Why fan rotate in one direction only, as it works on AC ? & What is the role of capacitor in fan ?

Asked by DEEPAK KOTHARI | 19th Oct, 2010, 12:00: PM

Expert Answer:

Dear student
Fan works on the principle of electromagnetic induction. AC is passed through an electromagnet, which creates a fluctutating magnetic field. This varying magnetic field, or field with continuosly changing direction, sets a rotor into motion as it exerts magnetic lorentz force on metallic rotor.
Following is the detailed account of 'How a fan rotates' :
A fan motor is an induction motor, with an aluminum rotor that spins inside a framework of stationary electromagnets. Aluminum is not a magnetic metal and it only becomes magnetic when an electric current flows through it. In the fan, currents are induced in the aluminum rotor by the action of the electromagnets.
Each of these electromagnets carries an alternating current that it receives from the power line and its magnetic poles fluctuate back and forth as the direction of current through it fluctuates back and forth.
These electromagnets are arranged and operated so that their magnetic poles seem to rotate around the aluminum rotor. These moving/changing magnetic poles induce currents in the aluminum rotor, making that rotor magnetic, and the rotor is dragged along with the rotating magnetic poles around it.
After a few moments of starting, the spinning rotor almost keeps up with the rotating magnetic poles.
Role of capacitor in the fan:
The ceiling fan motor consists of a starting and running winding. The capacitor is usually connected in series with the starting winding to give the unit enough starting torque. If the capacitor gets busted, the fan will not rotate.
The capacitor is used in an inductor-capacitor circuit to shift the phase on the single phase power going into the AC motor, causing high torque used for starting. Once it is up to speed, it switches off this circuit and runs on the low power low torque running windings of the motor.
We hope that your query is resolved.

Answered by  | 20th Oct, 2010, 09:27: AM

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