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#1
Old 12-05-2005, 01:23 PM
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Ceiling fan on a dimmer switch

So my wife wants me to put a dimmer switch on the light in the baby's room. Trouble is the light is part of a ceiling fan, so I'd have to run a separate 110v line for the light rather than dim the current switch (which turns on both light and fan), because you can't safely run a dimmer switch on a motor.

Unfortunately, my wife asked me why, and for the life of me I couldn't think of the correct reason. It's obvious the fan motor wouldn't work properly on a dimmer, but could somebody refresh my memory as to why this might be unsafe, or is this actually something that can be done? In short, how would having a ceiling fan running while connected to a dimmer switch be a safety issue?
#2
Old 12-05-2005, 03:34 PM
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Quote:
Originally Posted by CJJ*
So my wife wants me to put a dimmer switch on the light in the baby's room. Trouble is the light is part of a ceiling fan, so I'd have to run a separate 110v line for the light rather than dim the current switch (which turns on both light and fan), because you can't safely run a dimmer switch on a motor.

Unfortunately, my wife asked me why, and for the life of me I couldn't think of the correct reason. It's obvious the fan motor wouldn't work properly on a dimmer, but could somebody refresh my memory as to why this might be unsafe, or is this actually something that can be done? In short, how would having a ceiling fan running while connected to a dimmer switch be a safety issue?
Looks like something called an inductive dimmer switch may be possible. Check Home Depot or equivalent.

Electric motors draw a high peak of current at start-up, until the inductive load of the turning motor adds resistance (impedance) in the circuit. Not sure why normal dimmer switches would be frowned upon, but it must have something to do with that: heat or arcing with fire potential is my guess.
#3
Old 12-05-2005, 06:45 PM
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I'm not sure whether there would be an electrical problem with a dimmer switch on a ceiling fan, but there is a better solution out there for you, a ceiling fan remote with dimmer switch. When I put up a ceiling fan in my bedroom, I had a single 110v switched cable running to the ceiling box, and wanted to be able to switch the fan and light on independently without pull cords.

Here are some examples of remotes. I have the one marked "U", which allows you to dim the light as well as set the fan on three different speeds.

It cost about $35 and was simple to install. If you are thinking of replacing a switch with a dimmer, it should be within your technical competence.

Essentially, there is a small unit that fits up in the fan housing that is wired between the electric coming into the box and the light and fan wires on the ceiling fan. The instructions are easy to follow, and most models of remotes fit most fans.

Good luck.
#4
Old 12-05-2005, 11:51 PM
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Actually there are 2 circuits inside the fan. You would just need to "hard wire" the fan circuit to the existing 110, then connect the light circuit to the dimmer.

Th eonly problem is you now have to turn the fan on and off using the pull chains, but usually you leave your fan on full time and are only concerned about turning the light on and off.

MtM
#5
Old 12-06-2005, 12:23 AM
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A standard dimmer switch will fry your fan motor. To control the speed of the fan remotely you need a fan speed controller, which may be the same thing as the inductive dimmer mentioned above. To dim the light, you will either need to run a separate circuit for the light, which can be placed on a dimmer switch, or install the remote control unit suggested by Billdo. Running the new circuit isn't too tricky if you have access to the attic above the fan and light switch. After all, you only need one more wire to carry a separate 'hot' from the dimmer to the light. The neutral and ground are already there. If access is a problem, then the remote is definitely the way to go. I'd mount the remote to the wall so it doesn't get lost.

Also, the solution offered by McDeath_the_Mad won't work. There are two circuits in the fan, but they are both fed from the same switch leg and simply tied together inside the fan. It isn't possible to make the fan operate when the switch is off. The "existing 110" doesn't go to the fan, only to the wall switch.
#6
Old 12-06-2005, 10:40 AM
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I'll second the remote control idea. It's easier than re-wiring for a dimmer switch and more functional. Once you install the rheastat between the fan and the switch, simply mount the remote holder next to the light switch. The switch stays on all the time while the lights and fan are controlled by the remote. I have not used the pull chains on my ceiling fans/lights since they were installed.
#7
Old 12-06-2005, 10:50 AM
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I certainly appreciate all the good advice, particularly regarding the remote control unit.

However, other than Rhubarb's comment that "A standard dimmer switch will fry your fan motor," I'm not sure what will cause this when the fan is running (albeit weakly) off power supplied by a dimmer switch. I'm not planning on doing it because I have a giant warning bell going off in my head, but I'd like an explanation just so I can win the argument with my wife (it's such a rare victory, you see )
#8
Old 12-06-2005, 11:08 AM
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Quote:
Originally Posted by McDeath_the_Mad
Actually there are 2 circuits inside the fan. You would just need to "hard wire" the fan circuit to the existing 110, then connect the light circuit to the dimmer.

Th eonly problem is you now have to turn the fan on and off using the pull chains, but usually you leave your fan on full time and are only concerned about turning the light on and off.

MtM
That's how we did it. We had no problems. The fan is now dead, but we had it for like 12 years or something. My husband wants to replace it soon. I HATE THAT FUCKING THING. I hope he forgets.
#9
Old 12-06-2005, 11:17 AM
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Quote:
Originally Posted by CJJ*
I certainly appreciate all the good advice, particularly regarding the remote control unit.

However, other than Rhubarb's comment that "A standard dimmer switch will fry your fan motor," I'm not sure what will cause this when the fan is running (albeit weakly) off power supplied by a dimmer switch. I'm not planning on doing it because I have a giant warning bell going off in my head, but I'd like an explanation just so I can win the argument with my wife (it's such a rare victory, you see )
I am not an electrician, but I've tampered with my own household electrics a little, and I'd have thought the chief danger was that the motor would fry the dimmer switch, not the other way around. A dimmer can't give the motor more current than a straight switch, but a motor can sure as shooting draw more amps than a bunch of light bulbs. Surely there's some information on the dimmer packaging about the maximum current (or wattage) it should carry?

And when we say fry, we could literally be talking about a fire hazard, so be careful.
#10
Old 12-06-2005, 12:23 PM
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Not to disturb y'all with antedotal evidence to the contrary, but...

I did exactly what you've described, put a dimmer switch on a ceiling fan/light fixture.

It ran without frying anything, for over 7 years. And it was a very old house where if a problem had arisen I would not have been surprised. When I did it I was prepared to have to change it if it didn't work out. My brother, who both installed it and repairs all my appliances (once his trade) assured me it wasn't any real risk regardless of what other people told me.

A lot of people said, it will do this, that or the other thing, in fact, it did not do any of those things, it ran flawlessly without incident, naysayers be aware.

Now, generally I am a little overly cautious when it come to electrical things, I don't want any surprises but I have to say, my brother was right. The only down side was you couldn't really turn the light up to maximum brightness without the fan going so fast I thought the house might take flight.

But, like I said, seven years without difficulty. Of course, I think you should do what you're comfortable with, just thought I'd tell you I have heard of such a thing and nothing got fried.
#11
Old 12-06-2005, 01:05 PM
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Your run-of-the-mill dimmer switch is a phase-fired proportional controller. In English, this means the dimmer only passes a certain percentage of each sine wave to the load, depending on the setting. It uses a voltage comparator and triac to perform this feat. Because the triac is a fast-operating switch, a lot of harmonics are produced by the dimmer. Synchronous motors don't like high-frequency components, since much of this energy gets turned into heat. So don't connect a dimmer switch to a fan. Not only will it not slowdown the fan, but it could also damage it.

We have a ceiling fan in our living room. The guy who built the house only ran a hot, neutral, and ground to the fan. My wife wanted a light fixture attached to the fan. The fan was pretty old, so I went ahead and installed a new fan and light kit. The fan came with a control module that allows you to separately control the fan speed and lamp intensity using a remote.

The new fan and light fixture work well, except for one problem: The fan's light fixture eats compact fluorescent (CF) bulbs. I'm not sure why. I recall there was another thread on this very subject a couple months ago. I have a few hypotheses why this is occurring:

1. Sometimes my wife accidentally dims the CF bulbs using the remote. Perhaps this kills something in the electronic ballasts.

2. Vibration from the fan kills the bulbs.

3. There's a weird electrical interaction between the CF bulbs.
#12
Old 12-06-2005, 01:35 PM
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Quote:
Originally Posted by Crafter_Man
Your run-of-the-mill dimmer switch is a phase-fired proportional controller. In English, this means the dimmer only passes a certain percentage of each sine wave to the load, depending on the setting. It uses a voltage comparator and triac to perform this feat. Because the triac is a fast-operating switch, a lot of harmonics are produced by the dimmer. Synchronous motors don't like high-frequency components, since much of this energy gets turned into heat. So don't connect a dimmer switch to a fan. Not only will it not slowdown the fan, but it could also damage it.
Yes, but there are dimmers rated for fans. Motor rated dimmers are out there for controlling your ceiling fans.
Quote:
We have a ceiling fan in our living room. The guy who built the house only ran a hot, neutral, and ground to the fan. My wife wanted a light fixture attached to the fan. The fan was pretty old, so I went ahead and installed a new fan and light kit. The fan came with a control module that allows you to separately control the fan speed and lamp intensity using a remote.

The new fan and light fixture work well, except for one problem: The fan's light fixture eats compact fluorescent (CF) bulbs. I'm not sure why. I recall there was another thread on this very subject a couple months ago. I have a few hypotheses why this is occurring:

1. Sometimes my wife accidentally dims the CF bulbs using the remote. Perhaps this kills something in the electronic ballasts.
This is the most likely cause. You can't dim flourescents unless they are rated/designed for dimming.
Quote:
2. Vibration from the fan kills the bulbs.
'Nother possibility, though I haven't seen it in my house and we have three different ceiling fans with fourescents in them and not one has burned out yet.
We don't have those lights on dimmers either, so that eliminates the accidental dimming of the bulbs.
Quote:
3. There's a weird electrical interaction between the CF bulbs.
I'll leave that one up to you.
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