An In-depth Understanding Of Single-Phase Asynchronous Motors

Motors have become a significant part of our life with the advancement of technology. Research claims that 45% of global electricity is consumed by electric motors. It concludes that motors run from every household to commercial sectors. 

Single-phase asynchronous motors are widely used in domestic appliances and micro-scale industries. These motors are efficient, persistent, and cost-effective. Xinnuo Motor is China’s leading electric motor supplier that manufactures standard-quality single phase asynchronous motors. 

Figure 1 Single-phase Asynchronous Motors

Figure 1: Single-phase asynchronous motors

In this article, we will provide detailed knowledge of single phase asynchronous motors, their working, and their types. 

Here we go;

What are single-phase asynchronous motors? 

Single phase asynchronous motors are commonly known as “induction motors.” Single-phase asynchronous motors are perfectly suitable for the domestic setting because these motors offer satisfactory efficiency, reliable performance, and durability. Moreover, these motors are affordable and operate precisely without any malfunction. These motors do not have heavy-duty complex construction as three phase and industrial motors.

Check out our blog on 3-phase electric motors if you are interested in knowing more about them.

The working mechanism of single-phase asynchronous motors: 

The mechanism on which asynchronous motors operates is known as electromagnetic induction. Let’s understand the working principle of single phase asynchronous motors that make them superior to other domestic motors;

  • When AC is supplied to the single-phase motor, the alternating current begins to flow via the main winding. 
  • The alternating current produces flux called main flux because it originates from the main motor winding. 
  • The main flux connects with the squirrel cage rotor; thus, an emf is induced in the rotor of a single-phase motor. 
  • The main flux and rotor flux rotates the motors and produce torque to operate the single-phase motor. 
  • The frequency of rotating magnetic fields and rotor is not synchronized; therefore, these motors are named asynchronous motors. 

Why single phase motors are not self-starting? 

Single phase motors are not self-starting because they are unable to generate initial torque without an external power supply. These motors have low power factor and load capacity, which results in low efficiency and rotation speed.

A capacitor is the most commonly used device with single-phase motors to produce starting and running torque. Therefore, a capacitance device is connected in series with auxiliary winding to generate starting torque pulsations. 

For extensive knowledge about single phase motors, you can read our article on “Single phase electric Motor.” 

What are the different types of single-phase asynchronous motors? 

Single phase motors have four major types depending on their working and power source used in them. Let’s discuss these four types closely; 

1. Capacitor start induction motor:

Figure 2 Circuit Diagram of Single Phase Motor

Figure 2: Circuit diagram of single phase motor 

This type of induction motor has starting capacitor connected in series with auxiliary winding to help the motor generate initial rotations. When the speed of the single-phase induction motor reaches 75%, the start capacitor is switched off automatically. 

2. Capacitor start/Run induction motor:

The pulsating torque decreases considerably when the load on the single phase motor increase. For this purpose, a capacitor start/run motor is used to provide continuous rotation. A single phase tubular motors has both starting and running power source connected in series to ensure constant efficiency at high voltage load. 

3. Split-phase induction motor: 

The split-phase induction motors have a similar structure, but their auxiliary winding is placed outside stator coils. The auxiliary winding produces phase differences to induce starting rotations. Once the motor becomes self-starting, the main winding continues the rotation, and the starting winding becomes offset. 

4. Permanent split motor: 

Permanent split motors have a permanent running capacitor connected in series with auxiliary winding. It does not turn off via centrifugal switch after starting the motor. Instead, it provides constant power when the motor is running. 

Single phase asynchronous motor vs. synchronous motor: 

Asynchronous Motors 

Synchronous Motors

The speed of the rotor is less than stator magnetic fields.The stator and rotor run at synchronized speed. 
Single-phase asynchronous motors have slips ranging from 1% to 5% slip value.Synchronous motors do not have slip; thus, the value of slip remains zero.
Its speed decreases with the increase in load. The speed of synchronous motors is independent of load. 
Single phase asynchronous motors have a simple construction. These motors have complex internal construction.
These motors are affordable and demand less maintenance. Single phase synchronous motors are more expensive than an induction motor.

Table 1: Difference between single-phase asynchronous and synchronous motors

Applications of single-phase induction motors:

Single phase asynchronous motors have a diverse range of applications in the household setting. Some most common applications of single-phase asynchronous motors are discussed below. 

Let’s have a look;

  • Washing machines, refrigerators, and air conditioners  
  • Vacuum cleaners, grinders, and fan motors
  • Centrifugal pumps and blowers
  • Small household appliances 
  • Machining tools and small equipment 

Xinnuo Motor also offers various industrial motors, three phase motors, and OEM motors to its global customers. 


If you want reliable motors for a domestic setting, single-phase asynchronous motors are what you should choose. A single-phase asynchronous machine has outstanding features and protection; therefore performs for an extended period without costly maintenance. If you have any inquiries regarding electric motors, feel free to contact us. Our customer care is 24/7 responsive to address your queries and concerns. 

Single-Phase Asynchronous Motors-FAQs:

How do I change the direction of single-phase asynchronous motors?

Changing the direction of a single phase motor is not a hectic task. Following the described wiring connection, a person can easily change the direction of the motor. Here is how you can do it;

  • Connect the one end of the reverse forward switch with the starting capacitance device 
  • Link the other end of the device with the centrifugal wire of the motor. 
  • Now, connect the starting coil wire and running wire of the motor with the changing switch.
  • Connect the L and N pole of the main circuit with the switch box contrastingly to reverse the direction. 

Figure 3 Single-Phase Motor Wiring

Figure 3: Single-phase motor wiring 

Can I control the speed of the asynchronous motor? 

Yes absolutely! To achieve speed control, you can change the frequency or number of poles of the asynchronous motor. Once you have control over the applied voltage and frequency, you can regulate the speed of the motor. 

Scroll to Top