Short story is (see long reasoning below) that I am wondering if it is possible to use Shelly 3EM to output analog/PWM signal that represents total measured current at that moment. The signal would then be used by a "Smart EVSE" controller to pass on to the car. The goal would be to lower charging rate to avoid overpowering my main circuit breaker if other load is switched on suddenly, like an oven in the kitchen. Some call this "load balancing".
One of affordable DIY options to charge the car at home is this controller: https://ecoharmony.co.uk/collections/ev…=31930578042958
It's pretty simple actually, initially it does a handshake with the car, then enables contactor to provide the car with AC power, and then sends a PWM signal so the car switches on the onboard charger and knows what rate to charge at. Charging rate is proportional to the PWM, however this sends a static PWM to limit the power at certain level, unless you add several extra components to measure the current. Which adds up to the cost and complexity, and is a hassle to integrate.
Anyone see any possibilities how this could be done?
Alternatively, are there any other projects out there, maybe using different EVSE controller?
Long version:
There are two types of household EV "Wall boxes": smart ones, and the dumb. EV stands for electric vehicle.
Essentially it's just a 3-phase AC socket with contactor and some random other things, like energy metering, safety features, even wifi for some reason.
Among power terminals (three phases, neutral and ground) of the socket, there's two more signals - one being just a "fully inserted" detection pin, and one is PWM'ed to tell the car what's the maximum power of the box/source, so the car would limit charging power to not overpower your circuit breaker. To be clear, the car has an onboard AC->DC charger onboard, these may be from 3kW to 22kW. DC charging is different thing and not discussed here.
A dumb, or "standard" wall box is statically configured for specific power level, so it provides the same exact PWM to the car at all times. And it's your problem if there is another power consumer and available power is fluctuating.
Me, for example. I have a 14kW 3-phase grid connection to my house, and I want to charge an EV, that is capable of up to 22kW. On top of that I also have a solar generator up to 11kW (in parallel to house). So in my case, available power is fluctuating anywhere from 2kW to 24kW, depending on weather and what we are doing in the kitchen. If I connected my car at 22kW, or even 11kW, my connection could be overpowered easily in some cases.
So there comes a "smart" wall box. What it does is it measures the power at main connection to grid and adjusts the PWM sent to the car so it would lower it's power to a level where total power consumption of the car+house is below max capability of the connection.
This kind of functionality is still "new" in residential settings for some reason. There are several off the shelf products, however they run for 1000-2000 EUR. Which is far from adequate for a socket, basically. For example: https://myenergi.com/product/zappi/