How can I properly wire a variac to control the speed of a 240v fan?

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To wire a variac for controlling a 240V fan, it's crucial to determine the type of motor used; AC induction motors can work with variacs, but shaded pole motors, commonly found in small fans, may not be suitable. The Ruck 6" fan motor operates at 230V and 95W, and it is not a shaded pole motor, which raises concerns about overheating and exceeding variac ratings if used improperly. While some speed regulation is possible with AC induction motors, it is inefficient and can lead to increased heat generation. Proper wiring involves connecting incoming power to terminals 2 and 5, and the motor to terminals 2 and 3. Overall, caution is advised when using a variac for fan speed control to avoid damaging the motor.
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anyone point me in the right way to wire this variac up correctly...i'm wanting to control the speed of a fan running at 240v
 

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What type of motor does the fan use? You may not be able to it at all.
 


howdy Averagesupernova

its a ruck fan 6"
power 95w
voltage 230v
amp 0.45
 


If it is not a universal motor capable of running on DC it will not work.
 


Averagesupernova said:
If it is not a universal motor capable of running on DC it will not work.

AC induction motors will work just fine with variacs. I know this for a fact because I once worked for a manufacturer of AC induction motors. We used variacs all the time for powering and testing the motors.

Connect incoming power to terminals 2 and 5. Connect the motor to terminals 2 and 3.

Edit:
AC induction motors do not speed regulate very well without a variable frequency drive. Depending on the motor, it may be possible to get some speed regulation, but it will be inefficient and the motor may get hot.
 
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TurtleMeister said:
Edit:
AC induction motors do not speed regulate very well without a variable frequency drive. Depending on the motor, it may be possible to get some speed regulation, but it will be inefficient and the motor may get hot.

No way. A huge advantage of AC induction motors is that they regulate speed quite well at a set line frequency. Any induction motor I have seen that is run at line frequency (60 hertz) and reduced voltage will draw more current and heat up. The motors I have experience with a multiple horsepower, not a fractions of fractions like a small fan motor.
 


Most small fan motors are shaded pole motors. They have the disadvantage of low starting torque and very low efficiency, even at their designed operating voltage. But they also have the advantage of allowing some speed control below the synchronous speed. There normal operating speed is around 10% below synchronous.

The best I can tell from my google searching, the Ruck 6" motor is NOT a shaded pole motor. Therefore, I would not recommend using it with the variac as a speed control. Doing so would probably exceed the ratings of your variac and cause your motor to run hot.

Edit:
Averagesupernova, when I said ac induction motors do not speed regulate very well, I was referring to the fact that it is difficult to regulate the speed by varying the voltage. I can see how the sentence could be misinterpreted. Poor wording.
 
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