Duct Fan Motor Question from John

Custom Search

Question:

Dave, Do you have a shaded-pole fan motor in your booster unit?

This type of fan motor is normally quite inefficient and usually has a very low H.P. rating. Nevertheless, it is the only type of fractional H.P. AC motor one can safely use for speed control with a rheostat, as in your application. All others require a V.F.D.(freq. drive).

Adding any resistance to the power line of a motor causes increased slip. This further reduces efficiency. Slip should be approx 4-5% of synchronous speed.

The only two good ways to change speed is by varying the frequency or adding/removing pole pieces.

Speed = 120(x)freq./no. of poles.

I would think it might be better to install a single or 2-speed 120v induction motor and to use a damper to tailor the flow as needed. All other motor controls can remain the same.


Answer from Dave:

Hi John,

To be honest with you, I don't know what type of motor is in the fan - shaded pole or induction type. The question never came up before. The fan I bought came from Aero-flo and is a model AF-12. It is an axial flow and is made specifically for this application.

The fan motor and the variable speed switch came from the same manufacturer. The fan is rated for continuous operation, has a good warranty and is rated for temperatures up to 257 degrees.

We installed this unit several years ago and have experienced no problems with it. It keeps the upstairs office the temperature we want without having the expense of installing a second air conditioning system.

12" Aero-flo Fan Booster Specifications:

• 12" Diameter


• 9-1/8" Length


• 120 Volt / 60 hz motor


• 975 Max C.F.M.


• High quality galvanized hard steel housing & fan Blade material


• Weight 6 lbs


• 0.80 Max Amps


• 65 Max Watt


• Certified for use up to 257 degrees F


• Continuous Duty (These fans were designed to run all the time if needed)


• Permanent Lubrication


• Auto Thermal Overload


• Designed for round, square and rectangular 10" metal duct or larger


• 1 year warranty

To Duct Booster Fan Question from Steve

To Energy Conservation

To Home Page