What is a DC Machines?- DC Motors OR DC Generator.

Hello Everyone hope you all are doing great. The topic for today is DC machines. Moreover, it is a very vast topic to cover at once but, today our main focus will be on DC motors and DC generators. How do they work? Then its construction, principle, and applications. So now let’s start with the main part.


A DC machine is an electromechanical energy conversion device. The DC machines certainly consist of two main parts;

  • DC Motors
  • DC Generators


Above all the most important components of the DC, machine is the Magnetic field system, Armature, and commutator-brush arrangement. A DC generator can be used as a DC motor without and construction changes and vice-versa. Thus a DC motor and DC generator can be broadly termed as a DC machine

Now, let’s jump into the components and function of each of them;


  • The Yoke is the outermost covering of the DC machine.
  • Cast Iron or Steel is use to make it .
  • However, it not only provides mechanical strength to the system but also carries the magnetic flux produced by the field.
  • The field pole is fix to the inner part of the yoke

To sum up we can say that cast iron is use to make the yoke of low rating machines whereas, the yoke of high rating machine is of cast steel.


  • The poles of a dc machines are electromagnets.
  • field winding is wound over the poles
  • poles are joined to yoke with the help of bolts and welding.
  • Moreover poles produces magnetic flux as we excite the field
  • pole shoe is the fastened part of the pole. because of its typical shape it enlarges the area of the pole thus, more flux can pass through the air gap to the armature.
  • Thus poles shoe serves two purpose;
    1. supports the field coil
    2. spreads the flux evenly.
  • Low reluctance material for example cast iron or steel is mostly use for construction of poles and pole shoe.


  • Field winding or coil is former wind and then placed over each of the poles and is connected in series.
  • They are wind in such a way that during excitation they form north and south pole.
  • In other words field winding is know as excitation winding.
  • Certainly for manufacturing copper is use.


  • Armature core is the rotor part of the machine.
  • It is cylindrical in shape and consist of number of slots to carry armature winding.
  • Laminate steel sheets are use for making core because they help in reducing eddy current losses. It certainly provides low reluctance path for the flux.
  • It consist of number of air holes for the circulation purpose as it helps in faster cooling. subsequently armature is key to the shaft.


  • It is usually former wind and rests in the armature slots.
  • These windings are cut-off from each other and also from there core.
  • Armature winding can be mainly wind by two methods; Lap winding and Wave winding.wave winding in a dc machine
  • each slot carries two different coils. when these coils rotate because of the prime mover it cuts the magnetic lines of force and induces voltage in it.
  • However, the winding and the external circuit are joint together.


  • Physical connection to the coil is because of the commutator brush arrangement.
  • The function of commutator(made of mica sheets) in a DC generator is to collect the current from the coil whereas its function in motor is to give current to the coil.
  • It consist of set of copper segments.
  • The number of segments is equal to number of coils.
  • Since it rotates continuously it is not possible to connect the load directly
  • Hence the brush(made of copper) is present to transfer the current.
  • when the commutator rotates it slides on the surface keeping the contact as it is.


In the case, of a DC Generator, the EMF of rotation (Er) is equal to generated EMF (Eg). Fleming’s left-hand rule is use to find the direction of induced emf.

According to faraday’s law of electromagnetic induction the magnitude of emf is;

E = -dΦ / dt ___________(1)

for one complete revolution of conductor the flux cut is (PΦ) Wb and time is (60/N) seconds. thus equation one becomes

E = PΦ / (60/N)

= PΦN / 60

As Z conductors are divided into A parallel groups. Hence there are Z/A conductors in series.

E = PΦNZ / 60A


  1. P = No. of poles
  2. Φ = flux
  3. N = Armature rotation in rpm
  4. Z = Number of armature conductors in rps
  5. A = Number of parallel path
  6. E = EMF induced.


  • Separately Excited Generators
  • Self Excited Generators
    • Series Wound
    • Shunt wound
    • compound wound
      1. long shut
      2. short shunt


Certainly, an electrical generator is a machine that converts mechanical energy into electrical energy. The energy change is on the basis of the production of dynamically induce emf. As per Faraday’s law of induction whenever a conductor is placed in a varying magnetic field EMF gets induce in it.

However, the EMF causes the current flow if the conductor is closed. the direction is given by fleming’s right-hand rule.image of a dc generator


  • They are used for laboratory purpose because, of there wide range of output voltage.
  • especially Series type are used for arc lightening.
  • certainly used for charging batteries.


A DC motor is a machine that transmutes electrical energy into mechanical energy. It works on the principle that when a current-carrying conductor is placed in a magnetic field it faces a force. Whose direction can be found by Fleming’s left-hand rule and magnitude is given by;

F = BILSin(θ)

  • However, the construction of dc motor is in the same vein as that of dc generator
  • In a dc motor the field winding as well as the armature winding are in contact to the DC source.
  • The field current produces flux in the air gap between the armature and field winding.


working of dc motor
  • Whenever, the field magnets are excited they produce an alternate north and south pole
  • The current carrying conductor under north pole carry current in one direction whereas conductor under south pole carry current in one direction.
  • since, each conductor is carry current in a specific direction it experiences a force.
  • by using fleming’s left hand rule we can get the direction of the force however all this forces adds together to give the driving torque.
  • when the conductor moves from one brush to another the direction of force gets change in addition the it also comes under the effect of next pole.
  • subsequently the direction remains the same
Diagram of working of dc motor


When the motor rotates the armature rotates with it too and cuts the magnetic line of force. According to the law of electromagnetic induction, the direction of induced EMF opposes the direction of its source.

Thus because of its opposing nature, it is known as back EMF. Its mathematical representation is;

Eb = PΦNZ / 60A

Whereas; Eb = Bach EMF

Eb depends on the speed of the armature. if the speed is high then the bach EMf is more and hence as a result the current Ia is low. whereas if speed is low Eb and in turn the Ia is high.

Meanwhile, we can say that Eb is the control unit that controls the flow of current through it


Depending on the way in which the armature winding and the field are connected.

  • DC series motor
  • DC shunt motor
  • compound motor
    • long shunt motor
    • short shunt motor


  • uses of series motor
    • traction systems
    • cranes
    • vacuum cleaner
  • uses of shunt motor
    • lathe machine
    • pumps
    • fans
  • whereas uses of compound motors are
    • heavy machines
    • rollers


Consequently Here we are to the end of the blog. hope you all liked it and are satisfied with the data. If you like the content then please make sure to share it with others and most importantly comment down below the parts you liked or of having any doubts related to the topic. I’ll be very happy if you all suggest the topic next which you would like to read next on.

Have a nice day 🙂



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1 Comment

  • Kushal March 3, 2021 at 4:44 am Reply

    Absolutely brilliant
    So informative content

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