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Ceiling Fans

Ceiling Fans

Ceiling fans are a very efficient way of keeping cool. They use very little power and are generally very reliable running for many years with little attention. Here we look at how they work, how they should be mounted and balanced, they should be earthed, they need the correct type of speed controller and the problems of drooping and rusting blades.

ceiling fan

All about ceiling fans

The ceiling fan, that ubiquitous piece of electrical wizardry that sits forgotten on the ceiling and makes life bearable all over the tropical and sub tropical zones of the planet.

Ceiling fans do not cool the room, in fact the cooling effect of ceiling fans is achieved not by blowing cool air to cool the room but by blowing air over your skin, this increases the evaporation rate of perspiration so making your body's natural cooling process work better.

You might as well turn the ceiling fans off if there's no one in a room.

How much power does a ceiling fan use?

Mostly our ceiling fans are out of sight and out of mind but then, one day, they go wrong and we are reminded how useful they are. Surprisingly they very rarely do go wrong and, you may be pleased to know, they also use very little electricity (around 65 watts or about the power consumption of a medium sized standard light bulb).

They are simple but cleverly designed devices, an electric motor hanging on a pole with 3, 4, 5 or even 6 fan blades fastened directly to the motor. No gearbox and very little to go wrong. The secret of the ceiling fan lies in the fact that the rotor is heavy and acts as a flywheel. It takes a while for the motor to get turning but once it has got up to speed there is a lot of momentum in the flywheel and the motor doesn't have to work hard to keep it moving.

It takes more energy to start a ceiling fan than it does to keep it turning. If you remember in the recent article "Danish Bacon" (click here) we talked about how electrons zipping through wires make electric motors turn.

In a ceiling fan you may (depending on the design) have 2 different windings of copper wire in the motor, one (the main winding) to provide the power to keep it turning and a second (auxiliary winding) which is needed to get it started.

Ceiling fans need a capacitor to start the fan moving

Another important component in a ceiling fan is a capacitor. Simply speaking a capacitor is an electrical device that stores up electricity then releases it as a sudden burst of energy. The capacitor works with the auxiliary winding to provide a kick start to get the fan turning. Capacitors are also used to start flourescent lights, in photographic flash guns and in air conditioners.

If your ceiling fan won't start (you may hear it buzzing but it won't start moving) it could well be the capacitor. Try pushing the blades to start the fan turning, if the problem is the capacitor the fan may carry on running normally once you have manually started it.

You can do a similar trick with a flourescent light by stroking along the length of the tube with your hands, this generates static electricity which can “zap” the tube and get it started if the capacitor isn't working properly.

Controlling the speed

There are various different ways of controlling the speed of a ceiling fan and how these work is a little too complicated to go into here. I sense your brain is starting to glaze over but suffice it to say the speed controller should match the fan and it is best to use the speed controller supplied with the fan.

Earlier fans may have pull chains or rather large wall mounted rotary switches while these days there are some smart looking solid state rotary speed controls and even remotely controlled fans.

Light dimmers should not be used as fan speed controllers

Take care. The solid state rotary speed controls look very much like light dimmer switches but they are not the same. It is important to note that you should NOT use a light dimmer to control a ceiling fan. There are a number of people around who may call themselves electricians that may not know the difference.

If you do want to use a smart modern speed control for your fan it is best to buy a high quality unit specifically designed for the job.

For safety ceiling fans should be earthed (grounded)

Fans are driven by electric motors and so may use more peak power than lights and will need to be earthed (grounded). You shouldn't use existing lighting wiring to power a ceiling fan, you will need a higher rated 3 core cable.

Ceiling fans should have a strong mounting

You also need to think about how the fan is mounted to the ceiling. Remember a fan can be quite heavy and don't fly very well even though they are pushing air downwards, you don't want the fan to come loose during the kid's christmas party or you may well end up with a ceiling fan massacre. You need to make sure the fan is securely fastened to a reasonably substantial beam in the ceiling.

Take very careful note of the height of the fan. As Marie Antoinette found out, thin pieces of steel travelling at speed can remove even a robust sense of humour rather quickly. Exuberant fathers throwing their babies in the air under ceiling fans have caused more than a few tragedies around the world. You need to make sure that the fan blades are higher than baby tossing height ie. a tall man with his arms outstretched. Some people say 7 feet, I would say significantly higher to be safe.

A wobbly ceiling fan needs to be balanced

A ceiling fan should spin smoothly particularly at higher speeds. If the fan wobbles (and many do) it means that the fan is out of balance. Two things can put the fan out of balance: variation in the weights of the fan blades or variations in the position the blades are bolted on to the fan hub.

If your fan does wobble first check that the fan is clean, and that the blades are in good condition. Rusting of blades, different amounts of paint or even a wasps nest can make the blade weights vary. You can try removing the blades and then reinstalling them in different positions on the hub. If this doesn't work you can try adding small amounts of weight to the blades to get them back into balance. You might try a blob of chewing gum or blutak stuck on the end of the blade but it may take a bit of experimentation to (a) find the right blade and (b) get the right amount of weight added.

Rusting fan blades - a perennial problem

Some time ago I went to see a very nicely finished group of villas situated right on the beach. The living rooms were all finished in powdered palimanan stone which gave a beautiful natural finish to the rooms, but - each room had a brown line around the walls a metre down from the ceiling.

Examination revealed that the lines were caused by two ceiling fans in each room that had steel blades. Being exposed to constant sea breezes the blades had rusted and sprayed a line of rust around the room.

Nothing could be done about the walls. Palimanan is notoriously absorbent and once stained could never be cleaned. Attempting to repair the stained line would have shown badly however hard you tried. A very expensive luxurious wall finish had been destroyed by a stupidly simple but very common problem - rusting fan blades.

Ceiling fans come in many configurations and designs but most are basically the same. They are low cost, mass produced items and the vast majority have pressed steel blades finished with a coat of paint. Spinning continually through the air the paint on the leading edges of steel blades tend to fail fairly quickly and the blade starts to rust.

Most of the ceiling fans that are supposedly made from stainless steel also rust fairly quickly and in fact are not stainless steel at all but ordinary mild steel with a plated coating.

Drooping fan blades

This is not an easy problem to solve, it is not easy to find fans that have blades that don't rust unless you go for wooden blades. Many of the “colonial” style fans with brass centres and what at first glance appear to be wooden blades are not wood but a composite. They might not rust but they do tend to droop after a while.

If you hunt around you may be able to find fans with genuine stainless steel or wooden blades. Ceiling fans are generally very cheap items and it is worth paying a bit more for one that will last.

Copyright © Phil Wilson June 2011
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