TexasEV
Well-Known Member
Well, you’re partially right, but are still confusing things. You are correct that it’s not about the voltage exactly, but when people refer to those, they are comparing a NEMA 5-15 outlet, which is providing 1.4 kW to the car, versus something like a NEMA 14-50, which is providing about 9.6 kW. The power level definitely does contribute to an efficiency difference, because there is a decent level of overhead power being consumed by running the charging system. I think it’s around 400 W or so, so it’s about 1/3 of the power of the 120V wall outlet is being lost just going to running the charging circuit. That is why going to a 5-20 adapter makes such a difference if you have to use a wall outlet. It’s increasing the current from 12A to 16A, so a 33% increase in power, but the amount of energy getting into the car’s battery is a lot faster than 33% increase, because the overhead is already covered, so all the extra is going into the battery, rather than being partially lost.
So what you are referring to is at the high power levels, where loss from resistance in the wiring is the main thing that could be hurting efficiency, but it seems you were not considering about at really low power levels, where resistive losses are negligible, but the dominant factor is wasting a lot of energy from keeping the charging circuit running much longer than it needs to.
Yes-- this is what I was referring to when I posted above that charging at low amperage is less efficient.
