DC Series Motor Working and Its Applications

There are two types of DC motors based on the construction such as self-excited, and separately excited. Similarly, self-excited motors classified into three types namely DC series motor, DC shunt motor, and DC compound motor. This article discusses an overview of the series motor, and the main function of this motor is to convert electrical energy to mechanical energy. The working principle of this motor mainly depends on electromagnetic law, which states that whenever a magnetic field is formed in the region of current carrying conductor & cooperates with an outside field, then the rotating motion can be generated. Once the series motor is started, then it will give utmost speed as well as torque slowly with high speed.

What is DC Series Motor?

The DC Series Motor is similar to any other motor because the main function of this motor is to convert electrical energy to mechanical energy. The operation of this motor mainly depends on the electromagnetic principle. Whenever the magnetic field is formed approximately, a current carrying conductor cooperates with an exterior magnetic field, and then a rotating motion can be generated.

DC Series Motor
DC Series Motor

Components used in DC Series Motor

The components of this motor mainly include the rotor (the armature), commutator, stator, axle, field windings, and brushes. The fixed component of the motor is the stator, and it is built with two otherwise more electromagnet pole parts. The rotor includes the armature and the windings on the core allied to the commutator. The power source can be connected toward the armature windings throughout a brush array allied to the commutator.

The rotor includes a central axle for rotating, and the field winding must be able to hold high current due to the larger quantity of current throughout the winding, the larger will be the torque produced with the motor.

Therefore the motor winding can be fabricated with solid gauge wire. This wire does not permit a huge number of twists. The winding can be fabricated with solid copper bars because it assists in simple as well as efficient heat dissipation generated accordingly by a large amount of current flow during winding.

DC Series Motor Circuit Diagram

In this motor, field, as well as stator windings, are coupled in series by each other. Accordingly the armature and field current are equivalent.


Huge current supply straightly from the supply toward the field windings. The huge current can be carried by field windings because these windings have few turns as well as very thick. Generally, copper bars form stator windings. These thick copper bars dissipate heat generated by the heavy flow of current very effectively. Note that the stator field windings S1-S2 are in series with the rotating armature A1-A2.

DC Series Motor Circuit Diagram
DC Series Motor Circuit Diagram

In a series motor electric power is supplied between one end of the series field windings and one end of the armature. When voltage is applied, current flows from power supply terminals through the series winding and armature winding. The large conductors present in the armature and field windings provide the only resistance to the flow of this current. Since these conductors are so large, their resistance is very low. This causes the motor to draw a large amount of current from the power supply. When the large current begins to flow through the field and armature windings, the coils reach saturation that results in the production of the strongest magnetic field possible.

The strength of these magnetic fields provides the armature shafts with the greatest amount of torque possible. The large torque causes the armature to begin to spin with the maximum amount of power and the armature starts to rotate.

Speed Control of DC Series Motor

The speed control of DC motors can be attained by using the two following methods

  • Flux control Method
  • Armature-resistance Control Method.

The most frequently used method is armature-resistance control method. Because in this method, the flux generated by this motor can be changed. The difference of flux can be attained by using the three methods like field diverters, armature diverter, and tapped field control.

Armature-resistance Control

In the armature resistance control method, a changeable resistance can directly be connected in series through the supply. This can reduce the voltage which is accessible across the armature & the speed drop. By altering the variable resistance value, any speed under the regular speed can be attained. This is the most general method used to control the DC series motor speed.

Speed Torque Characteristics of DC Series Motor

In general, for this motor, there are 3-characteristic curves are considered significant like Torque Vs. armature current, Speed Vs. armature current, & Speed Vs. torque. These three characteristics are determined by using the following two relations.

Ta ∝ ɸ.Ia
N ∝ Eb/ɸ

The above two equations can be calculated at the equations of emf as well as torque. For this motor, the back emf’s magnitude can be given with the similar DC generator e.m.f equation like Eb= Pɸ NZ / 60A. For a mechanism, A, P, and Z are stable, thus, N ∝ Eb/ɸ.

The DC series motor torque equation is,

Torque= Flux* Armature current

T = If * Ia

Here If= Ia, then the equation will become

T= Ia^2

The DC series motor torque (T) can be proportional to the Ia^2 (square of the armature current). In load test on dc series motor, the motor should be activated on load condition because if the motor can be activated on no load, then it will achieve an extremely high speed.

DC Series Motor Advantages

The advantages of the DC series motor include the following.

  • Vast starting torque
  • Easy assembly and simple design
  • Protection is easy
  • Cost-effective

DC Series Motor Disadvantages

The disadvantages of DC series motor include the following.

  • The motor speed regulation is fairly poor. When the load speed increases then the machine speed will decrease
  • When the speed is increased, then the DC series motor’s torque will be decreased sharply.
  • This motor always needs the load before running the motor. So these motors are not suitable for where the motor’s load is totally removed.

Thus, this is all about the DC series motor, and the DC Series Motor Applications mainly includes, these motors can produce enormous rotating force and the torque from its inactive state. This feature will make the series motor fit for mobile electric equipment, tiny electrical appliances, winches, hoists, etc. These motors are not appropriate as a stable speed is necessary. The main reason is that these motors changes with an unstable load. Changing the series motors speed is also not a simple method to implement. Here is a question for you, what is the main function of the DC series motor?