Why a fan needs capacitor?

You must have seen an electrician changing a cylindrical part in a fan ! You guessed it right…It’s a capacitor!

But have you ever wondered why you need a capacitor in a fan? Have you ever wondered why modern fans doesn’t have a capacitor! Well you will get all the answers here! So keep reading till end and do follow and leave a comment in case you find it helpful.Your support is valuable to us!

Here is how a capacitor looks like (Ignore the dust ;{) )

Capacitor in a fan

As it is clear to you how a capacitor looks like and where it is located we can move forward to learn why we need a capacitor.

The motor that we use in a fan is a single phase induction motor.

Broadly motors can be classified as:

A.C motors

  • Induction motor (3phase,Single phase)
  • Synchronous motor

DC motors

  • Series motor
  • Shunt motor
  • Compound motor

BLDC motors

  • These motors are of synchronous type but requires DC supply as it has inverter inside

This is just a rough classification.There are many more types of motors.However above information is sufficient to understand what follows.

Single phase induction motor:

In fans a permanent split capacitor type single phase induction motor is used.In a single phase motor only one phase supply is given.

For any motor to move , it requires a rotating magnetic field .In a 3 phase induction motor this rotating field is generated with the help of phase difference between three phases.(This requires a separate blog.Link will be provided soon.Do comment.).Hence three phase induction motor is self starting

However, in a single phase induction motor there is no rotating magnetic field and hence it’s not self starting.

So to make induction motor self starting ( You don’t want to hit the fan and rotate it right :D) you need a capacitor!.

Now you might be thinking that we can disconnect the capacitor after starting, right? Well you can do that but doing this will make your fan noisier.

Thus in short ,a capacitor in a ceiling fan solve two purpose:

1. It makes your ceiling fan self starting so that you can just switch it on using the load break switch( name for the normal switch you use to switch on/off lights and fans)

2. It makes its operation less noisy.Single phase induction motor without capacitor can make really irritating noise! Trust us on that.

Starting methods:

Broadly classified as:

  • Split phase starting
  • Shaded pole starting
  • Repulsion motor starting
  • Reluctance starting

In ceiling fans we use Split phase starting.In split phase starting methods are further classified as:

  • Resistor split phase (Used in Blower ,pumps and refrigerator upto 200 watts)
  • Capacitor split phase (Compressor ,reciprocating pumps upto 800 watts)
  • Capacitor start and run (Office equipment,fans.Low noise application
  • Capacitor run motor ( Used in ceiling fans)

Now let’s talk about capacitor run motors.

Capacitor run motors have a capacitor connected to auxillary winding as shown:

Capacitor run motor

Here there are two winding

1. Main winding

2 Auxillary winding.

Two windings are used to provide the phase difference(Theoretically 90 degree) between two windings current I1 and I2.

This phase difference provides us with the rotating magnetic field which makes our fans self starting.

The capacitor start and run type has two capacitors , one for starting and other for running.It is costlier .

Why modern fans doesn’t have a capacitor?

New models of fans are based on BLDC i.e Brushless DC motors.These motors are self starting and doesn’t require any capacitor.Advancement in this field has made it possible to use BLDC motors in fans.Earlier it was a costly solution

Sometimes different starting methods are also used in single phase induction motor.But that is less common.

I hope this blog gave you a basic understanding of why you need a capacitor in ceiling fans.We will write many more blogs related to this.Do comment if you want us to write on a specific topic.Your contribution is precious.

Keep reading!

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