Centrifugal Switch

A centrifugal switch is an electrical switch powered by the centrifugal force created by a rotating shaft. This
centrifugal force is typically provided by a gasoline engine or electric motor. Centrifugal switches are designed to
activate or deactivate the rotational speed of the shaft.
How do Centrifugal Switches work?
A centrifugal switch is an electrical switch normally found in signal phase induction motors and split-phase
induction motors. This switch is used to provide a controlled switching operation that is required in the engine
when the specified engine speed is generated. The centrifugal switch is based on the concept of centrifugal
force. It’s just an electric switch. These switches are specially designed for induction motors in single and split
phases. As its operation is identical to that of a centrifugal clutch used in vehicles, the centrifugal switch is
generally known as a ‘clutch’. A single-phase AC engine has a centrifugal switch inside its case, which is attached
to the engine shaft. When the engine is off and motionless, the switch is closed. When the engine is switched on,
the switch drives electricity to the capacitor and the extra coil winding in the engine, increasing its starting
torque. As the engine’s revolutions increase per minute, the switch opens, as the engine no longer needs a
boost. A centrifugal switch solves a problem associated with single-phase AC electric motors. They do not
develop enough torque on their own to start turning from a dead stop. A circuit switches on the centrifugal
switch, providing the requisite boost to start the motor. The switch turns off the boost circuit until the motor
reaches its running speed, and the motor runs normally.
Centrifugal Switch Symbol : A centrifugal switch is a type of switch and it can be represented by an electronic
symbol. An electronic symbol is a pictogram used in the schematic diagram of an electrical or electronic circuit to
represent various electrical and electronic devices or functions, such as wires, batteries, resistors and transistors.
A switch is an electrical feature in electrical engineering that can disconnect or connect the conducting route in
an electrical circuit, disrupt or redirect the electrical current from one conductor to another.
How to Test a Centrifugal Switch?: Always it is better to test the centrifugal switch before using it for
applications. The following criteria should be met by an ideal centrifugal switch:
 Throughout its life cycle, the process should be uniform.
 For simplicity of design and low production cost, the number of components should be minimal.
 It should have marginal elements of friction.
 Without causing any significant design changes, the cut-out/cut-in ratio should be readily modifiable.
 The switch is accessible as the communication unit of the switch is present on the outside of the motor
frame. So, without dismantling the motor assembly, the switch can be tested, washed, and replaced.
What happens if the centrifugal switch does not open? : If the start switch does not open when it is needed, the
start winding will overheat and flame out, and the engine will not start next time. If the centrifugal start switch is
not closed, the engine will overheat the main winding without any main winding failure. The centrifugal switch
should be disconnected at about 70 to 80 per cent of the full speed of the engine. If it is not disconnected, a
heavy current will continue to flow through the starting winding of the engine, which eventually results in the
failure of the starting winding and engine. Also, the speed and the current cannot reach its maximum.
A centrifugal switch is an electrical switch that operates using the centrifugal force generated by a rotating shaft,
most commonly an electric motor or a gasoline engine. Here, the switch is used to disconnect the starting
winding of the engine as soon as the engine is approaching its normal operating speed.
There is no centrifugal switch so that the start winding becomes an auxiliary winding when the engine reaches
running speed, making it essentially a two-phase motor. They are considered to be the most reliable single-phase
motors because there is no centrifugal starting switch.
Centrifugal Switch in Induction Motors : To understand how this switch works in induction motors, let us first
understand the model of induction motors. Induction engines consist of the single stator winding and auxiliary
winding. A single-phase AC current is applied to the winding of the stator. But the single stator winding cannot
produce enough of the rotating field needed to generate the starting torque. As a result, an auxiliary winding is
provided. This auxiliary winding generates a field that is out of phase with the field generated by the winding of
the stator. The resulting field, therefore, produces a starting torque and starts the engine. Once the engine is
started, the rotor sets up a pulsating field that does not include the stator filed.
Centrifugal Switch in Induction Motor.
In all common induction motor which is used in drill presses, furnaces, table saws, pumps, grinders, washers and
dryers, the centrifugal switches are used together with an additional winding to start the motor. Single-phase
induction motors require the start of auxiliary circuits. In very small engines like cooling fans, they can be on the
circuit at all times. But it wastes electricity, and it generates heat. This is tolerable in a small engine, but above
1/10hp or so it becomes attractive to turn off the starting circuit after the engine is spinning. A centrifugal switch
is used to do this. The common induction motor for the single-phase cannot begin on its own, it only sits still and
noisy for about 30 seconds and then burns the isolation off the coils. So we have to start, and that’s where the
centrifugal switch and the extra winding come in. The engine starts happily on its own with an extra winding.
However, this must be turned off before maximum speed is reached; otherwise, the initial winding would burn
off, as the subsidiary winding is only planned for a few seconds. Three factors can be seen during engine
operation. The force of the spring decreases linearly. At the rate proportional to the rotor speed the centrifugal
force increases. The weight radius will be increased.

Centrifugal Switch in Single-Phase Induction Motors : Generally, the capacitor-start capacitor-run split-phase
motor does not contain a centrifugal switch to disconnect the starting winding. There is a cage rotor for the
Capacitor Start Capacitor Run Motor, and its stator has two windings, known as main and auxiliary windings. In
space, the two windings are shifted 90 degrees. In this system, there are two capacitors, one of which is used at
the time of start and is known as the starting capacitor. The other one is used to operate the motor continuously
and is known as a working condenser. So this engine is called Capacitor Start Motor Run Capacitor Run. This
motor is also known as the Two Value Capacitor Motor. In the below-shown figure, there are two capacitors in
this motor represented as start capacitor and run capacitor. Split-phase induction motor in which the capacitor is
permanently connected. It does not require a centrifugal switch. It also has a cage rotor, similar to that of a
Capacitor Start and Capacitor Start Capacitor Run Motor, and the two windings called as main and auxiliary
windings. It has only one capacitor with the starting winding connected in series. At both the starting and
running conditions, the capacitor C is permanently attached to the circuit. It is also called the Capacitor Motor
Single Value. Since the capacitor is still in the circuit, no starting switch is given for this type of motor.
Applications of a Centrifugal Switch : This switch is often used in systems where speed detection in systems is
necessary for the computer to be safe and operate properly. The following are some of the uses,
 Defense against Overspeed in motors, generators, etc.
 Used in DC motors, conveyors, escalators, lifts, etc.
 These are also used in devices such as blowers, fans as well as conveyors to detect under-speed.
 Material losses are often used in systems where the loss of speed could lead to damage of the device.
 ROTARY SWITCH

A switch is a device designed to disconnect electricity from a circuit. It can close or open a circuit. All
electrical and electronic applications use one or more switches to turn a device on and off. Therefore, the switch
is part of the control system and cannot be controlled without it. The switch has two functions: fully ON (closing
the contact) or fully OFF (opening the contact). The switches are divided into electronic and mechanical switches.
This article describes the working principle, circuit diagram, types, and interfacing of one of the types of
mechanical switches called a rotary switch.
Rotary Switch Definition: Rotary switches are multifunctional electromechanical switches that can be a great
alternative to pushbutton switches. Designed to rotate and turn 360° or move to the next position with an
internal rotating pin that allows the cap to rotate. The main characteristic of rotary switches is that they can be
used to control different circuits or controls with a single switch. These switches are available in various sizes,
shapes, and materials. Rotary switches are used to connect the functional circuit of the device to the power
supply. The electrical charge enters the switch and then transfers to the circuit currently selected by the switch.
Unlike software systems such as touch screens, rotary switches are a powerful machine control system that
provides immediate tactile feedback. In some cases, software bugs can be dangerous or cause serious problems.
Some of the more popular applications of rotary switches are variable speed fans, rotary light switches, dimmers,
professional audio splitters and converters, 3-way rotary and 6 position rotary switch guitars to switch between
different effects and tones, handheld radios to switch between different bands and channels, voltmeters and
similar gauges, car dashboards for adjusting functions of air conditioning or fans, Aircraft control panels, Various
industrial, medical, construction and military communication devices, e.g. speed control of conveyor belts,
frequency control of oscilloscopes, control of diagnostic equipment. Used to connect a line to one of several
lines. Examples of such switches are range selectors in electrical measuring equipment, channel selectors in
communication equipment, and band selectors in multi-band radios. It consists of one or more moving contacts
(called buttons or knobs) and one or more fixed contacts. This switch can be used on different contact point
configurations such as 12-way single-pole, 3-pole 4-way poles, 2-pole 6-way, and 4-pole 3-way.

Consider an application of brightening the lamp using the Double Pole Single Throw Rotary Switch (DPST rotary
switch). The circuit diagram of the DPST rotary switch for glowing the lamp is shown in the figure below. Note
that the Pole represents the switching function of the number of circuits. While the no. of throws represent the
no. of states to which the current can flow through the switch. The DPST rotary switch consists of 4 terminals: 2
input contacts and 2 output contacts. It works like two separate SPST rotary switch configurations operated at
the same time. Although there is only one ON position, each input contact can be connected to the
corresponding output contact by activating both contacts at the same time. In the OFF position, both switches
are open. This type of switch is used to control two different circuits at the same time. In addition, the contacts
on this switch can be configured as normally open or normally closed. When the switch contacts are closed, the
switch creates a closed path through which current flows, so the load absorbs the energy from the source. Then
the lamp glows. When the switch contacts are open, no power is absorbed by the load.
Another important function of this switch is to divert the current flow in the circuit. Consider the second circuit
as shown above to operate the motor and glow the lamp at the same time using the rotary switch.
 Rotary Switch Working Principle : The basic rotary switch working principle. Even though various designs and
configurations are available, they all have the same basic design, such as a spindle or a rotor. As the spindle
rotates on its axis or shaft, the spoke moves to different positions, making contact with the corresponding
electrical terminals and activates a connected circuit or changes an electrical state (for example, from on to off
state). This circuit passes through a circular component called a wafer. Several circuits can be connected in one
place. Most rotary switches have a star or notch-designed wheel rather than a smooth surface. This avoids
stopping in an. intermediate position between contact points or terminals. For the same purpose, a spring
mechanism called a detent can be installed. The terminals are usually placed around the spindle at fixed rotation
intervals (usually 30°, 45°, 60°, and 90°). This angle determines the number of available switch positions. The
number of user-selectable positions can be limited by some rotary switches by inserting washers into specially
designed slots. For example, if you need a 12 position switch, switch to a 4 position switch.
Advantages and Disadvantages
The rotary switch advantages are:
 This switch can make circular movements and can stop or interrupt in various positions.
 These are designed to operate multiple contacts simultaneously using the same switch position.
 This device has several advantages over other switches because the rotation of the actuator can turn the
circuit on or off depending on the position, and allows for different actuation positions.
The rotary switch disadvantages are :.
 Rarely used as complex switching tasks are performed using digital devices such as touch screens.
 The switches are still used, especially in devices where damage to the computer could be a security risk.
 Cost is more.
 More issues in broadcasting.
 Wear out of mechanical component with time.
 Physical contact is necessary.

Symbol Description

Single Pole, Single

Throw (SPST) Switch

Single Pole, Double

Throw (SPDT)

Double Pole, Single

Throw (DPST)
Symbol Description

Double Pole, Double

Throw (DPDT)

Three Way Switch

Four Way Switch

Float Switch

Thermal Magnetic
Switch
Symbol Description

Limit Switch Limit

Switch

Differential Switch
Differential Switch

Pulse Control Switch

Pulse Control Switch

Rotary Switch Rotary

Switch
Limit Switch

Pressure Switch

Temperature Switch

Joystick Switch

Push Button Switch

Symbol Description

Bipolar Transistor

Power Diode

MOSFET Switch

SCR Switch

DIAC Switch

TRIAC Switch

IGBT Switch