You have probably seen a DC motor or at least some equipment that has this type of motor. If you do not know the DC motors, rest assured, because the Electrical Industry explains in this article what DC motors are, how a DC motor works, what are the types of DC motor and their respective applications. Come on, guys!
DC motor: What is it?
Direct current motors (DC motor) are direct current machines (MCC), that is, they work both as motors and generators of electric energy. As the name implies, DC motors are driven by a direct current source.
They are motors that have permanent magnets or have field and armature, in this case, they do not have permanent magnets. DC motors are widely used and have several applications, such as toys, appliances, industrial machines, electric vehicles, among others.
DC motor: Main parts
The DC motor has several parts that are essential for its operation. Below is an image showing the internal structure of a DC motor.
Main parts of a DC motor.
Structure of a DC motor.
To facilitate understanding of the operation of the DC motor, it consists basically of armature winding, field winding, commutator and brushes, where:
Armature winding: it is located in the rotating part of the direct current motor (rotor), which is responsible for producing the electric torque that drives it when operating as a motor, as well as the output voltage when operating as a generator.
Field winding: it is the fixed part of the machine (stator), responsible for creating the magnetic flux that will pass through the armature. In it, the north and south magnetic poles are formed, creating an excitation field. In addition, it is important to mention the stator of the DC motor can also be made by permanent magnets;
Commutator: it has the function of keeping the current always circulating in the same direction in the armature, that is, it makes the generated torque always in the same direction. When operating as a generator, the commutator has the function of maintaining the voltage generated always with the same polarity;
Brushes: they are usually made of coal, charged with making contact with the armature winding so that electrical energy can be injected into the winding. When it is functioning as a generator it removes the electrical energy from the winding.
DC motors: Advantages and disadvantages
There are many advantages of direct current motors, among which we can mention:
Speed control for a wide range of values above and below the nominal value;
It is possible to accelerate, brake and reverse the direction of rotation quickly;
It is not subject to harmonics and has no reactive power consumption ;
It allows you to vary your speed keeping your torque constant;
It has a high starting torque, which is also known as torque or starting force;
The converters required for its control are less bulky.
Despite the advantages, DC motors also have some disadvantages, such as:
It has greater maintenance due to wear between the brushes with the commutator, except for the brushless motors;
In relation to AC induction motors of the same power, they have a higher price and size;
Because of the spark that occurs between your brushes and the commutators, with the exception of brushless motors, DC motors cannot operate in explosive environments.
DC motors: Modeling
A phenomenon described in terms of symbols and mathematical relations, which reproduces or transcribes the object studied, is called a mathematical model. Therefore, below we have represented the model of a DC motor.
DC motor, features and applications.
Modeling of a direct current motor.
Va = Armature stress
Ia = Armature current
La = Armature winding inductance
Ra = Strength of the armature winding
Ea = Armature induced stress
Vf = Field voltage
If = Field current
Lf = Field winding inductance
Rf = Field winding resistance
∅f = Magnetic flux of the field winding
Direct Current Motors: Classification
We can classify DC motors according to the connection mode of the inductor and the induced coils, being classified as series motor, parallel motor, compound motor and independent excitation motor, where:
The series motor has this definition because the inductor and armature windings are connected in series, standing out for having a high torque and fast acceleration. Due to its characteristics, the series motor is widely used in applications where greater traction is required, for example, electric trains, electric trams and electric winches.
Also known as a bypass motor or shunt motor, the parallel motor is named because the inductor and the induced windings are connected in parallel. It has the characteristic of easy regulation of its speed and is a type of motor widely used in machines, tools, elevators, tracks etc.
Known to some as a mixed engine, the composite engine has the characteristics of series engines and parallel engines. It has two inductor windings, one in series with the induced winding and the other in parallel.
This engine has the characteristic of keeping its speed steady when operating under load, so the compound engine is widely used in driving machines that are subjected to sudden variations in loads, such as presses and mechanical shears.
Independent excitation motor
The independent excitation motor gets its name from the fact that its inductor and its armature are powered by two independent energy sources. DC motors with independent excitation are normally used in machine tool drives, for example, advance tools, piston pumps, compressors, among other applications that require constant torque over the entire speed range.
Main parts of a DC motor.
Types of DC motors.
Motor types: Stepper motor
Stepper motors are direct current and have several coils, which when energized according to a sequence, cause their axis to move according to exact angles, submultiples of 360.
Stepper motors are used in applications that require high precision, as an example of application we can mention traditional printers, 3D printers, and many other position control systems. Although the stepper motor has high precision, it has very low torque, the higher its precision the lower its torque.
Motor types: Servo motor
Known as a servo, the servo motor is widely used in robotics applications. It is basically a motor that we can control its angular position through a PWM signal, used to position and maintain an object in a given position. Unlike stepper motors that can be rotated freely, the axis of a servo motor does not usually have as much freedom in its movements, which is usually only 180º.
Motor types: Brushless motor
Brushless motor means brushless motor, that is, this is a type of motor that does not need brushes to function. Brushless motors are similar to traditional brushed DC motors but are electronically switched (ESM), so they can be powered by a direct current source.
Because it has a brushless switching, the brushless motor is more efficient, requires less maintenance, less noise generation, has a higher power density and speed range compared to brush switching motors. Due to the many advantages of the brushless motor, it is widely used in drones and model aircraft, as well as being light and having a high rotation speed
As not everything is perfect, the brushless motor contains electronics that contribute to a higher acquisition cost, in addition to being normally more complex than brush-switching motors.
In addition to DC motors, there are many other types of motors such as single-phase and three-phase induction motors. If you want to learn more about induction motors, below is a complete lesson from the World of Electrical on three-phase electric induction motors.