And well... if your car still is too cold after electrical heating you can use old way. Make bonfire wait for the fire to go out so you get the hot red coal and put that under the engine with a shovel.
With the one output, you can control one of those big industrial contactors that can handle up to 250kW of power to preheat row of cars at the same time. So when the drivers come, they have warm car/truck to drive with.
For couple of days now, since completion the first working unit. I have been thinking about how to improve it. Schedule and Oled were there already, but what more. Current sensor to detect that there is something taking the power. Used power shown on screen? Also kind of "Stay warm" sollution that if car is still connected after 2 hours of heating it would go cycles 15min on, 15min till the lead is disconnected from car keeping it somewhat warm.
Also neater GUI using .html file and javascript is in planning.
Funny thing that the thing from viewtopic.php?f=45&t=7767 kinda makes making own pcb and populating it kinda useless (even tho it's more fun). With that you just need to connect couple mains cables and you are done.
http://jokenkosto.blogspot.com/