Whole house fan - possible to add variable speed?

[Tony]

What is the voltage and amperage ratings of the motor? Here are some speed controllers to choose from.

[bud--]

My fan has a 2 speed motor. The 2 speeds are from separate windings - each speed has a different number of poles in the motor.

You can easily control a "universal" motor - the type with brushes. Not likely that is what is in the fan.

Three phase motors can be controlled by changing the frequency. No possibility there is a 3 phase motor in the fan. The control would be relatively expensive. I have never seen info, but I suspect the new variable speed furnace motors are of this basically this type.

You could probably use a variable frequency control for a standard induction motor, but if the speed falls to where the start switch in the motor turns on you will probably burn out the motor. And probably relatively expensive.

If you use a "phase angle" controller, like a light dimmer, you could control the speed - the motor speed falls farther from the "rotating field" speed. Has the same problem with start switches. I believe the torque falls rapidly as the speed drops, but the power required for a fan, if I remember right, is about the 4th power of the RPM.

Briefly looking at the info for one of the speed controllers, it says it is for shaded pole motors (which are used in clocks and my bathroom fan) and permanent split capacitor motors, which is not likely what is being used for the fan. Not obvious from what I saw that the 10A speed control would work for a typical induction motor, which is probably what powers the fan. These controls are probably "phase angle" controllers - as above.

Outside of a 2 (or more speed) induction motor, I don't know how you reliably control the speed of an induction motor that probably powers the fan. How does the control work? How do you avoid problems with the start switch?

[mm]

It's said that motors won't run off of light dimmers, but of the 6 or so table fans I've used over the years, all but one worked fine. The other one required a fan speed control, usually used for ceiling fans. I got one at a surplus store.

I wouldnt' let the fan get so slow it stopped, althoughif the dimmer is at the very bottom when this happens, maybe it's okay.. Depending on the fan, it might well overheat if it did that, and burn out the fuse (or worse?). Also if a whole house fan gets too slow, it won't open the louvers I think, which are just sucked open.

[keith]

*Induction* motors won't run off light dimmers. Universal motors will (off dimmers rated for inductive loads). Small motors are almost always universal motors. Whole house fans are likely a mix, with the better ones being induction motors. Generally a belt is the tell (belt =3D> induction motor). I would guess the crossover is about 1/4HP.

[mm]

Originally they only came with one speed. Yes, I thought it was too loud on high, especially since it was right outside my open bedroom door.

[mm]

And of course, back to the oP's question, they sell fan speed controls that mount like wall switches. Often there's a switch there for the light that often comes with a ceiling fan. I presume whole-house fans use more current than ceiling fans, but would the speed control be big enough?

He could use teh toggle swtich for any old thing, including perhaps turning off the fan without changing the speed setting.

[krw]

You're not listening. Whole house fans often (if not usually) use induction motors. These motor controllers WILL NOT work with induction motors. You'll likely burn up both.

[Tony]

Uh... hello? A shaded pole motor IS an induction motor. Motor speed controllers will vary their speed by varying the frequency. Try google.

[Tony]

[keith]

Those are simple "dimmer" style controls. They are *not* for induction motors.

[JIMMIE]

The fan in my house was single speed. About the only thing it was practical for was evacuating smoke when my wife burned dinner. I had to replace the motor to get it to operate at lower speeds. Now its 3 speed and I stilll wish it had a slower speed. I am considering mounting some muffin fans in the corners of the chassis for when I want to draw a gentle flow into the house.

Jimmie

[bud--]

You will not find a shaded pole motor on a fan of any size - like a "whole house" fan that makes too much noise.

The motor controller I commented on (from your previous post) is almost certainly a "phase angle" control (like a light dimmer). It does not change the frequency.

The controller I looked at was also stated to work with a permanent split capacitor motor. If I remember right, they are a 2 winding motor with a capacitor in series with one of the windings. There is no start cap and no start switch. It is basically a 2-phase motor. (I don't remember ever seeing one.)

Neither of the motors that the controller said it was good for has a start switch. A "whole house" fan will almost certainly have an induction motor with a start switch. Using a dimmer-type control, as above, can easily burn out the motor. It is a misapplication according to the limited information provided with the control.

[Tony]

says Shaded Pole motors, which ARE induction motors. Unless you can show me a shaded pole motor that is not an induction motor? I'd love to see it!

[Tony]

What is it like to guess instead of going by the facts? Probably everything goes your way, if you don't read the specs.

There is a lot more info out there. I can't do all the work for you, look up KB Electronics and read the specs. And if you look at the picture, you will see that from the "off" position,the first "on" position is "high". Yes it will start the motor.

[Tony]

Is it belt driven? How about a smaller drive pulley?

[JimT]

>>>

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LOL....Always worked for me. :)

[RickH]

$39 is not too bad I dont think, I use the 10 amp one at the bottom of this page (my fan only draws 5 amps but I wanted the controller to run real cool so I oversized it): I got this same model for about $25 elsewhere.

[RickH]

Mine works great, the KB controller I got hooks up in series, I capped the low speed wire on the motor and just use the high speed one.

[RickH]

e:

Yes, below is the model I am using with the 30 inch belt drive WHF currently being sold by Home Depot (I think its called Master Flow).

Works great but I did want to inform the family to start it on high before turning it lower, but even if they did spin the knob to low from off quickly the motor still starts ok. The off click goes straight to High, turning the knob clockwise keeps getting lower, which is the proper configuration for a motor speed control.

Light dimmers are bad because they force the motor to start on Low and you must quickly crank the knob to get to High. Having the potentiameter go from Off click to High to Low as you move clockwise is the proper configuration for a fan control.

[keith]

e:

You won't find a whole house fan that uses a shaded pole motor, but go ahead and smoke your fan.