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## Re: Reducing speed of AC axial cooling fan

 Subject: Re: Reducing speed of AC axial cooling fan John Larkin Fri, 14 Apr 2006 21:03:56 -0700 sci.electronics.basics, sci.electronics.equipment, sci.electronics.misc
 ```On Fri, 14 Apr 2006 10:23:36 +0100, "techie_alison" wrote: >"John Larkin" wrote in message >news:d0rt325nitti35datdo1llf84e82kl2gkl@xxxxxxxxxx >> >> For an AC fan, do *not* use a dimmer or a diode. It's a shaded-pole >> induction motor and will not take kindly to either. >> >> A power resistor will work, although it will get warm. Calculate the >> motor impedance in ohms (rated fan voltage divided by rated current) >> and start with a resistor of equal value, and power rating equal to >> fan (volts*amps) to be on the safe side. It doesn't take a lot of >> voltage reduction to make a fan noticably quieter, so a smaller >> resistor could work. >> >> John >> >> (Yes, motors are reactive loads, but this is close enough.) > >Hi :) > >PVC = 240v * 0.1amps = 24watts > >VCR = 240v / 0.1amps = 2400 Ohms > >http://www.rapidelectronics.co.uk Stock # 62-8128 > >Tempted to buy a couple of 1K and see where that goes, bit of a stab in the >dark this as don't want to end up with a bag of different power resistors >that will never be used. Might have some high wattage resistors of unknown >values (right now) back at home. > >Aly > One resistor is 1K, two in series = 2K, 2 in parallel = 500 ohms. One of those ought to work. So buy a few 1K, 10 watt resistors. If they get hot, you can always fan cool them. John ```
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