Why does condenser used in ceiling fan?

Answer 1

In a ceiling fan there is an single phase induction motor.

Single phase stator produces a non rotating, pulsating magnetic field.The single coil excited by a single phase current produces two counter rotating magnetic field phases, coinciding twice per revolution at 0 degrees and 180 degrees. When the phases rotate to 90 degree and -90 degree they cancel. At 45 deg and -45 deg they are partially additive along the +x axis and cancel along the y axis. The sum of these two phases is a phasor stationary in space, but alternating polarity in time. Thus, no starting torque is developed.

So, in order to generate the starting torque we have to split the phase in two. This configuration comprises two windings main winding W1 and auxiliary winding W2, a centrifugal switch SW1 and a capacitor.

The two windings are wound with a geometric offset, effectively making a second set of poles phase shifted within the stator. The capacitor provides a phase shift to the current flowing in W1 and we therefore have a "two phase" motor while the switch is closed. When the motor is almost up to speed, the switch opens disconnecting W1 and the capacitor. The motor can be reversed by reversing the connections of either W1 or W2 (but not both)

The start winding (W1) and the start capacitor provide for a rotating magnetic field in one direction enabling the motor to start.