Which case, CPU, or other fan should you buy? Nov 2009

Computer fans can be purchased that are either 3 pin, 4 pin, variable speed, temperature controlled, and various other types.  Therefore, how does one know which one to buy?

When you look at the motherboard diagram below, you will notice that there are a total of 5 fan connectors.  2 are 4 pin while 3 are 3 pin and they are used differently.

NOTE:  For those wondering where these pictures came from, these are from the  motherboard user’s manual that comes with the motherboard.  If you do not have a user’s manual for your motherboard, the user’s manual can usually be downloaded from the motherboard manufacturer’s website.  You will have to know the model number of the motherboard which is written on the motherboard if you are trying to download the user’s manual.

GA-MA790FXT-UD5P Layout

When you look at the 4 pin CPU_Fan and the 4 pin Sys_Fan on the diagram below, the 4th pin is used differently.  The CPU_Fan’s 4th pin is for speed control while the Sys_Fan 4th pin is reserved.  Reserved probably means that it does nothing yet.

One could try attaching a 4-pin fan to see if PULSE_WIDTH MODULATION, which is supposedly a more energy efficient way to run the fan vs the standard method,  does work.  Although, one will have to purchase a PWM fan, which has 4 pins to test with.

GA-MA790FXT-UD5P fans

Strangely enough for this motherboard, pin 2 provides both power and speed control.  Therefore, is the 4th pin still required?  I sent an email out to a motherboard manufacturer for clarification.  Hopefully, I will get a response soon.

This is the answer I got from Gigabyte:

Only pin 4 controls fan speed, if you connect an 3 pin fan you will not be able to take advantage of fan speed on the board

The question I asked:

The CPU fan header on the GA-MA790FXT-UD5P has 4 pins.  Pin 1 is ground, Pin 2 is 12V/Speed control, Pin 3 is sense, and Pin 4 is speed control.

Is pin 2 speed control the same as pin 4 speed control?  If it is, can I connect any 3 pin fan to the CPU header, and the fan’s RPM will decrease and increase as needed?

I then asked another question since the customer service representative did not answer the 2nd part of my question.  Therefore, I asked the question again.  This is the answer from Gigabyte relating to the 3 pin Sys_Fan1:

The 3 wire fan will not increase of decrease speed; it will be consistent on the speed and will not be controlled by the heat sensor. There is a reason why the 4 pin is on the connector and that’s what controls the speed which comes from the heat sensor.

This is the question I asked:

The Sys_Fan1 header has 4 pins.  Pin 1 is ground, pin 2 is +12V/Speed control, pin 3 is sense, pin 4 is reserve.

Will a 3 pin fan increase or decrease in speed depending on the temperature detected by the motherboard?  I am assuming that pin 2 has speed control and will vary the speed of the fan connected to it.

I am also assuming that pin 4 does nothing also.

For the purpose of reducing noise, one should purchase a 4 pin fan for the CPU.  The CPU fan can slow down or speed up as needed to keep the temperatures ambient.  Therefore, a high RPM, 4 pin fan should be used here.  Currently, 2000 RPM fans are widely available.  A 3 pin fan in this connector causes the fan to run at full speed all the time, but depending on pin 2, this may no longer be the case.

With that said,  the Sys_Fan1 is identical to the CPU_Fan except that the 4th pin is not used yet.

NOTE:  Apparently, the Sys_Fan1 does  speed up or slow down the fan on my Gigabyte motherboard.  My intake fan that spins at about 1200RPM’s is currently running at 834RPM’s.

Fan speed and temps 2009

Sys_Fan2 and the Pwr_Fan both run at full speed since there is no  speed control.  Therefore, a fan should be used here that has noise levels that one is comfortable with.

Pin 3 is labeled sense.  Its purpose is to allow the motherboard to detect the fan’s RPM.  There is software available that will allow a user to view the various fan’s installed RPM.  The motherboard’s BIOS uses this information to detect if the installed fan is broken.  If the motherboard detects that the fan’s RPM is O RPM, and the BIOS is set up to detect fan failure, a warning message will be printed on the screen for the user.  This will enable a user to fix the problem if it is serious.

My BIOS is set to no warning; therefore, a fan failure will not result in an error message.  Although, I still monitor the fan speeds using Gigabyte’s fan monitoring software.

NOTE: The Pwr_Fan is designed to be connected to the power supply to monitor the power supply’s fan speed.  Depending on the power supply that one has bought, it may or may not have this connector.  Therefore, it can be used in 1 of 2 ways.  A power supply fan monitor, or an additional fan connector.

The NB_Fan is there for the sake of mass production.  It is faster and quite possibly cheaper to build all motherboards with the same components.  I believe that all similar motherboards are built the same way, so some stuff are added but not used.

Since this motherboard does not have a Northbridge fan(NB_Fan), this connector can be used to add a 5th fan to the computer.  Unfortunately, there is no way for the motherboard to sense the speed of the fan used here.  Pin 3 is NC which, I assume, is not connected(NC).

Therefore, to summarize what should be used:

  1. CPU_Fan – Any 2000 or faster RPM 4 pin fan.  The motherboard will change the speed as needed.
  2. Sys_Fan1 – Any 1200 RPM or slower 3 pin fan.  One will have to test to see if the 2nd pin actually does vary the speed depending on the temperature detected by the motherboard.  Every motherboard manufacturer may be different.
  3. Sys_Fan2, Pwr_Fan, and NB_Fan – Any 1200 RPM or slower 3 pin fan that will run at maximum speed.  If one wants a fan that slows down and speeds up as needed, a fan with built-in temperature control maybe a better alternative.  Unfortunately, this fan is more expensive.  Antec’s SmartCool can be seen at http://store.antec.com/Product/cooling-cooling_fan/120mm-smartcool/0-761345-75012-7.aspx.  I purchased one, but ran into some problems with it.  My results can be seen at http://aprivatebeach.com/blog/2009/11/antec-smartcool-120mm-problems/.
  4. A fan controller can be used to speed up or slow down various fans.  The list of various fan controllers that can be used can be seen at http://aprivatebeach.com/blog/2009/11/speed-up-slow-down-various-computer-fans/

For 120mm case fans, 720 RPM fans are the minimum I recommend.  Although slower and quieter ones are available, they barely push any air.

For 80mm case fans, 1400 RPM are the minimum I recommend.  Although slower and quieter ones are available, they also barely push any air.

NOTE:  1200RPM 120mm fans are said to be quiet and push enough air.  Of course, there are probably people out there who have purchased 4600RPM 120mm fans that would probably fly if not tied down.  Furthermore, I am pretty sure people in the room next door will hear your computer running.  4600RPM fan can be seen at http://www.sidewindercomputers.com/de12tfexhisp.html

These low RPM fans are much more expensive than the faster RPM fans.  Therefore, it maybe a better option to purchase a fan controller (http://www.scythe-usa.com/product/acc/028/km01_detail.html)  with cheaper high speed fans.   One may find that the price for a fan controller and 3 common RPM case fans will be similar to the price of purchasing 3 low RPM case fans. Furthermore, one can speed or slow down the fans with the knobs on the fan controller.

Before one goes out to purchase a fan, one must know how to read the data provided with every fan.

The data below is something you will typically see.  I will highlight the parts that are important.
Voltage 12VDC
Current (Ampere) 0.07A
Input (Watt) 0.84W
Speed (R.P.M.) 1200 R.P.M. + / – 10% – This is the maximum speed of the fan.  This number can vary anywhere from 900 to 2500 R.P.M’s.  A connector that has speed control can reduce the speed if needed.  Therefore, maximum speed is only reached if the temperature is above ambient.

For those that fan connectors that do not have speed control, the fan will always run at maximum speed.  In this case, the fan will always run at 1200 R.P.M’s.

Air Flow (CFM) 44.03 CFM + / – 10% – How much air is being pushed by the fan.  A higher number means more air is being pushed.
Air pressure (mmH2O) 1.83 mm H2O + / – 10%
Fan Noise Level (dB-A) 19.8 dBA – How much noise the fan makes at maximum speed.  under 25 dBA is considered silent while under 20 is considered noiseless.  This fan is rated noiseless, but manufacturers are known to state their fans quieter than they really are.  Therefore, one will have to use his/her own judgment.  A general rule is that the faster the fan spins, the more noisier it will be.
Weight 120g
Available Color Black
Bearing Type: Sleeve – These come in two types:  Sleeve and ball bearing.  A Google search will give many results that will help, but I will provide one for those lazy people.  http://www.frostytech.com/articleview.cfm?articleID=193
Connector 3 pin – This is a 3 pin fan, therefore, this fan does not have the 4th pin for speed control.
3 to 4 pin Adapter 1 piece – This is an adapter to a power supply.  This 3 pin fan can be connected to a power supply if one does not want to connect this fan to the motherboard.  This does not convert a 3 pin fan into a 4 pin fan.

An article that goes in depth about the different types of fans and the terminology used:  http://www.fantronic.com/case_fan_guide.html

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