Investigating EV Charger De-rating

I ran into an interesting issue with my Easee One EV charger recently. A couple of daytime charging sessions were slower than usual, and it turned out the app knew why.

Heat protection seemingly kicks in when the charger detects itself getting too hot. Nice safety feature, but I was concerned I’d not seen this before after 18 months of use. Annoyingly the Easee app doesn’t show a power log beyond the most recent charging sessions, but I could see the last two sessions had seen this occur.

My charger sits facing the sun so I did wonder if daytime charging in the sunshine was the problem. I contacted Easee support to discuss and it was a semi-frustrating experience. They acknowledged the issue and just wanted to send me a new charger under warranty, but I’d be paying for the electrician to replace it.

I wasn’t satisfied with this as numerous internal pictures didn’t show any actual problems, and their answers were vague and boilerplate to the point I wasn’t sure they actually understood what I was saying. I was curious whether I could get access to the temperature values myself and as it turns out, I can! Easee offer a very nice API which let me auth with my regular app credentials and immediately start hitting endpoints.

Sadly historical temperatures are not available, but they do offer an observations endpoint which gives you the last readings for a wide variety of sensors in the charger. I was quickly able to spin up a script that polls the endpoint every 5 minutes and pulls out the max temperature value as well as weather measurements from Open Meteo.

A few days of monitoring produces this:

The cloud cover is obviously approximate, as the measurement is not taken from my house, but the results are stark. We can see ambient temperatures are comfortable but the sun being out pushes charger temperatures to 40+ degrees internally. It’s not hard to see how charging on top of that might trigger some sort of de-rating.

Annoyingly after I did all this I found this page which pretty much nails the issue I’m seeing, so I guess it’s just to be expected.

I’m still waiting to hear back from Easee support, hopefully they’ll tell me what temperatures trigger de-rating, just to satisfy my curiosity.