DC motors are found in various portable home appliances, automobiles, and industrial equipment.
The video discusses the operation and construction of commercial DC motors.
Basic Components of a DC Motor
Stator: Provides a constant magnetic field.
Armature: The rotating part, consisting of a simple coil.
Commutator Rings: Connect the armature to a DC power source.
Operation of a Simple DC Motor
When current flows through the coil, an electromagnetic force is induced (Lorentz law).
The coil rotates due to this force.
Polarity of Current: The commutator rings ensure current flows away on one side and towards on the other, maintaining consistent torque direction.
Torque and Coil Rotation
Torque nears zero when the coil is perpendicular to the magnetic flux, leading to irregular rotor motion.
Solution: Add more loops to the rotor with separate commutator pairs to ensure continuous torque.
More loops result in smoother motor rotation.
Construction Details
In practical motors, armature loops are fitted inside slots with highly permeable steel layers to enhance magnetic flux interaction.
Spring-loaded commutator brushes maintain contact with the power source.
Types of Magnetic Stators
Permanent Magnetic Stator: Used in very small DC motors.
Electromagnetic Stator: Commonly used; powered by the same DC source.
Connection of Field Coils
Field coils can be connected in parallel or series to the rotor windings, resulting in two types of DC motors:
Shunt Motors: Low starting torque but maintain nearly constant speed regardless of load.
Series Motors: Good starting torque but speed drops significantly under load.
Unique Characteristics of DC Motors
Back EMF: A rotating loop in a magnetic field induces an EMF that opposes the applied input voltage.
Back EMF reduces armature current, is proportional to rotor speed, and is low at startup, which can lead to high armature current and potential rotor burnout.
A proper starting mechanism is essential to control input voltage in large DC motors.
Universal Motors
An interesting variation of DC motors that can operate under both AC and DC power sources.
More details available in the next video.
Conclusion
Understanding the components and operation of DC motors is crucial for their application in various fields.