Features → One cable, two cars

One charger, two cars, one cable

Plenty of two-car households have one wallbox and move the lead by hand. The wallbox has no idea which car it is attached to — it sees a car, not your car — and getting that wrong means commanding the wrong vehicle.

Why this is a real problem

If Sunplug believes car A is on the cable when car B actually is, everything downstream is wrong in a way that looks right. It reads A's state of charge to decide how urgent the charge is, credits A with the solar that went into B, and applies A's overnight floor to a car that does not have it. Nothing errors; the numbers are simply about the wrong car.

The cars already know

The saving grace is that each car reports, through its own connection, whether it is plugged in. That is usually enough to work out the answer without asking you anything.

If one car says it is plugged in and the other says it is not, there is nothing to decide. If both say they are unplugged and the wallbox says a car is drawing current, something is wrong with what a car is reporting rather than with the cable. The interesting cases are the ambiguous ones — and the useful thing about laying the problem out as a table of possibilities is that it makes clear which combinations are not an answer.

When it cannot tell

Two cars both reporting plugged in, on a household with one cable, is not a state the world can actually be in — so one of them is stale or wrong, and Sunplug will not guess between them. That is when it asks: you tap the car that is really on the lead, and it proceeds.

Asking is the right behaviour rather than a failure. Guessing wrong here is invisible for hours and corrupts a day of accounting; asking costs one tap.

If you have two wallboxes

None of this applies. Each charger is associated with its car and stays that way, which is the simpler arrangement and worth the money if you are choosing. The trade-off is covered in how fast a charger you actually need — two slower chargers frequently beat one fast one on a solar roof.

Stuck? Email me.