AC Freezer Question: PWM Control

BillytheImpaler

BillytheImpaler

BillytheImpaler

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I'm looking to upgrade a friend's CPU cooler becasue her current one is far too noisy when the motherboard spools it up into "hot" mode. It's a skt754 3200+ with the stock cooler. I'd like to install an Arctic Freezer 64 Pro becasue of that cooler's high performance to cost ratio. However, I'm concerned about the PWM speed control that that cooler uses. Her mobo does not have PWM control, it only has the old-style 3-pin fan header for the CPU. How can I get the new-style fan to work on the old-style header? Can it be done without sacrificing low-speed operation when temps are low?
 
Big.Wayne said:
I just bought one of these, what is this 'new' feature then? :confused:
Click to expand...
If by "new feature" you mean PWM speed control...

It's a method of speed control. The old style would change the speed of fans by varying the voltage output from the header. This is a bit of a sloppy way of doing it as you can't get good speed control that way. It also limits how low you can go in terms of speed. For instance the highest speed is when output is 12V. In "quiet" mode where the fan does not need to be spooled up all the way it might drop the voltage down to 7V. You could not drop the voltage to, let's say, 2V becasue the fan wouldn't spin at all.

PWM is Pulse Width Modulation. Instead of lowering the voltage to less than 12v to go slower it turns on and off the 12V supply quickly. The longer you leave the power on, the faster it goes until it peaks at always-on. the less frequency or duration you leave the power on the slower it will go. You can achieve almost any speed lower than the fan's maximum using this method.
 
Can somebody test or 100% confirm that it will work by plugging the 4-pin plug into the 3-pin header? Which end should hang off? I'm lookin' at you Snapshot. ;) :p

Any time Mr. Wayne. :)
 
Cyber-Mav said:
pwm is risky by turning something on and off thousands of times a minute you could either blow it up or worse.
Click to expand...
Blow the fan up? PWM is used in motor speed controllers in industry the world 'round. I don't get it. :confused:
 
AFAIK, Wayne, the AC Freezer's fan has always been PWM controlled. Methinks when they say "new" they mean it's the new hotness style, not the old and busted 3-pin design.
 
As demonstrated by Snapshot above the fan will attach with one socket hanging off the end. It will behave just like a regular 3-pin fan would. You won't have PWM control though becasue your mobo doesn't support it. What Snapshot did to test if it would work by voltage control (as a 3-pin fan does) was stell his motherboard not to use PWM control but to use voltage control instead. It did and it made me happy.

EDIT: He did not use a 3rd party adapter. He just plugged it in using an extension cable to make testing easier. One pin will hang off the end of the header.

Care to take some photos to make the explanation easier, Snapshot?
 
Definitive source: http://www.formfactors.org/developer\specs\REV1_2_Public.pdf (pdf warning)

Code: 
Pin  Function  Wire Color
1    GND       Black
2    12 V      Yellow
3    Sense     Green
4    Control   Blue

formfactors.org said:
The PWM input shall be delivered to the fan through the control signal on Pin 4 (see Section 2.4).
Fan speed response to this signal shall be a continuous and monotonic function of the duty cycle
of the signal, from 100% to the minimum specified RPM. The fan RPM (as a percentage of
maximum RPM) should match the PWM duty cycle within ±10%. If no control signal is present
the fan shall operate at maximum RPM. See Figure 2.
Click to expand...

Pin 4 is essentially communicating with a relay in the motor that is switching the power on and off as it specifies by switching itself on and off.
 
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