Onboard charger
The converter inside a plug-in vehicle that turns AC power into DC for the battery. Its kW rating caps how fast the car can charge from an AC source.
Batteries store direct current, but homes and most public posts supply alternating current. The onboard charger bridges the two: the US Department of Energy describes it as taking the incoming AC from the charge port and converting it to DC for the traction battery. Its kW rating limits how fast the car can charge from any AC source and differs between models, so check the spec sheet.
This explains a common surprise: a high-power wallbox charging a car at a lower rate. The EPA gives the example of a car with a 30-amp charging limit, which gains nothing from a charger that can supply 80 amps. The cable and electrical supply set limits too; the lowest wins.
DC fast charging bypasses the onboard charger, which is why DC power levels can be higher. What you can use depends on your supply. In the EU, the 7.4 to 22 kW band the observatory assigns to medium-speed AC points is three-phase, so a higher rating matters most with three-phase power. In North America, Level 2 runs on 240 V and the circuit's amps set the limit. In Australia, some EVs accept only 11 kW AC.
Differs by market
In North America, Level 2 AC charging on 240 V is limited by the circuit's amps and the car's rating. In the EU, single-phase and three-phase AC points are classed separately. Some Australian EVs accept only 11 kW AC.