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Old September 27, 2010, 10:57 PM
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Xeven Xeven is offline
Join Date: Aug 2010
Location: Vancouver, BC
Posts: 483

No you don't need to worry about it that much. Just know that because of the method used to control the fans, some problems might occur with low-end fan controllers. Typically, really cheap controllers try to save on parts and remove the output stage filters (usually LC) on PWM controllers. Because of this, noise is transmitted through the fan assembly from the impulse torque generated by the active portion of the PWM cycle. A simple LC filter will fix this, but you have to add this on your own and because of the method to determine the RPM or duty cycle, some of these controllers detect fan stalls instead. You could then use a pwm to linear converter, but add all the costs and work you have to put in, just buy a damn good one from the start.

The only benefit to getting PWM fans is just that. It's built in and you can normally control it through software or bios. It normally has an internal transistor acting as a switch (FET) gated by the extra pwm line. Basically, the duty_cycle on the pwm line is the duty_cycle impressed on the fan, and the voltage across the fan is ideally Vin * duty_cycle. So why not just feed a linear voltage across the fan? It's a question of efficiency, given a supply voltage of 12V and a "running" voltage of 7 volts that means that if a fan draws 0.5 amps, then you waste ~0.5 * 5 = 2.5W. In a pwm, the fan is only active when needed and turned off the rest of the time allowing for very high efficiencies. The only downside is a higher BOM because of the pulse shaping needed for a proper signal. Hence, cheap manufactures try to "save" as much as they can by removing supposedly "unimportant" parts of the circuit.

Blah blah blah, I talk too much.

Originally Posted by homer98 View Post
Hey all ! Was just wondering, If I was to buy a fan controller, not sure which one yet but doesnt really matter for this topic, do I need PWM designated fans? or can any fan be used with fan controllers?

Also, is there any benefit to having PWM fans if it isnt needed for fan controllers?? any insight would be greatly appreciated,


PSXeven. Batards of the World Unite!
The gap between happiness and utter misery is only but a few inches

Last edited by Xeven; October 5, 2010 at 11:26 AM.
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