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Electric Bus Charging Time Estimator

This estimator calculates the time required to add a selected amount of energy to an electric bus battery. It accounts for starting and target state of charge, usable battery capacity, charger power, charging efficiency, and an optional taper factor that represents slower charging near a high state of charge.

The result helps transit schedulers and infrastructure planners test whether a charging window fits a route schedule. Because real charging curves vary by bus, charger, battery temperature, and software limits, the estimate is most useful for comparing scenarios rather than predicting an exact unplug time.

Calculator inputs

kWh
%
%
kW
%
%
Result
—
Estimated charging time
Energy added—
Energy from grid—
Effective average power—
Minutes required—

1. Enter usable battery capacity
Use the energy capacity available for driving.

2. Set the charge window
Enter the starting and target state of charge as percentages.

3. Enter charger power
Use the lower of the charger rating and the bus’s accepted charging power.

4. Account for losses
Set an efficiency value that covers conversion and battery charging losses.

5. Allow for taper
Increase the taper adjustment when charging into a high state-of-charge range.

6. Check schedule fit
Review hours, minutes, battery energy, and grid energy required.

Battery energy added = Usable capacity × (Target SOC − Starting SOC)

Grid energy = Battery energy added ÷ Charging efficiency

Charging time = Grid energy ÷ [Charger power ÷ (1 + Taper adjustment)]

What the result means

The result estimates the elapsed time needed to move from the starting to target state of charge.

The taper adjustment converts rated charger power into a lower average power. It does not reproduce a vehicle-specific charging curve.

Given: 420 kWh usable battery, 25% starting SOC, 85% target SOC, 150 kW charger, 92% efficiency, and 10% taper adjustment.

Calculation: Battery energy = 420 × (0.85 − 0.25) = 252 kWh. Grid energy = 252 ÷ 0.92 = 273.91 kWh. Effective power = 150 ÷ 1.10 = 136.36 kW. Time = 273.91 ÷ 136.36 = 2.01 hours.

Result: The charging session is estimated at about 121 minutes.

Why is charging time not simply energy divided by charger power?

Charging losses and power taper reduce the average power delivered to the battery. The calculator includes both effects.

What power should I enter if the charger is rated higher than the bus?

Use the bus’s maximum accepted power if it is lower than the charger rating. The slower limit controls the session.

Does charging above 80% take longer?

It often does because many battery systems reduce power at higher states of charge. Use a larger taper adjustment when the target enters that region.

Can this estimate include queue or connection time?

No. It covers energy transfer only, so add time for parking, connection, authentication, queuing, and departure checks separately.

How should cold weather be handled?

Cold batteries may accept less power and consume energy for conditioning. Use a higher taper adjustment or a lower effective charger power for conservative winter planning.