Efficiency Measurement Boundaries
Last modified: Aug 02, 2026
An efficiency measurement boundary identifies exactly where input and output power are measured. Changing the boundary changes the result even when the hardware is unchanged.
Common boundaries
- Motor efficiency compares electrical power at the motor terminals with mechanical power at the shaft.
- Motor-and-inverter efficiency begins at the inverter's DC input and includes semiconductor and control losses.
- Drive-unit efficiency can also include gears, differential, bearings, seals, lubrication, and pumps.
- Battery-to-wheel efficiency adds battery, cables, contactors, auxiliaries, and the remaining driveline.
Why it matters
A high motor efficiency figure cannot be compared directly with drivetrain efficiency or battery-to-wheel efficiency. The test must also state direction, because motoring and regeneration reverse the energy flow and may use different operating limits.
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