Every (electric) fan I have ever used switches (via a knob or cord you can pull repeatedly) from off to the highest speed, then the next highest, and so on, to the lowest, and finally back to off. Why this order? Why have I never seen off, low, medium, high? (It would instead be off, high, medium, low on any fan I have ever used.)
I looked at that link and there are some, er, not easy to interpret comments.
Accelaration is the key, it takes more energy to accelarate up to a given speed than it does to maintain it plus there are fixed losses in a fan that are the same no matter what the speed such as stiction.
Most domestic fans are direct drive and the torque they produce is fairly small, reduce the current by trying to start on low speed setting and it will not have adequate torque to overcome the fixed losses quckly enough and this will cause a larger than normal current to flow, the motor windings will get hot.
When any motor is started it presents a low impedance(think of it as resistance to current flow) to the electrical supply and a large current flows, the smaller the motor the greater is the tendency for over current, (domestic fans are very small motors)6 to 8 times normal current flow and this generates a larger magnetic field, which in turn increases the motor torque.
This usually lasts for a very short time because as the motor turns it self-generates a current which opposes the incoming current, the faster the motor goes the greater is this reverse current (back electro-motive force - back e.m.f)
It may seem odd to think about it at first but the faster an AC motor goes the less current it will draw, but then this is because the load is at its lowest.(in fact if you then force the motor around faster than the supply is capable of driving it, it will generate power and send it into the mains)
Now by starting your domestic fan on low speed it takes that much longer for the motor to produce the back e.m.f which will limit the current.
Manufacturers of such fans state that fans like these should be started on the high setting to reduce the run up time for this reason and they make the controller units accordingly, human nature being what it is if the controller were the other way around then folk would not switch all the way through to the high setting and then back down to the lower settings.
There are ways to limit the flow of current under starting conditions but they add to the cost and are used in large industrial applications.
One place you do see this done is in portable electric drills with speed controllers on but these motors are far more robust, being designed to start with a high percentage of maximum rated load on them.
ok, but there are some things in these answers that still causes me to question the underlying explanations. First of all, I have a fan that has not a twist knob, but push buttons, permitting me to start and run the thing on any speed I want. So, the engineers who designed that apparently didn’t place much credence in the torque/acceleration problem. So I think I want to reject that explanation. And also, when I turn on other knob-type fans, if I want a low speed, I turn it almost instantly and immediately to the low setting, obviating any advantage of starting with a high setting. So, I don’t think the explanations offered have enough clear-cut virtue to answer the question. The problem is, I can’t think of another better one. But I’ll be watching.
Its down to design, some fans have such light loads and have such a high impedance that even when completely stalled they will not develop a harmful overcurrent, these are usually very small devices, desktop fans and the like.They do not produce much torque, hardly surprising since torque is related to magnetic fields which in turn are related to current.
There are many types of motor but it usually comes down to price, you use the cheapest motor possible to achieve the purpose.
Extractor fans and ceiling fans often have startup windings inside them and these windings cannot take much current for long, sometimes these windings are switched out of circuit when the motor reaches a certain speed using centrifugal switches, the main windings are designed for continuous operation.
Its a case of horses for courses, what is ok on one motor is not ok on another, state of the art is a variable frequency starter/speed controller but these are extremely expensive and generally used in very particular applications.
Cheapo variable resistors controlling thyristers can achieve the same thing but generally only in small applications.
CC
That fan with push buttons develops so little torque that when it’s left standing for a few months the grease in the bush bearings solidifies,this then stalls the motor and melts the thermal fuse in the motor windings, very common fault on them.
Planned obsolescence.
The faster you make a rinky-dink cheap fan go, the faster it’ll wear out, and the sooner you have to buy a new one.
You apparently haven’t used a Vornado. They have a knob that goes in the following order Off, I, II, III, with III being the fastest.
[hijack]I took a look at the Vorbado website… are those things really that much better than a regular fan?
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Vorbado? Jeez… someone hit me with a spellchecker
The 4 fans i own are configured like this:
Top Button: High
3rd Button: Medium
2nd Button: Low
Bottom Button: Off
I believe the button heirarchy is similar to light switches we see every day. (up is on, down is off)
The alternative is unthinkable. If I had to turn my fan off by pressing the top button…I’d…I don’t even want to think about that.
I have one and yes, they are much better than any other fan I’ve ever used. One summer, I was spending every day in an uncooled building (temps 95-105 outside, nearly that hot inside) in electrical closets, terminating network cables. Sitting on a ladder all day in the hottest part of the hottest room in the buildings would have killed me without my Vornado.
Short answer: When people turn on their fans, they usually want the High setting. Putting High first makes things more convenient.
There’s no AC at the Pacelli homestead, but lots of Duracraft fans. There’s one in each room, each one has its own extension cord so they can be moved around easily. In addition, I have lots of large windows, so those can be opened if need be.
It’s not as hot as you might think, really. If it gets too hot, even with the fans, a cold lemonade from the refrigerator usually helps. 