A Direct Current (DC) motor is a motor that turns energy from a direct current and turns this into mechanical energy. The first DC motor was developed around the 1830’s-1840s. They were commercially unsuccessful, because these motors were battery powered and batteries were still very expensive, and the quality was low. When the electrical grid was created and the rechargeable batteries were invented in the late 1800s, this all changed. The first commercially viable DC motors entered the market. DC motors have been improved continuously, but other types of motors, like the BLDC motor, have been developed in the meantime too. As a result, the use of brushed Direct Current motors in several applications is limited today.
HOW A DC MOTOR ACTUALLY WORKS
The rotor is normally located on the inside of the motor, while the stator is located on the outside. The rotor contains coil windings that are powered by the DC current and, the stator contains either permanent magnets or electromagnetic windings. When the motor is powered by DC current, a magnetic field is created within the stator, attracting and repelling the magnets on the rotor. This causes the rotor to start rotating. To keep the rotor rotating, the motor has a commutator. When the rotor aligns with the magnetic field, it would stop spinning, but in this case the commutator would reverse the current through the stator and this way reverse the magnetic field. This way the rotor can keep spinning. See the image on the right for a schematic display of how the Dc motor works.
FOUR TYPES OF DIRECT CURRENT (DC) MOTORS
There are four types of DC motors. All four types work in roughly the same way, as a Direct Current motor always consists of two main parts: a rotor and a stator.
- Permanent Magnet DC motor
- 1 Series motor
- 2 Shunt motor
- 3 Compound motor
ADVANTAGES AND DISADVANTAGES OF A DC MOTOR
When it comes to starting and regulating speed, brushed DC motors have a good performance. The torque density is relatively high for these motors. A Direct Current motor runs smoothly and the range of speed regulation is wide. The overload capability is strong, and the electromagnetic interference is small. A disadvantage of the DC motor is the structure. There is a sliding contact between the commutator and the brush. This causes sparks and mechanical wear. Direct Current motors have relatively short life expectancy because of this and the motor has high maintenance cost. It also raises reliability concerns.
DC MOTOR APPLICATIONS
Some examples of applications in which DC motors are still used are,
- 1 Cranes
- 2 Conveyors
- 3 Pumps
- 4 Fans
- 5 Machine tools
- 6 Air compressors
- 7 Toys
- 8 Motor starters in cars
Different Parts of the DC Motor
The Dc motor is composed of the following main parts::
Armature or Rotor
The armature of a DC motor is a cylinder of magnetic lamination that are insulated from one another. The armature is perpendicular to the axis of the cylinder. The armature is a rotating part that rotates on its axis and is separated from the field coil by an air gap. Field Coil or Stator
The Dc motor Field coil is a non-moving part on which a winding is wound to produce a magnetic field. This electromagnet has a cylindrical cavity between its poles.
Commutator and Brushes
The commutator of a DC motor is a cylindrical structure that is made of copper segments stacked together but insulated from each other using mica. The primary function of a commutator is to supply electrical current to the armature winding.
Brushes
The brushes of a DC motor are made with graphite and carbon structure. These brushes conduct electric current from the external circuit to the rotating commutator. Hence, we come to understand that the commutator and the brush unit are concerned with transmitting the power from the static electrical circuit to the mechanically rotating region or the rotor.
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