance!


I don’t see why one could not do this as long as the contactor was beefy enough.

But one thing you might come a cropper on is the Wi-Fi, assuming you are using a Wi-Fi connection. When the mains to the Wi-Fi PCB is turned off I don’t think it’s totally guaranteed it will reconnect again seamlessly. I have had mine on and off quite a bit whilst installing it and found it sometimes needed a fresh install rather than just picking up the old IP address etc. But fixing the IP address in your router may solve this.

Added a permanent mains connection to the PCBs is another solution.

This use case is supported natively via the WiFi and/or you can enable/disable the charging (and the rate) via the HTTP API.

1 Like

Before the EVSE opens its contactor, it signals to the EV to stop drawing current so the contactor is never opened under load. It’s not recommended to break a 32A circuit on full power, this will cause a significant arc which will mean a short lifespan for any contactor, this would also cause some EVs to throw a warning error if the power is cut unexpectedly.

A far better solution is to use the OpenEVSE push button, web interface, HTTP API or MQTT API to stop a charging session correctly.

1 Like

Thanks Glynn. Could you point me to a good overview of That interface please.
I had a google but Not found anything describing it as a whole.
I am thinking of getting a zappi v2 and have looked in the wiki under multiple outputs where there is an interesting diagram, do you know anyone who has used this? it would be great to talk to someone who has tried this approach.

Take a look at my Node-Red / MQTT code at https://github.com/thepaulcooper/victron-openEVSE

It is for a Victron solar system but the openEVSE controlling aspects and the dashboard should give you some ideas for your setup.