Single-phase induction motors are widely used in domestic and industrial applications where only single-phase AC supply is available. These motors include Split Phase, Capacitor Start, Capacitor Start–Capacitor Run, and Shaded Pole types — each differing in starting method, torque, and efficiency. Understanding their comparison helps in selecting the right motor for your application.
Comparison Table of Split Phase, CSCR, CSIR, Shaded Pole Motor:
| Feature | Split-Phase Induction Motor | Capacitor-Start Induction-Run Motor | Capacitor-Start Capacitor-Run Motor | Shaded Pole Motor |
|---|---|---|---|---|
| Starting Method | Uses resistance in starting winding to create phase difference | Uses capacitor in series with starting winding for better phase difference | Uses one or two capacitors — one for starting, one for running | Uses shading coil on pole for phase displacement by induction |
| Phase Splitting Method | Resistance type (high R, low X) | Capacitor type (electrolytic, short duty) | Capacitor type (oil/paper type for continuous duty) | Inductive shading coil |
| Centrifugal Switch | Used to cut off starting winding at 75–80% speed | Used to disconnect starting winding and capacitor at 75% speed | Not required (capacitor and both windings remain connected) | Not used |
| Starting Torque | 150–200% of full-load torque | 300–450% of full-load torque | 200–250% of full-load torque | Very low (only 30–50% of full-load torque) |
| Starting Current | 6–8 times full-load current | 4–5 times full-load current | 3–4 times full-load current | 1.5–2 times full-load current |
| Running Torque | Moderate | Good | Excellent (optimum starting and running) | Poor |
| Power Factor | 0.6–0.7 lagging | 0.75–0.8 lagging | 0.85–0.9 (high) | 0.3–0.5 lagging |
| Efficiency | Moderate | Better than split-phase | Highest among all single-phase types | Lowest |
| Speed Regulation | 2–5% (nearly constant speed) | Nearly constant | Very good | Poor |
| Noise and Vibration | Moderate | Quieter | Very quiet and smooth | Noisy at times |
| Cost | Moderate | High | Highest | Very low |
| Maintenance | Easy | Requires switch and capacitor check | Minimal (no switch) | Almost maintenance-free |
| Reversal of Rotation | By interchanging connections of main or starting winding | By reversing either main or starting winding | Easy with reversing switch | Difficult (rotation fixed from unshaded → shaded part) |
| Typical Applications | Fans, blowers, washing machines, small tools | Compressors, pumps, refrigerators | Air conditioners, conveyors, office equipment | Small toys, hair dryers, table fans, record players |
| Range of Power Output | 40–250 W (1/20 to 1/3 HP) | Up to 1 HP | Up to 2 HP | Up to 30–40 W |
| Special Features | Simple and robust | High starting torque suitable for heavy loads | Best overall performance | Cheapest and simplest motor |
FAQs on Single Phase Induction Motors
Q1. What are the main types of single-phase induction motors?
The main types of single-phase induction motors are:
- Split Phase Induction Motor
- Capacitor Start Induction Motor
- Capacitor Start Capacitor Run Motor
- Shaded Pole Induction Motor
Q2. Which single-phase motor has the highest starting torque?
The Capacitor Start Induction Motor has the highest starting torque among all single-phase induction motors. It can develop up to 300–450% of full-load torque, making it ideal for applications like compressors, pumps, and refrigerators.
Q3. Which type of single-phase motor has the best running efficiency and power factor?
The Capacitor Start–Capacitor Run Motor provides the best running performance with high efficiency and improved power factor (0.85–0.9). It runs smoothly and quietly, making it suitable for air conditioners, conveyors, and office machines.
Q4. Why does a shaded pole motor have low starting torque?
A Shaded Pole Motor has low starting torque because it uses a shading coil instead of a separate starting winding. The shading coil produces weak rotating flux, resulting in poor torque and efficiency, but it offers a very simple and inexpensive construction.
Q5. What is the main difference between Split Phase and Capacitor Start motors?
The Split Phase Motor uses a high-resistance auxiliary winding for starting, while the Capacitor Start Motor uses a capacitor in series with the starting winding.
As a result, the capacitor start motor develops higher starting torque and operates more efficiently than a split phase motor.
Q6. Which single-phase motor is most commonly used in household appliances?
The Shaded Pole Motor is most commonly used in small household appliances such as fans, hair dryers, record players, and small blowers, because it is cheap, compact, and requires no maintenance.
Q7. Which single-phase induction motor is best for constant speed operation?
The Capacitor Start–Capacitor Run Motor maintains almost constant speed with very low slip (2–5%), making it ideal for applications that demand smooth and continuous performance.
Q8. How can the direction of rotation be reversed in single-phase induction motors?
In Split Phase and Capacitor-type motors, the direction of rotation can be reversed by interchanging the connections of the main or auxiliary winding.
However, in Shaded Pole Motors, reversal is not possible because the direction is fixed from the unshaded to shaded part of the pole.
Q9. Which motor is most economical for low power applications?
The Shaded Pole Induction Motor is the most economical for very low power applications (up to 30–40 W) due to its simple design and low cost, even though it has poor efficiency and low torque.
Q10. What are the typical applications of single-phase induction motors?
- Split Phase Motor → Fans, blowers, washing machines
- Capacitor Start Motor → Compressors, refrigerators, pumps
- Capacitor Start–Run Motor → Air conditioners, conveyors, office equipment
- Shaded Pole Motor → Hair dryers, table fans, toys, record players