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Looking for nice way to stop charging

We’re going off grid and I’m looking for a way to signal to one of three hpwc gen2’s (master) to signal the cars to stop charging. Brute force would be to use a contactor to kill 240v. We have 12kw of inverters and I need the cars to stop charging if the hvac compressor needs to start and/or I f the house battery is low. The compressor is easy .... I just put a time delay on the compressor start of say 30 seconds and immediately signal for hpwc to stop. I’d hope the cars stop in 29 seconds. Low home battery can be signaled by a small relay inside the inverter.

ireally hate the idea of dropping a contactor on a 40 amp load. What about interrupting the ground to make hpwc fault? Or I could interrupt the pilot wire in the charge cable but I’d have to do that on all three hpwc.

anyone got any other ideas? I’m trying to keep this really simple. At one time I thought of running a raspi pi and Mqtt but that’s a lot of “moving parts”.
There is a project (maybe several cloned projects really) for the Raspberry Pi that lets you control the power on the Gen 2 HPWC. One of those is at dracoventions/TWCManager. This project is discussed here at New Wall Connector load sharing protocol. If your coding skills are good, you could update that to do the tasks you want to do.

In addition, there are various Raspberry Pi projects that use the Tesla API to communicate with the vehicle. You could script calling that to send start/stop charging signals to your Tesla.

Either of these methods should be easier to deal with than putting a big contactor on your HPWC and interrupting that 40 amp load or hacking a relay onto the pilot line in your HPWC.
If the above doesn't pan out, another (perhaps more complicated) option would be to tell the cars to stop charging via the Tesla API. You'd have to check their location to only do it if they seem to be charging at home I guess.
Normally, if it were a standard J1772 EVSE, I'd suggest setting the proximity be the not connected state (Basics of SAE J1772).

I can't speak to the WCs since the handle isn't J1772 and doesn't have the button that moves a latch and pushes on its switch. Not sure if pushing on a WC's handle's button achieves the same thing with respect to proximity signal.

I like OpenEVSE for this instead of Tesla unit. It is designed to dynamically change charge rate more easily than the Tesla units. Attached is a long running thread on the same topic but adjusting amps instead of just turning them off completely.