Fan voltage control?

[topslop1]

Is there a way to cut the voltage to a fan in half or reduce it without buying a fan controller? I'm looking to make an outtake fan in my case run at half speed rather than on or off. Without the controller is there a way I could possibly snip snip a wire or two on the fan and cut the power in half?

 

[GalvanizedYankee]

Compliments of http://www.jonnyguru.com/ ... http://www.sengpielaudio.com/calculator-ohmslaw.htm

Use OHM's Law to figure the resistence needed for a 5V drop based on the fan's wattage. 7V will keep most fans happy. Going to low can cause rumble & over heating.
Now buy a resistor rated at twice fanwattage for safety. Done. Just splice it into the yellow wire.


...Galvanized

 

[Navid]

Originally posted by: topslop1
cut the voltage to a fan in half

run at half speed

Those two are not the same. If you half the voltage across a fan, you will not half its speed.
An example relationship is shown on this page.
http://www.maxim-ic.com/appnotes.cfm/appnote_number/809/

So, as mentioned already keep the voltage at or above 7V to be sure that it starts.

 

[Zepper]

Alert! Alert! DO NOT splice resistor into Yellow fan wire - splice it into RED fan wire!!! The yellow wire on most fans is the speed sensor wire - I have seen the speed sensor wire be white or blue as well). The red wire has ALWAYS been the positive power lead in my experience.

.bh.

 

[GalvanizedYankee]

Zepper, I was thinking 4pin Molex when I said yellow wire. Yellow is 12V, red is 5V and blacks are the grounds.

On the fan's three wire. Red is 12V, black is the ground and most usually the sensor feed wire is yellow but can be another color.


...Galvanized