Copper, Iron, Eddy-Current, and Mechanical Motor Losses
Electric motors convert most input energy into motion, but several loss mechanisms turn part of it into heat. Their proportions change across the speed–torque map.
Copper losses
Current flowing through windings creates resistive, or copper, loss. It rises strongly with current and therefore becomes especially important at high torque. Winding temperature also changes resistance.
Iron and eddy-current losses
Alternating magnetic fields create hysteresis loss in electrical steel. They also induce circulating eddy currents in laminations, magnets, conductors, and other conductive parts. Thin insulated laminations, material selection, and electromagnetic design reduce these effects, but they do not remove them.
Mechanical losses
Bearings, seals, windage, lubricant churning, and attached pumps consume mechanical power. These losses often grow with rotational speed. Gear and differential losses belong to a drive-unit boundary rather than a motor-only boundary.
Why the mix matters
High-current operation can be dominated by copper loss, while high-speed light-load operation may expose magnetic and mechanical losses. Cooling determines how long the resulting heat can be tolerated, and control software chooses operating points that balance torque, voltage, and efficiency. EV motor construction and windings motor efficiency