Difference Between AC and DC Motors Explained with Examples
Electric motors are fundamental components in Physics and engineering, converting electrical energy into mechanical motion. They play a crucial role in various systems, from small devices to large industrial machines. Understanding their working principles and types helps students grasp applications in robotics, daily appliances, and automation.
Motors are commonly classified based on the type of current used and their internal construction. The major categories are AC motors, DC motors, and special purpose motors. Each type operates on specific principles and is chosen according to the required function and efficiency.
Types of Electric Motors
There are three main segments of electric motors: AC motors, DC motors, and special purpose motors. Each of these includes further classifications, suitable for various tasks and applications.
| Motor Type | Primary Subtypes | Typical Use Examples |
|---|---|---|
| AC Motor | Synchronous Motor, Asynchronous (Induction) Motor | Automation, Pumps, Appliances |
| DC Motor | Series, Shunt, Compound, PMDC | Elevators, Robotics, Toys |
| Special Purpose | Stepper, Servo, Linear Induction, Universal, Hysteresis, Reluctance | Printers, CNC machines, Audio Devices |
AC Motors: Construction and Working Principle
AC motors are powered by alternating current. The main kinds are synchronous motors, which rotate at a speed synchronized with the input frequency, and asynchronous (induction) motors, which operate at a speed less than the supply frequency.
In synchronous motors, both the stator and rotor magnetic fields rotate at the same speed. They are used where precise speed is needed.
Induction motors use the principle of electromagnetic induction. When the stator windings are energized, a rotating magnetic field is produced, which induces current and torque in the rotor. Induction motors are robust and commonly found in household appliances and industrial setups.
DC Motors: Types and Functions
DC motors operate using direct current. Their performance characteristics depend on how armature and field windings are connected. Key types include:
- Series DC Motor: Field and armature windings are in series. These provide high starting torque and are used in lifts and automotive applications.
- Shunt DC Motor: Armature and field windings are parallel. This configuration gives nearly constant speed, making it ideal for lathes and fans.
- Compound DC Motor: Combines series and shunt windings for both high starting torque and speed regulation. Used in presses, shears, and elevators.
- Permanent Magnet DC Motor (PMDC): Uses permanent magnets for the stator field. These motors are compact and efficient for applications like robotics.
Special Purpose Motors
Special types of electric motors are designed for specific roles in control and automation:
- Stepper Motor: Moves in discrete steps, suitable for precise control needed in plotters and PCB machines.
- Servo Motor: Used for accurate position control in automatic tools.
- Universal Motor: Can run on both AC and DC supply. Provides high speed and torque, found in mixers and power tools.
More details at: Universal Motor
- Hysteresis and Reluctance Motors: Offer smooth and quiet operation. Used in recording devices and sound players.
Key Formulas in Motor Physics
To solve motor-based problems, certain Physics formulas are essential:
| Formula | Description | Variables |
|---|---|---|
| P = V × I | Electrical Power Input | V = Voltage, I = Current |
| Mechanical Power = T × ω | Mechanical Output Power | T = Torque, ω = Angular speed |
Worked Example
A DC shunt motor is powered with 24 V and draws 2 A. The losses are 20%. Find the mechanical power output and the torque developed if it rotates at 1200 rpm.
- Total electrical power input = 24 V × 2 A = 48 W
- Mechanical output = 48 W × 0.8 = 38.4 W
- Angular speed ω = 2π × 1200 / 60 = 125.66 rad/s
- Torque T = 38.4 W / 125.66 rad/s ≈ 0.305 Nm
Stepwise Approach to Physics Problems on Motors
- Identify the type of motor and its configuration.
- List known quantities (voltage, current, power, speed).
- Use the relevant formula to find input power, output power, or torque.
- Account for any losses as a percentage or value reduction.
- Convert rotational speed (rpm) to angular speed (rad/s) using ω = 2πN/60.
- Calculate required quantity and verify units throughout.
Motor Types: Features at a Glance
| Motor | Current Type | Highlights | Where Used |
|---|---|---|---|
| Induction (AC) | AC | Simple, robust, economical | Fans, pumps, machinery |
| Shunt (DC) | DC | Constant speed | Blowers, lathes |
| Series (DC) | DC | High torque at start | Elevators, cars |
| Compound (DC) | DC | Torque and speed control | Presses, lifts |
| PMDC | DC | Permanent magnet, compact | Robotics, toys |
| Stepper | DC (pulse) | Moves in steps | Printers, plotters |
| Servo | AC/DC | Precision movement | Automation, robotics |
| Universal | AC/DC | High speed, portable | Mixers, power tools |
Next Steps and Practice
- Study Types of Motors for detailed classification.
- Understand core principles at Electric Motor - Principle, Construction and Working.
- Learn about differences in operation: Difference Between AC and DC Motor.
- Explore comprehensive DC motor types at Types of DC Motor.
Summary
A clear understanding of electric motor types strengthens the foundation for Physics studies and problem-solving. With the right approach—identifying type, calculating quantities, and applying key formulas—you can master both theory and practical applications. Use Vedantu’s resources to dive deeper into concepts and practice more problems effectively.
FAQs on Types of Motors: Definition, Classification, and Applications
1. What are the main types of electric motors?
The main types of electric motors are classified into:
- AC Motors (Induction motor, Synchronous motor)
- DC Motors (Series, Shunt, Compound, Permanent Magnet DC motors)
- Universal Motors (operate on both AC and DC)
- Special Purpose Motors (Stepper motors, Servo motors, Brushless DC Motors, Linear motors)
This classification is widely used for understanding motor applications in industry, robotics, and household appliances.
2. What is the key difference between AC and DC motors?
The key difference between AC and DC motors lies in the type of power supply and their working principle:
- AC motors run on alternating current, typically have simpler construction, and are often used for constant-speed applications.
- DC motors run on direct current, allowing for easy speed control and high starting torque.
Understanding this difference helps in selecting the right motor for various applications.
3. Where are stepper motors commonly used?
Stepper motors are used where precise position and speed control are needed.
Common applications include:
- Printers and 3D printers
- CNC machines
- Robotics and automation
- Camera platforms
They move in discrete steps, making them ideal for digital control systems.
4. What is a universal motor and where is it used?
A universal motor can operate on both alternating current (AC) and direct current (DC) supply.
Key features and uses:
- Provides high starting torque and high speed
- Commonly found in household appliances such as mixers, blenders, drills, vacuum cleaners
- Compact and lightweight, suitable for portable devices
5. What is the function of a servo motor?
A servo motor is designed for precise control of angular or linear position, velocity, and acceleration.
Features include:
- High precision and accuracy
- Used in robotics, automation, RC vehicles, and industrial machines
- Controlled by feedback signals for exact movement
6. What are the advantages of brushless DC motors (BLDC)?
Brushless DC motors (BLDC) offer several advantages:
- Higher efficiency and less maintenance (no brushes)
- Smooth and quiet operation
- Compact size with high power-to-weight ratio
- Widely used in drones, computers, cooling fans, and electric vehicles
7. What is the working principle of an induction motor?
An induction motor works on the principle of electromagnetic induction:
- When AC supply is given to the stator, a rotating magnetic field is produced.
- This rotating field induces a current in the rotor, generating torque to rotate the rotor.
- Used extensively in fans, pumps, and industrial machinery.
8. What are the three main types of DC motors?
The three main types of DC motors are:
- DC Series Motor: High starting torque, used in cranes and trains.
- DC Shunt Motor: Constant speed, suitable for lathes and blowers.
- DC Compound Motor: Combination of series and shunt, used where both high starting torque and constant speed are needed.
9. How do you calculate the power output of an electric motor?
To calculate power output of an electric motor:
- Use the formula: P (output) = T × ω
- Where T is torque (in Newton-meters) and ω is angular velocity (in radians per second)
- This formula helps determine how much useful mechanical work the motor delivers.
10. Which type of motor is mostly used in household fans?
AC induction motors are the most commonly used motors in household fans.
- Simple and robust
- Operate efficiently on AC mains supply
- Require minimal maintenance and offer reliable performance
11. Can a single-phase supply run all types of motors?
No, a single-phase supply cannot run all types of motors.
- Some motors, like large industrial three-phase motors, require three-phase supply.
- Certain motors, such as universal motors and small single-phase induction motors, are designed for use on standard single-phase AC supply found in households.
12. What is a compound DC motor?
A compound DC motor is a type of DC motor that combines both series and shunt wound field windings.
- Offers high starting torque along with better speed regulation
- Used in applications needing a balance of torque and speed control, such as presses and elevators
