Fan Speed Controls - Anyone know how they work?

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We use a "box" window fan -- with 3 speeds -- in the pull-down stairs opening to the attic to blow cooler air from the house up into the attic, to help the attic fan evacuate the hot air from the attic. (I figure it also pulls more cooler air at night into the house.)It's one of this kind:

Like most of them, this one has three speeds -- high, medium and low -- in one direction only. (The fan doesn't reverse.)Does anyone know how the speed control on these things works? Does it just use resistor(s) on medium and low to slow it down, like the fans used in cars?The reason I ask is, if it's just using a resistor(s) to slow down the fan, I'd rather use that energy to push more air (setting the speed control on "High") rather than just make more heat in the resistors...Thanks for any clues.
Reply:Pretty sure it doesn't have resistors. Just has different windings in the field to get the speeds.Ol' Stonebreaker  "Experience is the name everyone gives to their mistakes"Hobart G-213 portableMiller 175 migMiller thunderbolt ac/dc stick Victor O/A setupMakita chop saw
Reply:Resistors wouldn't do anything for an AC  motor.I think it applies voltage to 3 different points on the winding Sent from my SM-G973U using Tapatalk

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Reply:

Originally Posted by mla2ofus

Pretty sure it doesn't have resistors. Just has different windings in the field to get the speeds.
Reply:

Originally Posted by MetalMan23

Resistors wouldn't do anything for an AC  motor.
Reply:...."limited by the frequency of the power and the number of poles in the motor, just as other AC motors are limited."I don't think that is true of the motor in a box fan. I believe it would run a lot faster without fan blades.Other motors it is true. Most of the motors we use are affected by frequency & number of poles. 60 HZ power, a two pole wants to run 3600 RPM, 60 RPS. A four pole wants to run 1800 RPM 60 HZ X .5 revolutions per cycle X 60 seconds in a minute.An optimist is usually wrong, and when the unexpected happens is unprepared. A pessimist is usually right, when wrong, is delighted, and well prepared.
Reply:

Originally Posted by Willie B

...."limited by the frequency of the power and the number of poles in the motor, just as other AC motors are limited."I don't think that is true of the motor in a box fan. I believe it would run a lot faster without fan blades.Other motors it is true. Most of the motors we use are affected by frequency & number of poles. 60 HZ power, a two pole wants to run 3600 RPM, 60 RPS. A four pole wants to run 1800 RPM 60 HZ X .5 revolutions per cycle X 60 seconds in a minute.
Reply:Thanks for the help, guys. My main concern -- wasting energy and creating more heat through resistors -- is addressed. Just out of curiosity, would the motor in my box fan be considered an "induction" motor, like (for example) the motor on my table saw?I know almost enough about electricity to be a menace.
Reply:

Originally Posted by StandarDyne

Thanks for the help, guys. My main concern -- wasting energy and creating more heat through resistors -- is addressed. Just out of curiosity, would the motor in my box fan be considered an "induction" motor, like (for example) the motor on my table saw?I know almost enough about electricity to be a menace.
Reply:I would just get a whole house fan. Mine is single speed and it's still going after 40 years !