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Old 06-27-2008, 06:05 PM   #9 (permalink)
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Originally Posted by ttoyoda View Post
The other way you could test the fan HP is to mount that old fan on an electric motor that you have set up as a dyno (you let the motor pivot on an arm, and measure the force the arm pushes with using a scale. This force * the length of th arm is torque. Then multiply by rpm to get hp) Then run the motor at diffrent speeds and you will get the curve of fan power VS rpm.

That's exactly how some eddy-current dynamometers work. Just make sure that you include the distance from the center of the armature axis to the outside of the motor can when you measure your arm length. It's also important that this arm is the ONLY way you have to keeping the motor can from rotating. Most motors have a pinch clamp bolt where the bracket attaches to the motor can or housing, so you would need to freely loosen that up or mount it on bearings so that all the counter-rotational force of the housing goes through the load cell on the arm.
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