Difference Between DC Motor and DC Generator

DC Motor vs DC Generator

The basic internal structure of the DC motor and DC generator are the same and works on the Faraday’s laws of induction. However, the way DC motor operates is different to the way DC generator operators. This article takes closer look at the structure of DC motor and generator and how both operate and finally, highlights the difference between DC motor and generator.

More about DC Generator

Generators have two windings components; one is the armature, which generates the electricity through electromagnetic induction, and the other is the Field Component, which creates a static magnetic field. When the armature moves relative to the field, a current is induced due to the flux change around it. The current is known as the induced current and the voltage which drives it is known as electro-motive force. The repetitive relative motion required for this process is obtained by rotating one component relative to the other. The rotating part is called as rotor and the stationary part is called the stator. The rotor is designed as the armature, and the field component is the stator. As the rotor moves the flux varies with the relative position of the rotor and the stator, where magnetic flux attached to the armature varies gradually and changes polarity.

Slight change in the configuration of the contact terminals of the armature allows an output that does not change the polarity. Such a generator is known as a DC generator. The commutator, the additional component added to the armature contacts, ensures that the polarity of the current in the circuit changes every half cycle of the armature.

The output voltage of the armature becomes a sinusoidal waveform, because of the repetitive change in polarity of the field relative to the armature. The commutator allows change of the contact terminals of the armature to the external circuit. Brushes are attached to the armature contact terminals and slip rings are used to keep the electrical connection between the armature and the external circuit. When the polarity of the armature current changes, it is countered by changing the contact with the other slip ring, which allows the current to flow in the same direction.

Therefore, the current through the external circuit is a current which do not change the polarity with time, hence the name direct current. The current is time varying, though, seen as pulses. To counter this ripple effects voltage and current regulation must be done.

More about DC Motor

The main parts of the DC motor are similar to the generator. A rotor is a component that rotates, and a stator is the component which is stationary. Both have coil windings to create a magnetic field and the repulsion of the magnetic field creates the rotor to move. The current is delivered to the rotor through slip rings, or permanent magnets are used. The kinetic energy of the rotor delivered to the shaft connected to the rotor and the torque generated act as the driving force of the machinery.

There are two types of DC motors in use, and they are the Brushed DC electric motor and Brushless DC electric motor. The fundamental physical principle behind the operation of DC generators and DC motors are the same.

In brushed motors, brushes are used to maintain electrical connectivity with the rotor winding, and internal commutation changes the polarities of the electromagnet to keep the rotational motion sustained. In DC motors, permanent or electro magnets are used as stators. In a practical DC motor, the armature winding consists of a number of coils in slots, each extending for 1/p of the rotor area for p poles. In small motors, the number of coils may be as low as six while, in large motors, it may be as large as 300. The coils are all connected in series, and each junction is connected to a commutator bar. All coils under the poles contribute to torque production.

In small DC motors, the number of windings is low, and two permanent magnets are used as the stator. When higher torque is needed, number of windings and magnet strength are increased.

The second type is brushless motors, which has permanent magnets as the rotor and electromagnets are positioned in the rotor. A high power transistor charge up and drives the electromagnets.

What is the difference between DC Motor and DC Generator?

• The basic internal structure of the motor and the generator are the same and works on the Faraday’s laws of induction.

• The generator has a mechanical energy input and gives a DC current output while the motor has a DC current input and a mechanical output.

• Both uses commutator mechanism. DC motors use the commutators to change the polarity of the magnetic field while the DC generator uses them to counter the effect of the polarization and turn the output from the armature into a DC signal.

• These can be considered as the same device operated in two different ways.