How does an expansion bay fan controller work?

[Chemz11]

Never used one before, just assumed it only works on pwm fans. So how does it actually work? Does it work on all sorts of fans?

 

[alexoiu]

Some work with 4 pin, some with 3 pin fans, some with both. Just check the specs of the controller.
Ex: http://www.newegg.com/Product/Product.aspx?Item=N82E16811992005 - uses voltage control
http://www.newegg.com/Product/Product.aspx?Item=N82E16811992012 - PWM
http://www.newegg.com/Product/Product.aspx?Item=N82E16811992013 - both

 

[ssddx]

there are two kinds of front bay fan controllers.

digital versions which automatically regulate fan speed and voltages when you set certain values and manual versions which have knobs or sliders to manually adjust voltages to control fan speed.

as above, there are controllers which feature screens which tell you fan speed in rpm (which requires 4pin fans if you wanted to see this displayed) and those which do not which can use either 3 or 4 pin fans. in either case the speed of the fan is controlled by voltage regulation, the fourth pin just relays the rpm information. generally models which are manual and only have 3 pin connectors you can just overhang the plug and use 4pin fans as well just as you can use 3pin fans on the 4pin motherboard headers.