A DC motor is any one of a kind of rotary electric machines that converts DC power to mechanical power. The most common types are based on the forces produced by magnetic fields. Almost all types of DC motors have some internal mechanism, either electromechanical or electronic, to periodically change the direction of current flow in a part of the motor.
DC motors were the first widely used type because they could be powered by DC power distribution systems. The speed of a DC motor can be controlled over a wide range, either by using a variable supply voltage or by changing the current intensity in its field windings. Small DC motors are used in tools, toys and appliances. The universal motor can operate with direct current, but it is a light motor that is used for portable tools and appliances. The larger DC motors are used in the propulsion of electric vehicles, elevators and elevators, or in drives for steel rolling mills. The advent of power electronics has made it possible to replace DC motors with AC motors in many applications.
A wire coil with a current passing through generates an electromagnetic field aligned with the center of the coil. The direction and magnitude of the magnetic field produced by the coil can be changed with the direction and magnitude of the current flowing through it.
A simple DC motor has a stationary magnet assembly in the stator and an armature with one or more insulated wire windings wrapped around a soft iron core that concentrates the magnetic field. Windings generally have multiple turns around the core, and in large motors there may be several parallel current paths. The ends of the cable winding are connected to a switch. The switch allows each armature coil to turn itself on and connects the rotating coils to the external power supply through the brushes. (Brushless DC motors have electronic components that turn on and off the DC power of each coil and do not have brushes.)
The total amount of current sent to the coil, the size of the coil and its envelope dictates the strength of the electromagnetic field created.
The sequence of activating or deactivating a particular coil determines in which direction the effective electromagnetic fields point. By turning the coils on and off in sequence, a rotating magnetic field can be created. These rotating magnetic fields interact with the magnetic fields of the magnets (permanent or electromagnets) on the stationary part of the motor (stator) to create a force in the armature that causes it to rotate. In some DC motor designs, the stator fields use electromagnets to create their magnetic fields that allow greater control over the motor.
The different number of stator and armature fields, as well as the way they are connected, provide different inherent speed / torque regulation characteristics. The speed of a DC motor can be controlled by changing the voltage applied to the armature. The introduction of variable resistance in the armature circuit or field circuit allowed speed control. Modern DC motors are often controlled by power electronics systems that adjust the voltage by "cutting" the DC current in on-off cycles that have a lower effective voltage.
Since the series cordless DC motor develops its greatest torque at low speed, it is often used in traction applications such as electric locomotives and trams. The DC motor was the mainstay of electric traction motors in electric and diesel-electric locomotives, trams / trams and diesel electric drilling rigs for many years. The introduction of DC motors and a power grid system to operate the machinery from the 1870s began a new second industrial revolution. DC motors can operate directly from rechargeable batteries, providing the driving force for the first electric vehicles and today's hybrid and electric cars, in addition to driving a large number of wireless tools.