DC Motor - Definition, Working Principle, Types, Uses, FAQs

Edited By Vishal kumar | Updated on Jul 02, 2025 05:02 PM IST

We will discuss in this article DC motor, DC motor diagram, working principle of dc motor, the principle of and application of dc motor, construction of dc motor, construction of dc machine, dc motor parts, motor concept, bldc (bldc full form, brushless Direct current), pmdc motor, motor diagram, etc.

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DC motor construction and working -
Applications of DC motors:-
Disadvantages of DC motor:-

DC Motor - Definition, Working Principle, Types, Uses, FAQs

What is a DC machine?:- DC machine definition, “In the rotating electrical machine an electro-mechanical energy conversion takes place is called a DC machine.” In all the rotating electrical machines, a change in flux is associated with the mechanical motion to cause electromechanical energy conversion. When mechanical input energy is converted into electrical energy, the machine is called the generator and when the electrical energy is converted into mechanical energy, then the machine is called a DC motor.

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Construction of DC machine:- Basic structure of DC machine.

The electric machine has two parts

The stator of the machine does not move and normally, it is the outer frame of the machine.
Rotor: The rotor is free to move and normally it is the inner part of the machine.

The machine has two types of winding

Field winding:- The winding through a current is passed to produce the main flux is called the field winding.
Armature winding:- The winding in which voltage is induced is called the armature winding.

This is the construction details of the DC machine.

The working principle of a DC machine:- principle of DC machine is that when a current-carrying conductor is put in a magnetic field a force is produced on it. We know that DC machines are of two types DC motor and DC generator. So, we discuss the working of a DC machine as a DC motor.

In a simple way, the meaning of motor is that it is a type of machine which converts electrical energy to mechanical energy.
Motor definition or define the electric motor and motor concept “ a machine that converts the electrical energy into mechanical energy is called the motor machine or machine motor”. According to electromagnetic induction when any current coil is placed in a magnetic field then magnetic torque works on the coil and at a constant position, the current-carrying coil starts rotating in the motoring process. Electrical energy is provided through the terminals of stationary or moving coil and produces torque due to stationary or moving magnetic field and by this torque, it rotates the rotor and converts the electrical energy into mechanical energy and received on the rotor shaft in the form of mechanical energy. There are two types of motor AC motor and DC motor. Did you know, who invented the electric motor or DC motor? The electric motor is invented by William Sturgeon, who was the first man who invented the first electric motor with the commutator. Thomas Davenport of Vermont was the first who invented the first official battery electric power.
What is a DC motor:- DC motor is a type of machine which converts the direct current nature of electrical energy into mechanical energy. This is the DC motor definition. A current that always flows in the same direction through an electrical device is called a direct current ( DC ) and the dc motor’s full form is a Direct current motor. That’s all the DC motor theory.
The working principle of DC motor:-We explain the working principle of DC motor, as when a current-carrying conductor is put in a magnetic field a force is produced on it. Let us consider one such conductor placed on a slot of the armature and suppose it is acted upon by a magnet from the north pole of the motor. By applying the left-hand rule it is found that the conductor has a tendency to move to the left-hand side. Since the conductor is in a slot on the circumference of the rotor, the force (F= Bil) acts in a tangential direction to the rotor.

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DC motor construction and working -

Construction of dc motor:- The design of an electrical motor is shown in fig. A motor basically consists of a coil placed in a magnetic field. The DC electric motor parts are
Stator
Shaft
Brushes
Commutator
Armature
Poles
Field winding
Rotor

DC motor components:- The two main components of a DC motor is the stator and armature.

The coil is formed by winding of many turns over a soft iron core. DC motor winding consists of two windings namely field winding and armature winding. The core and coil together form an armature. The dc motor armature is fixed on the shaft on the motors and kept between the poles of a strong magnet. The two free ends of coils are connected to the two halves of a metallic split ring ( a ring split into two separate parts ). The split ring forms what is called the split ring commutator or simply commutator. When the shaft rotates, the commutator and coil rotate with it. Two carbon brushes, B₁ and B₂, press against two halves C₁ and C₂ of the commutator. A potential difference is applied to the brushes by connecting them to a source of the source DC, For example, a battery.

DC motor working:- How does a DC motor work? let’s explain the working of the DC motor, The brush B₁ is connected to the positive terminal of the battery, and B₂ is connected to the negative terminal. (But, what are the materials used for brushes in dc machines, Carbon is used for brushes.) So, a current flows in the coil along ABCD (A→B→C→D). Shows the position of a coil after a half rotation from the initial position. As a result of the rotation, the brushes with which two halves of the commutator in the two halves of the commutator were in contact got interchanged. This has reversed the battery connections to the two arms of the coil. Therefore, the current now flows along DCBA. That is the direction of current in two arms of the coil has got reversed. Such changes take place for each half rotation. In this way, the commutator changes the direction of the current in the coil after each half rotation

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The two arms of the coil carry a current in a magnetic field. So, each arm experiences a force. The directions of the forces are shown by arrows in fig. In the position shown upward, the arm AB experiences a downward force, while the arm CD experiences an upward force. This may be verified by using Flemming’s left-hand rule. The coil rotates in the core and is reversed, as explained above. Using Flemming’s left-hand rule, we find that arm AB now experiences an upward force, and the arm experiences a downward force. So, the coil continues to rotate in the anticlockwise direction.

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If the commutator is not used, the direction of the current in an arm of the coil will always remain the same. So, the 3 direction of the force on the arm will not change, and the coil will not be able to complete one rotation. For example, when the arm AB is near the north pole, the downward force will turn it anticlockwise. And when it is near the south pole, the downward direction swings it back, clockwise. Thus the rotation will not be completed. This motor is known as a simple DC motor.

When a current-carrying conductor is placed in a magnetic field it experiences a force.

In the case of a DC motor, The magnetic field is developed by field current, i.e., the current flowing in the field winding.
The armature winding is connected to an external Dc source, hence it plays a current-carrying conductor placed in a magnetic field.
Due to the force exerted on it when placed in a magnetic field, it starts rotating.
The direction of rotation is decided by Flemming’s left-hand rule.

Characteristics of DC Motor:- The characteristics of DC motor depends on three Categories

Speed characteristics:- If a graph is drawn between the speed of the motor ( N ) and Armature current (I) then it is known as speed (N/I) characteristics.
Torque characteristics:- If a graph is drawn between the armature torque (?) and armature current (I) then it is known as torque ( ?/I) characteristics.
Mechanical characteristics:- If a graph is drawn between the speed of the motor (N) and armature torque (?) then it is known as mechanical ( N/ ?) torque.
Uses Of DC Motors:- We used dc motors in various fields
DC series motor uses: Its high starting torque makes its part equally suitable for a wide range of traction applications. Industrial use are hoists, cranes, trolleys, cars, conveyors, Elevators, air compressors, vacuum cleaners, sewing machines, etc
Uses of shunt Motors:- The shunt motor is used where constant speed is required and starting conditions are not severed full start the various applications of DC shunt motor are in leather machines centrifugal pumps, fans blowers, conveyors, lift machines, spinning machines, etc

NCERT Physics Notes :

Applications of DC motors:-

Application of DC series motor:-It is a variable speed motor. The uses of this motor are in lifts, rolling mills, railway engines, cranes, trams, and electric traction. The starting torque of these motors is high.

Applications of DC shunt motors:-DC shunt motors are constant speed motors. The starting torque of shunt motors is not high. So, these motors are used in places where constant speed is required.

The use of these types of motors is in grinders, shapers, drilling machines, vacuum cleaners, and fans.

Applications Of DC compound motors:-Compound motors have low starting torque. These motors have constant speed at low loads. Therefore these machines are used, where load increase suddenly and work has to be done at high load.

Disadvantages of DC motor:-

(i) DC motor has a high cost.

(ii) We cannot use it in explosive and hazardous conditions because sparking may occur in the brushes.

(iii) Its maintenance is difficult.

DC motor function is to convert electrical energy to mechanical energy.

DC motor examples:- DC motor used in various places like electric fans, washing machines, etc.

Ceiling fan working principle:-The ceiling fan has a motor. The motor converts electrical energy into mechanical energy. The capacitor present in a ceiling fan torques up the electric motor, which makes it start and run. As soon as the electrical current passes through the motor (placed in the metal base), it enters into the wire coil of the motor and creates the magnetic field that further exerts force in a clockwise direction. So, the motor converts the electrical energy to mechanical energy and causes the fan to spin.

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Frequently Asked Questions (FAQs)

1. Which DC motor is preferred for elevators?

DC compound motor is preferred for elevators.

2. Which DC motor is generally preferred for cranes and hoists?

Series motor is used for cranes and hoists.

3. Where is the DC motor used?

DC motor is used in rolling mills, elevators, lifts, water pumping, and fans, etc.

4. What is the full form of the bldc motor?

The full form of the bldc motor is a brushless motor.

5. Why starter is required for DC motor

The starter is required for the DC motor because it protects the DC motor from high current and torque during the startup.

6. What is the importance of the load line in DC motor operation?

The load line in DC motor operation represents the relationship between the motor's speed and torque for a given load. It's crucial for understanding how the motor will perform under different operating conditions. The intersection of the motor's speed-torque curve and the load line determines the motor's operating point. This concept is essential for selecting the right motor for a specific application and for predicting motor behavior under varying load conditions.

7. How does the moment of inertia of the rotor affect DC motor performance?

The moment of inertia of the rotor in a DC motor plays a significant role in its dynamic performance. It represents the rotor's resistance to changes in rotational speed. A higher moment of inertia results in slower acceleration and deceleration, making the motor less responsive to rapid changes in load or control input. Conversely, a lower moment of inertia allows for quicker speed changes and better dynamic response. The choice of rotor inertia is a critical design consideration, balancing factors like speed stability, acceleration capabilities, and energy storage. In applications requiring frequent starts and stops or rapid speed changes, minimizing rotor inertia is often desirable for improved responsiveness.

8. What is the role of field weakening in DC motor control?

Field weakening is a technique used in DC motor control to extend the speed range of the motor beyond its base speed. It involves reducing the strength of the motor's magnetic field, typically by decreasing the current in the field windings. As the field weakens, the back EMF decreases, allowing the motor to rotate faster for a given applied voltage. However, this comes at the cost of reduced torque capability. Field weakening is particularly useful in applications requiring a wide speed range, such as in electric vehicles or industrial drives, where it allows for efficient operation at higher speeds without the need for excessive supply voltage.

9. What is the significance of the motor constant in DC motors?

The motor constant, often denoted as Km, is a key parameter that relates the motor's torque to the current input (or back EMF to angular velocity). It's a measure of the motor's ability to convert electrical power into mechanical power. A higher motor constant generally indicates a more efficient motor. This constant is crucial for motor selection and control system design, as it helps predict motor performance under various conditions.

10. What is the significance of the torque constant in DC motors?

The torque constant (Kt) in DC motors is a crucial parameter that defines the relationship between motor torque and armature current. It represents the torque produced per unit of current. The torque constant is closely related to the motor's construction, particularly the strength of its magnetic field and the number of armature windings. A higher torque constant means the motor can produce more torque for a given current, which is generally desirable for efficiency. However, it also implies a higher back EMF constant, which can limit the motor's maximum speed. Understanding the torque constant is essential for motor selection, control system design, and predicting motor performance under various operating conditions.

11. What is a DC motor and how does it differ from an AC motor?

A DC motor is an electrical machine that converts direct current electrical energy into mechanical energy. It differs from an AC motor in that it uses direct current rather than alternating current. DC motors typically have simpler construction and offer easier speed control, while AC motors are often more efficient for high-power applications.

12. How does the principle of electromagnetic induction apply to DC motors?

Electromagnetic induction is fundamental to DC motor operation. When current flows through the motor's armature windings, it creates a magnetic field. This field interacts with the permanent magnets or electromagnets in the stator, causing the armature to rotate. The continuous rotation is maintained by switching the current direction in the armature windings using a commutator.

13. What is the function of a commutator in a DC motor?

The commutator in a DC motor acts as a rotary electrical switch. It reverses the direction of current flow in the armature windings at the appropriate times, ensuring that the magnetic field of the armature always interacts with the stator field in a way that produces continuous rotation. Without the commutator, the motor would simply oscillate back and forth instead of rotating continuously.

14. How does Fleming's Left-Hand Rule relate to DC motor operation?

Fleming's Left-Hand Rule is crucial for understanding DC motor operation. It states that when a current-carrying conductor is placed in a magnetic field, it experiences a force. In a DC motor, this rule helps predict the direction of rotation based on the directions of the magnetic field and current flow. The thumb represents the direction of motion, the forefinger the direction of the magnetic field, and the middle finger the direction of current.

15. What is back EMF in a DC motor and why is it important?

Back EMF (Electromotive Force) is the voltage generated in the armature windings of a DC motor as it rotates in the magnetic field. It opposes the applied voltage and limits the current flow in the motor. Back EMF is crucial because it automatically regulates the motor's speed and prevents excessive current draw, which could damage the motor. It also allows the motor to act as a generator when not powered.

16. How does core loss affect the efficiency of a DC motor?

Core loss in a DC motor refers to the energy lost in the iron core of the motor due to hysteresis and eddy currents. These losses contribute to reduced efficiency and increased heat generation. Hysteresis loss occurs due to the continuous magnetization and demagnetization of the core material, while eddy current losses are caused by circulating currents induced in the core. To minimize core losses, motor designers use laminated cores made of high-quality magnetic materials and optimize the magnetic circuit design. Understanding and managing core losses is crucial for improving overall motor efficiency, especially in high-performance applications.

17. How does armature inductance affect DC motor performance?

Armature inductance in a DC motor affects its dynamic performance. It resists changes in current flow, which can impact the motor's response to rapid changes in voltage or load. Higher armature inductance can slow down the motor's response to control inputs and load changes. It also influences commutation quality, as it affects the rate of current change in the armature coils. Understanding and managing armature inductance is crucial for optimizing motor control and performance, especially in applications requiring quick response times.

18. What is the purpose of compensating windings in a DC motor?

Compensating windings in a DC motor are additional conductors embedded in the pole faces of the main field poles. Their primary purpose is to counteract the armature reaction effect. By carrying a current proportional to the armature current but in the opposite direction, compensating windings help maintain the original distribution of the main field flux. This improves commutation, reduces sparking at the brushes, and allows the motor to operate more efficiently over a wider range of loads and speeds.

19. How does the choice of brush material affect DC motor performance?

The choice of brush material significantly impacts DC motor performance. Common materials include carbon, graphite, and metal-graphite composites. Each material offers different characteristics in terms of conductivity, friction, wear rate, and current-carrying capacity. Softer materials like pure carbon offer good commutation but wear faster, while harder materials like metal-graphite composites last longer but may increase commutator wear. The optimal choice depends on factors such as motor speed, current density, and operating environment. Proper brush selection is crucial for minimizing wear, reducing electrical losses, and ensuring reliable motor operation.

20. What is the significance of the commutation angle in DC motors?

The commutation angle in DC motors refers to the angular position of the brushes relative to the neutral plane of the motor. It's crucial for optimizing motor performance and minimizing sparking at the brushes. The ideal commutation angle ensures that current reversal in the armature coils occurs when they are in the neutral plane, where the induced EMF is zero. Proper adjustment of the commutation angle can improve efficiency, reduce wear on brushes and commutator, and extend motor life. In some advanced motors, the commutation angle may be dynamically adjusted to optimize performance across different operating conditions.

21. What is the purpose of brushes in a DC motor?

Brushes in a DC motor are stationary conductors, typically made of carbon, that make sliding contact with the rotating commutator. They serve to transfer electrical current from the external power source to the armature windings through the commutator. As the commutator rotates, the brushes maintain electrical contact, allowing for continuous current flow and motor operation.

22. How does the speed of a DC motor relate to its voltage?

The speed of a DC motor is directly proportional to the applied voltage. Increasing the voltage increases the motor speed, while decreasing the voltage reduces the speed. This relationship is due to the increased current flow and stronger magnetic fields produced at higher voltages, resulting in greater rotational force and speed.

23. How do series and shunt DC motors differ in their characteristics?

Series and shunt DC motors differ in how their field windings are connected. In a series motor, the field windings are connected in series with the armature, while in a shunt motor, they are connected in parallel. This results in different speed-torque characteristics. Series motors provide high starting torque and variable speed, making them suitable for applications like electric vehicles. Shunt motors offer more constant speed under varying loads, making them ideal for applications requiring steady speeds, like machine tools.

24. What is the armature reaction in a DC motor and how does it affect performance?

Armature reaction in a DC motor refers to the distortion of the main magnetic field by the magnetic field created by the armature current. This distortion can lead to reduced torque, sparking at the brushes, and decreased efficiency. To mitigate these effects, motors often employ compensating windings or interpoles to counteract the armature reaction and maintain optimal performance.

25. How does the torque of a DC motor change with speed?

In a DC motor, torque generally decreases as speed increases. At low speeds, the motor can produce high torque because there's less back EMF opposing the applied voltage. As speed increases, back EMF rises, reducing the effective voltage and current in the armature, which in turn reduces torque. This inverse relationship between speed and torque is a key characteristic of DC motors and influences their application in various scenarios.

26. How do permanent magnet DC motors differ from wound field DC motors?

Permanent magnet DC motors use fixed magnets in the stator to create the magnetic field, while wound field DC motors use electromagnets. Permanent magnet motors are simpler, more compact, and often more efficient at lower power ratings. However, wound field motors offer greater control over the magnetic field strength, allowing for better speed and torque control, especially in higher power applications.

27. What is the purpose of the yoke in a DC motor?

The yoke in a DC motor, also known as the frame or housing, serves multiple purposes. Primarily, it provides a return path for the magnetic flux, completing the magnetic circuit. It also acts as a protective enclosure for the internal components, provides structural support, and often assists in heat dissipation. In wound field motors, the yoke may also support the field windings.

28. How does armature winding configuration affect DC motor performance?

The armature winding configuration in a DC motor significantly impacts its performance characteristics. Lap windings, where conductors are connected in parallel paths, are used for high-current, low-voltage applications and provide good commutation. Wave windings, with conductors connected in series, are suitable for high-voltage, low-current applications and offer higher speed. The choice of winding affects the motor's speed-torque characteristics, efficiency, and suitability for specific applications.

29. What causes sparking at the brushes in a DC motor and how can it be minimized?

Sparking at the brushes in a DC motor can be caused by several factors, including armature reaction, poor commutation, worn brushes, or misaligned commutator segments. It can lead to reduced efficiency, increased wear, and potential damage. To minimize sparking, techniques such as using interpoles, optimizing brush grade and pressure, maintaining proper commutator condition, and employing compensating windings are used. Regular maintenance and proper motor design are crucial for minimizing brush sparking.

30. How does the number of poles in a DC motor affect its performance?

The number of poles in a DC motor influences its speed, torque, and overall performance. Motors with more poles generally run at lower speeds but produce higher torque. Increasing the number of poles also tends to make the motor larger and more expensive. The choice of pole number is a trade-off between desired speed range, torque requirements, and physical size constraints of the application.

31. What is the function of interpoles in a DC motor?

Interpoles, also known as commutating poles, are additional small poles placed between the main field poles in larger DC motors. Their primary function is to counteract the armature reaction and improve commutation. By creating a magnetic field that opposes the armature reaction field, interpoles help reduce sparking at the brushes, improve commutation, and allow for better motor performance over a wider speed range.

32. How does temperature affect the performance of a DC motor?

Temperature has significant effects on DC motor performance. As temperature increases, the resistance of the windings increases, which can lead to reduced efficiency and power output. High temperatures can also degrade insulation, potentially leading to motor failure. Additionally, permanent magnets in some DC motors can lose magnetic strength at high temperatures. Proper cooling and temperature management are essential for maintaining optimal DC motor performance and longevity.

33. How do brushless DC motors differ from traditional brushed DC motors?

Brushless DC motors (BLDC) differ significantly from brushed DC motors in their construction and operation. BLDC motors use electronic commutation instead of mechanical brushes and a commutator. They typically have permanent magnets on the rotor and electromagnets on the stator. This design offers several advantages, including higher efficiency, lower maintenance, longer lifespan, and better speed-torque characteristics. However, BLDC motors require more complex control systems and are generally more expensive.

34. What is the significance of the air gap in a DC motor?

The air gap in a DC motor is the space between the rotor (armature) and the stator (field magnets). It's crucial for motor performance as it affects the strength of the magnetic field interaction. A smaller air gap generally results in a stronger magnetic field and higher efficiency, but it also requires more precise manufacturing. The air gap must be carefully designed to balance magnetic field strength, mechanical clearance, and cooling requirements.

35. How does the choice of bearing type affect DC motor performance and lifespan?

The choice of bearing type in a DC motor significantly impacts its performance, efficiency, and lifespan. Common bearing types include ball bearings, roller bearings, and sleeve bearings. Ball and roller bearings offer low friction and high load capacity, making them suitable for high-speed and high-load applications. They generally provide longer life and maintain alignment better than sleeve bearings. Sleeve bearings, while simpler and cheaper, are more suitable for lower speed and lighter load applications. The bearing choice affects factors like friction losses, noise levels, maintenance requirements, and motor reliability. Proper bearing selection and maintenance are crucial for ensuring smooth operation, minimizing power losses, and extending the motor's operational life.

36. What is the importance of the magnetic saturation curve in DC motor design?

The magnetic saturation curve is crucial in DC motor design as it represents the relationship between the magnetic field strength and the magnetic flux density in the motor's core material. Understanding this curve is essential because as the magnetic field increases, the core material eventually reaches saturation, where further increases in field strength result in diminishing returns in flux density. This saturation affects the motor's performance, efficiency, and control characteristics. Designers use the saturation curve to optimize the motor's magnetic circuit, determine appropriate field current levels, and predict motor behavior under various operating conditions. Proper consideration of magnetic saturation helps in achieving the best balance between motor size, weight, efficiency, and performance.

37. How does the commutator pitch affect DC motor performance?

The commutator pitch in a DC motor refers to the angular distance between adjacent commutator segments. It plays a crucial role in determining the motor's commutation quality and overall performance. The pitch affects factors like the distribution of armature reaction, the magnitude of circulating currents, and the effectiveness of commutation. A properly chosen commutator pitch can minimize sparking at the brushes, reduce armature reaction effects, and improve overall motor efficiency. However, an incorrect pitch can lead to poor commutation, increased wear on brushes and commutator, and reduced motor performance. The optimal commutator pitch depends on factors like the number of armature slots, the type of winding, and the motor's intended operating characteristics.

38. What is the effect of armature skew in DC motors?

Armature skew in DC motors refers to the slight twisting of the armature slots along the length of the rotor. This design feature has several important effects on motor performance. Primarily, it helps to reduce cogging torque and torque ripple, resulting in smoother motor operation. Skewing also helps to distribute the magnetic forces more evenly along the length of the rotor, which can reduce noise and vibration. Additionally, it can improve commutation by reducing the abruptness of flux changes as the rotor rotates. However, excessive skew can reduce the overall torque output of the motor. The optimal degree of skew is a balance between smooth operation and maintaining high torque production.

39. How does the choice of lamination material affect DC motor efficiency?

The choice of lamination material in a DC motor significantly impacts its efficiency. Lam