Definition
A single-phase alternating current (AC) induction motor that uses a capacitor wired in series with an auxiliary starting winding to produce the rotating magnetic field needed to start the motor under load. Once the motor reaches roughly 75% of its rated speed, a centrifugal switch disconnects the starting winding and capacitor, and the motor continues running on its main winding alone.
Plain English
An electric motor that uses a small electrical component called a capacitor to give it a strong twist when starting. Once it's spinning fast enough, the capacitor drops out and the motor keeps running normally.
Context Anchor
Seen in aircraft maintenance and electrical-system discussions, especially when describing AC-powered motors used in equipment that must start under load.
Derivation
Capacitor comes from the Latin capacitas, meaning 'capacity to hold' — the component holds an electrical charge. Induction refers to inducing (creating) a current in the rotor through magnetic fields rather than through direct electrical connection.
Why Pilots Care
Pilots and maintenance technicians encounter these motors in aircraft auxiliary systems and ground equipment. Knowing the motor relies on a capacitor and a starting winding helps when troubleshooting a motor that hums but won't spin up — usually a failed capacitor or stuck centrifugal switch.
Analogy
Think of it like push-starting a car. The capacitor and starting winding give the motor an initial shove to get it turning. Once it's rolling at a good speed, that helper drops away and the motor keeps going on its own power.
Grounding Statement
The key idea is that the capacitor helps the motor get moving, but it is usually not meant to stay in the circuit during normal running.
Intuition Check
Do not assume the capacitor powers the motor by itself. It only helps shape the starting current so the motor can develop enough turning force to begin rotating.
Example Sentence 1
The hangar's hydraulic test stand uses a capacitor-start induction motor, which is why it needs a moment to spin up before reaching full pressure.
Example Sentence 2
During preflight, the mechanic confirmed the starting capacitor on the motor was still within tolerance.