In any electric motor, operation is dependent upon simple electromagnetism. A current carrying conductor generates a magnetic field, when this is then placed in an external magnetic field; it will encounter a force proportional to the current in the conductor and to the strength of the external magnetic field.It is a device which converts electrical energy to mechanical energy. It works on the fact that a current carrying conductor placed in a magnetic field experiences a force which causes it to rotate with respect to its original position.

Classification or Types of Motor

The primary classification of motor or types of motor can be tabulated as shown below:

DC Motor

DC power systems are not very common in the contemporary engineering practice. However, DC motors have been used in industrial applications for years Coupled with a DC drive, DC motors provide very precise control DC motors can be used with conveyors, elevators, extruders, marine applications, material handling, paper, plastics, rubber, steel, and textile applications, automobile, aircraft, and portable electronics, in speed control applications

A DC motor is an electric motor that runs on direct current power.

Practical DC Motor consists of field windings to provide the magnetic flux and armature which acts as the conductor.

Brushless DC Motors Work

The input of DC motor is current/voltage and its output is torque. Understanding the operation of DC motor is very simple from a basic diagram is shown in below. DC motor basically consist two main parts. The rotating part is called the rotor and the stationary part is also called the stator. The rotor rotates with respect to the stator.

The rotor consists of windings, the windings being electrically associated with the commutator. The geometry of the brushes, commutator contacts and rotor windings are such that when power is applied, the polarities of the energized winding and the stator magnets are misaligned and the rotor will turn until it is very nearly straightened with the stator’s field magnets.

As the rotor reaches alignment, the brushes move to the next commutator contacts and energize the next winding. The rotation reverses the direction of current through the rotor winding, prompting a flip of the rotor’s magnetic field, driving it to keep rotating.

Working of DC Motor

Working principle of DC Motor mainly depends upon Fleming Left Hand rule. In a basic DC motor, an armature is placed in between magnetic poles. If the armature winding is supplied by an external DC source, current starts flowing through the armature conductors. As the conductors are carrying current inside a magnetic field, they will experience a force which tends to rotate the armature. Suppose armature conductors under N poles of the field magnet, are carrying current downwards (crosses) and those under S poles are carrying current upwards (dots). By applying Fleming’s Left hand Rule, the direction of force F, experienced by the conductor under N poles and the force experienced by the conductors under S-poles can be determined. It is found that at any instant the forces experienced by the conductors are in such a direction that they tend to rotate the armature.

Again, due this rotation the conductors under N-poles come under S-pole and the conductors under S-poles come under N-pole. While the conductors go form N-poles to S-pole and S-poles to N-pole, the direction of current through them, is reversed by means of commutator. Due to this reversal of current, all the conductors come under N-poles carry current in downward direction and all the conductors come under S-poles carry current in upward direction as shown in the figure. Hence, every conductor comes under N-pole experiences force in same direction and same is true for the conductors come under S-poles. This phenomenon helps to develop continuous and unidirectional torque.

Advantages of DC motors:

1. It is easy to control their speed in a wide range; their torque-speed characteristic has, historically, been easier to tailor than that of all AC motor categories. This is why most traction and servo motors have been DC machines. For example, motors for driving rail vehicles were, until recently, exclusively DC machines.

2. Their reduced overall dimensions permit a considerable space saving which let the manufacturer of the machines or of plants not to be conditioned by the exaggerated dimensions of circular motors.

Disadvantages of DC motors

1. Since they need brushes to connect the rotor winding. Brush wear occurs, and it increases dramatically in low-pressure environment. So they cannot be used in artificial hearts. If used on aircraft, the brushes would need replacement after one hour of operation.

2. Sparks from the brushes may cause explosion if the environment contains explosive materials.

3. RF noise from the brushes may interfere with nearby TV sets, or electronic devices, Etc.

4. DC motors are also expensive relative to AC motors.

Thus all application of DC motors have employed a mechanical switch or commutator to turn the terminal current, which is constant or DC, into alternating current in the armature of the machine. Therefore, DC machines are also called commutating machines.

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