Centrifugal Switches and Prices in 2024

Centrifugal switches offer a valuable combination of simplicity, affordability, and adaptability, making them a popular choice for applications requiring automatic control based on rotational speed.The following is the basic product information, operating principles, application fields and product prices that everyone is most concerned about.

What Is A Centrifugal Switch

Centrifugal switches are essential components in various machinery. They are electrical switches that operate automatically, depending on how fast a shaft is rotating. Typically found in electric motors or gasoline engines, these switches play a crucial role in changing the motor's operating state when it hits a particular speed.

The Operation Principle Of Centrifugal Switch In Single-Phase Motor

The centrifugal switch in a single-phase induction motor plays a crucial role in getting the motor started and then transitioning it to normal operation. 

A single-phase motor is  a type of electric motor that uses a single-phase AC power supply to convert electrical energy into mechanical energy. Similar to three-phase motors, they have a stator (stationary part) with windings that generate a magnetic field and a rotor (rotating part) that converts that magnetic field into torque.However, unlike three-phase motors which have three windings to create a rotating magnetic field, single-phase motors have only one main winding.

Due to the single winding, they cannot generate a perfectly rotating magnetic field on their own. This presents a challenge in starting the motor.To overcome this, they often use a centrifugal switch or a capacitor to create a secondary, out-of-phase magnetic field during startup. This helps the motor achieve initial rotation and then the centrifugal switch disconnects the starting component for normal operation.

Operation:

1. Motor Start: When the motor is first turned on, the centrifugal mechanism is at rest because the motor shaft isn't spinning yet. The spring holds the weighted arms in a position that keeps the contacts closed. This allows current to flow through the starting winding of the motor, creating a rotating magnetic field.

2. Speed Increase: As the motor starts to rotate, the centrifugal force acting on the weighted arms increases due to their rotational inertia.

3. Switch Activation: Once the motor reaches a predetermined speed (typically around 75% of its operational speed), the centrifugal force overcomes the spring tension. This causes the weighted arms to pivot outward, pushing the contacts open.

4. Starting Winding Disconnect: With the contacts open, the current flow through the starting winding is interrupted. The motor continues to operate solely on the running winding, which is sufficient to maintain normal operation.

Which single-phase motors are not required centrifugal switches

Centrifugal switches are not required in all single-phase motors. Here are two common types of single-phase motors that don't use them:

1. Permanent Split Capacitor (PSC) Motor:

• This motor utilizes a capacitor that is permanently connected in the circuit. This capacitor creates a second, out-of-phase magnetic field with the main winding, similar to what the starting winding does with a centrifugal switch.

• Since the capacitor is always connected, the PSC motor is self-starting and doesn't require the additional mechanism of a centrifugal switch to disconnect the starting component.

• PSC motors offer higher efficiency and better starting torque compared to split-phase motors with centrifugal switches. However, they are also slightly more complex and expensive.

2. Shaded Pole Motor:

• This is a very simple and low-cost type of single-phase motor. It has a single winding with a shaded pole. The shaded pole is a section of the stator with a short-circuited copper ring placed around a portion of the pole.

• When the AC current flows through the winding, it induces eddy currents in the copper ring, creating a weak secondary magnetic field that is slightly out of phase with the main field.

• This slight phase difference is enough to provide a small starting torque for the motor to get going. However, shaded pole motors have very low starting torque and are generally used in low-power applications like small fans or turntables where a high starting torque is not critical.

Which single-phase motors must have centrifugal switches

Specifically, split-phase motors are the type of single-phase motors that must have centrifugal switches.

Here's why:

• Split-Phase Motor Design: A split-phase motor has two windings in its stator: a main winding and a starting winding. The starting winding has a higher resistance and fewer turns compared to the main winding.

• Starting Challenge: With only single-phase AC power, these motors struggle to generate a rotating magnetic field on their own.

• Starting Winding's Role: The starting winding creates a temporary, out-of-phase magnetic field with the main winding during startup. This helps the motor achieve initial rotation.

• Centrifugal Switch's Role: However, the starting winding is not needed for continuous operation and can even overheat if left engaged. Here's where the centrifugal switch comes in. It's a speed-sensitive mechanism that disconnects the starting winding from the circuit once the motor reaches a predetermined speed (typically around 75% of its operational speed). This allows the motor to run solely on the main winding for efficient operation.

Operation principle of centrifugal switch in split phase motor

The centrifugal switch in a split-phase motor plays a critical role in assisting the motor during startup and transitioning it to normal operation.

A split-phase motor is a type of single-phase AC induction motor that utilizes two windings in its stator (stationary part) to achieve rotation. Unlike three-phase motors with three windings, a split-phase motor has two windings:

• Main Winding: This winding is designed for continuous operation and provides the primary torque for the motor.

• Starting Winding: This winding has a higher resistance and fewer turns compared to the main winding. It's used to create a temporary boost during startup.

Due to the single-phase power supply, a split-phase motor, like other single-phase motors, struggles to generate a perfectly rotating magnetic field on its own. This makes it difficult for the motor to initiate rotation from a standstill.To overcome this starting challenge, the split-phase motor employs a centrifugal switch. This switch is connected to the starting winding and plays a crucial role in the starting sequence:

1. Motor Start: When the motor is first turned on, the centrifugal mechanism is inactive because the motor isn't spinning yet. The spring in the switch holds the contacts closed, allowing current to flow through the starting winding.

2. Starting Boost: The current flowing through the starting winding creates a magnetic field that is out-of-phase with the main winding's field. This interaction of magnetic fields helps the motor overcome inertia and begin to rotate.

3. Switch Activation: As the motor shaft gains speed, the centrifugal force acting on the switch's weighted arms increases. Once the motor reaches a predetermined speed (around 75% of its operational speed), the centrifugal force overcomes the spring tension.

4. Starting Winding Disconnect: This triggers the centrifugal switch to open the contacts, interrupting the current flow through the starting winding. The starting winding is no longer needed for continuous operation.

The Commonly Used Centrifugal Switches In 2024 And Their Prices

Centrifugal switches are still widely used in 2024, particularly in AC induction motors. There aren't necessarily specific models or brands to discuss as they are more functional components rather than consumer products. However, here's a breakdown of the common types you'll encounter:

1. Single-Phase Induction Motor Centrifugal Switch:

This is the most widely used type. It's a simple and reliable device used in single-phase AC induction motors to provide a boost to starting torque. The centrifugal mechanism is located on the motor shaft and consists of weights or flyweights that move outward due to centrifugal force as the motor speeds up. These weights are connected to contacts that interrupt the starting winding circuit when a specific speed is reached.

2. Two-Phase Induction Motor Centrifugal Switch:

Two-phase induction motors are less common than single-phase motors but still used in some applications. Their centrifugal switches function similarly to those in single-phase motors. The key difference is that they are designed to disconnect the starting capacitor or winding once the motor reaches operational speed. This helps improve efficiency and prevents overheating of the starting components.

The applications of single-phase and split-phase centrifugal switches are essentially the same because split-phase motors are a type of single-phase motor. Here's a breakdown of the common applications where you'll find these centrifugal switches:

Household Appliances:

• Fans: Ceiling fans, exhaust fans, and portable fans commonly use single-phase motors with centrifugal switches. The switch helps the motor overcome initial inertia and reach operational speed quickly.

• Refrigerators: The compressor in a refrigerator is often driven by a single-phase motor with a centrifugal switch. The switch ensures the motor starts and maintains the cooling cycle efficiently.

• Washing machines: The agitator or spin cycle in a washing machine might utilize a single-phase motor with a centrifugal switch for starting and maintaining the desired spin speed.

Power Tools:

• Drills: Many handheld drills rely on single-phase motors with centrifugal switches. The switch helps the motor achieve drilling speed quickly.

• Saws: Circular saws, reciprocating saws, and jigsaws commonly use single-phase motors with centrifugal switches for starting the blade rotation efficiently.

How Does A Centrifugal Switch Work

Here's a step-by-step explanation of how a centrifugal switch works:

1. Motor At Rest:

Spring Tension: When the motor is at rest, the springs hold the weights close to the center of the rotating shaft.

Contacts Closed: In this position, the cam or lever mechanism keeps the switch contacts closed, allowing electricity to flow (typically to a motor's start winding).

2. Motor Starts To Spin:

Centrifugal Force: As the motor shaft starts rotating, the weights are subjected to centrifugal force, which tries to pull them outwards, away from the center of rotation.

Initial Resistance: Initially, the spring tension is strong enough to counteract the centrifugal force, and the weights do not move significantly.

3. Critical Speed Reached:

Force Overcomes Springs: When the motor reaches a certain speed (usually about 75% of full speed), the centrifugal force becomes stronger than the spring tension.

Weights Move Outward: The weights start to move outwards, away from the shaft.

4. Switch Activation:

Cam/Lever Action: The outward movement of the weights pushes against the cam or lever mechanism, which physically changes the state of the switch contacts.

Contacts Open Typically, the contacts are designed to open at this point, cutting off the current flow (usually disconnecting a start winding for a motor).

5. Motor Continues Running:

Constant Outward Force: As the motor continues running at its operating speed, the centrifugal force maintains the position of the weights and keeps the switch contacts open.

6. Motor Slows Down:

Spring Takes Over: When the motor is turned off and starts to slow down, the centrifugal force decreases.

Weights Return: The spring tension pulls the weights back to their original position.

Contacts Close: The cam or lever mechanism allows the switch contacts to close again, ready for the next start-up cycle.

Several Applications Of Centrifugal Switches

Centrifugal switches have numerous applications in various devices and systems. Here's a breakdown of their common uses:

1. Electric Motors

Single-phase induction motors: Perhaps their most well-known application is within single-phase motors. Here, the centrifugal switch disconnects the starting winding once the motor reaches a predetermined speed (usually about 75% of full operating speed). This protects the winding from overheating and allows the motor to run efficiently on its main winding.

Other motor types: Centrifugal switches can also be found in some DC motors and universal motors, where they might serve similar functions of switching circuits or triggering speed-dependent actions.

2. Industrial Machinery And Equipment

Conveyors: Used to detect under-speed conditions in conveyor systems. If the conveyor belt slows down or stalls, the switch can trigger an alarm or shut down the system to prevent damage.

3. Escalators and Elevators: 

Ensure that these systems operate only within safe speed limits. The centrifugal switch can engage safety measures or shut down the system in case of overspeed scenarios.

4. Centrifuges and other rotating equipment: 

Utilized to control operation or provide safety features based on rotational speed.

 

Conclusion

Centrifugal switches are versatile components used extensively to automate safety and efficiency functions in various machines and systems that involve rotating parts. Their ability to trigger actions based on rotational speed makes them invaluable in diverse applications.