Specialists working with electric tools, drives for sewing machines, as well as other devices involved in various industrial and domestic spheres, often have to deal with the need to adjust the speed. It is not a good idea to conduct such a procedure through power down. At the same time the power of the electric motor is lost, it reduces the speed, eventually stops.
The scheme of the engine with an internal rotor.
Therefore, the best option for the implementation of speed management is considered to be voltage regulation and reverse communication with the load current in the engine.
General concepts of motor speed control
Usually, in electric devices and instruments, universal-collector motors with series excitation are applicable. Their work has proven itself in direct and alternating currents. The features of this motor controller include the occurrence of self-induction impulses of counter-electromotive force. This occurs during the opening of the armature windings located on the lamellae of the collector, in the case of their switching. These pulses are the same as feeding in amplitude, but in phase they are completely opposite.
The guide angle by which the counter-electromotive force is displaced is determined by the external properties of the electric motor, its load, and so on. The negative impact is as follows:
Typical scheme of the regulator drill speed.
- motor power is lost;
- a spark appears on the collector;
- heating of the winding is formed above the norm.
A certain amount of back electromotive force is canceled by capacitors shunting the node.
The processes that occur under the regime of a regulator with a feedback link can be represented in this way. The reference movement, which determines the speed of rotation of the electric motor, is strictly formed by means of a resistive-capacitive circuit.
When the load increases, the torque decreases, and with it the speed of rotation decreases. The resulting counter-electromotive force, which was directed between the cathode and the charging electrode, decreases.
It always comes down to increasing the voltage on the thyristor. It starts at a misfire angle and delivers a greater amount of current to the electric motor, at the same time compensating for the decrease in the speed of rotation.
Thus, the voltage pulse becomes balanced, which can make the motor speed controller. With the help of the desired switch, you can energize without making additional adjustments. A properly selected thyristor with the lowest switching current better stabilizes the speed of turns.Back to table of contents
Use of rotation control for engines of different power
The principle described above also applies to high power engines. The only difference is that the installation of the transistor is made on the radiator, the total area of which is from 25 cm² and more.
The equipment with low power is applicable power, the DC level of which is 12 V. The same applies to obtain a low speed. When exposed to high voltage, the working microcircuit is powered by a parametric stabilizer, whose maximum is 15 V. Moreover, the speed is regulated by changing the average values of the pulses applied to the equipment.
If you need to adjust the speed of the electric motor, on the shaft of which there is a high torque, you will need power at maximum. A damping resistor and diodes provide power to the device. The charge of the capacitor from the source provides a phase delay in the opening of the thyristors.
The capacitor is charged to the level at which the transistor is triggered, and the thyristor is started with a positive anode voltage. After the discharge of the capacitor, the unijunction transistor is turned off. The type of motor and the estimated depth of the feedback determine the value of the resistor.