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# electric fan speed controller or regulator

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#### PG1995

##### Active Member
Hi,

I was trying to understand the operation of a speed controller or regulator for an electric fan. There are primarily three types of regulators: resistive speed controllers, capacitor based controllers, electronic speed controllers.

I was having problem with understanding the operation of capacitor based speed controller. Figure 1 shows a practical circuit diagram of a capacitor based regulator while Figure 2 is a simplified version. If the capacitance is increased then the voltage across the capacitor decreases allowing more voltage across the fan motor. Hence, if capacitance is increased, speed of the fan motor also increases.

Why is there a resistor across the capacitor? How does the parallel RC circuit reduce the voltage across fan? Thank you for your help!

Figure 1:

Source:
https://www.circuitspedia.com/ac-dimmer-fan-regulator-circuit/ (very good source)

Figure 2:

Source: https://www.quora.com/How-does-a-fan-speed-regulator-work (very good source with few good answers)

1: https://www.hunker.com/12003281/how-does-a-ceiling-fan-speed-control-work
2: https://www.westfloridacomponents.com/blog/how-does-a-fan-regulator-work/
3: https://www.bijlibachao.com/fans/ch...r-for-ceiling-fan-for-electricity-saving.html
4: watch the vide titled "capacitor inductor time constant series"
6: electric ceiling fan motor uses starting winding without any centrifugal switch /watch?v=xFkkVjiQbIs
7: /watch?v=odCNCjCMDfs (very good animation, use subtitles)

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The R across the C is only for discharging the capacitor on shut down, for safety.

A capacitor has an impedence of 1 / ( 2 * pi * f * c ) ohms.
As a thumb rule, a 1 uF capacitor will offer 3142 ohms (say 3 K) at 50 Hz; a 2.2 uF will be 1.5 K and 3.3 uF 1K.
Since there is no power loss in the capacitor, it will behave like a lossless Resistive regulator.

I can't find the website that was really good, so **broken link removed** 1st pic.

It's common for a lot of ceiling fans. A three lead capacitor, 2 values. One, the other or both in parallel.
You can change speeds with taps too. There's another method too. On the website I'm looking for the mispelled fan as fand and it's in canada.

I found the info: http://waterheatertimer.org/pdf/Ceiling-Fan-wiring-Diagrams.pdf

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