- Fan control
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Fan control is the management of the rotational speed of an electric fan. There are many types of electric fans and many types of fan controls. This article principally describes the control of a computer fan, to provide adequate cooling while lowering noise.
Contents
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 with the fifth power of the fan[1] 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 have at least two pins on the connector. These two pins connect to the fan motor, usually a brushless DC type. Extra pins may be present, with either or both of the following features:
- A tachometer that measures the actual speed of the fan as a pulse train, frequency being proportional to speed.
- Control of fan speed using PWM (Pulse-width modulation.)
Two-pin fans operate either as an on/off fan, or can be controlled by varying the voltage.
Fans will have either two, three, or four pins on the connector.
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, 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. Since the voltage drop is proportional to the current, the fan may not start. They need to be of the appropriate power rating. 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 output to the fan. You can use a silicon diode with a fixed voltage drop of about 0.7V per diode. The power rating should be noted.
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 +12V rail, producing a total of +24V.[2] 24V can destroy the fans, other options are 17V and 15.3V.
Pulse-width modulation
Pulse-width modulation (PWM) is a common method of controlling computer fans. A PWM capable fan is usally connected to a 4-pin connector (pinout: Ground, +12V, sense, control). The sense pin is used to measure the rotation speed of the fan and the control pin is a open-drain or open-collector output, which requires a pull-up to 5V or 3.3V in the fan. Unlike linear voltage regulation, where the fan voltage is proportional to the speed, the fan is driven with a constant supply voltage; the speed control is performed by the fan based on the control signal.
The control signal is a square wave operating at 25kHz, with the duty cycle determining the fan speed. Typically a fan can be driven between about 30% and 100% of the rated fan speed, using a signal with up to 100% duty cycle. The exact speed behaviour (linear, off until a threshold value, or a minimum speed until a threshold) at low control levels is manufacturer-dependent.[3]
Fan speed controllers
A fan controller with LEDs to indicate fan status and potentiometer and switch to control fan speed.
Another method, popular with 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 by which the software physically controls the fan is usually PWM (see above). Many companies now provide software to control fan speeds on their motherboards under Microsoft Windows.
- AOpen motherboards can use "SilentTEK".
- ASUS motherboards can use "Q-Fan".[4]
- MSI motherboards can use "Core Center".
- Universal abit motherboards can use "μGuru".
- Gigabyte motherboards can use "EasyTune 6".
- Intel desktop boards (older socket 478 etc.) use "Active Monitor" and "Desktop Control Centre".[5][6]
- Intel desktop boards (newer socket 775 etc.) use "Desktop Utilities".[7]
- Dell Inspiron/Latitude/Precision computers can use "I8kfanGUI".[8]
- Various computers can use the freeware "SpeedFan".[9]
Computers running Linux can use lm sensors.[10]
See also
References
- ^ http://books.google.co.uk/books?id=UocszU-e2WgC&lpg=PA341&ots=EMHJiQNH__&pg=PA341#v=onepage&q&f=false
- ^ "Overspin Your Fans", http://www.afrotechmods.com/fanmod.htm
- ^ "4-Wire PWM Controlled Fans Specification". 2005-09. http://www.formfactors.org/developer/specs/4_Wire_PWM_Spec.pdf. Retrieved 2011-07-21.
- ^ ASUS Q-Fan
- ^ [1]
- ^ [2]
- ^ [3]
- ^ Dell I8kfanGUI
- ^ SpeedFan
- ^ lm-sensors
External links
Categories:- IBM PC compatibles
- Computer hardware cooling
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