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Let say i want 40CFM push onto the cpu, how to manage it using ite smartguardian??

This is the spec of my fans

thats only a 25cfm fan you cant make it do 40 cfm

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For three pin fan header connectors the following applies:

The fan's red wire goes to the 12 volt source.

The fan's black wire goes to the ground pin.

The fan's yellow wire is the fans speed sensor.


For four pin molex connectors the following applies:

The fan's red wire goes to the yellow pin.

The fan's black wire goes to the black pin.

The fan's yellow wire is not connected to the 4 pin molex.


Not all of the motherboard fan headers are capable of speed sensing. Only three are. The CPU, Chipset, and there is one header near the CPU plug typically used for rear case exhaust. The pin layout of the motherboards fan header is standard as follows:

pin 1 is 12 volt source.

pin 2 is ground source.

pin 3 is speed sensor.


If you get a rheobus fan controller then you can modify your cables so that the speed sensor is still plugged into your motherboard. The speed sensor has nothing to do with controlling the speed of the fan merely reporting the speed. The variable voltage control on the three aforementioned fan headers is temperature based and can be controlled via the bios or by software such as Smartguardian/MBM5. The percentage control that is offered by some softwares is telling the percentage of the maximum voltage and not the percentage of RPM. Although the RPM is directly related to the voltage this is an additional equation not considered by the motherboards voltage dividers.


External rheobus fan controls have a higher wattage capacity which is often needed when employing 80~120mm fans with high current demands. By using the motherboard to vary the voltage you place demands on voltage dividing circuits that will generate heat. This reason alone is a very good idea to use external fan controllers. If you have low cfm, low current draw fans than the motherboard fan headers will suffice and not have to deal with excessive voltage drops along with the heat dissipation.


Anytime a fan is controlled using variable voltage a trade off exists somewhere in the system. That trade off is watts being dissipated by a capable power resistor or transistor. So the final question is where do you want the heat to be generated?


Hopefully this provides you with enough information about fan control.

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