Charging (In)Efficiency

The power supplied by the 120v charger is so low it doesn’t need to slow down more when it gets over >80%. When I charge mine at the full rate, 7.5KW, it drops down from the full ~32Amps toward the end but I don’t remember what it was. The best charging efficiency I’ve gotten, ~88%, was achieved by charging as soon as I got home from 25% to 100% at the “reduced” rate (16Amps).

 

I didn't know the voltage wasn't constant throughout the charging process. Perhaps at 10A, you're charging with the same meager wattage the SE allows from more powerful EVSEs for the final 10% when topping up the battery.

 

Charging batteries in general has two phases. First is the constant current phase. In this phase, the voltage rises over time to keep the current the same. This is because the battery voltage rises and current is proportional to the voltage difference.

The second stage is the constant voltage stage. In this phase, current tapers off as the voltage differential tails off over time.

As mentioned by others, it is rarely noticeable on slower chargers, even L2, since the charge cable is the limiting factor. It is most noticeable on high speed DC chargers that can supply more power than the car can accept.


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