Speed control of DC motor, dc motor speed control

In this article we will learn about how to speed control of dc motor. we will also discuss different type dc motor speed control , different method of speed control of dc motor.

Speed  control of   DC   motor 

speed control of DC series motor

Dc series motor speed can varies by changes in supply voltage and armature current

N = Back EMF / Flux

Back EMF =  Supply voltage(V) - Armature voltage drop 

N = Supply voltage - Armature voltage drop / Flux


from above equation Speed(N) is inversely  proportional to Armature current and directly proportional to supply voltage .  we can also  change of speed by flux control because flux is inversely proportional to speed from above equation.

Methods which are used to vary in speed

1. Field diverter method

2. Armature diverter method

3. Field tapped control method 

4. paralleling field winding method

1. Field diverter method

it is common type of speed control of dc motor.

Speed control of dc motor, speed control of dc series motor ,speed control of dc shunt motor

In this method a variable resistance (which called divert er)is connect across(parallel) the series field winding  . In this type some series field current  flow through diverter and less current flow through field winding which cause flux become less and  motor will increase.


2. Armature diverter method

 it is simple way of speed control of dc motor.
In this method a variable resistance (diverter) connect  across(parallel) the armature.

Speed control of dc motor, speed control of dc series motor ,speed control of dc shunt motor
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In this method supply current will increase and flux will also increase from these cause motor speed become less. By this method we can reduced the speed of motor.

3. Field tapped control method





Speed control of dc motor, speed control of dc series motor ,speed control of dc shunt motor

In this method provide tapping on field winding of DC series motor. this type according to no. of turn of field winding we can varies the speed of motor by change of taping position.


4. Paralleling field winding method 

In this method field coils connect in parallel in each other which cause supply current divided in two part . from this method motor speed will increase
By using this method we can increase speed of DC series motor


Speed control of dc motor, speed control of dc series motor ,speed control of dc shunt motor





Speed control  of DC (shunt) motor


Back EMF = Flux * Z*N*P/60A 

where Z is no. of conductor

N speed of motor in RPM

P is no. of poles in motor

A is no. of parallel path in Armature

N is directly proportional to EMF and inversely proportional to flux

Back EMF = V -  Armature voltage drop 

DC shunt motor speed can change by use of different method

A. Flux/Pole control

B. Armature current or Armature Resistance

C. Control of Supply voltage

A. Flux/ Pole method

By decreasing the flux, the speed can be increased and vice-versa. Hence, the name flux or field controls method. One important thing with this control method. One important thing with this control is that speeds lower than the rated speed cannot be obtained because the field cannot be made any stronger, it can only be weakened.

Speed control of dc motor, speed control of dc series motor ,speed control of dc shunt motor

Flux / pole method

N is inversely proportional to flux
so we can change the speed of motor by change in flux . In this method a rheostats (Resistance) connected with field winding . which cause field current value become less and flux is also less so speed of motor increase.
By using this method motor speed only can be increase.

B. Armature control method 


This method is used when speeds below the no-load speed are required. As the supply voltage is normally constant, voltage across the armature is varied by inserting a variable rheostat or resistance (called controller resistance) in series with the armature circuit. As controller resistance is increased, p.d across the armature decreased, thereby decreasing the armature speed.

Speed control of DC motor , speed control of dc series motor , speed control of dc shunt motor

Speed is inversely proportional to Armature current
In this method a variable resistance connect with Armature series which cause Armature voltage drop increase hence speed become less.
So by using this method motor speed being less.

C. Voltage control 

It is divided in two part
1. Multiple voltage control method
2. Ward Leonard method

1. Multiple voltage control method 

In this method field winding connect to directly  from line and given supply to Armature by help of varrier.
Supply voltage is directly proportional to motor Speed

2. Ward Leonard method 


Voltage control method or Ward Leonard method
This system consists of simply running the motor with a constant excitation and applying a variable voltage to its armature to give required speed. The variable voltage is obtained from motor generator set as shown below.

In this method , motor and generator set are used to speed control of motor
Speed control of dc motor, speed control of dc series motor ,speed control of dc shunt motor



Advantage of Ward Leonard system:

  • . Uniform acceleration can be obtained.
  • . Speed regulation is good
  • . The wide range of speed from stand still to high speeds in either direction
  •  Rapid and instant reversal without excessively high armature current
  •  Starting without the necessary of series armature resistances.
  •  Steeples control from stand still to maximum speed in either direction. 

Hence from above method we can get variation in speed of DC  motor

so it is the basic type of speed control of dc motor. it is the main speed control method of dc motor if you fined any incorrect in this article please comment below.


For knowing more about speed control of dc motor please sea this video.

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