Centrifugal switch
Encyclopedia
A centrifugal switch is an electric switch that operates using the centrifugal force
Centrifugal force
Centrifugal force can generally be any force directed outward relative to some origin. More particularly, in classical mechanics, the centrifugal force is an outward force which arises when describing the motion of objects in a rotating reference frame...

 created from a rotating shaft, most commonly that of an electric motor
Electric motor
An electric motor converts electrical energy into mechanical energy.Most electric motors operate through the interaction of magnetic fields and current-carrying conductors to generate force...

 or gasoline engine. The switch is designed to activate or de-activate as a function of the rotational speed of the shaft.

Perhaps the most common use of centrifugal switches is within single-phase
Single-phase electric power
In electrical engineering, single-phase electric power refers to the distribution of alternating current electric power using a system in which all the voltages of the supply vary in unison. Single-phase distribution is used when loads are mostly lighting and heating, with few large electric motors...

, split-phase induction motor
Induction motor
An induction or asynchronous motor is a type of AC motor where power is supplied to the rotor by means of electromagnetic induction. These motors are widely used in industrial drives, particularly polyphase induction motors, because they are robust and have no brushes...

s. Here, the switch is used to disconnect the starting winding of the motor once the motor approaches its normal operating speed. In this case, the centrifugal switch consists of weights mounted to the shaft of the motor and held near the shaft by spring force. At rest, levers attached to the weights press a low-friction
Friction
Friction is the force resisting the relative motion of solid surfaces, fluid layers, and/or material elements sliding against each other. There are several types of friction:...

, non-conductive
Electrical insulation
thumb|250px|[[Coaxial Cable]] with dielectric insulator supporting a central coreThis article refers to electrical insulation. For insulation of heat, see Thermal insulation...

 plate against a set of electrical contacts mounted to the motor housing, closing the contacts and connecting the starting winding to the power source. When the motor approaches its normal operating speed, centrifugal force overcomes the spring force and the weights swing out, raising the plate away from the electrical contacts. This allows the contacts to open and disconnects the starting winding from the power source; the motor then continues operating solely using its running winding. Motors using such a centrifugal switch make a distinct clicking noise when starting and stopping as the centrifugal switch opens and closes.

A variation of the centrifugal switch used a changeover contact to ensure that the auxiliary windings remain in the circuit through a running capacitor. These motors are called two-value or capacitor start capacitor run motors.

Centrifugal switches were also used in early electric fans, particularly those made in the 1900s and early 1910s.

In aircraft, centrifugal switch is to control the starting and ignition circuit,the governed speed indication circuit and the overspeed protection circuit of AUXILIRY POWER UNIT. This switch is mounted inside a rotating body. This can be set to activate or deactivate a circuit as the rpm of device increases or decreases.
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