cmm1@msb.com (Chris Mauritz) (04/11/91)
Hello! I want to add a pot to an AC fan I added to my power amplifier.
I can't seem to find my old physics book and my electronics knowledge
is rather limited. :-) What would be a suitable pot to use?
I'm assuming that the wiring would look like:
hot----------pot-------|-fan
hot--------------------|-fan
Sorry if this seems a little basic, but there have been a lot of beers
between my last physics class and now. :-)
Cheers,
Chris
--
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Chris Mauritz |People are strange
mpoint!cmm1@uu.psi.com |when you're a stranger.
cmm1@cunixa.cc.columbia.edu |-The Doors-whit@milton.u.washington.edu (John Whitmore) (04/16/91)
In article <1991Apr11.131807.2565@msb.com> cmm1@msb.com (Chris Mauritz) writes: >Hello! I want to add a pot to an AC fan I added to my power amplifier. Sorry, won't work. For best efficiency, many (most) AC motors operate as hysteresis/synchronous motors, so to change the speed requires changing the AC line frequency. Adding resistance as you propose will reduce the stall torque first, then (as the lubrication and air drag begin to stall the motor) will cause the motor to overheat and slow. If you want to make the fan QUIETER, consider mounting it in a longish pipe, so the turbulence off the blade edges doesn't hit nearby objects in the air path. A hunk of 'rubatex' pipe insulation is a good sound-dead material for such an acoustic application. There ARE AC motors that CAN be slowed as you suggest, but those motors have brushes (so-called universal motors). While this type of motor isn't as maintenance-free as the usual type, you MIGHT be able to find a fan with this sort of motor. If you do, the acid test is to see if it runs on DC (use low voltage, 'cuz the wrong type of motor will just burn the fuse out if you don't feed AC to it like it wants.) John Whitmore