Difference Between DC Motor and DC Generator

The difference between dc motor and dc generator is quite obvious and simple but looking at their construction, components, and structure, they look alike. Keep in mind that a dc motor converts electrical energy into mechanical energy while a dc generator converts mechanical energy into electrical energy.

Why is that?

The EMF produced by armature in a dc motor is lower than the voltage across the source terminal. Thus the motor is supplied by the source.

On the other hand, the EMF produced by armature in a dc generator is higher than the voltage across the source terminal. Thus the generator acts as a source.

Keep in mind that the current is flowing from higher potential to lower potential, this way we can understand how the EMF value determines which one is motor or generator.

Take note the main idea behind motor vs generator is that the motor consumes electrical energy while generator produces electrical energy.

We will fully understand that after learning this topic through the end.

What is a DC Motor

A dc motor is constructed from:

  • A stator or field winding,
  • A rotor or armature winding,
  • Brushes,
  • Commutators, and
  • A yoke,

For complete construction, you may read Basic Parts of a DC Motor.

difference between dc motor and dc generator 1

Source: Wikipedia.

Above is the illustration of a dc motor. The parts we can observe above are:

  • The field or stator windings can be substituted with permanent magnets, both are fine as long as they can produce two poles of magnetic fields (N and S).
  • The rotor or armature winding is placed in between two magnetic poles.
  • One end of the armature is placed in a split ring, known as the commutator.
  • A pair of brushes is placed close to the split ring. These brushes are connected to the voltage source terminal.

Now the dc motor working principle:

  • The source transmits electric current to brushes.
  • These brushes will transmit the electric current to the armature through the split rings when the split rings make contact with the brushes.
  • A force will be produced by the current-carrying conductor in a magnetic field.
  • Armature is rotating clockwise or counter clockwise depending on the current direction.

difference between dc motor and dc generator 2

DC motor is based on Fleming Left Hand Rule,

difference between dc motor and dc generator 3

A current-carrying conductor in a magnetic field will cross the magnetic flux, producing electromotive force (EMF).

Motor has back EMF with

    \begin{align*}E_b=V-I_aR_a\end{align*}

Where:

Eb = back EMF
V = voltage across the source terminal
Ia = armature current
Ra = armature resistance

Application of DC Motor

DC motors has many applications across the various sectors, may it be manufacturing, production, heavy machines, home appliances, and robotics.

For different applications, dc motors are further separated into many types. They are series motor, shunt motor, compound motor, and separately excited motor.

You may read the complete characteristics of DC motors.

Small dc current can operate small dc motors such as small robots, toys with batteries, home appliances, and electric tools.

High dc current can operate big dc motors such as heavy machines, electric cars and bikes, lifts, escalators, and many mass production machines.

What is a DC Generator

There is no difference in construction for both dc motors and dc generators. Every part of the dc motor can be used as a dc generator but we will reverse its process. Instead of using electrical current to move the armature, we will move the armature to produce electrical current.

There is no harm using a dc motor for generator.

A dc generator is constructed from:

  • A stator or field winding,
  • A rotor or armature winding,
  • Brushes,
  • Commutators, and
  • A yoke,

Based on Fleming Right Hand Rule,

difference between dc motor and dc generator 4

DC generators operate on the principle of electromagnetic. The rotating current-carrying conductor in a magnetic field will cross the magnetic flux, producing induced current by the generated EMF in the armature when the armature circuit is closed.

Now the dc generator working principle:

  • The armature is moved by external mechanical force (wind or hydro).
  • The current-carrying conductor crosses the magnetic flux in a magnetic field.
  • Induced current is generated in the armature.
  • Current is transmitted to the load circuit through the connection of commutators and brushes.

Generator has generated EMF with

    \begin{align*}E_g=V+I_aR_a\end{align*}

Where:

Eg = generated EMF
V = voltage across the source terminal
Ia = armature current
Ra = armature resistance

Application of DC Generator

Just as its name implies, the dc generator is used to generate something. This time, this dc machine is used to generate electrical energy from mechanical energy. Unlike a dc motor that has different applications, this one only has one application.

DC generators can be classified further into self excited and separately excited. Doesn’t matter what type, the electrical will only flow in one direction.

The brushes and commutators which are used to deliver electricity to the circuit are easily worn out. So, regular maintenance and replacement are needed to operate properly. Why are they worn out easily? Because it will produce electric sparks each time the commutator and brushes connect each other.

Difference Between DC Motor and DC Generator

From the long explanation above we have read, the essential difference between a dc motor and dc generator is their energy conversion.

A dc motor is a machine powered by electricity to produce mechanical energy.

A dc generator is a machine powered by mechanical energy to produce electricity.

A dc motor and a dc generator are the two sides of the same coin. Why? Because you will find most dc machines can be operated as a motor or generator as long as we determine which energy supplies the motor.

Is it electrical energy?

Or is it mechanical energy?

MotorGenerator
Input and OutputMotor has dc current as an input and mechanical energy as an output.Generator has dc current as an output and mechanical energy as an input.
EMF (Electromotive Force)EMF is used to energize the coil to rotate the armature.EMF is generated around the coil and transmitted to the load or another section of the circuit.
Generated EMFMotor has a generated EMF less than the voltage across the source terminal (EMF<V).Generator has a generated EMF more than the voltage across the source terminal (EMF>V).
EMF CalculationEb = V – IaRaEg = V + IaRa
Electric currentElectric current is used to energize the armature winding through the commutator.Electric current is generated from the armature winding to the commutator.
RuleFleming Left Hand RuleFleming Right Hand Rule
Work principleOperated by a current-carrying conductor in a magnetic field and generates forces.Operated by mechanical force that rotates the armature in a magnetic field and generates induced current.
Armature shaftThe armature is supplied by an electrical current in a magnetic field.The armature is rotated by a mechanical energy in a magnetic field.
Energy conversionThe motor will rotate faster when supplied with higher power up to its maximum power rating.The generator will likely produce fixed voltage with rated rpm.
ExamplesRobotic motors, production and manufacturing tools and machines, printers, and many more.Wind turbines, hydro power plants, dynamos, alternators, and many more.
Difference between dc motor and dc generator

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