Can I plug a 4 pin fan into a 3 pin header? (PWM)

ComputerWizKid · 09-14-2007, 04:53 PM

I found a great deal for 80 MM PWM Fans which my older case uses and my fans are all old and about to die (Plus there full of cat hair) so can I plug these fans into a regular 3-pin MB header or a Molex with the proper adapter? Since these fans put out 59/46 CFM/DBA I want to build a fan bus what would I need to use the PWM circuit already in the fan in my fan bus? Thanks

Zepper · 09-14-2007, 05:30 PM

Yes! You will note that the first three pins of a PWM fan connector have the same form as any stamdard 3-pin fan - the 4th pin (PWM) sort of hangs out there by itself.

.bh.

ComputerWizKid · 09-14-2007, 08:47 PM

What kind of circuit would I need to make to simulate a 4-Pin MB header? and if I just give the fan straight 12 Volts will it run at full speed? Thanks

Zepper · 09-14-2007, 11:08 PM

12V=full speed=yes - IDK what signal you would need to supply the fourth pin (more than likely either a variable resistance or voltage) but I'm sure you could find out with a little intelligent searching on the web - starting with Wikipedia.

.bh.

Mark R · 09-15-2007, 04:18 AM

The 4 pin fans simply use a 4 pin version of the 3 pin Molex connector used on older fans.

The 4th pin is the PWM input signal. When pin 4 is connected to +12V (or unconnected) the fan motor runs. When pin 4 is connected to ground, the fan motor stops. Speed control is achieved by switching the PWM signal a few hundred times per second (varying the amount of time spent in the on and off states).

No current is taken by the fan on the PWM line - it's purely for control. Motor power comes from the standard +12 V line.