How Do You Control the Speed of A DC Motor? – (Follow the Best Methods)

You must be confused when it comes to choosing the best way to control the speed of a DC motor. It is necessary to control the speed so that the motor works properly. So, you won’t have to worry. You are at the relevant place to learn about it. So, how do you control the speed of a DC motor?

A DC motor’s speed depends on the voltage of the electrical energy. The more the voltage is, the more the motor’s speed will be. Moreover, some ways to control the motor speed are Armature Resistance, Field Resistance, Armature Voltage, and Flux Control methods.

Here I will discuss how to control DC motor speed, what is a speed controller, what is a potentiometer, and many more. Please read till the end to find out! 

What Is a Speed Controller? 

A speed controller is a machine or device which helps the motor’s speed to increase or decrease. To say it more precisely, this device has a regulator that controls the rotational energy of the DC motor. So, the machine you want to operate will work properly using the speed controller. 

People may think that the controller only controls the speed of the DC motor. But it is more than that. It also controls the position and torque of the machine. You can learn how a speed controller helps to work machines better through below points: 

  • The DC speed controller helps to control the total output of a rotational force that a DC motor builds. The total output of that force is called torque. A torque forces the object to rotate about a fixed axis
  • This variable-speed DC motor with a controller also helps to maintain the position of a rotor/motor shaft. The motor shaft works to convert torque and output the rotational energy to the end application. So it is more than important for a motor to maintain the position of the motor shaft. Because it will affect the transfer of energy to the end application 

How Do You Control the Speed of a DC Motor? 

Starting a DC motor requires a starter but a controlling device is also required to control the DC motor’s speed. We have known earlier that the speed of a DC motor is based on the voltage of the current. But there are some ways you can manipulate the voltage of current. You always try to make things easier. Don’t you? So using these methods can help you to manipulate the speed most easily.

Some of these methods can have more benefits than others. Also, it can have disadvantages too. These methods are –

  • Armature Resistance Control Method 
  • Field Resistance Control Method 
  • Armature Voltage Control Method 
  • Flux control method 

Further, you will get to know the best methods to control the speed of a DC motor in more detail. 

Best Methods of DC Motor Speed Control 

As you have learned about the speed controller, you must be aware that the speed focuses on the voltage. So there are multiple techniques of DC motor speed control. It helps to regulate the voltage of the motor. Let’s learn the best methods of DC motor speed control through the below ways:

1. Armature Resistance Control Method 

You have the Armature motor, so you want to control the speed of this machine. In this case, the more resistance you put in the series, the flow of current and the speed decreases. Here is the DC motor speed control theory: 

EMF (Electromotive Force) = V – IR

It explains that when you turn on the current and put resistance in the series, the speed and flow of current (I) become proportional to each other. So when you put resistance, the speed and current lessens. 

2. Field Resistance Control Method

A field resistance control method is a method where the resistance is put on the field circuit to increase or decrease the speed. As the resistance adjusts the magnetic field called flux, the speed changes depending on its resistance.

The more resistance you put in, the speed decreases. At the same time, when you decrease the resistance, the speed will increase. 

3. Armature Voltage Control Method 

You would need a rheostat to control the speed. When you apply voltage to the winding with rheostat, the armature current flow stays the same. But it results in decreased voltage due to extra resistance. Hence, the speed of the motor decreases. 

The principle of this method is that the speed and the voltage are proportional to each other. As you give more resistance to the Armature, the speed decreases. And the less resistance you give, the speed increases.

4. Flux Control Method 

A flux is a magnetic field line that is caused by the permanent magnets in the electromagnetic field. So, you can change the speed of the motor by changing the magnetic flux through putting resistance. This theory has a principle behind it: The speed of the motor is proportional to the magnetic flux.

So, if you increase the flux, the speed can be decreased. On the other hand, if you decrease the flux, the speed can be increased. So you would need a rheostat and add it in the series with the coil of wire. So when you put resistance in the winding, the speed will change. 

However, the speed depends on how much resistance you are putting on. If you give more resistance, it will decrease the flux. Hence it increases the speed. If you give less resistance, it increases the flux. Hence, the speed will decrease. 

Advantages and Disadvantages of the Speed Control Method 

As I have said before, speed control methods have benefits and disadvantages. Here I have written about the advantages and disadvantages of the four methods. Please check out below:

MethodsAdvantages Disadvantages 
Armature Resistance Control MethodThe constant flow of current and torqueThe control equipment is expensive
Field Resistance Control MethodGives good performance to the end application with excellent torqueLimits on the speeds. It means you cannot operate the motor below the normal speed
Armature Voltage Control Method The constant flow of current Not energy sufficient
Flux Control Method A simple and inexpensive method gives easy controlLimit on speeds

How to Use a Potentiometer to Control Motor Speed? 

A potentiometer is a variable resistor in a circuit. It has three terminals. The first terminal is the input terminal. The second terminal is the output terminal.  The middle terminal is called a slider. 

You can change the resistance of the circuit by turning the slider. Hence, it changes the voltage and affects the speed. 

Through the Potentiometer, you can know the unknown voltage by comparing it to the known voltage. So, how can you use a Potentiometer to control the motor speed? Well, check out the below ways to learn about it:

  1. Connect the positive pole circuit to the first terminal of the Potentiometer
  2. Connect the negative pole circuit to the last terminal of the Potentiometer
  3. Connect the wiper terminal to the circuit of the device you want to control 
  4. You can see a knob on the top of a middle terminal. This knob can be turned on or off to control the resistance of circuits
  5. As you turn the knob, the voltage of the circuit is changed. It’s because of the resistance you put in circuits through the middle terminal 
  6. As the voltage is changed, the speed also changes 

How to Wire a DC Motor Speed Controller? 

You need to wire the DC motor controller perfectly. Because you want to make sure that the current flows smoothly to the end application. So, how to wire a DC motor speed controller? Well, you can understand it through the below points: 

  1. Take a potentiometer, DC motor, and power supplier. You will need this to wire the DC motor 
  2. Now take a wire stripper and cut both ends of the wire. You will need to cut the wire in a proper size so the circuit works properly. Please make sure to use insulated wires
  3. Now mount the batteries into the power pack 
  4. Connect the potentiometer’s first and last terminal to both ends of the wire 
  5. Connect the wiper terminal to the DC motor 
  6. Now adjust the motor speed through the potentiometer. It will change the speed
  7. Finally, you’re done!

Brushless DC Motor Speed Controlling Process 

The brushless DC motor is different in changing speed than the usual DC motor control speed. While the DC motor control speed focuses on the voltage, the Brushless DC Motor focuses on the direct current. You do this by manipulating the rotation of flux. 

There are multiple ways you can control the Brushless DC Motor. Some of the common ways are pulse frequency, external analog system, communication signal RS485, etc. Please check out below to learn about it: 

1. Pulse Width Modulation (PWM) 

You can use the PWM method to control the Brushless DC Motor. It is quite simple. You need to adjust the frequency of the PWM so that it can be controlled through the duty cycle. 

To make it clear, there is a series of pulses, which turns the motor on and off. 

So you can control the speed of the motor by switching the power of the motor off or on. 

2. External Analog System 

You can use the external analog system to control the DC motor speed. In this method, the driver receives signals from the controller. Then the analogue systems are converted to digital signals. As the driver receives the signal, it starts to output the voltage and control the motor speed. 

3. Communication Signal RS485

The Communication Signal RS486 is connected to the BLDC controller (brushless direct current motor). The Communication Signal sends commands to the brushless direct current motor (BLDC) controller to control the motor speed. It gives noise immunity and a good date rate to the device. So this method is a beneficial one.

Why Is DC Motor Speed Control Necessary? 

A DC motor speed control is necessary because the machine won’t work properly without perfect control. You need to control the position, torque, and speed of the motor to deliver the best performance to the end application. Check out the below that explains the importance of DC motor speed control:  

  • DC motors speed control contributes an essential part in robotics and automation. There are many more motors in the industry. But when it comes to DC motors, it is highly used in the industry. The reason is that this motor makes it easy to maintain balance in machinery work.
  • The DC motor is used in electrical vehicles. It turns electrical energy into mechanical energy. The DC motor speed determines the speed rate of the machine that will operate. Hence this machine needs to work properly to safely operate the end application.


As the machines need to work properly, you need to have a well-functioning DC motor. So the machine will work perfectly at your desired speed. So, you must know that you have to choose the best way to control the speed according to your preference. 

Moreover, there are advantages and disadvantages of these methods. So comparing them with the other may help you to make decisions better according to your requirements. This was all about speed control. I hope this article helped you to learn how do you control the speed of a DC motor.

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