Computer fan control

Fan control is the management of the rotational speed of an electric fan, typically a computer fan, to provide adequate cooling while lowering noise.

The Need for Fan Control

As modern PCs grow more powerful so do their requirements for electrical power. Computers convert most of this electrical power into heat generated by all major components.

Some early generation PCs did not need active ventilation. Power supplies eventually needed forced cooling, and soon took up the duty of cooling the rest of the PC with the ATX standard. The byproduct of increased heat generation is that the fan(s) need to move increasing amounts air and thus, need to be more powerful. Since they must move more air through the same area of space, fans will naturally become more noisy.

In fact, if one installs extra fans in a PC case, the noise levels can reach 70 dB. Since fan noise increases exponentially to the fan rotation speed, reducing rotations per minute (RPM) by a small amount potentially means a reduction in fan noise. This must be done cautiously, as excessive reduction in speed may cause components to overheat and be damaged. If done properly fan noise can be drastically reduced.

Fan Types

Common cooling fans will have either two, three, or four pins on the connector.

• Two-pin fans operate either as an on/off fan, or can be controlled by varying the voltage.
• Three-pin fans add a tachometer reporting wire so the controlling system can measure the actual speed.
• Four-pin fans add a fourth wire to control fan speed using PWM (Pulse-width modulation.)

Types of Control

No Control

The simplest method of fan control is simply to leave the fan on all the time. This creates quite a bit of noise and increases power requirements, but keeps the system the coolest.

Thermostatic

In this style of fan control, the fan is either on or off. A system thermistor checks the temperature inside the chassis, and if it detects a temperature outside of range, it spins the fans up to maximum. When the temperature drops below a threshold again, the fans are turned back off. This control method reduces power requirements during periods of low usage, but when the system is operating at capacity, the fan noise can become a problem again.

Linear Voltage Regulation

A standard cooling fan is essentially a bladed DC motor. By varying the voltage input across the acceptable range for a fan, the speed of the fan will increase (to added voltage) and decrease (to reduced voltage). A faster fan, obviously, means more air moved, and thus a higher heat exchange rate. There are a few ways to perform this regulation:

Resistors

Resistors are the simplest method of reducing fan noise but they add to the heat generated inside the computer case. They need to be of the appropriate power rating (i.e. higher than the fan). For variable fan control, potentiometers could be used along with a transistor such as a MOSFET whose output voltage is controlled by the potentiometer. It is possible to use a rheostat instead.

Diodes

A diode in series with the fan will reduce the voltage being outputted to the fan. You can use a zener diode (select one for the desired voltage drop) or a silicon diode (Produce the required voltage drop by connecting multiple diodes in series. Each diode reduces the voltage by approximately 0.75 volts.)

Voltmodding

Voltmodding describes the practice of varying the voltage fed to a component, in this case, a computer fan. This can be achieved by connecting the ground wire of the fan to the +5V rail and the positive wire to the +12V rail of a typical PC power supply to achieve a theoretical +7V (positive seven volts). However, this is a potentially risky method: the parts on the +5V power line might be exposed to overvoltage in case of a short in the fan. A less common variation is to increase the voltage to the fan by connecting the ground wire to a -12V rail (located on the motherboard ATX connector) and the positive wire to the 12+ rail, producing a total of +24V.

Pulse-width modulation

Pulse-width modulation (PWM) is a common method of throttling fans, but has a big disadvantage if used to silence fans. If the frequency used is in the audible frequency-range of 20-20,000 Hz, it will be transmitted via the fan, acting like a loudspeaker in which the motorcoils and the fan blades act as coil and membrane of the speaker respectively.

Unlike the linear methods above that are based on voltage loss, PWM switches the input voltage between (nearly) fully on and fully off. This means there is practically no voltage or power loss and associated heat output. PWM controller can be a relatively small, low-power and cool-running, albeit complex, component that doesn't require heavy duty resistors, diodes or transistors and associated heatsinking.

Fan Speed Controllers

A fan controller with LEDs to indicate fan status and potentiometer and switch to control fan speed.

Another method, popular with the gamers, is the manual fan speed controller. They can be mounted in an expansion slot, a 5.25" or 3.5" drive bay or come built into the computer's case. Using switches or knobs, attached fans can have their speeds adjusted by one of the above methods.

Software

The method in which the software physically controls the fan is usually PWM (see above). Many motherboards now include software to control fan speeds.

• AOpen motherboards use "SilentTEK".
• ASUS motherboards use "Q-Fan".
• MSI motherboards have "Core Center".
• Universal abit motherboards use "μGuru".
• Gigabyte motherboards use "Easy Tune5".
• Dell Inspiron/Latitude/Precision fan control utility can be "I8kfanGUI".
• A freeware application is "SpeedFan".

See also

• Computer fan
• Computer cooling
• Quiet PC

External links

• Why and How to Control Fan Speed for Cooling Electronic Equipment