AC charging uses the vehicle’s onboard charger to convert the supply to DC. DC charging bypasses the onboard charger and supplies DC directly to the battery, which is why it can deliver much higher power. In both cases the battery, the charger and the thermal system limit the power that can be accepted at any moment.
Charging time estimate
Problem. A 60 kWh battery is charged from 0% to 100% with an 11 kW charger at an overall efficiency of 0.90. Estimate the time.
Solution. Ideal time = 60 ÷ 11 = 5.45 h. Corrected for efficiency: 5.45 ÷ 0.90 = 6.06 h, approximately 6.1 h.
Why the real curve tapers
A battery does not accept full power across the whole state-of-charge range. Charging power typically tapers as the battery fills and as temperature limits are reached. The straight-line estimate is therefore a lower bound on time for a full charge, not a prediction of the exact curve.
- AC charging uses the onboard charger.
- DC charging supplies DC directly to the battery.
- Efficiency losses mean more energy is drawn than is stored.
- Charging power tapers with state of charge and temperature.
- Cable, connector and supply limits also cap the power.
- AC charging goes through the onboard charger.
- DC charging feeds the battery directly.
- t = E/(P × η) estimates charging time.
- Real charging tapers, so the estimate is approximate.
Worked example
Adding 30 kWh with a 7 kW charger at 0.90 efficiency takes 30 ÷ (7 × 0.90) = 4.76 h, approximately 4.8 h.