Ceiling Fan motor operation

[auburnengineer]

My husband asked a question earlier this evening, which has given me pause. I've looked everywhere I can think of and came across this forum. Maybe someone here knows the answer.

Why do ceiling fans (and similar residential/box style fans) go from the off position to the highest possible speed setting before moving to slower speed settings?

As an electrical engineer, I just couldn't come up with a response that was satisfactory to me.

My postulation is that it has to do with the startup of the motor to begin with. Since the motor will overshoot upon startup anyway, it seemed logical to have the highest speed setting come first before slowing the motor to lower settings.

Thoughts?

 

[RonL]

My husband asked a question earlier this evening, which has given me pause. I've looked everywhere I can think of and came across this forum. Maybe someone here knows the answer.

Why do ceiling fans (and similar residential/box style fans) go from the off position to the highest possible speed setting before moving to slower speed settings?

As an electrical engineer, I just couldn't come up with a response that was satisfactory to me.

My postulation is that it has to do with the startup of the motor to begin with. Since the motor will overshoot upon startup anyway, it seemed logical to have the highest speed setting come first before slowing the motor to lower settings.

Thoughts?

I'm not an electrical engineer, but a quick guess might have to do with power through switches in a fashion that least likely will cause arc burn to the contacts.
A mentor might move this thread to the EE forum for a better chance of getting the right answer:)

Welcome to PF:)

 

[Danger]

I'm not familiar with the concept. I don't have a fan in my house. When I lived with the ex- in a 4-plex, we had one installed in the kitchen. As with any others that I've seen, there were 3 bead chains hanging from it. One turned the light on or off. The other two toggled between high and low speed, depending upon which one was in the "pulled" position. The instructions specified, however, that we had to shut off the mains at the wall switch before changing speeds.

 

[RonL]

I'm not familiar with the concept. I don't have a fan in my house. When I lived with the ex- in a 4-plex, we had one installed in the kitchen. As with any others that I've seen, there were 3 bead chains hanging from it. One turned the light on or off. The other two toggled between high and low speed, depending upon which one was in the "pulled" position. The instructions specified, however, that we had to shut off the mains at the wall switch before changing speeds.

I suspect that had to do with changing direction of rotation.

 

[Evo]

I've had celings fans for decades and only had two switches, one for the light, the other for the speeds. The chain for speed was pulled repeatedly to get to the speed you wanted and there was no requirement to turn off the power between speed changes. Never seen a fan like the one you described. :)

Moved.

 

[Danger]

I suspect that had to do with changing direction of rotation.

Now that you mention it... hmm...
Maybe rather than changing speed, it just redirected the airflow in a less efficient direction. All I remember for sure was that there was a lot less breeze on one setting than the other. If that's the case, then I guess that I've never actually met a multi-speed fan. Sorry for the distraction.

 

[RonL]

I've had celings fans for decades and only had two switches, one for the light, the other for the speeds. The chain for speed was pulled repeatedly to get to the speed you wanted and there was no requirement to turn off the power between speed changes. Never seen a fan like the one you described. :)

Moved.

You might recall having a small slide switch up on the body of the fans ?

 

[Evo]

You might recall having a small slide switch up on the body of the fans ?

No, never seen a slide switch. I've had ceiling fans since their renewed popularity in the late 70's.

 

[RonL]

No, never seen a slide switch. I've had ceiling fans since their renewed popularity in the late 70's.

The fans I'm familiar with are "Hunter" and "Hampton Bay" they all have the two chains and the switch on the side, they range back to 1992.
I'm sure there's someone that will pop in soon and answer the first post. :)

 

[Evo]

What is the switch on the side for? Surely they didn't expect people to climb a ladder to switch the fan off to change the speed?

 

[RonL]

What is the switch on the side for? Surely they didn't expect people to climb a ladder to switch the fan off to change the speed?

The switches on mine, are for changing spin direction, the choice of moving air flow up or down can have a dramatic affect on room conditions, I really hate having air blowing down on a perfectly cooked steak

Moving air up against the ceiling can have an affect of airflow to the sides of a room, instead of straight down in the center.

PS. I do have to get a step ladder (3 step) to change directions, but that is just on very rare occasions, and only in a few rooms.

 

[Evo]

ok, I could change spin directions by the sequence of pulls on the speed cords, but I'd have to test the cheap ones i have now to see if they do that

 

[RonL]

ok, I could change spin directions by the sequence of pulls on the speed cords, but I'd have to test the cheap ones i have now to see if they do that

Just to make sure I was clear about my fans,...they have one chain to turn on the lights, one chain to turn on and off and give the three speeds, and the slide switch that changes directions.

 

[Evo]

Seems you're right, there had to be some switch somewhere or a remote that switched direction.

 

[RonL]

Seems you're right, there had to be some switch somewhere or a remote that switched direction.

I have far too many TV remotes to even want a fancy fan with yet another remote

 

[edward]

What is the switch on the side for? Surely they didn't expect people to climb a ladder to switch the fan off to change the speed?

The switch on the side reverses the rotation of the blades. This is supposed to bring warm air down from high ceilings in the winter. I don't use it. In addition to reaching the switches they just seem to kick up all of the dust that settled in nooks and crannies with the fan running the other direction.

As far as the fans always starting on high speed it probably goes back to the time when fan blades were much heavier. The high current draw to get the heavier blades rotating would put an unwanted load on the motor. Times and technology have changed and with the newer lightweight fans it probably wouldn't matter. The fan manufacturers may keep it the same just to avoid confusion.

 

[edward]

I have far too many TV remotes to even want a fancy fan with yet another remote

Yep a remote for the cable box and a second one for the TV, perhaps a third for the VCR, then bring in the cordless phone plus a cell phone in a pocket. Now just try to find the blasted fan remote with two phones ringing and a annoying commercial blasting on the TV.

 

[zoobyshoe]

As far as the fans always starting on high speed it probably goes back to the time when fan blades were much heavier. The high current draw to get the heavier blades rotating would put an unwanted load on the motor. Times and technology have changed and with the newer lightweight fans it probably wouldn't matter. The fan manufacturers may keep it the same just to avoid confusion.

Yes, any fan, not just ceiling fans, that has three speeds, starts off in high speed and has to be switched down to lower speeds, in my experience. However, I happen to have a fan that has three separate buttons for the three separate speeds. It can be started in any speed. Therefore, I think starting in high speed is nothing more than a convention that might have had a purpose at one time, but is now just convention.

 

[Windadct]

Typically these are shaded pole motors - but that really should not be an issue for needing to start at high speed.

As for direction - my understanding is they should blow "up" in the winter to force the warm air near the ceiling out and down along the walls, and then blow down in the summer - to move the air past the people for max cooling.

 

[Averagesupernova]

I suspect it has always been convention since fans are often switched by a wall switch which of course will make no guarantee what speed it starts on.

 

[zoki85]

My husband asked a question earlier this evening, which has given me pause. I've looked everywhere I can think of and came across this forum. Maybe someone here knows the answer.

Why do ceiling fans (and similar residential/box style fans) go from the off position to the highest possible speed setting before moving to slower speed settings?

As an electrical engineer, I just couldn't come up with a response that was satisfactory to me.

My postulation is that it has to do with the startup of the motor to begin with. Since the motor will overshoot upon startup anyway, it seemed logical to have the highest speed setting come first before slowing the motor to lower settings.

Thoughts?

Ceiling fan usually have a permanent split capacitor single phase induction motor, which has switchable number of poles to tap into desired speed. For fan motors, a high starting torque isn't necessary becouse the load is small at low speeds (increases aprox as a quadratic function of speed). It is better and easier to make system which switches from lower to higher number of poles in energized motor. During start up the motor accelerates to higher speeds, and then, if desired speed is lower, switching stator windings to higher number of poles/coils decelerates motor to lower speed. http://gifyu.com/images/Unt.png for this situation. Of course, superior speed and power control of induction motor can be achieved by varying motor input voltage and frequency by inverter drive. Also it eliminates need for a mechanical, manual or automatic one, speed variation employed in standard solutions.

 

[zoobyshoe]

It is better and easier to make system which switches from lower to higher number of poles in energized motor.

I don't get how it's better and easier. You have, essentially, three different motors wound onto the same stator, each with a different # of poles. Why would it matter which you energize first?

 

[zoki85]

I don't get how it's better and easier. You have, essentially, three different motors wound onto the same stator, each with a different # of poles. Why would it matter which you energize first?

In the case of a multispeed single phase PSC, a tapped winding or several alternated winding connection construction is used. Consider simple case of a tapped auxiliary winding for 3 speeds (image b ).To normally start, PSC motor needs whole auxiliary winding. If it uses smaller portion of it, not just it will have difficulty to start but inital peak current stress will be higher. Bad for motor, bad for network. Recommendation motor be set to max speed is for good reasons. Multispeed three phase induction motors, use special connection schemes to avoid problems concerning switching to different number of poles.