On Fri, 14 Apr 2006 10:23:36 +0100, "techie_alison"
>"John Larkin" <jjlarkin@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx> wrote in message
>> 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.
>> (Yes, motors are reactive loads, but this is close enough.)
>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.
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.