Notes on DC Motors

Overview of DC Motors

• Application: Found in portable home appliances, automobiles, and industrial equipment.
• Purpose of the Video: To understand the operation and construction of commercial DC motors.

Basic Structure of a DC Motor

• Components:
  • Stator: Provides a constant magnetic field.
  • Armature: Rotating part, typically a simple coil.
  • Commutator Rings: Connect armature to DC power source.

Operation Principle

• Electromagnetic Force:
  • Current through the coil induces electromagnetic force (Lorentz law).
  • Coil rotation is initiated when current flows through it.
  • Torque action is consistently in the same direction due to commutator rings.

Torque Behavior

• Torque Action:
  • Torque nears zero when the coil is perpendicular to magnetic flux.
  • Results in irregular rotor motion if not addressed.
• Solution:
  • Add an additional loop to the rotor with a separate commutator pair.
  • Ensures consistent torque as the loops alternate connections with the power source.
  • More loops equate to smoother motor rotation.

Armature Design

• Construction:
  • Armature loops fitted inside slots with highly permeable steel layers.
  • Enhances magnetic flux interaction.
  • Commutator Brushes: Spring-loaded to maintain contact with power source.

Types of Stator in DC Motors

• Permanent Magnetic Stator: Used in small DC motors.
• Electromagnetic Stator: Most commonly used, powered from the same DC source.

Motor Types Based on Field Coil Connection

• Shunt Motor:
  • Low starting torque.
  • Maintains nearly constant speed irrespective of load.
• Series Motor:
  • Good starting torque.
  • Speed drops significantly with increased load.

Unique Characteristics of DC Motors

• Back EMF:
  • Induced EMF opposes applied input voltage due to electromagnetic induction.
  • Proportional to rotor speed.
  • Reduces armature current significantly.
• Starting Mechanism:
  • Necessary to control input voltage to prevent rotor burnout, especially at startup when back EMF is low.

Special Variation of DC Motors

• Universal Motor:
  • Can run on both AC and DC power sources.

Conclusion

• Further exploration on universal motors in the next video.