Enter the horsepower, load (output power), and input power into the calculator to determine the motor efficiency of an electric motor.
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Motor Efficiency Formula
The following formula is used to calculate the efficiency of an electric motor.
n = .7457 * HP * L / iP *100
- Where n is the efficiency (%)
- HP is the motor horsepower (hp
- L is the load (percentage of rated power i.e .50 for 50%)
- iP is the input power (kW)
Motor Efficiency Definition
What is motor efficiency? Motor efficiency is the ratio or percentage of input power that a motor, typically an electric one, can convert into useful output work or power.
How to calculate motor efficiency?
- First, determine the input power.
For this example, we are analyzing an electric motor in a car that receives its power from a battery back. The input power is 85 kW.
- Next, determine the maximum horsepower.
The maximum rated horsepower of the engine/motor is 150 hp.
- Next, determine the load.
The percentage of the max horsepower that the engine is running at is .65 or 65%.
- Finally, calculate the motor efficiency.
Using the formula above, the motor efficiency is found to be .7457 * 150 *.65 / 85 *100 = 85.53 %.
About Motor Efficiency
How efficient are electric motors? Electric motors typically run at 90% or more efficiency. These efficiencies are usually achieved at loads of around 75% load.
Why does motor efficiency increase with load? As the load increases the relative motion between the rotor and the stator magnetic fields increases, which leads to more efficient operating conditions.