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To anyone thinking of purchasing an AC fan: I recommend you get a fan cord.
The fan cord has a special little plug on the end of it (actually a little
receptacle) that plugs into the two prongs on the fan. It uses regular zip
cord that can be wired up normally or can be used with one of the clamp-on
plugs from the hardware store to let you plug it into a regular power
outlet. Using the fan cord is both lots easier and lots safer than
soldering to the fan's terminals unless you are going to use heat-shrink
tubing to insulate the connections. Using the fan cord also allows for easy
replacement of the fan after it gets filled with plant bits and calcium
deposits (c'mon, we all know we abuse our fans in the humid environments we
run them in :-).
For speed control with DC fans, don't just use a resistor -- use a voltage
regulator such as the LM317 chip. This is *much* safter and will do a
better job to boot. The chip can be purchased from radio shack, and with
one or two additional components will create a variable voltage regulator
for a few bucks. Be sure to mount it on a little heatsink (or just use a
piece of aluminum).
Note also that brushless fans don't always take kindly to speed controls.
They are "brushless" because there is some circuitry inside that generates
a polyphase electrical waveform to make them turn, and sometimes the
circuitry won't work properly at reduced (or overly raised) voltages. In
most cases you will be OK, but sometimes the fan won't start at the lower
voltage or will just "buzz".
UNIX Systems Administrator