Single phase motors Capacitor start/Induction run (CSIR)

Single phase motors - Capacitor start/Induction run (CSIR) -

Also known as CSIR (Capacitor start/Induction run)
motors, this is the largest group of single-phase
motors.

CSIR motors are available in sizes ranging from fractional to 1.1 kW. Capacitor start motors feature a special capacitor in a series with the starting winding.
The capacitor causes a slight delay between the current in the starting winding and main winding. This cause a delay of the magnetisation of the starting winding, which result in a rotating field effective in producing torque. As the motor gains speed and approaches running speed, the starting switch opens. The motor will then run in the normal induction motor mode. The starting switch can be a centrifugal or electronic switch.

CSIR motors have a relatively high starting torque,
between 50 to 250 per cent of the full-load torque.
This makes them a good single-phase motor choice for
loads that are difficult to start, e.g. for conveyors, air
compressors, and refrigeration compressors.



CSIR motor. Schematic diagram and torque/speed curve