EVSE disabling when house load high

I’ve just got my hands on an emonEVSE. Very nice kit. Haven’t got an EV yet, but wanted the EVSE so I can get it installed when some building work might be carried out, and at least then it’s ready and waiting. It also gives me something else to play around with until then.

Something I want to ensure, is that the EVSE will automatically go into Disabled mode if the total house current exceeds the service head fuse rating. In my case I have a 100A fuse on my single phase supply. It’s not uncommon though to have a much lower service head fuse in the UK, either 80A or 63A. Whilst the likelyhood of ever exceeding the service head rating are low (diversity and all that), it wouldn’t hurt to minimise the risk even further in software if possible. Last thing I want is to call out the SEB for a blown fuse or overheated service head!

With that in mind, I have set up an MQTT feed of emon/emonpi/power1 and a simple if statement to send the MQTT message “openevse/rapi/in/$FD” to the openEVSE to tell it to shut down if the total household wattage exceeds say 20kW. At least it reduces the chance of taking out a service head fuse! I can be more conservative with the value too if needed.

Wouldn’t be too difficult either to start throttling by changing the pilot setting when certain emon/emonpi/power1 thresholds are met and increasing them again after waiting 5 mins and checking if there is headroom to increase the pilot current again in 1A increments. I’m sure I have read somewhere that many electricity supplies in mainland Europe have a much lower main service head rating and users pay higher standing charges for a bigger incoming supply rating? If that is the case, it could be very useful for those users who have much lower rated supplies and want to maximise charging speed whilst reducing the risk of taking out the main fuse or trip.

Has anyone else played around this this and if so, how far down this rabbit hole did you go? I saw this Max Utility Power Shedding Mode · Issue #133 · OpenEVSE/ESP8266_WiFi_v2.x · GitHub but it hasn’t had much done on it by the looks of it. @glyn.hudson any plans for this in the v3 WiFi version?

Nice work. This is a feature we would like to add. It’s also been discussed here:

It’s also dependent on


To disable the EVSE or put it into a low charge current mode if it looses WiFi / MQTT connection.

A solution in the meantime is to use a Matt:e SP-EVCP-MC unit with over current protection. A Matt-e unit is often needed to provide O-PEN protection if it’s not possible to easily fit an earth rod.

Great to see this is on the roadmap. Totally agree that a loss of MQTT should force the EVSE into 6A or Disabled mode too.

I have also looked at the Matt:e and the Garo O-PEN protection devices, mostly out of technical curiosity. Someone on SpeakEV forum has taken the sticker off their O-PEN protection device and it turns out it’s simple voltage protection relay that shuts off after 4 seconds of exceeding voltage tollerance!

I’m personally not on a PME supply so I don’t need such a widget, but going forward, it would be relatively easy for OEM to supply a version of the emonEVSE with a similar voltage protection relay and a 3 pole contactor to disconnect L, N & E in the event of a loss an open PEN fault so that the product can be sold to the PME market without a 3rd party add-on? I assume this would go hand in hand with adding the RCM14-01 Western Automation DC fault detection coil rather than having to use an external type-B RCD?

Do we know if there are any plans for this adjustment to the EVSE ?

Looking at a new EV charger for Q3/Q4 and having to get an earth rod installed will just be a bit of a mess and extra cost. Really would prefer this open hardware but this is a barrier to entry for me.


I have just pulled request on the git something that should fit those use case.

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