Thanks! Hadn’t thought of that, especially since I thought this was more noticable at higher amperages/temperatures/charging speeds.
I’ve only got a single phase 16a at home so I guess it’s something I’m stuck with. I still don’t quite understand how 3 phase charging yields a lower charging loss? 3 times the power = 3 times the loss, no?
Well. It depends. There are two competing charging losses to look at.
First, there is "operating the car". I'm guessing it has two standby modes, "properly off" likely uses some low amount of power, "off but charging" definitely uses more because it has to power more computers, power the high voltage electronics, etc.
You could say the difference between those two modes is your first charging loss, and this increases with the amount of time you spend charging, so it increases with slower charging speed.
Second, there is "actual charging loss", ie the ratio of "energy entering the charging electronics" and "energy actually stored in the battery".
This should be higher with AC compared to DC because the car has to convert it to DC, while the to-DC-conversion in a DC charger likely isn't counted towards your charged amount.
This probably should also be higher with higher charging speeds, but that's just gut feeling. Battery chemistry and charging electronics might each have an optimum charging speed for efficiency that might be somewhere in the middle, or near the bottom, or (less likely) near the top.
Now, which is worse? It depends, I guess.
Very slow charging, ie single phase 3.x kW, is very likely going to be impacted by the "operating the car" issue.
Wether very fast charging introduces other losses that outweigh the saved higher "operating the car" losses, who knows.
One thing you could test to at least partially optimize this: How much power does your car draw if you have it plugged in at home, but it's not charging? e.g. it's set to charge to 80% and has reached 80%, how much is it drawing to maintain that SoC and the electronics around it?
Then compare that to how much % it loses if you keep it unplugged and undriven, assuming you have long enough periods of non-use to get a significant percentage drop that's not just 1% or so because of rounding errors and such.
If the car is dumb about this then "8h with single phase AC" might be more efficient than "8h plugged in with triple phase AC where only 2h are actually charging, but faster, and the other 6h are still operating all the wasteful electronics".
If the car is smart and powers itself way down then triple phase will likely be more efficient.