Why are Capacitors Used in Ceiling Fans?

I agree to the comments of sparkstation. In India the capacitor in the fan is generally used to give the phase split for starting and after that Power factor improvement. Generally the fan motors are capacitor start & capacitor run motors.

I have observed form personal experience that, sometimes fan rotates at lower speed and once the capacitor is changed it goes back to normal speed. Also I got a case where a fan starts rotating in opposite direction and changing capacitor it becomes alright. What could be the reason?

Dear Mr. Biswanath.das,

If the capacitor becomes weak, the phase splitting angle reduces and hence the resultant torque is reduced and hence low speed. This is taught in our Engg. classes.

Reversed Running, I do not remember, and I will verify my class notes and post here.

DHAYANANDHAN.S

Along the lines of power factor correction, the ceiling fan is a motor, which is essentially an inductive load. Putting the capacitor in their helps to balance the inductance and make the load more like a purely resistive load.

Permanent split capacitor motors are small inexpensive single phase fractional horsepower motors often used in applications that don't require high starting torque, like fans. They are less inefficient than shaded pole motors, which were widely used in this application several years ago.

Permanent split capacitor motors have the added advantage of being easily reversible, which makes them an excellent choice for ceiling fans. There are good explanations and schematic diagrams here: http://www.allaboutcircuits.com/vol_2/chpt_13/9.html

BY INVERTING THE PHASE THIS WILL ADJUST THE BLADE DURATION

We are talking about the normal household fan, correct.

The cap is there to aid in starting.

It is not for power factor correction, its a single phase motor.

Small fractional horsepower with cap start.

Hello T Man

<"We are talking about the normal household fan, correct.

You have assumed the fan is electric propulsion, of the style or type at left.

The cap is there to aid in starting.

It is not for power factor correction, its a single phase motor.">

The Topic starter did not ever refer to "normal household fan".

I have worked on ceiling fans with motors of over 125HP.

Because the Topic Starter was non-specific about the type of ceiling fan, I gave my original answer to cover all possible electric-powered ceiling fans.

There are other types of non-electric powered ceiling fans,and the ceiling fan operated by a punkah wallah, comes to mind.

These type of ceiling fans were powered by the arm of a servant (wallah = chap) and used mainly in India, during the days of the British Raj.

So as you may see, it does not always prove advisable to leap to assumptions.

Kind Regards....

Thats great stuff!

Wasn't exactly sure of the type and size of fan involved. I think from all the posts the user has recieved the answer they desire. Just might have to chug a little math.

Thanks

Regards to all !

#4

I fully agree with your comments.

I add:

The question is surely about a fan which uses a CAPACITOR & suspended to the cieling of a room.

<< what is requirment of capactor in ceiling fan ? >>

There is no Fan other than an Electric-Cieling-Fan in today's technology.

The capacitor is not only for Phase-Shift but also a Running capacitor.

Expriment the following:

1.

a. Disconnect cap.

b. Switch-on. Fan will HUMMMM but not start.

c. Give a push to any direction, it will start in that direction.

d. Try to stop by your palm's push-up, it will stop easily.

So it is also a RUNNUNG Cap.

If dried out [very-lo-capacity] will run slow or not start at all.

2. In case of #6

<< I have observed form personal experience that, sometimes fan rotates at lower speed and once the capacitor is changed it goes back to normal speed. Also I got a case where a fan starts rotating in opposite direction and changing capacitor it becomes alright. What could be the reason? >>

As pointed out in [ 1. a. above ] a bad-capacitor.

Hello Haajee

When there are several possibilities in the Specification, because the Topic Poster has thought we are all mind-readers and not stated the situation clearly, it is important that no assumptions are made, unless you carefully state so, in a reply.

<"The question is surely about a fan which uses a CAPACITOR & suspended to the cieling of a room.">

I disagree, because the Topic Poster had not specified such a fan of the domestic type to which you are referring.

I have worked on very large fans, used in freezing chambers and also mounted on the ceiling, refer: http://cr4.globalspec.com/comment/192902/Re-Why-are-Capacitors-Used-in-Ceiling-Fans

That is why I placed the 3 alternatives in my first reply Post: http://cr4.globalspec.com/comment/191976/Re-electrical, because capacitors are used in those 3 different situations, in ceiling mounted fans.

If you are in any industry where you specify, or are intending to purchase or install some thing, it is quite important to leave no possibility of error in a Specification.

If there is a "loose or fuzzy, non-fully-described Specification", it may well cost you and the Company you work for, a lawsuit, expensive costs, plus your reputation.

Specifying correctly, therefore, is of utmost importance, and best learned early in one's career.

Trust that explains the reasoning behind my Post: http://cr4.globalspec.com/comment/191976/Re-electrical

Kind Regards....

My dear Sparkstation !

Regards & thanks for your remaks & added info.

But sir what I say is clear in the question "Cieling Fan"

Regards

Hello Haajee

<"....what I say is clear in the question "Cieling Fan"">

Not a great deal, because it is not entirely clear.

I try and help others, both on the CR4 Forum and elsewhere, and as you may be aware, some Topic or Questions are not always grammatically correct, or entirely clear.

So I thought: Perhaps English is not the first language of the Question asker, thus there was a mini-translation done by myself, as I prepared my reply, which hopefully covered all possibilities.

I cannot ever guarantee to be 100% correct, I just do my best at the time.

In the Topic Question, there are 4 descriptive words: requirements; capacitor; ceiling; fan.

From those, it was probable that the Question asker wanted to know about a combination of any of those words.

1. Requirements = what is it there for?
2. Capacitor = Mis-spelled, but I could translate the word to Capacitor.
3. Ceiling = There could be much needed to know about ceilings, but it was probably descriptive of something else.
4. Fan - Something used to move or shift air.

So my reasoning went: The question is not about Ceilings in particular, the word "ceiling" is describing some thing = the Fan.

From my experience the Question is thus: The Question asker is wanting to know why the Capacitor is there, installed as connected to a "Ceiling Fan".

This Question is one which is often asked, because the capacitor just "sits there, connected, but does not appear to do anything useful".

However, there are 3 possible answers to the Question, and thus I gave the 3 possible answers.

Hope that assists you, in following my reasoning.

Regarding (2) above, there is an interesting analysis of how words are perceived.

QUOTE:

<"Aoccdrnig to a rscheearch at Cmabrigde Uinervtisy, it deosn't mttaer in waht oredr the ltteers in a wrod are, the olny iprmoetnt tihng is taht the frist and lsat ltteer be at the rghit pclae. The rset can be a toatl mses and you can sitll raed it wouthit porbelm. Tihs is bcuseae the huamn mnid deos not raed ervey lteter by istlef, but the wrod as a wlohe.">

The full article, with the explanation, may be located here: http://www.mrc-cbu.cam.ac.uk/~mattd/Cmabrigde/

Enjoy the reading at the above webpage.

Kind Regards....

Regards & thanks for more info.

I remember that there was a discussion on the "Spellings" on CR4 & all this & more info on this craze.

It was just a discussion & was not appreciated by the PURISTS in UK.

More over a writing by any body how known personality he may be is not final word.

I will try to find the link & refer it.

Regards.

I promised to find the link in CR4 about the "Spellings". It is here.

http://cr4.globalspec.com/thread/18481?frmtrk=cr4sd#newcomments

and

http://cr4.globalspec.com/thread/2419

Hope you would like to read.

Hello Haajee

Thank you for your thoughtfulness with providing the above two links re spellings.

Your first link brings us to this very Topic, the one in which we are right now, itself.

The second brings us to the discussion on nooalf.com, and another way of spelling English, which might be helpful to some.

Kind Regards....

Thanks & regards

Regards All !

But no response from dharmendra_prp yet.

Ceiling fan is a Single phase Induction motor.Generally we use a capacitor start &Run AC Motor for ceiling Fans. Motor principle: whenever current carrying conductor is placed in a magnetic field-it experiences force. Stator: supplied by 1-phase voltage, current will produce in the stator winding-so magnetic field. But AC motor needs a rotating magnetic field in order turn the motor shaft (fan blades). This is done by applying voltage with different phases to different windings. In a single phase system (like at your house where you would use a ceiling fan) there is only one voltage phase. The capacitor is used to provide a phase shift (i.e. a time offset between currents) in the windings of the motor, making it appear that the motor is operating in a multiphase system.In Simple Terms, A single Phase is Split Into Two. There are also other methods to split Phase But using a capacitor is less expensive. Now we have magnetic field. We need current carrying conductor: Because of Induction, voltage will develop in rotor as It is a closed circuit current will produce-so current carrying conductorp laced in magnetic field. Rotor will rotate.

Dear Mr.dharmendra prp,

A ceiling fan is which has single phase supply, the starting torque direction is reversed 100 times per second, since the supply frequency is 50 c/s. If it is 60c/s, the reversal will be 120 times. In a 3 phase fans the reversel of torque does not occur.

If Capacitor is provided it will provide a split current, and will provide the starting torque, and fan will start and pick up speed.

DHAYANANDHAN.S