DC Motor, How it works?

Summary

This video script offers an insightful look into the operation and construction of commercial DC motors, which are widely used in portable home appliances, automobiles, and industrial equipment. It explains the basic components, including the stator, armature, and commutator rings, and how they work together to produce motion. The script delves into the principles of electromagnetic force and the Lorentz law, highlighting the importance of the commutator in maintaining torque direction. It also discusses the role of additional loops and highly permeable steel layers for smoother operation. The script further explains different types of DC motor constructions, such as shunt and series motors, and their respective torque and speed characteristics. A unique feature of DC motors, the production of back EMF, is also covered, along with the need for a proper starting mechanism to prevent motor damage. The video concludes with a mention of universal motors, which can operate on both AC and DC power sources, inviting viewers to explore further in the next video.

Takeaways

• 🔋 DC motors are found in home appliances, automobiles, and industrial equipment.
• 🛠️ The simplest DC motor consists of a stator providing a constant magnetic field and a rotating armature coil.
• ⚡ The armature is connected to a DC power source through commutator rings, inducing electromagnetic force that rotates the coil.
• 🔄 The commutator ensures the direction of current flow and torque remains consistent, allowing continuous rotation.
• ⚙️ Adding more loops to the rotor and separate commutator pairs smoothens motor rotation and enhances performance.
• 🔧 Practical motors use armature loops in slots with highly permeable steel layers to enhance magnetic flux interaction.
• 📈 Spring-loaded commutator brushes maintain contact with the power source, while larger motors use electromagnetic stators.
• 🔌 DC motors can have field coils connected in parallel (shunt motors) or series (series motors), affecting starting torque and speed regulation.
• ⚖️ Shunt motors maintain almost constant speed regardless of load, while series motors have high starting torque but speed drops with load.
• 🌀 DC motors produce BACK EMF, which reduces armature current and prevents rotor burnout, necessitating proper starting mechanisms.
• 🔄 Universal motors can run on both AC and DC power sources, offering versatility in various applications.

Q & A

What are the common applications of DC motors?

DC motors are commonly found in portable home appliances, automobiles, and various types of industrial equipment.

What is the basic construction of a simple DC motor?

A simple DC motor consists of a stator that provides a constant magnetic field and an armature, which is the rotating part, typically a simple coil connected to a DC power source through a pair of commutator rings.

How does the Lorentz law relate to the operation of a DC motor?

The Lorentz law states that an electromagnetic force is induced on a current-carrying conductor in a magnetic field. In a DC motor, this force causes the armature coil to rotate when current flows through it.

Why does the torque action on the coil change direction as it rotates?

The torque action changes direction because the commutator rings are connected with the power source of opposite polarity, ensuring that the torque is in the same direction throughout the motion and allowing the coil to continue rotating.

What is the issue with torque action when the coil is nearly perpendicular to the magnetic flux?

When the coil is nearly perpendicular to the magnetic flux, the torque action nears zero, which can result in irregular motion of the rotor.

How can the problem of irregular motion be overcome in a DC motor?

This problem can be overcome by adding more loops to the rotor, each with a separate commutator pair, ensuring that the motor force is always present in the system and providing smoother rotation.

What role do the armature loops and highly permeable steel layers play in a practical DC motor?

In a practical DC motor, the armature loops are fitted inside slots with highly permeable steel layers to enhance magnetic flux interaction, improving the motor's performance.

What are the two different ways field coils can be connected to the rotor windings in a DC motor?

The field coils can be connected to the rotor windings in two different ways: in parallel or in series, resulting in two different types of DC motor constructions known as shunt and series motors.

What are the characteristics of a series wound motor compared to a shunt motor?

A series wound motor has good starting torque but its speed drops significantly with the load. In contrast, a shunt motor has a lower starting torque but can run almost at a constant speed regardless of the load.

What is the unique characteristic of DC motors known as BACK EMF?

BACK EMF is a unique characteristic of DC motors where an internal electromotive force (EMF) is induced in the rotating armature loops that opposes the applied input voltage. This BACK EMF is proportional to the speed of the rotor.

Why is it necessary to control the applied input voltage during the starting of a DC motor?

It is necessary because at the start, the BACK EMF is too low, which results in a high armature current that could lead to the burnout of the rotor if not controlled properly.

What is a universal motor and what makes it special?

A universal motor is a variation of a DC motor that is capable of running under both AC and DC power sources, making it versatile for different applications.