Single Phase Motor With Capacitor

Single phase electric motors are not self-starting; therefore, these motors have a limited range of applications. However, single phase motor with capacitors are widely used for various applications because it increases the torque and efficiency of the motor. Adding right capacitors can upgrade performance and working capacity of a single-phase motor. A capacitor improves the starting rotations and accelerates the overall torque rate of a motor. Xinnuo Motor is a leading electric motor supplier that delivers premium-quality affordable motors globally. 

Figure 1 Single Phase Motor With Capacitor

Figure 1: Single phase motor with capacitor

In this article, we will discuss a single phase motor with capacitor, its types, advantages, and drawbacks. Let’s get into it. 

Why do single phase motors need capacitors?

The pulsating nature and low power output of single phase motors are not advantageous for diverse applications; thus, single phase motors require capacitors for constant efficiency. A capacitor is a device that increases the efficiency of a single-phase motor. A capacitor provides the required phase difference; thus, the motor self-start and runs the winding current. A capacitor increases the power factor because a single winding cannot produce RMF itself. 

A capacitor in series is connected to the auxiliary winding to provide a 90-degree phase difference to produce a rotating magnetic field. A single phase motor with a capacitor generates high starting torque. The auxiliary and running winding voltage provides 90-degree displacement, which upgrades the running condition of the motor.

Types of capacitors used by single phase electric motor:

Figure 2 Circuit Diagram of Single-phase Motor with Capacitors

Figure 2: Circuit diagram of single-phase motor with capacitors 

An efficient capacitor can increase the low torque of single-phase motor during each revolution. A capacitor driven motor can maintain forward and reverse wiring connection by interchanging the terminals of auxiliary winding. A Single phase motor uses two types of capacitors. Let’s discuss them in detail. 

Start capacitor:

A starting capacitor is used to produce initial rotation in the single-phase motor. A Cs is connected in series with the auxiliary winding of the stator. These capacitors are used for a short period until the motor becomes self-starting. After producing the rotor speed of approximately 75%, the starting capacitor is disconnected from the circuit. 

Run capacitor:

This capacitor is connected to the winding to improve power output and efficiency. These capacitors are long-term and stay connected in the circuit. A single phase motor with capacitor Cr generates high and constant torque. 

Calculating the capacitor value for single phase motor:

If you are choosing a single phase motor with a capacitor, you should identify and calculate its capacitor value. Let’s find out how to calculate the capacitance and voltage value;

Value of capacitance:

The capacitance value is directly proportional to the power factor of the single phase motor. It also depends on various specifications like size, winding, and induction. However, to calculate the capacitor value for single phase motor, use this formula; 

C (µF) = P (W) x η x 1000) / (V(V) x V(V) x f)

Voltage rating:

The voltage rating is equal to the product of voltage (Vp) calculated at both ends of the windings and the number of turns between the main/auxiliary winding of the motor. 

The formula to accurately calculate the voltage rating for single-phase electric motor is given below; 

Voltage Rating= V (p) √ (1+n2)

Advantages and drawbacks of single-phase electric motor:

Some of the common perks and limitations of single-phase motors are as follows, 


  • It has a robust internal construction. 
  • Single phase motors do not require frequent maintenance and repairing. 
  • Single phase 10 HP motors provide high RMF and efficiency. 
  • These motors are long-lasting and cheaper than other motors. 


  • Single-phase motors are not self-starting; therefore, they need a capacitor to produce initial rotations. 
  • The PF rating of single phase electric motors is considerably low. 
  • It generates low torque during each revolution.  

Xinnuo Motor offers various types of cost-effective three-phase motors, industrial and OEM motors


If you are tired of the low efficiency of single-phase motor, choose single phase motor with capacitor. The capacitor driven motors are efficient and low power consuming; hence, it increases the average performance of single phase motors. For a free quotation, feel free to contact us. Our customer care team is 24/7 available to address your queries and concerns.

Single phase motor with capacitor-FAQs:

Can I run a single phase electric motor without a capacitor?

Yes, a single phase motor can work without a capacitor if it is not capacitor-driven. The specific type of single phase motor with capacitor cannot produce rotations without a capacitor. Therefore, you should always analyze the internal parts of single-phase motor before purchasing it. 

How do you wire capacitors to single-phase electric motors?

The wiring of a single-phase motor is simple and robust. To wire a single phase motor with capacitors, follow these steps;

  • Connect the terminal of running/starting winding with the terminal box of the motor.
  • Now, connect the capacitor with the U1 and V1 terminals of the motor.
  • Take a circuit breaker; connect the input main phase and the neutral wire.
  • Now connect the output of the circuit with the R terminal and neutral with the C terminal.
  • Open the switch box, and the wiring connection is maintained.

Figure 3 Motor Wiring Diagram Single Phase with Capacitor

Motor wiring diagram single phase motor with capacitor


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