How to Control Speed of DC Motor?

Electric motors are used in almost every industry and in a wide range of applications. Electric motors are available in a wide range of sizes and types. These motors can be selected based on their functioning, voltage, and applications. Using the proper motor with high-quality parts and performing regular maintenance keeps your motor running smoothly and protects endpoint equipment from wear and power spikes.

The speed control mechanism can be employed in a variety of situations, including managing the movement of robotic vehicles, motors in paper mills, and elevators with various types of DC motors. One of the most useful aspects of a DC motor is its speed control.This blog discusses about how to control the Speed of a DC Motor.Let’s Get Started


In DC Motors,Direct current electric energy is converted into mechanical rotational energy. You can also utilize the device in reverse to generate DC electrical power by turning a motor shaft (making the device function as a generator). The winding connections, in which how the two coils in the motor are coupled to each other, can be used to classify DC motors.

A magnetic field is formed in the stator of a DC motor when it is turned on. The field causes the rotor to rotate by attracting and repelling magnets on the rotor. The commutator, which is hooked to brushes connected to the power source, supplies current to the motor’s wire windings to keep the rotor revolving.

Speed Control of DC motor

We frequently need to change the speed of a DC motor on demand. A DC motor’s speed control is the intentional changing of drive speed.

We can manually control the speed of a DC motor or use an automatic control system. This differs from speed regulation, which allows the speed to adjust to a natural variation in speed caused by a change in the load on the shaft.

A DC motor’s speed (N) is equal to

N = K (V – IaRa)/ ø Where, K is a constant.

This implies three things:

  • The motor’s speed is proportional to the supply voltage.
  • The armature voltage drop is inversely proportional to the motor’s speed.
  • Due to field results, the motor speed is inversely proportional to the flux.

A DC motor’s speed can be controlled in three ways:

  • Through field winding, you may change the flux and the current.
  • By adjusting the armature voltage and resistance, you can achieve different results.
  • Through the supply voltage   

1. Flux Control Method

The magnetic flux varies due to the field winding, allowing the motor’s speed to be varied. Because the magnetic flux is determined by the current passing through the field winding, it may be changed by adjusting the current. This can be accomplished by connecting a variable resistor to the field winding resistor in series.

The rated current flows through the field winding due to a rated supply voltage while the variable resistor is kept at its minimal point, and the speed remains normal. The current via the field winding diminishes as the resistance increases progressively. As a result, the flux produced is reduced. As a result, the motor’s speed exceeds its typical range.

2. Armature Control Method

The voltage drop across the armature is controlled by adjusting the armature resistance. The DC motor’s speed can be controlled using this way. A variable resistor is also used in series with the armature in this manner.

The armature resistance is normal when the variable resistor reaches its minimal value. As a result, the armature voltage falls. The voltage across the armature drops as the resistance value increases. This, in turn, causes the motor’s speed to drop. This approach lowers the motor’s speed below its regular range in this way.

3. Voltage Control Method

Both of the approaches listed above are unable to give speed control in the desired range. Furthermore, the flux control approach can have an impact on commutation. The armature control method, on the other hand, suffers from significant power loss due to the use of a resistor in series with the armature. As a result, a different strategy – controlling the supply voltage to control the motor speed – is frequently preferred.

The field winding receives a fixed voltage, but the armature receives a variable voltage in this manner. The use of a switch gear mechanism to supply a changeable voltage to the armature is one such voltage control approach. Another method is to supply variable voltage to the armature using an AC motor-driven generator (named as Ward-Leonard System).

Apart from these two methods, the most generally used method for controlling the speed of a DC motor is pulse width modulation. To adjust the voltage provided to the motor, PWM entails applying varied width pulses to the motor driver. This method is particularly efficient because the power loss is kept to a minimum and no complicated equipment is required.

To adjust the applied voltage of the motor, PWM is performed by altering the pulses applied to the enable pin of the motor driver IC. The microcontroller changes the pulses based on the input signal from the push buttons.


Hope, this blog helps you to understand how to control the speed of DC motors. We will be back with more informative blogs soon.

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