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How does a fan work?

Updated: May 11, 2023

Maybe one of the simplest and the most well popular home appliance is the fan. Its simplicity knows no bounds. A motor rotating and helping us against a warm summer day. However, the exact workings of a fan might still be a mystery to most of us. How does it increase and decrease in speed? What if you provide too much potential to it? How is it even hanging up there? Today, we dive into how a fan actually works. On our way, we'll figure out some key concepts in electronics and physics, in general.

An electric fan
An electric fan
The circuit behind it all

The ceiling fans that we're most aware of have seemingly simple circuits. If a person had to guess, maybe a motor, a resistor and a bunch of wires. However, there are little details in the fan circuit that makes it such a widespread appliance. Without these little details, we'll face problems we had never thought of.

Ceiling fan has a “capacitor start motor” in its inside. AC single phase capacitor start motor has two winding; one is starting winding and another is running winding. As it is a capacitor start-capacitor run type motor; there a capacitor is used in series with the Starting Winding, It defines the direction of rotation. It is an electrolytic capacitor.


Circuit diagram for a capacitor based ceiling fan
Circuit diagram for a capacitor based ceiling fan

As you can see in the diagram, the rotor is dependent on the starting winding, running winding and the capacitor. If you're wondering why a fan spins anticlockwise, it's because the capacitor is in connected in series with the Starting Winding. If you want to flip the direction the fan spins in, you just have to put the capacitor in series with the running winding!


What do these components do exactly?

Let's have a look at the components in this circuit one by one. We have a basic main AC Supply which supplies the potential different needed for the fan. Note how the supply is always on; to control the flow of current in the circuit, we've placed a switch. The switch S can break the flow of current, stopping the fan from spinning, which is what happens when you turn off the fan. The rotor needs, in order to rotate, a Starting Winding wire and a Running Winding wire. These two, with the help of a capacitor, which acts just like a reverse resistor, helps the rotor rotate.


How do we control the speed of the fan?

The diagram above shows a "Capacitor" fan. We discussed earlier that a fan can also have a resistor, but in our model, it doesn't. The entire concept of slowing down the fan is based upon how much current is passing through the circuit. The more current passes through the circuit, the greater would be the speed.

In a resistor model, as shown below, the fan has a resistor which can limit the flow of current through the wire. This simply decreases the speed of the fan.

A reistor based fan model circuit diagram
A reistor based fan model circuit diagram

However, as you can clearly see from the diagram, the resistor model is denser with more components. Moreover, instead of just using one capacitor, it uses three separate resistors. This causes two problems: energy loss and ineffectiveness. The current that a resistor limits is lost as heat and that causes problems because it puts the circuit in danger of burning, and it overall degrades the quality and the durability of the model.

Capacitor based models of fans are simple and yet more efficient with low energy needs. Hence, we tend to use the capacitor models more often.


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