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PWM fans?

post #1 of 11
Thread Starter 
So I'm really confused about the difference between the 4-pin fans and the 3-pin fans. So I heard that the 4th pin controls the fan's pulse according to the temperatures but I have plugged 3 pin fan in my motherboard which I also can control their speed. So correct my if I'm wrong but the conclusion is that the 4-pin ones use a different type of fan controlling (don't know which type) while the 3-pin ones are getting controlled by the voltage right? So both of them do the same job but in different ways..?
post #2 of 11
Quote:
Originally Posted by TheByt3 View Post

So I'm really confused about the difference between the 4-pin fans and the 3-pin fans. So I heard that the 4th pin controls the fan's pulse according to the temperatures but I have plugged 3 pin fan in my motherboard which I also can control their speed. So correct my if I'm wrong but the conclusion is that the 4-pin ones use a different type of fan controlling (don't know which type) while the 3-pin ones are getting controlled by the voltage right? So both of them do the same job but in different ways..?

that is correct. pwm adjusts the frequency at which the current for the fan "pulses" whereas in a 3 pin, the current is always on. you seem to have understood it already! thumb.gif
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post #3 of 11
Thread Starter 
Quote:
Originally Posted by rakunSA View Post

that is correct. pwm adjusts the frequency at which the current for the fan "pulses" whereas in a 3 pin, the current is always on. you seem to have understood it already! thumb.gif

Thank you for your reply, I wanted to see if I was right or not tongue.gif. Thank you once again
post #4 of 11
Quote:
Originally Posted by TheByt3 View Post

So I'm really confused about the difference between the 4-pin fans and the 3-pin fans. So I heard that the 4th pin controls the fan's pulse according to the temperatures but I have plugged 3 pin fan in my motherboard which I also can control their speed. So correct my if I'm wrong but the conclusion is that the 4-pin ones use a different type of fan controlling (don't know which type) while the 3-pin ones are getting controlled by the voltage right? So both of them do the same job but in different ways..?
Yup, you are correct... more info:


4-pin PWM = Pulse Width Modulation. It controls the fan speed by pulse the current at different frequencies.
1 - Ground
2 - 12V
3 - Sense for RPM
4 - Pulse

3-pin fan headers that can control fan speed do so by reducing voltage.
1 - Ground
2 - 12V (down to usually 5-7v)
3 - Sense for RPM


PWM have the advantage of more accurate RPM control since the fan's resistance curve does not matter as much.
PWM also allows for lower speeds. Many fans require around 5-7v to spin up so that is the lower limit of voltage controllers.
PWM also save power... marginally.
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post #5 of 11
Thread Starter 
Quote:
Originally Posted by DuckieHo View Post

Yup, you are correct... more info:
4-pin PWM = Pulse Width Modulation. It controls the fan speed by pulse the current at different frequencies.
1 - Ground
2 - 12V
3 - Sense for RPM
4 - Pulse
3-pin fan headers that can control fan speed do so by reducing voltage.
1 - Ground
2 - 12V (down to usually 5-7v)
3 - Sense for RPM
PWM have the advantage of more accurate RPM control since the fan's resistance curve does not matter as much.
PWM also allows for lower speeds. Many fans require around 5-7v to spin up so that is the lower limit of voltage controllers.
PWM also save power... marginally.

Thank you but let me ask something really stupid, is it possible to mod a 3-pin fan to a 4-pin one just to take advantage of the PWM? I'm pretty sure it's not possible but I'm asking anyway tongue.gif
post #6 of 11
no thats not possible
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post #7 of 11
Thread Starter 
Thanks!
post #8 of 11
Quote:
Originally Posted by TheByt3 View Post

Thank you but let me ask something really stupid, is it possible to mod a 3-pin fan to a 4-pin one just to take advantage of the PWM? I'm pretty sure it's not possible but I'm asking anyway tongue.gif

The fan itself must have the extra circuitry to read the PWM signal.

You could build a 3-pin to 4-pin adapter.... but why? thumb.gif
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post #9 of 11
Thread Starter 
Yes I imagined that it would need an extra circuitry but I also thought that maybe they already have it but it's just not connected tongue.gif. Anyway no I wouldn't build a 3-pin to 4-pin adapter I'm at least that smart to know that this would be totally useless tongue.gif
post #10 of 11
Quote:
Originally Posted by TheByt3 View Post

Yes I imagined that it would need an extra circuitry but I also thought that maybe they already have it but it's just not connected tongue.gif. Anyway no I wouldn't build a 3-pin to 4-pin adapter I'm at least that smart to know that this would be totally useless tongue.gif

Nope... fans are commodity parts and are quite simplistic. Extra circuits means higher cost and more chance of failure.
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