MOSFET

Metal-Oxide-Semiconductor Field-Effect Transistor. The power switches on your wheel’s control board that regulate current to the motor. They’re either on or off, switching thousands of times per second (that’s the PWM). When they fail, the motor loses power instantly.

Why they burn

Excessive current draw. Sustained high load (steep hills at speed, heavy rider, hot day). Manufacturing defects. Insufficient cooling. When a MOSFET burns, it often takes neighboring components with it - this is the “magic smoke” riders joke about.

What it means for you

A MOSFET failure is a true cutout - sudden, complete loss of motor power. No warning. No tiltback. The board dies and you’re on a very expensive paperweight rolling at whatever speed you were doing.

555 take

You can’t prevent MOSFET failure through riding technique alone, but you can reduce the risk. Don’t sustain max load for extended periods. Give the wheel rest on long climbs. And understand that this is why conservative firmware limits exist - the manufacturer is protecting these components, sometimes at the cost of your convenience. The MOSFETs, controllers, and cutouts article explains how the power stage fails and why language matters after an incident.