Types of DC Motors
Author: steve Published Under: Home
When many people think about the word motor, they usually think of a four cylinder gasoline powered engine, like the one in their passenger car, or perhaps the large jet engine found on an airplane. However, electric motors are just as important, if not more so, and probably have a much bigger impact on most peoples everyday life than they might imagine. Electric motors are used in power tools, home appliances, clocks, and countless other places, with many also being used in automobiles and air planes.
One of the reasons that electric motors are so popular is due to their dependability and low cost of operation. In fact, electric motors are so common that they are used in the majority of all industrial situations.
There are many types of electric motors, but they can be classified as either an AC Electric Motor or a DC Electric Motor.
DC Electric Motors draw their power from batteries, relying upon stored energy to function. AC Electric Motors, on the other hand, draw their power directly from a power source, such as an electrical outlet.
DC Motors, which are very common, are designed using either series, shunt, or compound configurations.
Shunt DC Motors
Shunt DC Motors are one of the most versatile types of electric motors, which provides a very reliable and constant speed. With the proper type of circuitry, the speed of a Shunt Motor can be accurately regulated, much more so than other types of motors.
Typically, Shunt DC Motors can achieve speeds of 1140, 1725, 2500, and 3450 RPM, although they can be designed to work at almost any speed.
Shunt Motors are also reversible, both when at rest and in operation, which is achieved by reversing polarity of the field voltage or armature. This means that the motor can change direction while it is moving.
While it is possible to reverse the voltage to change direction, in most cases, it is the armature that is reversed. This is because in practice, reversing the field voltage results in high inductance, causing arcing around the switch when the voltage is reversed, which could shock the user.
Shunt motors have many applications, often being used in car fans and windshield wipers, as well as some types of printing devices. Their main advantage being that with proper voltage and load, a shunt motor is able to offer better control and constant speed.
In most cases, brush life in a shunt motor is relatively long. The shunt and armature are the most likely areas that will need service. However, the practice of plugging, which is reversing the motor while it is moving, and dynamic braking, which is shorting the armature when power is cut, can greatly reduce the life span of the motor, causing the brushes to wear much faster than normal.
Compound Motors
Compound motors are typically rather large, with most moving at a rate greater than 1 horsepower. Compound motors offer constant speed as well as high starting torque, offering similar qualities to that of a shunt motor. In fact, compound motors feature a shunt coil, as well as a series.
Due to its high initial torque, the compound motor is well suited for use in elevators, as well as grain milling situations. Compound electric motors come in two basic designs, either cumulative compound or differential compound.
A cumulative compound DC Motor has two fields that are wound in the same direction, with the speed being directly related to the sum of these two fields. This offers a higher torque than a shunt motor, but this is at the expense of speed regulation.
A differential compound DC Motor, on the other hand, has coils that are wound in opposite directions, with the shunt coil wound opposite from the series coil. In this case, the speed is based upon the difference of these two fields, with lower torque than a shunt motor. When the load is applied, the speed increases in a differential compound motor.
In some cases, the differential motor has been designed to work at a set speed, which is referred to as a flat compound motor.