If you open and look at the ceiling fan, you will notice a black box inside the switch housing. That is nothing but a capacitor. This is an important part of the fan that makes it work properly. The capacitor is used not only to start the fan but also to make it spin. In simple words, the capacitor creates a magnetic flux (torque) which makes the fan rotate.
Generally, two capacitors in parallel series are used in the ceiling fan. The motor is known as “two value capacitor run motor” or “permanent split capacitor motor”. Here, one capacitor with high capacitance will be connected in the starting winding of the split-phase induction motor. Another one with low capacitance is used in the running winding.
If we were to ask, what is the purpose of a capacitor on a motor? Well, a motor with either a start or run capacitor becomes an electrical capacitor that changes the current to multiple windings of a single-phase AC induction motor. This creates a magnetic torque.
Also Read: Capacitors in Series
In other words, a fan will have a single-phase induction motor in it. The problem here is that this motor does not start by itself. It requires an external force to run it at the time of starting.
To overcome this shortcoming, a capacitor is used. It is connected across a part of the winding in the fan motor. The capacitor splits the current into different phases or it creates a phase difference between the windings. A magnetic field (torque) is produced which makes the rotor rotate in the direction of the generated magnetic field. The capacitor is usually connected via a centrifugal switch which increases the efficiency of the fan.
If a capacitor is absent then the magnetic flux shifts completely for each current cycle. This leads to no magnetic fields being generated. On the contrary, capacitors are not used in exhaust fans because they are usually small and balanced. Some table fans also come with a capacitor wherein the capacitor as stated above helps to create magnetic flux which makes the fan rotate.
Check Out: JEE Main Capacitor Previous Year Questions with Solutions