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Fan Capacitor

Last updated date: 23rd May 2024
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Why is a Capacitor Used in a Fan?

If you open and look at the ceiling fan, you might notice a black box inside the switch housing, so what is that black box? Why is it important to have that box?

Well! The black box is a capacitor. The use of a capacitor is not only to start the fan but also to make it spin, also it is used in day-to-day electrical devices. A capacitor has its working basics on which it prevents the flow of AC and DC.

Now, a question arises: what are the basics of capacitors and why do we prefer capacitors in all our electrical devices such as smartphones, electrical appliances, and also in the medical field? These questions are very important to understand. 

This page will help us understand the function of a capacitor in a fan, and the importance of a capacitor, especially a fan capacitor along with its functioning.

Basics of Capacitors 

Assume that the road is a circuit and charges are like vehicles moving on the road. 

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In case, you find bumpy roads or speed breakers (which are resistors), the speed of charge flow would reduce.

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Now, a power supply is a device that provides a potential difference of voltage of “V” volt is connected at the two ends of a road, i.e., a circuit. You can say that this potential difference is the same as your car that is automatically carried up by an elevator to the position of height ’h’ without using its power.

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Now, you need a parking lot to park your car. So, this parking lot is a capacitor that stores your vehicle and the charge it carries. Also, please note that the same number of charges are always stored at the plus and minus sides in an electronic circuit.

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So, why is a capacitor used in a fan? Well, it is needed to have one capacitor installed on each single phase motor of a fan to generate net positive magnetic flux. 

However, in the absence of a capacitor, there will be a complete shift in magnetic flux for each current cycle; that leads to net-zero magnetic fields that would not make the fan rotate.

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Now, let us understand how a capacitor works in a fan or we can say the function of a fan capacitor.

What is Capacitor Used in a Fan: Ceiling Fan Capacitor

The function of a capacitor in a fan is to store electrostatic energy in an electric field and where possible, to supply this energy to the circuit. The role of a capacitor in a fan is to prevent a dangerous failure of the circuit, they allow the AC to move but block the flow of DC.

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Generally, two capacitors are used in the ceiling fan, i.e., one parallel and one series. The motor used in a fan is a “two value capacitor run motor” or “permanent split capacitor motor”. 

Here, one capacitor with high capacitance is also connected in the starting winding of the split-phase induction motor. Along with this, another capacitor with low capacitance is used in the running winding.

Now, a question arises: what is the purpose of a capacitor on a motor? Well, a motor that runs a capacitor makes it an electrical capacitor that changes the current to multiple windings of a single-phase AC induction motor. This, in turn, creates a magnetic torque.

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Now, the problem here is that this motor will not start by itself. It requires an external force to run it at the time of starting.

To overcome this problem, a capacitor is used. A capacitor is connected across a part of the winding in the fan motor that splits the current into different phases or it creates a phase difference between the windings. 

After the phase difference generates in windings, the magnetic field (torque) is produced that makes the rotor rotate in the direction of the generated magnetic field. The capacitor is usually connected through a centrifugal switch that increases the efficiency of the fan.

Now, if a capacitor was absent then what would happen? Well, without a fan capacitor,  the magnetic flux would shift completely for each current cycle. This would not generate a magnetic field in a fan and in turn, the fan would not spin. This is the reason we use a ceiling fan capacitor. 

However, in reverse, capacitors are small and balanced so we avoid using them in exhaust fans, as they can get damaged. 

Besides these ceiling fan capacitor specifications, some table fans also come with a capacitor that helps create magnetic flux which makes the fan rotate. The ceiling fan capacitor value is from 1.5 to 10 μF.

From the above text on a fan capacitor (both ceiling and table), we noticed the capacitor functioning. Now, let us determine the fan capacitor rating.


Well! The rating of the fan motor capacitor must have a range of 1.5 to 10 μF (similar to a table fan capacitor value), with voltage classifications of 370 V or 440 V. However, if a wrong capacitance value is installed, it can cause an uneven magnetic field around the rotor.

Capacitor for a Fan: Facts and Information

  • RIC Capacitors have excellent self-healing properties to prevent any electrical short circuit inside the element in milliseconds without affecting the normal functioning of the capacitor.

  • There is a capacitor named “high-speed fan capacitor,” these capacitors are used to increase the ceiling fan speed. One of the examples of the same is as follows:

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(You can find that a high-speed fan capacitor value is so high, i.e., around 3.15 mfd (microFarad).

FAQs on Fan Capacitor

1. What happens if the capacitor fails in the fan?

If the capacitor loses its efficiency, the fan will receive power. Since the start coil gets affected, it won’t develop enough torque to start the fan. 

One thing you can do is, you need to start the fan yourself, however, by giving it a push, it will keep running. 

In the nutshell, a bad capacitor can also make the fan function erratically.

2. What causes a capacitor to fail?

The classic capacitor failure mechanism is the dielectric breakdown. Dielectric breakdown may occur as a result of misapplication or high voltage transients (surges). The capacitor may survive many repeated applications of high voltage transients; however, this may cause a premature failure.

3. Is a fan capacitor useful as a battery substitute?

Since there is an electric field inside the capacitor, there is also energy stored in it. Thus, a capacitor can be used to store energy. However, if you connect a plain DC battery to a capacitor, the charge will start to build upon the plates. 

Along with this, we can replace a capacitor with a battery because, in capacitors, energy densities are much lower, which is the reason the phones have very limited power on time unless you use multiple capacitors.

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