DC motor: principle of operation, design, advantages and disadvantages
The electric motor consists of rotating injection elements placed on a statically fixed frame. Such devices are widely demanded in technical areas where an increase in the speed adjustment range is required, maintaining a stable rotation of the drive.
Structurally, the DC motor consists of a rotor (anchor), inductor, collector and brushes. Let's take a look at what each element of the system represents:
- The rotor consists of a set of coils that are covered with a conductive winding. Some 12 volt DC motors contain up to 10 or more coils.
- Inductor - fixed part of the unit. Consists of magnetic poles and bed.
- The collector is a functional element of the engine in the form of a cylinder placed on the shaft.It contains insulation in the form of copper plates, as well as protrusions that are in sliding contact with the motor brushes.
- Brushes - fixed contacts. Designed to connect electric current to the rotor. Most often, the DC motor is equipped with graphite and copper-graphite brushes. The rotation of the shaft leads to the closing and opening of the contacts between the brushes and the rotor, which causes arcing.
DC motor operation
The mechanisms of this category contain a special excitation winding on the inductor part, where a direct current flows, which is subsequently converted into a magnetic field.
The rotor winding is influenced by the flow of electricity. From the side of the magnetic field, this Ampere force influences this structural element. The result is a torque that rotates the rotor part by 90about. The rotation of the working shafts of the engine continues due to the formation of the switching effect on the brush-collector node.
When electric current is applied to the rotor, which is under the influence of the magnetic field of the inductor, DC motors (12 volts) create a moment of force, which leads to the development of energy during the rotation of the shafts.Mechanical energy is transferred from the rotor to other elements of the system through a belt transmission.
Currently, there are several categories of DC motors:
- With independent excitation - the power winding comes from an independent source of energy.
- With sequential excitation - the armature winding is connected in series with the excitation winding.
- With parallel excitation - the rotor winding is connected to the electrical circuit parallel to the power source.
- With mixed excitation - the motor contains several windings: serial and parallel.
DC motor control
The engine is started at the expense of the work of special resistors that create the active resistance included in the rotor circuit. To ensure a smooth start of the mechanism, the rheostat has a stepped structure.
To start a rheostat, all its resistance is involved. As the speed of rotation increases, a reaction occurs, which imposes a limit on the growth of the inrush current. Gradually, step by step, the voltage applied to the rotor increases.
DC motor allows you to adjust the speed of rotation of the working shafts, which is carried out as follows:
- The rate of speed below the nominal is adjusted by changing the voltage on the rotor of the unit. In this case, the torque remains stable.
- The rate of work above the nominal is regulated by the current that occurs on the field winding. The torque value decreases while maintaining constant power.
- The rotor element is controlled by means of specialized thyristor converters, which are direct current drives.
Advantages and disadvantages
Comparing the DC motors with units operating on alternating current, it is worth noting their increased performance and increased efficiency.
Equipment in this category copes with the negative impact of environmental factors. The presence of a fully enclosed housing contributes to this. The design of DC motors provides seals that prevent the penetration of moisture into the system.
Protection in the form of reliable insulation materials makes it possible to use the maximum resource of the units. It is allowed to use such equipment under temperature conditions ranging from -50 to +50.aboutWith and relative air humidity about 98%. The launch of the mechanism is possible after a period of prolonged downtime.
Among the shortcomings of DC electric motors, rather rapid wear of the brush units comes to the first place, which requires corresponding maintenance costs. This also includes extremely limited service life of the collector.