EV charging time and site power calculator
Two quick estimates for planning: how long a charge takes, and how many chargers your supply can run at once.
Charging time
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Estimate at 90% charging efficiency, at the lower of charger and vehicle power. Real DC charging slows down above about 80% state of charge.
Chargers per supply
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Simplified estimate (power factor 1, no other loads). With load management, more chargers can share the same supply at reduced power. Your electrician must size the installation.
Worked examples
Same 45 kWh charge at different power levels (90% efficiency).
| Charge | Charger | Estimated time |
|---|---|---|
| 75 kWh battery, 20 → 80% (45 kWh) | 7.4 kW AC | ≈ 6 h 45 min |
| 75 kWh battery, 20 → 80% (45 kWh) | 22 kW AC (car accepts 11 kW) | ≈ 4 h 33 min |
| 75 kWh battery, 20 → 80% (45 kWh) | 60 kW DC | ≈ 50 min |
| 75 kWh battery, 20 → 80% (45 kWh) | 180 kW DC (car accepts 150 kW) | ≈ 20 min |
How the calculator works
How is charging time calculated?
Energy needed (battery capacity × the percentage you add) divided by the charging power, allowing about 10% for losses. Charging power is the lower of the charger’s output and the vehicle’s maximum.
Why does DC charging slow down near full?
Vehicles reduce charging power as the battery fills, usually above about 80%, to protect the battery. That is why fast-charging times are quoted from 10–20% to 80%.
How many chargers can a supply run?
Divide the supply’s capacity (√3 × voltage × current per phase for three-phase) by each charger’s power. With load management, more chargers can share the same supply at reduced power.
Want us to size your site?
Send the number of vehicles, their battery sizes, dwell times and your supply — our engineers suggest a charger mix.