Free +7 Volt source
Use the YELLOW wire (+12V) as positive and
the RED wire (+5V) as the ground (not the black one).
The result is +7 Volts: reduces the fan speed nicely.
Cost: Free or less than $1 for a four pin molex power connector
Rheostat variable speed control
Radio shack sells a 25 ohm 3 Watt rheostat
(cat. no. 271-265) for $3.99. You need more
resistance than that. So also get a package of five
33 ohm 1/2 watt resistors (cat. no. 271-1104) for $0.99.
Now take two and make them in parrallel. Take another
two in parrallel. Now take those and make them in series.
You now have made a 33 ohm 2 watt resistor. Place that in series
with the rheostat. You now have a 33 to 58 ohm rheostat.
Use the formulas found on the Cisco PIX Project page
to calculate the volage drop for your fans. Just place in the +12V lead
to the fan. This range is good for fans with about 100mA draw. For a 100mA fan the volatage will vary between 8V and 9.4V.
© 2003 Cuzuco, Inc.
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