Electric motor

Direct current (DC) motor, types and uses

Direct current (DC) motor, types and uses

A direct current motor or, simply continuous motor or DC motor, is a rotating electrical machine that transforms electrical energy in the form of direct current into mechanical energy through electromagnetic interactions.

Virtually all electric motors are reversible, that is, they can transform mechanical energy into electrical energy by working as dynamos. DC motors base their operation on Lorentz's law, also called Laplace's law when it is applied to a conductor, as is the case with motors.

Types of direct current (DC) motors

DC motors are classified according to the way they are connected, in:

  • Serial engine. The electrical constitution of the series motor has all the circuit elements in series, armature windings and inductors. The series motor is characterized by having a high torque at startup and its highly variable speed depending on the load, making it an unstable motor.
  • Compound engine. A compound motor (or compound excitation motor) is a direct current electric motor whose excitation is caused by two independent inductor windings; one arranged in series with the armature winding and another connected in shunt with the circuit formed by the windings: armature, series inductor and auxiliary inductor.
  • Shunt motor. In this type of electric motor, the main field winding is connected in shunt or parallel with the circuit formed by the armature and auxiliary field windings.
  • brushless electric motorBrushless electric motor. This type of DC motor does not require electrical sliding contacts (brushes) on the rotor shaft to run. The commutation of the current that circulates in the stator windings and, therefore, the variation of the orientation of the magnetic field generated by them, occurs electronically.

In addition to the above, there are other types that are used in electronics:

  • Stepper motor
  • Servomotor
  • coreless motor

What are direct current motors used for?

DC electric motors are especially suitable for certain applications. Every day they are more employed in the industrial field.

These types of motors offer a wide speed range, are very easy to control and have great flexibility in torque-speed curves. They also feature high performance over a wide speed range. DC motors have a high overload capacity. This capacity makes them more suitable than AC motors for many applications.

These motors are ideal for pulling machines that require a wide range of speeds with precision. This characteristic has caused that lately, these motors have more presence in various industrial processes.

DC motors are used in turntables, CD players, and magnetic storage drives. These types of mechanisms use fixed magnet brushless motors. These motors provide effective speed control and high starting torque.

In the field of toys, DC electric motors are also often selected.

Another significant advantage is the ease of reversing the rotation of large motors with high loads, while they are capable of acting in a reversible way, returning energy to the line during braking and speed reduction times.

In the physical aspect they are usually very small with little contamination in the environment.

History of direct current motors

At the beginning of the 19th century, the galvanic cell was discovered. With this invention began a whole process of research on electricity that would end up giving rise to inventions such as the electric battery or the direct current motor.

In order to create any type of DC motor, some electrical components were needed. These electrical elements were developed by William Sturgeon. Sturgeon created the first electromagnet that could move more than it weighed. This invention turned out to be one of the indispensable parts of the motor stator. Later came the commutator. The commutator was very important in the first electric motor, since it was the element that rotated periodically inverting the direction of the current, making possible the continuity of movement in the motor. 

Thanks to the invention of these two devices, Sturgeon was able to invent the first archaic DC motor. Sturgeon used a pair of flexible conductive brushes and taking advantage of his previous inventions in 1832 he assembled the first machine capable of converting electrical energy into mechanical energy.

In 1837, Thomas Devenport received his patent for the direct current motor (US Patent No. 132). The difference of this electric motor is that it no longer used a commutator to maintain the continuity of the cycle. In this new invention, he made use of the brushes and split the collector, managing to invert the polarity of the circuit. With these changes the engine was much more efficient.

In 1860, Antonio Pacinotti made a dynamo one with a multipart manifold. This dynamo allowed the development of more reliable and powerful generators. Pacinotti insisted on the reversibility of his dynamo to function as a motor. Despite the improvements, the engines were still quite basic and not suitable for industrial use.

In 1872, Friedrich von Hefner-Alteneck created the first modern drum rotor. With this rotor he left behind the archaic T-shaped rotors that overheated and had poor performance. In 1873, Zénobe Gramme, a Belgian inventor, discovered that applying current to his generator with multiple electromagnets created a motor. The fact of using many electromagnets made Gramme the creator of the first motor efficient enough to be used industrially. From this moment the innovations in the DC motor were small tweaks to improve performance slightly.

The direct current motor was a widely used motor industrially, but with the appearance of alternating current motors (synchronous and, more recently, asynchronous) they have ceased to be used. Even so, they are still useful machines in many applications, in precision applications, since you can have very precise speed control (unlike asynchronous motors, for example, that do not rotate in solidarity with the inductor field), thus being very useful. for programmable machine tools or robotic arms.

They are also the most used for systems that require a lot of power and are not in danger of going out of control, such as trams, trains or subways. But the field where they are most used is low-voltage electronics and electricity, where they are the only motors that can be used in machines that need them and run on direct current, such as robots, computers, hard drives, although variants such as motors are also used. stepper or servo motor.

Publication Date: November 16, 2016
Last Revision: November 26, 2018