Pulse width modulation (PWM) is the default choice for laptop and PC fan controllers on the circuit boards of computers from many leading manufacturers. Users can preset fans to run at certain times and speeds. This is an electrical timer controlling a set of switches. Time switch controllers make use of a timer switch. This reduces fan noise when usage levels are low. Sensors monitor the temperature within the chassis and switch the fan on or off according to predefined settings. Meanwhile, thermostatic models respond directly to temperature. The amount it can store is called its capacitance.Ĭapacitor-based models are typically smaller and provide fine, linear control of speed. A capacitor is a device which stores energy as an electrical charge. This means that no heat and energy are lost through electrical resistance. Capacitor-based models address this issue by increasing the speed of the fan when the voltage drops - and decreasing it when the power increases. However, this electrical resistance produces heat and so uses energy which could potentially match the energy saved by reducing the speed of the fan. Higher levels of resistance will reduce speed or switch off the fan altogether.

Adjusting the dial on the fan speed control switch aligns a conductor with a particular fan - a process called placing it in series - and the new level of electrical resistance then changes the power reaching the fan, and thereby its speed. These devices contain wire spools - conductors - with varying amounts of resistance to electrical current. They contain a wired controller circuit attached to an adjustable dial or toggle for changing the speed of the attached fans. Fan speed controllers can be divided into five key types.Ĭonventional models rely on electrical resistance.

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