Universal Motor – Connection, Function, Working Principle, and More

Universal Motor – Connection, Function, Working Principle, and More

Introduction

A Universal Motor is a type of electric motor that can operate on either AC (Alternating Current) or DC (Direct Current) supply. It is called “universal” because of this ability to run on both types of power.
Universal motors are known for their high starting torque, compact size, and high speed, which is why they are widely used in portable tools and household appliances.

1. 1. Construction of a Universal Motor

A universal motor is essentially a series-wound motor where the field winding is connected in series with the armature winding. The main parts include:

• Stator (Field Winding): Creates the magnetic field; connected in series with the armature.

• Armature (Rotor): Contains the winding in which current is induced; mounted on a laminated core to reduce eddy current losses.

• Commutator: A rotary switch that reverses the current direction in the armature winding to maintain unidirectional torque.

• Brushes: Made of carbon, they provide current to the rotating armature through the commutator.

• Frame: Holds all parts together and provides mechanical strength.

2. Connection of a Universal Motor

The field winding and armature winding are connected in series with each other.
When AC or DC supply is given:

• The same current flows through both the armature and field winding.

• In AC operation, both the current and magnetic field reverse direction together, so the torque direction remains constant.

Basic Series Connection Diagram:

Supply → Field Winding → Armature → Back to Supply

3. Working Principle

The universal motor works on the principle of electromagnetic induction and the Lorentz force law:

1. When DC Supply is Applied:

   • Current flows through the field winding and armature winding in series.

   • The field winding produces a magnetic field.

   • Current in the armature conductors interacts with this magnetic field, producing a force (torque) that causes rotation.

2. When AC Supply is Applied:

   • Both the current and the field reverse direction each half-cycle.

   • Because both reverse together, the torque produced is always in the same direction.

   • The commutator ensures proper current direction in each armature coil for smooth operation.

4. Characteristics

• Speed: Very high (up to 20,000 RPM in some applications).

• Starting Torque: Very high compared to other single-phase motors.

• Speed Control: Easy to control by varying the voltage or adding series resistance.

• Operation: Noisy due to high speed and brush-commutator contact.

5. Advantages

• Can operate on both AC and DC supply.

• High starting torque, ideal for heavy-load starting.

• Compact size with high power-to-weight ratio.

• Wide speed range.

6. Disadvantages

• Requires frequent maintenance due to brushes and commutator wear.

• Noisy operation.

• Shorter lifespan compared to induction motors.

• Less efficient under continuous load due to high speed and heating.

7. Applications 

Universal motors are used where high speed and high torque are needed for short durations:

• Portable drills and grinders

• Hair dryers

• Vacuum cleaners

• Sewing machines

• Mixers and blenders

• Electric shavers

• Power tools like saws and sanders

8. Summary Table

Conclusion:
The universal motor is a versatile, high-speed motor that works on both AC and DC supply, making it ideal for portable tools and household appliances. While it offers high performance in small devices, its high noise and maintenance needs make it unsuitable for continuous heavy-duty operation.