What Is a DC Motor?
A DC motor is a motor that runs on a DC power source. It generally refers to brushed motors.
There are two types of electricity: DC and AC. DC power is a power source in which the direction of the current is always in one direction, while AC power is a power source in which the direction of the current is periodically switched. In English, DC stands for Direct Current, and AC is Alternate Current. They are called DC power supply and AC power supply, respectively. Therefore, a DC motor refers to a motor that uses a DC power supply.
Uses of DC Motors
DC motors are widely used for both industrial and general applications. For general use, they are used in radio-controlled toys and automobile models. DC motors are often used in toys because of their simple and inexpensive structure and because dry-cell batteries can power them.
In industrial applications, DC motors have been used in train running motors since the 1800s. In recent years, DC motors have been used in running motors for electric vehicles and motors for HDD rotation.
Principle of DC Motors
Inside DC motors, a rotor with a coil wound around it is installed in the center, and a stator polarized into N and S poles is installed around it.
When an electric current is applied to the DC motors, a magnetic field is generated in the coil according to Fleming’s law. When the magnetized rotor poles and stator poles are the same, a repulsive force is induced, and when they are opposite poles, an attractive force is induced, causing the rotor to rotate.
Reversing the current flowing through the rotor changes the attractive and repulsive forces, which are repeated alternately to rotate the rotor in a fixed direction. The power required for magnetization is provided by a conductor brush in contact with a part called the commutator.
Due to its simple structure, a motor with high output torque efficiency can be manufactured cheaply. However, because the commutator and brushes rotate in contact with each other, the brushes wear out. Therefore, for small brushed DC motors, brush life is motor life.
Types of DC Motors
Permanent magnet DC motors and electromagnet field DC motors are the two main types of DC motors, although brushless DC motors have also become available in recent years.
1. Permanent Magnet Type DC Motors
Permanent magnet DC motors use a permanent magnet in the stator. The rotor is an electromagnet consisting of an iron core and a coil. Since there is no need to energize the stator, the structure and control are simple.
2. Electromagnet Field Type DC Motors
The stator and rotor are both electromagnets in the electromagnet field-type DC motors. Since the field flux increases as the current to the stator increases, these motors have been used in medium to large-sized DC motors.
3. Brushless DC Motors
Brushless DC motors use permanent magnets in the rotor. The displacement of the rotor is read by a magnetic sensor and controlled by changing the magnetic field generated by the stator. While brushless motors have a long service life and are easy to maintain due to the absence of brushes, they require the use of a power supply dedicated to brushless DC motors.
Other Information on DC Motors
1. Differences between DC Motors and AC Motors
The difference between DC motors and AC motors is the power source: DC motors are driven by a DC power source, while an AC power source drives AC motors. The features of each are listed below.
2. Features of DC Motors
- Battery power can be used as it is
- Stable rotational characteristics
- It can be manufactured at a low cost
- High torque control performance and stable response
- Uneven rotation
- Difficult to generate high DC voltage, making it difficult to produce larger motors
3. Features of AC Motors
- The commercial power supply can be used as it is
- No brushes, simple and robust structure
- Easy to generate high voltage and can be enlarged in size
- Rotation speed is constant according to power supply frequency
- VVVF device is required to control rotation speed
The power supply provided by the power company is AC power. When driving DC motors from an AC power source, a rectifier (converter) is used to convert it into a DC power source.