In my last house, I had a whole-house fan that had a what looked like a normal rotary lighting dimmer that worked as a variable speed control for the fan. It’s been several years since I lived in that house, and I can’t say that the fan was anything special but as far as I know, the fan was a standard type that could be purchased at Lowe’s or HD, but I don’t know that for a fact.
I would like to install a whole-house fan in my new house, and I like having a variable speed control. All of the fans available at HD or Lowe’s are two speed, and a web search reveal very few that have feature variable speed control.
Can a normal lighting dimmer, provided it’s sized to accommodate the load (correct amperage rating), act as variable speed control for these types of fans? If so, are there any tricks or caveats to be aware of when wiring this? If not, is there a way to do this?
Those fans use simple AC synchronous motors which spin at some multiple of the line frequency. If you hook a typical dimmer to one you’ll reduce the fan’s torque but not its speed. It may “slip” and slow down some but that’s not what you want.
You might be able to find a variable speed controller for an AC synchronous fan motor, but I don’t know how much it would cost. It might be cheaper just to get a variable speed fan unit. They may not be available at Lowe’s but I don’t think they are that uncommon.
Thanks for the reply, engineer_comp_geek. I have another question about this:
The GAF MasterFlow fan sold by HD (shown here) is described as a “1/3 hp permanent split capacitor design.”
Additionally, the KB Electronics Solid State Variable Speed AC Electric Motor Control (shown here) is described “provides infinite variable speed for shaded pole and PSC motors…”
Assuming “PSC” means “permanent split capacitor”, wouldn’t the 8.0 or 10.0 amp versions of the controller do the job? This is certainly not the lighting dimmer that I described above, but it seems correct.
Sychronous motors are rare except in clocks and appliance timers. It is almost certainly an induction motor. Induction motors tend to run near line-synchronous speed, but when the load has a steep torque versus speed characteristic, as fans and blowers do, then reducing the voltage can provide a range of speed control. This works best with motors designed to operate at high slip fractions…cieling fans being a perfect example.
The increased slip frequency causes heating in the rotor due to hysterises losses in the solid iron. Motors intended for such service have laminated rotors.
… but I’ve dealt with essentially the same problem!
What you need is a fan speed controller/switch. The most straight-forward and flexible solution I found was from Lutron. You can get them at Lowes or HD. Go by the ceiling fan section and ask for one.
Odds are that you’ll need to install the switch at the wall AND put a controller in-line within the fan’s junction box. You leave the fan on max/high and then the little controller handles all the waveform adjusting for controlling the fan speed.
FWIW, the controller unit and the switch are sold together in these big box stores. If you need them separate (e.g., two fans on one switch), you’ll need to special order from an electric supply store.
Thanks, JerseyFrank. Were you dealing with ceiling/paddle fans like those made by Hunter or Hampton Bay? If so, I think that they may be different from the fan-type that I need…
The cieling fan is a fractional Hp motor, like 1/25 hp if I remember right. the Whole house fan is 1/3 hp. The cieling fan controller will propably be two small.
I was dealing with 2 ceiling fans on 1 switch. (I should’ve mentioned that!) Find out how many amps the whole house fan draws. You should be able to find a switch that can handle that amperage. Check with Lutron to be sure. You might just want to give them a call and get a part number for what you need.
Browsing Lutron’s site shows me that they have 5.0A controllers, but they are listed under the “fully variable” section, which I suspect won’t work for you.
edit: Looking at the manual for Lutron SFS-5E, it says…
The NTFS-12E- and NTFS-6E- handle 12 and 6 amps, respectively. Now I’m thinking that this is what you need. Check this out from the manual. I’ve bolded parts that I think are important…
I used the “Q” (quiet) kind for my installation, but you shouldn’t use that one. It looks like if your fan has a PSC motor, the NTFS-6E (or 12E) is exactly what you need. There are a bunch of different styles. Some are not available at the right amperage rating for you though. Find the model number of a few that you like. Go to Lowes/HD and see if they have 'em. I had better luck at Lowes for variety, but ultimately I had to special order it from a supply house to get exactly the control I wanted.
Would the permanent split capacitor motor have a very high starting current? I think that I was lucky to find the overall current rating (and motor type) online - there isn’t much information on these.
Sorry to say, I don’t know a “shaded pole” from the North Pole, and I would hate to spend a few hundred bucks doing this just to burn it up by using the wrong controller…
Your motor will still have a high starting current but not as high as some other motors. My connection right now is sporadic, if IT gets me fixed up I should be able to help you out with the controller soon. In the meantime, have you settled on a fan so that we can look at exactly what you would be dealing with for a motor?
One belt drive and one direct drive from Home Depot made by GAF Master Flow, the others from Lowe’s made by Air Vent, both direct drive. I’m leaning toward the larger belt drive model. I was able to find that the GAF Master Flow has a PSC motor. Post #4 upthread contain links to each of the manufacturers (or perhaps the distributors).
The parts you linked to look correct except that the fan control should be used on a direct-drive motor, which is the 1/4 hp fan on that page. The fan motor will be receiving a ‘chopped’ waveform and could run hotter than normal so they want the fan to help cool down the motor. The fan control is listed as being specifically for shaded pole and PSC motors which indicates the manufacturer has designed it to handle the start-up current for the motor. You should also check to see if the fan motor has a built-in thermal overload because it’s being used with a solid-state controller. I don’t know if that’s code in the U.S. but it is here in Canada and the two codes are usually quite similar.