Hot Rods Question for the electrical gurus

I got a large fan in my shop that has a small 110 volt, maybe 1/2 hp,
electric motor turning a large blade with a belt. Works great, but some times I want a little less air. Can I put a reostate or something to slow it down without hurting the motor?

Bones

 

Not if it is AC, they are a constant speed motor. You could change the pulley or use an adjustable pulley. Or block the intake.

 

Hey hey, sure thing...a dimmer switch will do it....

 

Well, it depends on what kind of AC motor it is. More than likely it's a brushless squirrel-cage type, and you'll need a frequency drive to adjust speed. These are now pretty cheap (compared to what they cost when they first came out) but will still set you back about $200. You can change a lot of pulleys for that...

There's a remote chance it's a 'universal' motor (like what you'll find in hand-held power tools) and those can be controlled with a potentiometer (dimmer switch).

 

You can indeed control the speed of an AC motor with a variable autotransformer (aka: Variac).

 

throw a piece of cardboard on the back side of the cage to limit air in.
or, just get you one of these...
https://www.zoro.com/westward-motor-pulley-***embly-tt10407911a1g/i/G8104056/
Chappy

 

A box fan will run you about $20....

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I would use the dimmer light switch.....

 

Now's the time to tell the wife you need a bigger shop to fit the fan!

 

Crazy and Gimpy are right, it is possible to control the speed of an AC motor IF it is the right type of motor, made for such use. OP did not specify, just that it was some kind of large fan with a 1/2HP motor. 99 chances out of 100 such a fan uses a common type of motor that must run at some multiple of 60 cycles per second if it is not to overheat and burn out.

Or if you use an expensive type of controller which not many of us have lying around.

If he said ceiling fan, then it would most likely have a variable speed motor.

 

I'm picturing either a squirrel cage fan off an old furnace or a large industrial exhaust fan like a giant box fan.

 

Probably the cheapest solution would be to buy a pulley with graduated sizes and switch the belt to change speeds.

 

I think you would need two multi-groove pulleys, or continually have to change the depth of the remaining single pulley so the belt runs straight.


Phil

 

I'd like to help, but I am an electrical swami not a guru.

 

You would need to adjust the belt or put the motor on a spring loaded mount.

 

Check the motor , may be able to wire for 2 speeds.

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Drive ratio of the driven (motor) to the driver (fan).
If the motor has a variable pitch pulley, you can open it up. This moves the belt deeper in the pulley making it effectively smaller so it has to turn more times to one revolution of the fan. Pulls less current too.

 

The winning suggestion!!! And 3-speeds too. 8^)

 

A lot of them have capacitive start and an internal gizmo that switches the capacitors 'Off' when the motor hits 'run' RPM, if you use a frequency drive to lower it below that RPM bad juju will happen.

 

There are variable pitch[diameter] sheaves available. Buy one that the od is the same as the one on the motor and open it up so the belt drops in deeper to slow the fan.

 

Me thinks a dimmer light switch taint rated high enuff fer the amp / current load

 

Here's one

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I'm on the side of no did you ever have a motor fry because of low voltage. https://www.quora.com/Can-I-put-a-variable-speed-control-on-any-motor

 

Thanks guys, I’ve been out camping... no service. I think the answer for me is to put some hinged doors on the back of the fan to restrict the air. Is an upright shop fan about four foot blades. I built it years ago to cool the shop at the dept. Was Ok there in the big shop, just pushed it back to where I liked it, now my home shop is not that big. Thanks.

Bones