Opinions on PWM

[ekoostik]

What are the advantages and disadvantages of PWM case fans?

I'm looking at these 2 Scythes (120mm), and one of the differences is PWM:
Kama http://www.microcenter.com/sin...tml?product_id=0262707
S-Flex http://www.microcenter.com/sin...tml?product_id=0253411

I know there are other differences. But if I was using PWM as a deciding factor, is PWM a good thing or not? Why or why not?

 

[Rubycon]

PWM gives you much better control of the fans speed through the motherboard's own PWM four pin header. External four pin controllers will also allow for turn on at nearly single digit speed and smooth control until top RPM, etc.

 

[Modelworks]

Go with PWM if that is the only difference. Fans without it are designed with one voltage in mind and while they may work at different voltages , they also may not. The reason PWM was put on fans is because without it , it is hard to make a fan turn really low by dropping the voltage to 5 volts then fast at 12 volts . Usually the fan will stop completely at the lower voltage.

 

[Tullphan]

What are the best application for these PWM fans? Intake? Exhaust? HSF?

 

[zerogear]

I always use PWM for cpu fan, everything else, I use voltage controller (fan controller) manually.

 

[ekoostik]

Originally posted by: zerogear
I always use PWM for cpu fan, everything else, I use voltage controller (fan controller) manually.

Since this is for a case fan and I'm not planning on getting a voltage controller - is it still ok to hook up an intake PWM fan since I'm not getting a manual controller? Based on the other replies, it looks like the answer is yes.

 

[PM650]

Originally posted by: ekoostik

Originally posted by: zerogear
I always use PWM for cpu fan, everything else, I use voltage controller (fan controller) manually.

Since this is for a case fan and I'm not planning on getting a voltage controller - is it still ok to hook up an intake PWM fan since I'm not getting a manual controller? Based on the other replies, it looks like the answer is yes.

If you're planning on connecting the fan to a PWM mobo header, you may have to change settings to get it to run at 100%, depending on the board. Otherwise, connecting the PWM fan to any standard 3-pin header will cause it to run at 100% (PWM/blue wire is left unconnected).

 

[Cookie Monster]

Originally posted by: Tullphan
What are the best application for these PWM fans? Intake? Exhaust? HSF?

The only difference between a PWM controlled fan and your standard fan is that controlling the fan speed via PWM is the best.

With PWM you have the ability to control it realtime (adjust speed according by varying the duty cycle when heat rises for instance) and provides more flexibility when it comes to selecting the desired speed.

 

[CurseTheSky]

In the case of those two fans, there's one even more drastic difference - the Kama is a (cheap) sleeve bearing, while the S-Flex series use S-FDB.

Generally speaking, sleeve bearings are inexpensive, but can also be noisy. They also tend to wear out somewhat quickly when mounted horizontally (parallel to the ground). S-FDB fans are much more expensive, but having used one myself, they're significantly quieter for a given amount of air flow. Sleeve bearing fans often emit a buzz or whine from the motor / bearing, while I can't hear anything other than rushing air from my S-Flex.