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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Working:
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 is the main purpose of a capacitor in a ceiling fan?
The primary purpose of a capacitor in a ceiling fan is to create a rotating magnetic field. A fan's single-phase induction motor generates a pulsating magnetic field, which can keep the fan running but cannot start it from a standstill. The capacitor introduces a phase shift in the current supplied to an auxiliary winding, converting the pulsating field into a rotating one that provides the initial starting torque needed to make the blades spin.
2. Why can't a single-phase fan motor start without a capacitor?
A single-phase induction motor, like the one in a fan, produces a magnetic field that only alternates in direction but does not rotate. This results in a net starting torque of zero, meaning the rotor is pushed equally in opposite directions and cannot begin to spin on its own. The capacitor is essential to create a phase difference between two windings, which generates the required rotating magnetic field to initiate movement.
3. How is a capacitor connected within a fan's motor circuit to make it rotate?
In a fan motor, which is a type of permanent split-capacitor motor, the capacitor is connected in series with the auxiliary or 'starting' winding. This entire combination is then placed in parallel with the main or 'running' winding. This setup causes the current in the starting winding to be out of phase (ideally by about 90 degrees) with the current in the main winding, establishing the rotating magnetic field necessary for torque and rotation.
4. Does installing a capacitor with a higher capacitance value make a fan spin faster?
Not necessarily. While a capacitor is crucial for operation, using one with a capacitance value significantly higher than the manufacturer's specification can be harmful. It can lead to an uneven magnetic field, causing the motor to overheat, make a humming noise, and potentially suffer damage. The optimal fan speed is achieved with the correctly rated capacitor that creates a balanced magnetic field and efficient torque.
5. What are the common symptoms of a failing fan capacitor?
A faulty or degraded fan capacitor typically presents several clear symptoms. The most common signs include:
- The fan does not start on its own but will spin if you give the blades a manual push.
- The fan runs noticeably slower than its normal speed.
- A distinct humming sound comes from the motor housing when you turn the fan on, but the blades do not move.
6. What is the typical capacitance range and voltage rating for a ceiling fan capacitor?
For most standard ceiling fans, the capacitance value typically ranges from 1.5 to 10 microfarads (µF). The voltage rating is equally important; it is usually 370V or 440V AC. This high voltage rating is a safety margin to handle the peak voltage of the AC supply and prevent the capacitor's internal dielectric material from breaking down.
7. How does the energy storage in a capacitor differ from that in a battery?
A capacitor and a battery both store energy, but they do so in fundamentally different ways. A capacitor stores energy in an electric field between its plates and can discharge this energy almost instantly. A battery stores energy chemically and releases it through a slow, controlled chemical reaction. Consequently, capacitors have a very low energy density compared to batteries but a very high power density, making them ideal for providing a quick burst of energy, such as starting a motor.
8. What type of motor is used in a ceiling fan, and why does it need a starting mechanism?
Ceiling fans typically use a single-phase induction motor, often specifically a 'Permanent Split Capacitor' (PSC) motor. This type of motor is cost-effective and reliable but is not self-starting when connected to a single-phase AC supply. It requires a starting mechanism, like a capacitor, to create a multi-phase effect from a single-phase source, which in turn generates the rotating magnetic field needed for initial torque.
9. What are the primary physical reasons a fan capacitor might fail?
The most common cause of capacitor failure is dielectric breakdown. This can happen suddenly due to a high voltage surge or gradually over time. Continuous exposure to heat from the motor and electrical stress can degrade the dielectric material, causing it to lose its ability to hold a charge effectively. This leads to a decrease in its capacitance, eventually rendering it incapable of starting the fan motor.
