Electric Cars
Slow Home Charging: Why Isn't My Wallbox Fast?
The wallbox only charges at a fraction of its rated speed, or slower than expected.
What causes it
The car's onboard charger limit, single-phase vs three-phase wiring, a reduced amp setting, or a derating wallbox in hot weather.
What to do
- Know your car's AC limit - if the onboard charger is 11 kW but the wallbox is 22 kW, you still get 11 kW.
- Check the amp setting in the wallbox - most default to 16A (≈3.7 kW on single phase); raise to 32A if wiring allows.
- Verify single vs three phase - three-phase wiring is required for 11+ kW.
- Feel for heat - a hot cable or wallbox derates itself to stay safe.
- Test with another EV or cable to isolate the cause.
Realistic speeds
- 2.3 kW (household socket) ≈ 12-15 km/h.
- 7.4 kW (32A single phase) ≈ 40-50 km/h.
- 11 kW (16A three phase) ≈ 65-75 km/h.