[amluto]

It’s a safety system, a billing system, and possibly a coordination system to avoid overloading an upstream circuit. Also it’s a special fancy outlet that tells the load how much current it may use.

There’s a nice open source implementation called OpenEVSE.

[rlkf]

Not only can you coordinate several chargers (if you are in a shared garage), but you could also coordinate usage across other devices connected to the same residential fuse box (all such in Norway has a HAN interface); for instance you could restrict the charge to the car when the dishwasher is running. (Sadly, the IEC 62196 control pilot pin seems to be a very primitive system).

[thfuran]

>Also it’s a special fancy outlet that tells the load how much current it may use.

Isn't that the sort of thing that can typically be accomplished with nothing more than a resistor or two?

[sokoloff]

Simple resistor signaling wouldn’t work for current sharing; two EVSEs with a single 40A supply [32A continuous] can advertise 32A if only one is in use and switch to 16A if both are in use. (Same concept extends to a larger pool of EVSEs which can limit to a max total current across the pool.)

[thfuran]

Ah, okay, that is fancier than just advertising a fixed max current.

[_ea1k]

Tesla's Mobile connector supports different pigtails for the input circuit. That way it can support anything from a regular outlet (NEMA 5-15) up to something more common for an electric range (14-50).

The mobile connector detects which one based upon resistance.

As others have mentioned, this is often too simple for EVSE to Vehicle connections, as that might require the power level to be dynamic. Load sharing, limitations in supply capacity, or heat may all be potential reasons to limit available power.

[jeffbee]

It's based on a square wave duty cycle, so you'd need something more like a '555. But yes, J1772 is designed to be dead simple and cheap to implement.

[amluto]

By the time you implement the rest of the protocol, you might as well have an actual microcontroller, at which point you don’t need the 555.

(Please don’t build an EVSE without the big relay and its associated safety controls. No one needs an outdoor cable supplying ~240V pin-to-pin that’s live while you hold it on a rainy day.)