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· Registered
1,073 Posts
PWM fans can have their speed controlled by your motherboard's PWM capabilities and software like SpeedFan. If you have a fan controller it does not matter because fan controllers control voltage going to the fan and can change the speed on either kind of fan.

· Registered
1,662 Posts
PWM means pulse width modulation. PWM is when you pulse a DC voltage off and on. The pulses are going so fast that they do not turn the fan off and on. All the fan sees is the "average voltage".

For example: 12V going at a PWM of 50% is the same as 6V into the fan. 12V with a PWM of 75% is the same as 9V into the fan.

A PWM output looks like this


In a regular fan controller you use a voltage regulator to control the fan.

Example: If you want 6V, you give the fan 6V

Advantage VS Disavantages-

1.) PWM is more efficient. With a voltage regulator if you need 6V and have 12V, the other 50% of your power is completely wasted. (dissipated as heat) PWM systems are much more efficient and wast very little power.

2.) PWM is controlled digitially. PWM is also more accurate. Because it is controlled digitally, it is easy to control from your motherboard.
Originally Posted by The Master Chief;13109839
pwm can automatically adjust the fans RPM's depending on the temperature.
I could build a fan controller to automaticall adjust the fans RPM's without useing PWM. It just would all analog electronics. EDIT: Connect output of RTD sensor to opamp. Use opamp to control adjustable 12V voltage regular and wala! I know no one cares, but just sayin'.

· Premium Member
28,486 Posts
Hello there OCN and sorry for the stupid/noob question...
So, what's the difference between a regular and a PWM fan?
PWM controllers control the PWM signal from fan by pulsing it.
Almost all PWM fans work fine on variable voltage. This is basically because with PWM fans the PWM signal (powered from fan) is controlled by PWM fan header (on motherboard or fan controller. So if a PWM fan is plugged into a variable voltage header the PWM signal is open (because there is no PWM control) and fan gets constant power .. on 3-pin variable voltage fan header this is from about 5-12v to fan motor of both 3-pin variable voltage and PWM fans.
  • A PWM controller controls the PWM signal from fan by pulsing it.
  • When signal circuit is closed the fan motor's power circuit is off and when the signal is open the fan motor's power circuit is on .. for PWM this is 12v power.
  • So if a PWM fan is plugged into a variable voltage header the PWM signal is open (because there is no PWM control) and fan gets constant power .. for variable voltage this is variable from about 5-12v.

If you plug a variable voltage fan into a PWM header the fan only runs at full speed. This is because pin-2 on PWM header is 12v, while on a variable voltage fan header it is variable voltage varying from about 5v idle speed to 12v full speed.

Also if u have a fan controller which of those 2 types would u prefer?
Depends what fan controller you have. Most low and mid-level fan controller are not much good. They are totally manual controllers with very limited load ratings. Most users are much better served by using motherboard fan headers that regulate fan speed based on system temps, so fans slow down when system is idling like when surfing web and only speed up as needed when system works harder, like when playing games.

There are some very nice fan controllers that have PWM control. Noctua N A-FC1, aquaero 5 and aquaero 6 have PWM controls .. Aquaero also have variable voltage on some channels and have temperature to PWM% control like motherboard headers. Aquaero fan controllers are quite expensive, but they do almost anything you could ever want a controller to do .. except wash windows.

crimsontears809739 explaination is good. :thumb:

But percent of PWM is not same as percent of voltage or percent of fan speed. The pulse rate is not fixed at 50% to 50% PWM. It is whatever curve the fan company wants the fan to be programmed for. As you can see in the graph below the original TY-140 and TY-147 fans havd a different curve than Thermalright TY-147A. Original poo colored TY-140 was changed to black/white TY-147 wiht both having same idle to top speed. TY-147A changed the PWM to rpm curve was changed to idle at 300rpm and run a little slower at same PWM signal up to about 9[email protected]%, they the the curve progressively ramps up to same 1300rpm top speed.


More detailed information about PWM fans in link below:
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