Technical Support

I have recently acquired an EV and initially changed to an electricity tariff which gives cheaper rates overnight. My inverter had 5 of the timers set to grid charge during this time. One timer covering peak rate was set to discharge batteries to 20%. This worked ok.

I then changed to a “smart tarrif” where in exchange for an even cheaper rate the supplier dynamically charges the car which can include additional periods outside of the normal cheap rate. The obvious problem is that I don’t want the inverter to supply the EV load and drain the batteries.

I thought I had a solution using Home assistant. I used the electricity companies HA integration to identify the additional cheap periods and created a HA automation to switch the inverter into grid charge mode.

This does work but occasionally there are MQTT errors where the inverter does not respond to the request, typically one time in 20 and this results in the batteries being heavily discharged. There may be a way to trigger a retry in the event of a failure but I’ve not found a way to do this.

The ideal solution would be to feed power to the EV charger upstream of the incoming CT but as my consumer unit is in the centre of the house and the charger is remote in a garage this is not practical.

I do however have cat6 cables which would allow using 2 identical CT clamps (same turn ratio) one on the incoming feed and one on the EV supply. If the outputs are connected in parallel and antiphase the output across the internal inverter resistor should give the difference, effectively reading the house load – EV load.

I haven’t tried this yet and suspect there may be inaccuracies introduced but I can live with that as long as there is a net zero current to the grid when the inverter is discharging.

Is there anyone out there who has tried something similar or maybe knows of a flaw to this idea?