2022-12-17 15:53:58
DC motors are widely used in various industries due to their ability to convert electrical energy into mechanical energy. Controlling the speed of a DC motor is crucial for optimizing its performance and achieving desired outcomes in different applications. In this article, we will explore the best and most reliable methods to decrease the speed of a DC motor. By understanding these techniques, you will be equipped with valuable knowledge that can enhance your career in the field of electrical engineering.
Before delving into the methods of decreasing DC motor speed, it is essential to grasp the fundamental principles of DC motor operation and speed control. A DC motor operates on the principle that when a current-carrying conductor is placed in a magnetic field, it experiences a mechanical force, resulting in rotational motion. The speed of a DC motor can be controlled by manipulating the supply voltage, the armature voltage, or the field flux.
Simple DC Motor Voltage Equation
From the above figure, it can be seen that the voltage equation of a simple DC motor is:
V = Eb + IaRa
Among them, V is the supply voltage, Eb is the back electromotive force, Ia is the armature current, and Ra is the armature resistance.
We know that the formula for calculating the back electromotive force (EMF) Eb is:
Eb = (PøNZ) / 60A
Among them, P is the pole number, A is the constant, Z is the number of conductors, N is the motor speed, and ø is the magnetic flux.
Substituting the value of Eb into the voltage equation, we can obtain:
V-IaRa=(PøNZ)/60A
Equivalent to: N = K(V - IaRa)/ø
Where K is a constant.
This means:
From the above minutes, it can be concluded that the speed of a DC motor can be changed in three ways:
There are several reliable techniques available to decrease the speed of a DC motor. Let's explore the most prominent ones:
This method involves connecting a regulating resistance in series with the motor supply. By increasing the resistance, the voltage across the armature decreases, leading to a reduction in motor speed. Armature controlled resistance is commonly employed in applications where a persistent torque is required, such as cranes, trains, and vehicles.
In this technique, a rheostat is connected in both series and shunt configuration with the armature. By varying the series rheostat, the voltage applied to the armature can be adjusted, while the shunt rheostat controls the excitation current. Shunted armature control allows for some degree of speed regulation, although it may not exceed the normal speed range. This method is cost-effective but can result in significant power losses.
The field diverter technique involves shunting a portion of the motor current across the series field, thereby reducing the flux across the field winding. By decreasing the resistance of the diverter, the field current is reduced, resulting in a decrease in motor speed. This method is suitable for applications where speed needs to increase with decreasing loads.
In this technique, the speed of a DC motor is increased by reducing the number of turns in the field winding. By decreasing the field winding turns, the flux is reduced, leading to an increase in motor speed. Controlling of tapped field is commonly used in electric tractions.
By varying the armature voltage and resistance simultaneously, the speed of a DC motor can be effectively controlled. Decreasing the armature voltage and increasing the armature resistance contribute to reducing the motor speed. This method is suitable for applications where precise speed control is required.
While implementing speed control techniques for a DC motor, it is essential to consider certain factors:
Controlling the speed of a DC motor is vital for optimizing its performance and achieving desired outcomes in various applications. By employing reliable and effective speed control methods such as armature controlled resistance, shunted armature control, field diverter technique, controlling of tapped field, and varying armature voltage and resistance, it is possible to decrease the speed of a DC motor accurately. Understanding these techniques and considering factors such as efficiency, load characteristics, and cost-effectiveness will help you use your device better.