[outworlder]

I think they have to be somewhat not dumb and communicate with the car before it will close the traction battery contactors?

[zrail]

A little bit but not much. They're a contactor, a GFCI, some current sensors and limiters, a small section to determine if the EVSE is operating at L1 or L2, and a small microcontroller to control it all. They're very simple devices.

Edit: info from here: https://www.barbouri.com/2017/03/10/diy-open-evse-v4-23/

[thescriptkiddie]

The signaling is surprisingly simple. There is no active negotiation, the EVSE just outputs a PWM signal to specify how much current the car is allowed to draw, and the car uses a variable resistor to request the power be turned on or off.

https://en.wikipedia.org/wiki/SAE_J1772#Signaling