What is DC Motor?

A DC motor is one of a class of rotary electrical motors that converts direct electrical energy into mechanical energy. The most common types rely on the magnetic field forces generated. Nearly all types of DC motors, electromechanically or electronically, have an internal function to adjust the direction of current in part of the engine periodically. 

DC motors were the first form of motor used extensively since they were operated by existing lighting distribution systems with direct current. A variable supply voltages or changing current intensity in its field windings allow a DC motor speed to be regulated over a broad range. In device, small DC motors are used.

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DC motor is one of a series of rotary electric motors that converts direct electrical energy into mechanical energy. The most popular types depend on the forces generated by the magnetic field.

Working principle of DC Motor

 The DC motor is the device that converts the direct current to mechanical work. 

It is based on the Lorentz Law principle, which states that "the current conductor put in a magnetic and electrical field experiences force." And this force is called the Lorentz Power. The Fleming law of the left hand provides the direction of the power.

Via the interaction of the forces (produced by the coil and the magnet), the resultant field forms around the conductor. The resulting field appears to recover its initial location, i.e. in the central field axis. The field exerts energy at the ends of the conductor, and the coil continues to spin.

Let the field output Fm in the main field, and this field rotates in the clockwise direction. As the current flows through the coil, they generate their own magnetic field, says Fr. Fr is attempting to come in the direction of the main sector. Thereby, the torque works on the armature coil.

DC Motor Diagram

The Realistic DC Motor consists of field windings that supply the magnetic flux and the armature to serve as the conductor. The input of the brushless DC motor is current/voltage and the output is torque. Knowing the operation of the DC motor is very simple from the basic diagram seen below.A mechanism that transforms DC electrical power to mechanical power is known as a direct current generator. DC motor operation is based on the idea that when a current conductor is put in a magnetic field, the conductor may feel a mechanical force.  The position of this force is given by the left-hand rule of Fleming, and the magnitude is given;  

F = BIL Newton      

According to the left-hand law of Fleming, when an electrical current travels through a coil in a magnetic field, the magnetic force produces a torque that activates the DC motor. The position of this force is perpendicular to the wire and the magnetic field.

Fleming Left Hand Rule

If the thumb, middle finger and the index finger of the left hand are displaced from each other by an angle of 90°, the middle finger represents the direction of the magnetic field. The index finger represents the direction of the current, and the thumb shows the direction of forces acting on the conductor.

DC Motor Construction 

Armature and stator are the two central components of the DC engine. The armature is the revolving component and the stator is the stationary part of it. The armature coil is attached to the DC power supply. 

The armature coil consists of switches and brushes. The turn transforms the AC into DC in the armature and the brushes shift the current from the moving portion of the engine to the stationary exterior load. The armature is located between the north and the south poles of a permanent or electromagnet. For simplicity, consider that the armature has only one coil placed in the magnetic field shown in Figure A. When the DC supply is given to the armature coil, the current starts to flow through it. This current is forming its own field around the coil. Figure B indicates the current being generated around the coil. The main DC motor consists of a significant number of armature coils. The output of the motor is directly proportional to the number of coils used in the motor. Such coils are held under the control of the magnetic field.   

The one end of the conductors is kept under the control of the north pole, while the other end is kept under the control of the south pole. The current reaches the armature coil from the north pole and passes back through the south pole. As the coil shifts from one brush to another, the polarity of the coil varies at the same time. The position of the force or torque acting on the coil remains the same. The torque allows the coil to become zero when the armature coil is perpendicular to the central field. The zero torque means the motor stops spinning. The number of the armature coil in the rotor is used to solve this problem. If one of their coils is perpendicular to the ground, the other coils will cause a torque and the rotor is rotating constantly.   

Also, in order to obtain a continuous torque, the arrangement is maintained in such a way that the direction of the current in the coils is reversed whenever the coils cut the magnetic neutral axis of the magnet. It can be achieved with the aid of a click.

How Does a Dc Motor work?

Consider a part of a multipolar DC motor. When the terminals of the motor are connected to an external source of DC supply the field magnets are excited developing under the N-pole bear currents through the plane of the paper. So the conductors under the S-pole take the currents out of the paper plane.   

Because each armature conductor holds current and is put in a magnetic field, a mechanical force is applied to it. When applying Fleming's left-hand law, it is obvious that the force on each conductor appears to rotate the armature in the anticlockwise direction. All these forces are applied together to create a moving torque, which causes the armature to rotate. If the conductor shifts from one side of the brush to the other, the current in the conductor is reversed. Around the same time, it is under the power of the next axis, which has an opposing polarity. As a consequence, the position of the force on the conductor remains the same. It should be noted that the function of the commutator in the motor is the same as that of the generator. By reversing the current in each conductor as it travels from one pole to another, it helps to create a constant and one-way torque.

Types of DC Motor

• Permanent Magnet DC Motor (PMDC Motor)
• Separately Excited DC Motor
• Self-Excited DC Motor
• Shunt Wound DC Motor
• Series Wound DC Motor
• Compound Wound DC Motor
• Short shunt DC Motor
• Long shunt DC Motor
• Differential Compound DC Motor

Separately excited dc motor

As the name suggests, in case of a separately excited DC motor the supply is given separately to the field and armature windings. The main distinguishing fact in these types of DC motors is that the armature current does not flow through the field windings, as the field winding is energized from a separate external source of DC current.

From the torque equation of the DC motor, we know Tg = Ka φ Ia. So the torque, in this case, can be varied by varying field flux φ, independent of the armature current Ia.

 Permanent Magnet DC Motor

The permanent magnet DC motor (also known as a PMDC motor) consists of an armature winding as in case of a usual motor but does not necessarily contain the field windings. The construction of these types of DC motors is such that, radially magnetized permanent magnets are mounted on the inner periphery of the stator core to produce the field flux.

The rotor, on the other hand, has a conventional DC armature with commutator segments and brushes.  

Here φ is always constant, as permanent magnets of required flux density are chosen at the time of construction and can’t be changed thereafter.

Self-Excited DC Motor

In the case of a self-excited DC motor, the field winding is connected either in series or in parallel or in part in series, partly parallel to the armature winding. On this basis, self-excited DC motors can be categorized as

• Shunt-wound DC motor
• Series wound DC motor

• Compound wound DC motor

Shunt Wound DC Motor

In case of a shunt wound DC motor or more specifically shunt-wound self-excited DC motor, the field windings are exposed to the entire terminal voltage as they are connected in parallel to the armature winding.

Series Wound DC Motor

In the case of a series wound self-excited DC motor or merely a series wound DC motor, the entire armature current flows through the field winding as it is attached in series to the armature winding. The series of wound self-excited DC motors is diagrammatically shown below for clear understanding.

Compound Wound DC Motor

The compound excitation characteristic in a DC motor can be obtained by combining the operational characteristic of both the shunt and series excited DC motor. The compound wound self-excited DC motor or simply compound wound DC motor essentially contains the field winding connected both in series and in parallel to the armature winding.

Cumulative Compound DC Motor

When the shunt field flux assists the main field flux, produced by the main field connected in series to the armature winding then it’s called cumulative compound DC motor.

 Differential Compound DC Motor

In the case of the differentially compound self-excited DC motor i.e. the differential compound DC motor, the configuration of the shunt and the series winding is such that the field flux created by the shunt field winding reduces the flux effect of the main series field winding.

 Short Shunt DC Motor

If the shunt field winding is just parallel to the armature winding and not to the series field winding, then it is known as the short shunt DC motor or more precisely the short shunt style DC winding generator.

Long Shunt DC Motor

If the shunt field winding is parallel to both the armature winding and the series field winding, then it is known as a long shunt type compounded wound DC motor or simply a long shunt DC motor.

What is Brushless DC Motor?

In a brushed DC motor, the rotor rotates 180 degrees when the electrical current is switched to the armature. In brushless DC motors, the permanent magnets are on the rotor and the electromagnets on the stator. The computer then charges the electromagnets in the stator to spin a complete 360-degree rotor.

Advantages of Brushless Dc Motor

The benefits of brushless motors over brushed motors are high power-to-weight ratio, high speed, remote control and low maintenance. Brushless motors are found in areas such as electronic peripherals (disk drives, printers), hand-held power devices and cars ranging from model aircraft to automobiles. These types of motors are highly efficient in producing a large amount of torque over a wide range of speeds. In brushless motors, permanent magnets rotate around a fixed armature to overcome the problem of connecting the current to the armature. Commutation with electronics has a wide range of capabilities and flexibility. They are known for their smooth operation and holding torque when stationary.