The DC motor consists of a rotating discharge elements, statically placed on the fixed base frame. Such devices are widely demanded in the technical field to increase the range of adjustment speed, stable rotation of the actuator.
Constructively the DC motor consists of a rotor (armature), an inductor, a collector and brushes. Let's look at what each element of the system represents:
- The rotor consists of a number of coils that are covered by a conductive current winding. Some DC motors of 12 volts contain up to 10 or more coils.
- Inductor – fixed part of the unit. Consists of magnetic poles and anchors.
- Collector – a functional element of the engine in the form of a cylinder, placed on the shaft. Contains insulation in the form of copper plates and the tabs that are in sliding contact with the brushes of the motor.
- Brushes – the fixed contacts. Designed for liner of electric current to the rotor. Most often, the DC motor is equipped with graphite and copper-graphite brushes. Rotation of the shaft causes the closure and opening contacts between the brushes and the rotor, which causes sparking.
Operation of DC motor
Mechanisms in this category contain a special field winding on the inductor portion, which receives a constant current, which subsequently is converted into a magnetic field.
The rotor winding can be affected by the flow of electricity. Magnetic field on the structural element affected by the ampere force. The result is a torque that turns the rotor part 90 O. Continues the rotation of the working shaft of the engine due to the formation of the effect of commutation at the brush-collector node.
When applying electric current to the rotor, which is under the influence of the magnetic field of the inductor, the DC motors (12 volt) create a moment of force that results in the production of energy in the process of rotation of the shafts. The mechanical energy transmitted from the rotor to the other system elements via a belt transmission.
Currently, there are several categories of DC motors:
- With independent excitation - the winding feed comes from an independent source of energy.
- Sequential excitation of the armature winding connected in series with the excitation winding.
- With parallel excitation - the winding of the rotor is included in the electrical circuit in parallel with the power source.
- With mixed excitation the motor comprises several windings: serial and parallel.
Control of DC motor
The engine start is carried out through the work of the special devices that create a resistance included in the circuit of the rotor. To ensure a smooth start of the mechanism, the rheostat has a stepped structure.
To start the rheostat is activated all of his resistance. The growth speed there is the opposition that imposes a restriction on the growth of the power inrush currents. Gradually step by step increases supplied to the rotor voltage.
The DC motor allows you to adjust the rotation speed of the spindles, which is as follows:
- The speed index below the nominal is corrected by changing the voltage on the rotor of the unit. At the same time, the torque remains stable.
- The rate of operation above the nominal is regulated by the current that appears on the field winding. The torque value is reduced while maintaining a constant power.
- Control of the rotor element is carried out using specialized thyristor converters, which are direct current drives.
Advantages and disadvantages
Comparing DC motors with AC-operated units, it is worth noting their increased performance and increased efficiency.
Equipment this category copes with the negative impact of environmental factors. This contributes to the presence of a fully enclosed body. Design of DC motors requires seals that prevent the entry of moisture into the system.
Protection in the form of reliable insulation materials makes it possible to use the maximum capacity of the units. Allowed to use such equipment under temperature conditions ranging from -50 to 50 C and relative humidity of about 98 %. The launch of the mechanism possible after a period of prolonged inactivity.
Among the disadvantages of electric DC motors in the first place is a fairly rapid wear of the brush of nodes, which requires appropriate maintenance costs. This includes the very limited life of a collector.