I heard something today that makes me very skeptical. A dealership claimed that charging an EV with 11 kW has higher energy efficiency than charging with 6 kW. (And they didn’t mean 3-phase vs. 1-phase!)
Even if it is somehow related to battery temperature and receptiveness, that would still be heat loss. With higher currents, resistance increases, too, no? Or is it proportional and always the same percentage?
In any case, I find it foolish to follow such advice because there are other factors involved, mainly a battery suffering more regarding longevity if charged faster, and that is a lot more expensive of a loss, eventually, also because an older battery is generally less efficient in several ways. (internal resistance, self-discharge)
Plus more load spike on the grid, external and house. But I don’t want to rant too much about the lack of reason in the world that seems to be a self-amplifying spiral of doom. Apparently house charger impatience is a thing. Three hours of charging twice a month - absolutely intolerable to some.
It’s a very small difference. An EV might have 200 watts of “overhead” needed simply for battery thermal management and the standby load of the onboard charge unit. So yeah, it’ll be maybe 1.5% more efficient at 11.5 kW vs 5.7 kW.
But on the other hand when you double your speed, your circuit wires, socket, EV charge cable etc. are losing 4 times as much power to voltage drop. If all that adds to 1.5%, that wipes out that efficiency gain. Nevermind the fact that all those things running 4 times warmer increases the chance of equipment meltdown.
And tell me again what you are trying to save? Pennies on electricity? Well, destroying a $400 EVSE or $800 charge port really wipes out all those pennies.