Why capacitor is needed in single phase ac motor?
if you do not use the capacitor in single phase ac motor then it will not run at all.because one winding can not create rotation in any means
Single phase motors specially split phase motors needs capacitors for high starting torque.
The capacitor in series with the starting winding on a cap-start induction motor is there to create a lag in the current through this winding relative to the run winding. The two coils fields are thus a little bit out of phase with each other, which imparts a little bit of direction to the overall magnetic field. Essentially, it creates a second phase. This is required, since with only one coil (one phase) all attraction and repulsion between the coil and the induced field in the rotor would be exactly perpendicular to the motor shaft. The field has to be have some component tangential to the shaft to start things rotating.
Single phase motors (some of them) require a capacitor to create turning torque for the armature. Once started, these capacitors are disconnected from the circuit by centrifugal switches. Some small motors use a shaded pole to apply the torque to start the motors. A capacitor connected in the circuit creates an essential magnetic force which imparts a torque to the motor similar to the action of bringing similar poles of two magnets together. Like pole repel.
