Three questions come before any wallbox installation: how long does charging take, which cable is laid, and what does the grid operator require? The EV Charger Calculator (Charging Time, Cable, Fusing) answers all three in one pass.
The basic calculation
Charging time = energy to be recharged ÷ charging power – plus charging losses of typically 10%, which occur in the cable, the onboard charger and the battery. The energy to be recharged results from battery capacity × (target SoC − start SoC).
Step by step
- Enter vehicle data: battery capacity in kWh, start and target state of charge in percent
- Select the wallbox: 3.7 / 11 / 22 kW – also note the maximum of the car's onboard charger
- Specify cable length: the calculator sizes the cross-section for a maximum 1% voltage drop
- Read the result: charging time incl. losses, charging current, recommended cross-section and registration duty
Worked example
60 kWh battery from 20 to 80% on an 11 kW wallbox: 36 kWh net, with 10% losses the car draws around 39.6 kWh from the grid – charging time about 3 hours 36 minutes. For a 15 m cable run, 5×2.5 mm² is usually sufficient; from about 25 m, 5×4 mm² becomes necessary.
Don't forget registration
Under the German § 19 NAV: wallboxes up to 12 kVA must be reported to the grid operator; from 12 kVA (practically every 22 kW box) they need his approval before installation. The installation itself belongs in the hands of a registered electrical contractor – who usually also handles the registration.
