Technical doubt about ceiling fan

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mango-man

Recently, noticed that one of my ceiling fans runs slower than normal. Changed the condenser/capacitor and now it’s working fine. This got me thinking:


1. From what I’ve read the capcaitor is connected to the auxuliary winding and is powered only while starting the motor, remaining unused during the rest of the operation. If that is the case then why does the motor run slowly when the capacitor becomes old? Why doesn’t the motor reach full speed after starting?

2. If the motor runs slower than normal at max setting due to a bad/old capacitor, does it mean that the power consumption is also less?

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kukdookoo wrote:

@andromeda

Appreciate the curiousity.

The capacitor splits the current into different phases or in other words it creates a phase difference between the windings. A magnetic field (torque in other words) is produced which makes the rotor winding rotate in the direction of the generated magnetic field.

Coming to the other question, it doesn’t consume less power since it runs at lower speed. The phase difference created by the weak capacitor results in poor power factor or inefficient in other words. Observe if the fan gets abnormally hot, which is nothing but the wasted energy.

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andromeda wrote:

Appreciate the curiousity.

The capacitor splits the current into different phases or in other words it creates a phase difference between the windings. A magnetic field (torque in other words) is produced which makes the rotor winding rotate in the direction of the generated magnetic field.

Coming to the other question, it doesn’t consume less power since it runs at lower speed. The phase difference created by the weak capacitor results in poor power factor or inefficient in other words. Observe if the fan gets abnormally hot, which is nothing but the wasted energy.

okay, but why doesn’t the motor reach full speed when the capacitor is bad? Isn’t the auxiliary winding and the capacitor’s role limited to giving the initial push for the rotation? Once the motor starts rotating, shouldn’t it reach full speed irrespective of the condition of the capacitor?

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mango-man wrote:

okay, but why doesn’t the motor reach full speed when the capacitor is bad? Isn’t the auxiliary winding and the capacitor’s role limited to giving the initial push for the rotation? Once the motor starts rotating, shouldn’t it reach full speed irrespective of the condition of the capacitor?

The phase difference I’m talking about in the first part of the answer is the reason. The phase difference created between two windings when at 90 degrees, the torque generation will be maximum. When the torque is max, it results in max speed. Any deficiency in reaching that 90 degrees will result in weak magnetic field resulting in reduced torque/speed. 


To bore you/others more, the torque generating formula will have a sine signal with the angle as phase difference. A sine signal will reach unity at 90 degrees.

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The capacitor is used not only to start the fan but also to make it spin. In simple words, the capacitor creates a magnetic flux (torque) which makes the fan rotate. Generally, two in parallel series are used in the ceiling fan. One capacitor with high capacitance will be connected in the starting winding of the split-phase induction motor. Another one with low capacitance is used in the running winding.

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capactr charge or discharge hota h 50-60 times in a second, discharge hote time currnt flow fan mai jata hai jisse woh tez chalta hai

Deal Cadet Deal Cadet
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11 me science le lete ajj aye doubt na ata 🤣🤣🤣

pura 1 lesson tha ispe 😂😂

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andromeda wrote:

The phase difference I’m talking about in the first part of the answer is the reason. The phase difference created between two windings when at 90 degrees, the torque generation will be maximum. When the torque is max, it results in max speed. Any deficiency in reaching that 90 degrees will result in weak magnetic field resulting in reduced torque/speed. 


To bore you/others more, the torque generating formula will have a sine signal with the angle as phase difference. A sine signal will reach unity at 90 degrees.

Okay. And is the starting winding disconnected using a centrifugal switch after starting, in a conventional ceiling fan?

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Vip-in wrote:

11 me science le lete ajj aye doubt na ata 🤣🤣🤣

pura 1 lesson tha ispe 😂😂

I have a degree in electrical engineering. Still can’t remember these things. 😄

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You are thinking capacitor in a fan as a starter, which is partially wrong. It is ON (i.e. being used) all the time the fan is powered. It not only helps the fan to rotate automatically when its switched ON (i.e. acts as a rotation starter), but also helps it to keep rotating till its powered ON. Think of it this way. A capacitor creates tiny kickers that keeps the fan kicking in for e.g. clockwise direction till the time the fan is powered ON. When capacitor degrades, these tiny kickers kick in a different direction (although the kicking force remains same) which causes the resultant kicking force in the clockwise direction to be lowered and fan starts rotating slowly.

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A ceiling fan has a single-phase electric motor and hence, a start capacitor is provided across one of the two windings. which goes out of circuit once the motor starts. After the start, a run capacitor is there in the service which improves the power factor and keeps the motor running at its rated speed. In order to regulate the fan speed, a regulator is provided which varies the voltage across the winding and thus controls the speed. Lower the voltage lower the speed of the fan. So a regulator controls the voltage levels for the fan.

Regulator can be Electric Regulator or Electronic Regulator.electric regulators(the bulk ones)  have resistors to decrease the voltage for the ceiling fan. The resistor heats up while decreasing the voltage and thus the electricity saved by reducing the fan speed is lost as heat in the regulator. 

Electronic regulators use capacitors instead of resistors to decrease the voltage. Capacitors regulate the fan speed by regulating the waveform of power supply. These do not get heated up and thus save electricity when the fan is running at lower speeds (at higher speeds electricity consumption of fan is the same with both regulators). These regulators save up to 40% at speed 1 and about 30% at speed 2 compared to electric regulators. With proper stepped electronic fan regulators, when switching speeds, there are a lot of transients created which are also harmful to fan capacitors, but more importantly, kill the regulator itself prematurely. So the ideal method is to turn off from the switch, change the speed, and then turn the switch back on

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mango-man wrote:

I have a degree in electrical engineering. Still can’t remember these things. 😄

capacitor ka pura function phdya jta haii arrangements bhi kha pe kitna current flow krega and potential nikla etc. And physical internal part etc. Hmre state board k sarkari school me bhi cbse or icse me to aur 9th se aa jata haii ab syd

Bhai apki degree me shq haii 😄😄😄 tbhi desh andhre me haii 🤣🤣🤣 

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mango-man wrote:

Okay. And is the starting winding disconnected using a centrifugal switch after starting, in a conventional ceiling fan?

Nope there is no such switch in the usual ceiling fans. The motor type is called “permanent split capacitor motor” This kind of motors don’t need a centrifugal switch and the capacitor always remain connected. They are similar to squirrel cage induction motors. You can imagine something like a a capacitor which does both start and run.

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Bhai aap logo ka knowledge toh kamaal ka hai fearful

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