DC motor speed control is a useful feature of the motor. By controlling the speed of the motor, you can vary the speed of the motor according to the requirements and can get the required operation. Both reduction and increase of the motor speed can be realized, but here we only introduce 4 ways for motor speed control for reduction purposes.
According to how does a DC motor work, its working principle implies four things:
1) Speed of the motor is determined by the speed controller;
2) Speed of the motor is directly proportional to supply voltage;
3) Speed of the motor is inversely proportional to armature voltage drop;
4) Speed of the motor is inversely proportional to the flux due to the field findings.
Thus, the speed of a DC motor can be controlled in four ways:
1) By adding a DC motor controller;
2) By varying the supply voltage;
3) By varying the armature voltage, and by varying the armature resistance;
4) By varying the flux, and by varying the current through field winding.
4 Ways for DC Motor Speed Control
1. Add a DC Speed Controller
A gearbox — otherwise known as a gear reducer or speed reducer — is a set of gears that can be added to a motor to drastically decrease output speed and/or increase torque. The speed reduction is determined by the gear ratio and efficiency of the gearbox. Thus, it plays the role of a DC motor controller.
How to achieve DC motor control?
The drives by ZHAOWEI with an integrated speed controller combine the advantages of DC motors and their electronic control. Controller parameters and operating mode can be adjusted via motion manager. Depending on the desired speed range, the rotor position is detected by means of digital or optionally available analog Hall sensors. That is to say, the speed control settings can be configured in combination with motion manager via programming adapters.
As for the micro electric motors, there is a series of DC motor controllers according to voltage supply on the market that can alter the motor speed, including 12V DC motor speed controller, 24V DC motor speed controller, 6V DC motor speed controller, etc.
2. Voltage Control Method
Electric motors are characterized by their variety, ranging from fractional horsepower units for small appliances to motors with thousands of hp for heavy industrial use. Actually, the speed of an electric motor is also determined by its physical construction and the frequency of the voltage supply. Setting the load aside, the speed of a motor is proportional to the supply voltage. So, if the voltage decreases, the speed of the motor will accordingly decrease. Electrical engineers select motor speed based on the needs of each application, similar to how horsepower is specified based on the mechanical load.
3. Armature Voltage Control
This speed control method is used only for small motors. In this method, the field winding is supplied by the constant supply. But the armature winding is supplied by a separate variable DC source. With this method, the speed of the DC motor can be controlled by controlling the armature resistance to control the voltage drop across the armature. This method also adopts a variable resistor in series with the armature. When the variable resistor reaches its minimum value, the armature resistance is at a normal one, and therefore, the armature voltage drops; while when the resistance value is gradually increased, the voltage across the armature decreases. This, in turn, leads to a decrease in the speed of the motor. In this way, the speed of the motor below its normal range can be achieved. But, the armature control method involves huge power loss due to its usage of the resistor in series with the armature.
4. Flux Control Method
In this method, the magnetic flux due to the field windings is varied in order to vary the speed of the motor. As the magnetic flux depends on the current flowing through the field winding, it can be varied by varying the current through the field winding. This can be achieved by using a variable resistor in a series with the field winding resistor.
Initially, when the variable resistor is kept at its minimum position, the rated current flows through the field winding due to a rated supply voltage, and as a result, the speed is kept normal. When the resistance is decreased gradually, the current through the field winding increases. This, in turn, increases the flux produced. Thus, the speed of the motor decreases below its normal value. This method contributes to DC motor speed control, but the flux control method can affect commutation.
Those mentioned above are only some of the main ways for DC motor speed control. After comparison, you may know it is wise to add a micro gearbox as the DC motor controller for ideal speed and select the DC motors with suitable voltage supply, which is a convenient and cost-effective way.