Electric Vehicle Charging Time Calculator

How is charging time calculated?

Charging time is the energy to be added to the battery divided by the power that reaches it:

time = capacity × (target charge − starting charge) / (charging power × efficiency)

With capacity in kWh and power in kW the time is in hours.

Charging power

For AC charging the power follows from the current the charge point supplies. Single phase gives P = V × I and three phase gives P = 3 × V × I, where V is the line to neutral voltage. At 230 V the common figures are:

• 10 A single phase: 2.3 kW (household socket)
• 16 A single phase: 3.7 kW
• 32 A single phase: 7.4 kW
• 16 A three phase: 11 kW
• 32 A three phase: 22 kW

However strong the charge point, AC charging cannot exceed the rating of the on board charger. A car with an 11 kW charger on a 22 kW point charges at 11 kW. Enter that limit and the tool uses the lower value.

Example

Taking a 60 kWh battery from 20 to 80 percent needs 60 × 0.6 = 36 kWh. On an 11 kW three phase point (3 × 230 × 16 = 11.04 kW) at 90 percent efficiency, 9.94 kW reaches the battery. The time is 36 / 9.94 = 3.62 hours, or 3 hours 37 minutes. The energy drawn from the grid is 36 / 0.9 = 40 kWh.

Why efficiency matters

Not all the energy drawn from the grid ends up in the battery. The on board charger, the cables, the battery and thermal management turn part of it into heat. The energy you pay for is more than the energy stored. At low power the fixed overheads weigh more, so the loss percentage is higher.

Limits

The calculation assumes constant power. On DC fast chargers power tapers as the battery fills, so enter the average power and treat results above 80 percent as a lower bound. Battery heating in cold weather and the consumption of the car itself while charging are not included. The result is an estimate.