DC motors are used in nearly every application in our life, from ceiling fans to elevators. The motors are easy to repair or replace their worn components, but first, you should know their terminals. So, how to identify a DC motor’s positive and negative terminals.
How To Identify Positive and Negative Terminals of a DC Motor?
DC motors are like batteries; they have two terminals; positive and negative terminals. To know which one is the positive terminal and which one is the negative one, you have to connect the motor. If the motor rotates clockwise, you have connected the positive terminal to the positive and the negative to the negative terminal.
However, if it rotates counter-clockwise, you have connected the negative to the positive terminal and the positive to the negative terminal. This is because the motor’s terminals are connected to the motor’s brushes and the arms inside the cover.
What Are DC Motors?
The direct current motors, or the DC motors, are electrical machines that use the magnetic field created by the direct current. The DC motors use the magnetic field to change the electrical energy into mechanical energy, which is the primary purpose or job of a DC motor.
The magnetic field is the main factor responsible for motor motion. The magnets are attracted and repelled by the magnetic field on the rotor; this makes the rotor rotate. The wire windings of the motor are connected to the power supply source, which is connected to the brushes and the commutator; this keeps the rotor to continue rotating.
The most important feature of a DC motor is that its speed can be precisely controlled; therefore, this makes them more preferred over any other type of DC motor; the ability to control speed in DC motors is required in any industrial machinery. In addition, any DC motor can reverse, stop, and start immediately.
What Are The Types of DC Motors?
Each DC motor has its features and importance, so you have to understand the different types of DC motors. When making a DC motor purchase, you must know its features and characteristics before deciding which type to get. The DC motors have two significant advantages over the AC motors; they require low maintenance and are easy to install.
The difference between any type of DC motor is the connections between the armature and the field winding. The armature and the field winding can be connected either in series or parallel, and in some cases, the connection can be both series and parallel. Another difference between the DC motor types is how the rotor is powered.
The rotor can be powered either brushless or with brushes; for example, the rotor receives the current through brushes in the brush DC motor. In brushless DC motors, their rotor has a magnet. DC motors are widely used and can be found in nearly any application; therefore, each application has a particular type to meet the application’s needs. For example:
1). The Brushed DC Motor
The current passing through the brush and the commutator connected to the rotor produces a magnetic field in the DC motor. The DC motor’s brushes can be made of carbon, and they can be either self-excited or excited separately. The enclosure that contains the magnetic field and the motor’s components is called the stator.
The current can be reversed using the commutator, so the current passing from the power source to the rotor can change its direction. This method is used to affect the windings by an electric current; reversing the current’s direction generates a rotating and steady torque.
In addition, there is a set of contact bars found in the motor’s shaft; the set is used to attach the commutator’s sections to the windings. Brushed DC motors have three main types:
- Permanent Magnet
- Separately Excited
In the permanent magnet type, the magnetic field is produced by a strong magnet. Meanwhile, in the self-excited and separately excited types, the magnetic field is made in the structure of the stator through electromagnetic.
a) Self-Excited DC Motor
Self-excited motors have three types compound, series, and shunt. The excited compound divides into two kinds, differential and cumulative, with long and short shuns in both. In the Self-excited DC motors, the armature windings are connected to the field, and there is only one supply source to both.
The connections in the self-excited type can be either series or parallel, with a series wound or a parallel shunt wound. For example:
- The Self-Excited Shunt
The armature windings are connected to the field parallelly in the self-exited DC motor; the terminal voltage is exposed to the field windings. So, although it’s the same supply used for the field and the armature windings, the current entering the armature windings is different than the one entering the field.
The self-excited shunt DC motor has a constant speed, and it doesn’t change by changing the mechanical loads.
- The Self-Excited Series
In this type of DC motor, the power supply is connected to the armature windings and the field in series. The current entering the armature windings is the same as entering the field. The current supplying the self-excited series motor can be either AC or DC, so it’s a universal motor.
The series DC motor’s speed changes as the mechanical load changes; however, its rotation direction is the same no matter the voltage source.
- The Self-Excited Compound
The self-excited compound motor is a combination of the shunt and the series motors. The field windings are connected parallelly; meanwhile, the armature windings are connected in series. The self-excited compound motors divide into differential and cumulative.
The series field flux helps the shunt field move in the same direction in the cumulative compound motors. Meanwhile, the shunt and the series fields fluxes move in the opposite direction in the differential compound motors. As a result, the shunts of differential and cumulative motors can be either short or long.
b) The Separately Excited DC Motor
In the separately excited motor, the armature windings and field windings have a separated power supply; this isolates them electrically. The actions of armature and field windings don’t interfere with their operations, but the total power coming in is their sum.
c) The Permanent Magnet DC Motor
The permanent magnet DC motors don’t have winding for the field, but they have windings for the armature. The magnetic field is produced by the permanent magnet located at the stator core’s inner surface. The permanent magnet motor has a regular design for its armature, brushes, and commutator.
This type is less expensive and has a small size, and they use uncommon magnets from the earth, for example:
- Neodymium Iron Boron
2). The Brushless DC Motor
The brushless DC motor consists of two essential parts a coil wound and a permanent rotor’s magnet; this removes the necessity for a brush. In addition, the rotor’s permanent magnet eliminates the probability of tear and wear because the heat produced is minimal. On the contrary, the brushes produce a lot of heat; this makes them tear and wear.
The brushless DC motor is often costly due to its efficiency and lasts more than the brushed DC motor.
3). The Servo DC Motor
The servo DC motor consists of four main parts:
- Position Sensing Unit
- Control Circuit
- DC motor
The speed can be changed into a slower, practical one from high speed using the gearbox. If an error happens in the circuit, it can be detected by the control circuit. The feedback given to the control circuit is sent by the shaft’s position in a closed loop. If the position of the shaft mismatch the reference position, it’s an error.
Then, a signal is sent to the amplifier responsible for error detection to handle the error.
What Are The Uses of DC Motor?
Compared to induction motors, DC motors have a high torque; this makes them used in a wide range of applications. In addition, brushed DC motors are easily miniaturized, they have high efficiency, and their rotation can be easily controlled. Meanwhile, Brushless motors can be maintained easily and generate no noise.
In addition, they last for a very long time because they have no brushes, so they don’t wear or tear from the heat that brushes usually produce. As a result, the DC motor has been the main component in many applications for a long time exceeding 130 years, and you can easily find them in any application.
Their applications have a wide range, from large applications such as elevators to small applications such as ceiling fans. For more detailed examples:
- The Elevator
It’s hard to decelerate and accelerate high-speed elevators using an AC motor; the elevators need to be controlled quickly to level them with the floor accurately. The DC motors solve this problem because the current entering its armature can be adjusted to control its speed. In addition, transformers are used to convert the AC into DC.
- The Electric Vehicle
The windows of any electric vehicle use DC motors specifically brushed ones; the motor is used to position and retracts the window. However, many vehicle cars use brushless motors instead of brushed ones because they last longer and generate no noise. Other applications that use DC motor in vehicles are CD players and windshields.
In appliances that overhaul loads, it’s essential that the application’s motor has the ability to maintain the load at no speed, so no breaks are required. The DC motors provide the safest and the most effective option, and their size and weight are significant benefits.
- The Diesel-Electric Locomotive
The diesel engine converts the combustion energy from the diesel engine into rotational energy, and then a generator converts the rotational energy into electric energy. Finally, the electric energy produced goes to a DC motor connected to wheels.
- The Conveyor System
These systems need high torque and a steady speed; this makes the DC motor a perfect option. In addition, the DC motors have a high torque when starting up and can reach steady speeds, as seen in many other applications. For example, brushless DC motors are used for conveyor systems.
- The Ceiling Fan
The DC motor ceiling fans have recently become more popular; they have a high starting up torque and use much less power. Transformers are used to convert the AC in homes into DC; this decreases the power required to operate the fan. In addition, the brushless DC motors are used in fans due to their features.
What Are The Advantages of DC Motors?
The 12-volts and 14-volts motors are highly demanded because the DC motors provide an effective solution to the high cost of other motors. In addition, many applications use the DC motors, such as marine, solar, and truck equipment, and depend on DC motors. Although DC motors are old technology, they develop over time and become more effective.
The DC motors have many advantages; they can be adjusted and adapted to be used in many applications, for example:
- High Starting Torque
DC motors are the perfect solution for applications that need high torque, and these motors can have a high starting torque providing a constant and steady speed.
- No Consistent Effects
Over time the system’s reliability and performance can be affected by the harmonic or consistent effects; this could cause a safety problem. Therefore, whenever there are consistent effects, you must identify and fix them. In addition, when equipment is damaged, this could lead to them heating up and being unsafe.
- Controlled Speed
DC motors’ speed can be controlled precisely by adjusting the current entering the armature; this makes the DC motors more suitable for applications that deal with heavy loads at zero speed.
The DC motors are easy to repair or replace because they have a simple design. Every technician or electrician must have worked on a DC motor before, so anything can be fixed at a very low price when it comes to a DC motor. In addition, the components of the motor can be replaced easily, such as brushes, magnets, armature, and others.
- The Low Cost
The AC motors are more expensive than DC ones; the low cost is a significant advantage for DC motors. On the other hand, the brushless motors can be costly, but they last for a long time, compensating for their high price. On the contrary, the brush motors have a short life span and require more maintenance but at low prices.
To sum up, DC motors are electrical machines or devices used to convert electrical energy to kinetic energy, “rotational energy.” To find the positive and negative terminals of a DC motor, you have to connect them first; if the motor rotates clockwise, you have connected the positive to the positive terminal.
However, if the motor rotates counter-clockwise, you have connected the negative to the positive terminal and the positive to the negative terminal. The main feature of a DC motor that makes it more preferred than the other motors is that its speed can be controlled precisely and accurately.
The DC motor also has easier installation and less need for maintenance than the AC motor. In addition, the induction motors have no chance against DC motors when it comes to high torque; this makes the DC motor used in a wide range of applications.
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