What is DC motor? Structure of the DC motor in the treadmill

Surely all of us have heard about the DC motor in the structure of the treadmill. A quality treadmill depends a lot on whether the DC motor is working efficiently or not. So what is a DC motor and how does it work? Let’s find out with Tnhelearning.edu.vn through the article below!

What is DC motor? Advantages of DC motor

DC motors (Direct Current Motors) also known as DC motors are used and applied in direct current. DC motor is also considered as an electrical machine that converts electrical energy into mechanical energy.

DC motor

1.1. Working principle of DC motor

DC motors take electrical energy through direct current and convert this electrical energy into mechanical rotation. When the DC motor gets electrical energy, a magnetic field is generated in the stator. This magnetic field will attract and repel the magnet on the rotor, causing the rotor to rotate.

This principle of operation is also known as the “Left Hand Rule” taught in Physics. However, in order for the machine to work, the rotor needs to rotate continuously without stopping, a converter will be attached to the brush connected to the current to provide power to the motor windings.

In addition, the rotation speed of each type of DC motor will vary and vary from time to time, which can be rpm or thousand rpm depending on the application for each different device.

It can be said that DC motor is the simplest and most common type of motor, applied in many manufacturing and manufacturing industries such as in household appliances, ceiling fan assembly, smart razors, electric windows car,…

Working principle of DC motor

1.2. Advantages of DC

DC motor has a simple structure and operation, but plays a very important role in the technology of manufacturing and manufacturing some objects. Although simple and small, DC motors bring many outstanding benefits and advantages:

• DC motor has a capacity of 35 – 60W, consumes less power because it only supplies power to the stator, not the Roto. Therefore, DC motors are much more economical than other DC motors.
• DC motors have a simple design and use permanent magnets, so they can operate more reliably and increase their lifespan (average 15 years).
• DC motors are capable of continuously changing currents, so they are suitable for many different currents while ensuring efficient operation.
• The weight is quite light, so it can be easily installed even in high places and has high safety.
• Brushed DC motors are highly rated with good starting and tuning performance.
• DC motors are most commonly used in the assembly and production of ceiling fans with the ability to save electricity and make no noise.

DC motor has a simple structure and has many advantages

1.3. Disadvantages of DC

Along with the outstanding advantages, DC motors also inevitably have disadvantages during operation such as:

• The cost is higher than other DC motors such as AC.
• DC motor has a simple structure but has a contact between the brush and the commutator, capable of generating electric sparks during operation and mechanical wear. Therefore, it increases the temperature of the DC motor and can damage and short-circuit when operating excessively.

Classification of DC motors

Depending on the principle of operation and different goals, DC motors will be divided and manufactured for applications, suitable for different types of items. Each engine type will have different structure and advantages and disadvantages. In which, there are 5 types of DC motors below.

2.1. Brushed DC Motor

Brushed DC motors generate a rotor (rotating part) magnetic field by passing current through the commutator and brush. The magnetic field of the stator (stationary part) is generated either by winding the stator magnetic field or using a permanent magnet. Therefore, DC motors are said to be cheap, easy to use and control compared to other types of DC motors.

Advantage:

• Low cost, safe and easy to use
• Moderate performance
• Can be maintained when the brush is worn

Defect:

• Lifespan is reduced when used with high power
• Carbon brushes are easy to wear when used, so they must be maintained and replaced regularly.

Brushed DC motor generates Roto magnetic field (Brushed DC Motor)

2.2. Separately excited DC motor

The feature of a separately excited DC motor is that there is a separate power supply for the windings and the field windings to be applied, electrically separate from each other.

Separate excitation DC motor construction

Therefore, the activities of the induced current and the electric field current do not interfere with each other’s operation. The input current will be the sum of these 2 currents. Features of the operating principle of the separately excited DC motor:

• The speed of the motor does not change, regardless of the load. Therefore, separately excited DC motors are widely used with low starting torque such as machine tools.
• The speed can be adjusted by adding a resistor in series with the hardware (reducing the operating speed) or adding a resistor in series with the goji circuit (increasing the operating speed).

Separately excited DC motor with its own power supply

2.3. Brushless DC motor

Brushless DC motor also known as BLDC motor (Brushless DC motor) generates a rotor magnetic field (rotating part) using a permanent magnet and the displacement of a moving electromagnetic circuit. around the stator.

Brushless DC motor is a synchronous motor, the rotor speed is equal to the magnetic speed, more efficient and longer life than brush DC motor. So this motor is widely used in auto industry, printing machine, automobile, medical and instrumentation industry.

Brushless DC motor

Advantage:

• High performance, smooth, quiet operation
• Can increase/decrease speed for a short time
• Engine efficiency is up to 90% while other engines only achieve 70-75%
• Neat structure, light weight
• There are no “brushes” or more commonly known as brushes, so there is no wear and spark. Therefore, brushless DC motor has a longer life than brush DC motor.

Defect

• The cost of the brushless DC motor is quite high because it is composed of a permanent magnet and a Hall sensor. At the same time, the price increase is also due to the strong application and popularity in the market.

Brushless DC motor

2.4. Self-excited DC motor

Self-excited DC motors will include series, parallel and mixed connections. Each connection will have its own structure and function to ensure that the self-excited DC motor can operate normally and efficiently.

Self-excited DC motors have field and application windings connected together. At the same time, they also have the same and only power supply. Parallel or series connections with parallel will be performed as shunt wound while the series version is series wound.

Characteristic:

• Speed limited to 5000rpm
• It is necessary to avoid operating the series motor at no-load because the DC motor will accelerate to an uncontrollable rate.
• Self-exciting DC motors in series are suitable for applications requiring large starting torques such as cranes and winches.

Self-excited DC motor

Structure and working principle of DC motor

To better understand DC motors and their working principles, let’s learn more about each part that makes up a DC motor and how each part works.

DC motor construction

The structure of a DC motor includes:

3.1. Stator

The stator (stator) is a stationary part on the motor with one or more pairs of permanent magnets/electromagnets with the function of protecting and supporting the motor. The stator provides a rotating magnetic field that drives the Roto or application control and receives the power supply through its terminals.

Stator of DC motor

3.2. Axis

The shaft of a DC motor is located in the center of the motor center and is surrounded by other components. The shaft of a DC motor is usually made of hard metal and will be surrounded and fastened by other parts.

Shaft of DC motor

3.3. Terminals

The terminal will have a motor housing commutator. These components are easily removable and fastened to protect and isolate the DC motor from the outside environment. A DC motor will have two terminals, positive and negative.

When the positive (+) wire is connected to the positive (+) terminal and the negative (-) terminal is connected to the negative (-) terminal, the motor rotates clockwise. Conversely, when mounted with opposite signs together, the motor will rotate counterclockwise.

The terminals supply power to the motor and are connected to the brush brush) and the brush arm inside the back cover so that the motor can work normally and continuously.

Motor-mounted terminals of DC motors

3.4. Magnet

The magnet will surround into a circle with equal pieces, surrounded by the Roto, and the coil is wound evenly to be fixed. The magnets used in DC motors are permanent magnets.

At that time, the motor’s magnetic field is always active. Two magnets will generate a strong magnetic field. So two magnets will be included in the DC motor around the Roto such that a strong magnetic field passes through the Roto.

Permanent magnets in DC motors

3.5. Rotor

The rotor (roto) is a continuously rotating and moving core made from coils and wound to form an electromagnet. Rotor is made of multiple discs, insulated from each other with laminated plates and used to make mechanical revolutions, wide application.

Multiple discs prevent the generation of a large eddy current. The rotor is an essential part in the operation of the DC motor. The smaller the rotor discs, the higher the motor efficiency will be.

Rotor in DC motor

3.6. Coil

This coil will be surrounded, wrapping the Roto and creating a strong magnetic field. Each type of wire creates a weak magnetic field when electricity passes through it, but when combined with all the different windings, a strong magnetic field is created.

Normally, DC motors will have a minimum of three windings to ensure efficient and responsive operation because when the motor has 2 windings, it is easy to jam and stop the motor. As more windings are added to the rotor, its rotation becomes smoother because of more windings.

Coil in DC motor

3.7. Brush

Depending on different goals and needs, there are brushless DC motors and brushless DC motors. These two types will have different ways of working but still have the same goal of creating the Roto magnetic field and making the Roto rotate.

The brushes of a DC motor provide the windings with power and are pieces of metal that act like springs because the brush has a conductive material made of carbon. The brushes are connected directly to the terminals or the power supply of the motor.

Brush position in DC motor

3.8. Adapter

Typically, the converter of a DC motor is made of small copper plates that mount on the shaft and rotate as the shaft rotates. When the rotor rotates, the poles of the power supply to the coils will be changed.

Each coil will be connected to two converters, interconnected by coils and electrically isolated from each other. With devices with positive and negative terminals connected to two converter plates, current flows easily and an electromagnetic field is generated.

Converter of DC motor

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