How to make a single speed, 12 volt fan, a variable speed.?

Question

have a small single speed 12V fan (1 black wire & 1 red wire), that I run off a power supply. I would like to be able to adjust the speed. I tried a light dimmer, but that didn't work. Any ideas?

Answer 1

He is talking about a low voltage dc fan not a mains fan, and when using resistors to lower voltage, this also lowers the current (perhaps too much in some cases) so certainly will not cause damage to the fan through overcurrent, besides which the fan repressents a load and ONLY tries to pull the current needed to operate regardless of how much current is availalbe on the power supply.

In answer to the original question, a series of small diodes inline with the positive lead will lower the voltage without limiting current (which is still needed to start the fan) an costs very little to assemble. Simply add or subtract amount of diodes to obtain needed speed (approx 0.7v per diode depending on type used.)

Alternativley look into using a 5v voltage regulator with a variable resistor for variable speed control.