"Trevor Wilson" wrote in message


**12 Volt DC fans are difficult to control.

Simply not true.

They have internal circuitry which regulates the speed.

Nope. Some have tachometers, but any speed regulating circuitry involved is
not in the fan.

Varying the input Voltage, is not very successful.

It's very successful. There are even inexpensive products that make
controlling them literally plug-and-play. This is an example:

http://www.computergate.com/products...?prodcd=BCFZFM

It's just a variable voltage regulator with support circuitry and heat sink
in an insulating case, with plug-and-play wires attached. Often available
for as little as $4.95 $US. One of many products that are available for the
purpose. IME very effective.

The rule of thumb is to keep the applied voltage above 7 volts. This allows
almost a 2:1 adjustment range which is more than enough for a vast number of
purposes. Take a fan that spins at 5,000 rpm and knock it down to less than
3,000, and the noise decrease is impressive. Another rule of thumb is to
avoid using series resistors.

I covered most of these points (except the Fanmate) in a post yesterday
morning. Did it get lost in the bowels of Usenet?