DC Motor, How it works?
The first DC motor was developed around the 1830’s-1840’s but was commercially unsuccessful. These motors were primary battery powered. Poor batteries and high costs resulted in no practical markets around the mid 1800’s. The first commercially viable DC motors entered the market in the late 1800’s due to inventions to the electrical grid and possibilities to build rechargeable batteries.
Consequently brushed DC motors were continuously improved and are still widely used in many applications. But also other types of electromotors were developed, like brushless DC motors and induction motors. As a result in several applications the use of brushed DC motors is limited today.
The Function of a Brushed DC Motor
Like every electromotor, a brushed DC motor consists of two main parts, the rotor and the stator. The DC motor contains either permanent magnets (PMDC) or electromagnetic windings (SWDC) on the stator, which is on the outside of the motor. On the inside, the rotor or “armature” is located. The rotor contains the coil windings that are powered by DC current. When powered by DC current a magnetic field is created around the rotor. Rotation is caused by the fact that one side of the rotor is attracted by the magnetic field in the stator and the other side is repelled.
The rotation continues due to the commutator. Basically, this commutator manages the direction of the flow of current and thereby the direction of the magnetic field, as shown in the image to the right. When the rotor turns due to attraction and repulsion and the rotor becomes horizontally aligned, both brushes will make contact with the opposite side of the commutator. This way the current through the rotor is reversed. As a consequence, the magnetic field is reversed. This process repeats itself as long as power is supplied to the DC motor.
Different Types of Brushed DC Motors.
Within the brushed DC motors you have 4 main different types:
1. Permanent Magnet DC motor.
2. Series motor.
3. Shunt motor.
4. Compound motor.
Advantages of a Brushed DC Motor
The brushed DC motor is an electric motor, which is easy to understand and has a simple and cheap drive design. Basically, for a DC series motor there is a linear relationship between the applied voltage and the speed, given a certain load. The higher the voltage, the higher the rpm. This means that speed and torque can simply be controlled by changing the applied voltage. Also it doesn’t need complex electronics to be controlled. Finally, the DC motor allows for quick start-stop acceleration.
Disadvantages of a Brushed DC Motor
The main disadvantage of the brushed DC motor is the presence of brushes. These wear down relatively quickly which leads to high maintenance costs. Moreover, the motor cannot operate under hazardous conditions, and sparks might occur due to the brushes. Furthermore, although changing the voltage gives you control over speed and torque, this control is not sophisticated. So for applications in which high control is required with a high level of precision, extra complex electronics are needed to provide the desired level of control.
Applications of a DC Motor
It depends on the type of DC motor, which applications are ideal. Generally speaking, the following applications are common:
• Machine tools
• Air compressors
• Motor starters in cars