AC Series Motor: Working Principle, Diagram & Applications

An AC series motor is a type of electric motor that can operate on alternating current (AC) supply while maintaining characteristics similar to a DC series motor. Because of its high starting torque and compact design, it is widely used in household appliances and power tools.

If you are an electrical engineering student, technician, or someone interested in motor technology, understanding the AC series motor diagram and its working principle will help you grasp how this motor performs efficiently under AC supply.

What is an AC Series Motor?

An AC series motor is essentially a modified DC series motor designed to operate on AC supply. In this motor, the field winding and armature winding are connected in series, meaning the same current flows through both.

However, since AC current reverses direction periodically, certain design modifications are made to reduce losses and improve performance when running on AC.

AC Series Motor Diagram

Main Parts Shown in the AC Series Motor Diagram:

1. Field Winding (Series Field) – Connected in series with the armature.

2. Armature Winding – Rotating part where EMF is induced.

3. Commutator – Converts alternating torque into unidirectional torque.

4. Carbon Brushes – Provide electrical contact with the commutator.

5. Laminated Core – Reduces eddy current losses.

The AC series motor diagram clearly shows that both field and armature windings carry the same current, which is key to its working principle.

Working Principle of AC Series Motor

The working principle of an AC series motor is based on the interaction between the magnetic field produced by the field winding and the current flowing through the armature conductors.

Here’s how it works:

• When AC supply is given, current flows through both field and armature windings.

• The magnetic field is generated in the stator (field winding).

• The armature current interacts with this magnetic field.

• Even though the current reverses direction, both field and armature currents reverse simultaneously.

• As a result, the direction of torque remains the same.

This is why the motor continues to rotate in one direction even with AC supply.

Construction Features of AC Series Motor

To operate efficiently on AC supply, the motor includes:

• Laminated magnetic circuit to reduce eddy current losses.

• Low inductance field winding to reduce reactance.

• Compensating winding (in some designs) to improve commutation.

These modifications distinguish it from a regular DC series motor.

Characteristics of AC Series Motor

1. Very high starting torque

2. High speed at no load

3. Speed decreases with load

4. Operates on both AC and DC (also called Universal Motor in many cases)

Because of these properties, it is commonly used in small appliances.

Applications of AC Series Motor

Due to high speed and strong starting torque, AC series motors are widely used in:

• Electric drills

• Mixers and grinders

• Vacuum cleaners

• Sewing machines

• Hair dryers

These applications require lightweight motors with high rotational speed.

Advantages of AC Series Motor

• High starting torque

• Compact and lightweight

• Simple construction

• Can operate on AC and DC supply

Disadvantages of AC Series Motor

• Poor speed regulation

• Not suitable for heavy industrial loads

• Produces noise and sparks due to brushes

Conclusion

The AC series motor is a powerful and versatile motor widely used in household and portable electrical equipment. By understanding the AC series motor diagram, you can clearly see how the field and armature windings are connected in series and how the motor maintains unidirectional torque even under alternating current supply.

For electrical students and professionals, mastering the working principle, construction, and characteristics of the AC series motor is essential for understanding small motor applications and universal motor technology.

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