Variable speed Fan


Old 08-22-11, 10:55 AM
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Variable speed Fan

Can an attic vent fan be connected to a variable speed switch? I know that a motor uses a different type switch, not a variable light switch.

I want to use an attic fan for special ventilation and would like different speeds.
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Old 08-22-11, 11:40 AM
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Could you possibly use a variac?
Old 08-22-11, 12:03 PM
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A ceiling fan speed control might work. Please explain exactly what you are trying to achieve and we can better help you.
Old 08-22-11, 12:29 PM
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Originally Posted by Justin Smith View Post
Could you possibly use a variac?
No. A Variac is an adjustable autotransformer and will allow varying the voltage but that will have a minimal effect on the speed while having a large deleterious effect on the power of the motor.

The fan speed controller MIGHT work depending on the horsepower rating of the motor. Those simple fan speed controllers won't handle more than a 1/4 horsepower motor at best. They are also noisy when the motor is running at less than full speed, the slower the noisier. You also have to be careful of the motor overheating because of the slower speed the internal fan will be flowing less air over the motor coils.
Old 08-22-11, 01:33 PM
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Originally Posted by Justin Smith View Post
Could you possibly use a variac?
I think you might be thinking of a VFD (variable frequency drive) unit which will alter the run speed of a motor, but the cost is far beyond a simple attic ventilation project.

Basically you can't do much to alter the speed of a motor electrically unless both the motor and the controller were designed for variable speed. If either of them wasn't, you'll get buzzing, overheating and an all-around lousy outcome. If your fan is belt driven you could swap out of the pulleys.
Old 08-22-11, 05:56 PM
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I think I'd give a speed control a shot, something like this.

Fan Speed Controls - ZORO tools

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