Commutator motors can often be found in household electrical appliances and power tools: washing machine, grinder, drill, vacuum cleaner, etc. Which is not at all surprising, because commutator motors allow you to obtain both high speeds and high torque (including high starting torque ) - which is what you need for most power tools.
In this case, commutator motors can be powered by both direct current (in particular, rectified current) and alternating current from a household network. To control the rotor speed of a commutator motor, speed controllers are used, which will be discussed in this article.
First, let's remember the design and principle of operation of a commutator motor. The commutator motor necessarily includes the following parts: rotor, stator and brush-collector switching unit. When power is applied to the stator and rotor, their magnetic fields begin to interact and the rotor eventually begins to rotate.
Power is supplied to the rotor through graphite brushes that fit tightly to the commutator (to the commutator lamellas). To change the direction of rotation of the rotor, it is necessary to change the phasing of the voltage on the stator or on the rotor.
The rotor and stator windings can be powered from different sources or can be connected in parallel or in series with each other. This is how commutator motors of parallel and series excitation differ. It is the series-excited commutator motors that can be found in most household electrical appliances, since such inclusion makes it possible to obtain a motor that is resistant to overloads.
Speaking about speed controllers, first of all we will focus on the simplest thyristor (triac) circuit (see below). This solution is used in vacuum cleaners, washing machines, grinders, and shows high reliability when operating in alternating current circuits (especially from a household network).
This circuit works quite simply: at each period of the mains voltage, it is charged through a resistor to the unlocking voltage of the dinistor connected to the control electrode of the main switch (triac), after which it opens and passes current to the load (to the commutator motor).
By adjusting the charging time of the capacitor in the triac opening control circuit, the average power supplied to the engine is regulated, and the speed is adjusted accordingly. This is the simplest regulator without current feedback.
The triac circuit is similar to a regular one; there is no feedback in it. To provide current feedback, for example to maintain acceptable power and avoid overloads, additional electronics are required. But if we consider the options from simple and straightforward circuits, then the triac circuit is followed by a rheostatic circuit.
The rheostat circuit allows you to effectively regulate speed, but leads to the dissipation of a large amount of heat. This requires a radiator and effective heat removal, which means energy loss and low efficiency as a result.
Regulator circuits based on special thyristor control circuits or at least on an integrated timer are more effective. Switching of the load (commutator motor) on alternating current is carried out by a power transistor (or thyristor), which opens and closes one or more times during each period of the network sinusoid. This regulates the average power supplied to the engine.
The control circuit is powered by 12 volts DC from its own source or from a 220 volt network through a quenching circuit. Such circuits are suitable for controlling powerful motors.
The principle of regulation with DC microcircuits is of course. A transistor, for example, opens with a strictly specified frequency of several kilohertz, but the duration of the open state is regulated. So, by rotating the handle of the variable resistor, the rotation speed of the rotor of the commutator motor is set. This method is convenient for maintaining low speeds of a commutator motor under load.
Better control is direct current regulation. When PWM operates at a frequency of about 15 kHz, adjusting the pulse width controls the voltage at approximately the same current. Let's say, by adjusting the constant voltage in the range from 10 to 30 volts, they get different speeds at a current of about 80 amperes, achieving the required average power.
If you want to make a simple regulator for a commutator motor with your own hands without any special requests for feedback, then you can choose a thyristor circuit. All you need is a soldering iron, a capacitor, a dinistor, a thyristor, a pair of resistors and wires.
If you need a higher-quality regulator with the ability to maintain stable speeds under dynamic loads, take a closer look at regulators on microcircuits with feedback that can process the signal from the tachogenerator (speed sensor) of a commutator motor, as is implemented, for example, in washing machines.
Andrey Povny
Connects between the power supply and the load. Power can be supplied from a battery or AC/DC adapter of suitable load.
The load can be any DC motor or incandescent lamp. Thanks to pulsed operation (PWM), the circuit operates with almost no energy loss. The control transistor does not require a heatsink.
The regulator circuit is ideal for adjusting the speed of a drill for drilling circuit boards. At low speeds it ensures the drill operates with relatively high torque.
Description of the electric motor speed controller
Logic elements DD1.1, DD1.2 are used in the form of a classic PWM generator. Resistor R1 performs only a protective function. The frequency of the generator is determined by the capacitance C2 or C3 and the resistance of the potentiometer PR1 together with R2, R3. Parallel connected logic elements DD1.3, DD1.4 control the MOSFET transistor (VT1).
When using a MOSFET transistor in the circuit, resistor R4 is not needed and a jumper is installed in its place. This resistor (R4) is provided only if a Darlington transistor of the n-p-n structure, for example, BD649, is installed instead of a MOSFET. Then, to limit the base current, resistor R4 should have a value of 1k...2.2k.
PR1 allows you to change the duty cycle of the generated signal within a very wide range, from approximately 1% to approximately 99%. The signal from the generator periodically opens and closes transistor VT1, and the average power supplied to the load (connector Z2) depends on the duty cycle of the signal. Thus, potentiometer PR1 allows for smooth adjustment of the power supplied to the load.
The reverse-connected diode VD4 is indispensable when using an inductive load (for example, an electric motor). Without diode VD4, at the moment of shutdown, pulses may appear at the drain of transistor VT1 that significantly exceed the permissible value for a given transistor and this can damage it.
Thanks to pulsed operation, the power losses on transistor VT1 are small and therefore do not require a radiator, even at currents of the order of several amperes, that is, load power up to 100 W. It should be borne in mind that the device is a power regulator, not an engine speed stabilizer, so engine speed depends on its load.
ATTENTION! The circuit regulates power in pulsation mode, applying a meander to the load. Such pulses can be a source of electromagnetic interference. To minimize interference, short connections between the unit and the load should be used.
The connecting cord should be in the form of a twisted pair (ordinary two wires twisted together). It is also recommended to additionally connect an electrolytic capacitor (set of capacitors) with a capacity of 1000 ... 10000 microns to the power connector Z1.
The circuit provides an additional capacitor C3, connected using jumper J1. Turning on this capacitor causes the generator frequency to decrease from 700Hz to approximately 25Hz. This is useful in terms of the electromagnetic interference generated.
Although in some cases, reducing the frequency may be unacceptable, for example, it may cause the lamp to flicker noticeably. Then you need to independently select the optimal capacity C3.
The electric motor is necessary for smooth acceleration and braking. Such devices are widely used in industry. With their help, the rotation speed of the fans is changed. 12 Volt motors are used in control systems and automobiles. Everyone has seen the switches that change the rotation speed of the stove fan in cars. This is one of the types of regulators. It's just not designed to run smoothly. The rotation speed changes in steps.
Application of frequency converters
Frequency converters are used as speed regulators and 380V. These are high-tech electronic devices that allow you to radically change the characteristics of the current (signal shape and frequency). They are based on powerful semiconductor transistors and a pulse-width modulator. All operation of the device is controlled by a microcontroller unit. The rotation speed of the engine rotor changes smoothly.
Therefore, they are used in loaded mechanisms. The slower the acceleration, the less load the conveyor or gearbox will experience. All frequencies are equipped with several degrees of protection - for current, load, voltage and others. Some models of frequency converters are powered from single-phase and turn it into three-phase. This allows you to connect asynchronous motors at home without using complex circuits. And there will be no loss of power when working with such a device.
For what purposes are regulators used?
In the case of asynchronous motors, speed controllers are needed for:
- Significant energy savings. After all, not every mechanism requires a high motor rotation speed - sometimes it can be reduced by 20-30%, and this will reduce energy costs by half.
- Protection of mechanisms and electronic circuits. Using frequency converters, you can control temperature, pressure and many other parameters. If the engine operates as a pump drive, then a pressure sensor must be installed in the container into which it pumps air or liquid. And when the maximum value is reached, the motor will simply turn off.
- Performing a soft start. There is no need to use additional electronic devices - everything can be done by changing the settings of the frequency converter.
- Reduced maintenance costs. With the help of such speed controllers for 220V electric motors, the risk of failure of the drive and individual mechanisms is reduced.
The circuit according to which frequency converters are built is widespread in many household appliances. Something similar can be found in uninterruptible power supplies, welding machines, voltage stabilizers, power supplies for computers, laptops, phone chargers, ignition units for backlight lamps of modern LCD TVs and monitors.
How do rotary controls work?
You can make an electric motor speed controller with your own hands, but to do this you will need to study all the technical aspects. Structurally, several main components can be distinguished, namely:
- Electric motor.
- Microcontroller control system and converter unit.
- Drive and mechanisms associated with it.
At the very beginning of operation, after voltage is applied to the windings, the motor rotor rotates with maximum power. It is this feature that distinguishes asynchronous machines from others. To this is added the load from the mechanism that is driven. As a result, at the initial stage, power and current consumption increase to a maximum.
A lot of heat is generated. Both the windings and wires overheat. Using a frequency converter will help get rid of this. If you set a soft start, then the engine will not accelerate to maximum speed (which is also regulated by the device and may not be 1500 rpm, but only 1000) not immediately, but within 10 seconds (increase 100-150 rpm every second). At the same time, the load on all mechanisms and wires will decrease significantly.
Homemade regulator
You can make your own speed controller for a 12V electric motor. This will require a multi-position switch and wirewound resistors. With the help of the latter, the supply voltage (and with it the rotation speed) changes. Similar systems can be used for asynchronous motors, but they are less efficient. Many years ago, mechanical regulators were widely used - based on gear drives or variators. But they were not very reliable. Electronic means perform much better. After all, they are not so bulky and allow you to fine-tune the drive.
To make an electric motor rotation controller, you will need several electronic devices, which can either be purchased in a store or removed from old inverter devices. The VT138-600 triac shows good results in the circuits of such electronic devices. To make the adjustment, you will need to include a variable resistor in the circuit. With its help, the amplitude of the signal entering the triac changes.
Implementation of a management system
To improve the parameters of even the simplest device, you will need to include microcontroller control in the electric motor speed controller circuit. To do this, you need to select a processor with a suitable number of inputs and outputs - for connecting sensors, buttons, electronic keys. For experiments, you can use the AtMega128 microcontroller - the most popular and easiest to use. You can find many schemes using this controller in the public domain. Finding them yourself and applying them in practice is not difficult. In order for it to work correctly, you will need to write an algorithm into it - responses to certain actions. For example, when the temperature reaches 60 degrees (measured on the radiator of the device), the power should be turned off.
Finally
If you decide not to make a device yourself, but to purchase a ready-made one, then pay attention to the main parameters, such as power, type of control system, operating voltage, frequencies. It is advisable to calculate the characteristics of the mechanism in which it is planned to use the motor voltage regulator. And don’t forget to compare it with the parameters of the frequency converter.
An acquaintance once asked me to look at and repair a homemade speed controller for an electric stove motor from his “penny”. He praised the regulator because it was possible to smoothly change the engine speed, but something broke in it.
The dimensions of the regulator body immediately alerted me, it was too bulky, when I took it apart I saw inside a massive radiator with a couple of KT819 transistors, still in a metal case, and some kind of circuit assembled by soldering leg to leg from which wires went to a variable resistor and to power transistors. The power transistors turned out to be broken. Since the engine consumed quite a bit of current, the power transistors, especially at low speeds, got quite hot. Considering such an adjustment scheme to be outdated, I decided to assemble a PWM (pulse width modulation) regulator with a powerful field-effect transistor as a key element. As the actual PWM modulator, it was decided to use the well-known 555 timer. It would seem that what can be done on a microcircuit that was developed more than 30 years ago. However, the range of applications for the 555 timer (our analogue of the KR1006VI1) is almost limitless. The use of basic operating modes and their modified variants allows the timer to be used in a variety of devices. It is known that the following basic functional devices can be assembled on chips of the 555 and 556 families:
- - monostable generator (one-shot);
- - generator - multivibrator;
- - time delay generator;
- - pulse width modulator;
- - pulse detector;
- - frequency divider.
The circuit of the electric motor speed controller turned out to be simple, with a minimum of external wiring:
I didn’t etch the printed circuit board for the electric motor speed controller, I just cut through the contact areas for the timer with a cutter:
I soldered the timer and assembled the kit.A powerful n-channel field-effect transistor with an insulated gate, the so-called Power MOSFET IRF540, is used as a key element.
I attached it to a small radiator - we select the dimensions based on the operating current of the electric motor. If it is small, then the transistor may not need cooling at all.
Hello everyone, probably many radio amateurs, like me, have more than one hobby, but several. In addition to designing electronic devices, I do photography, video shooting with a DSLR camera, and video editing. As a videographer, I needed a slider for video shooting, and first I’ll briefly explain what it is. The photo below shows the factory slider.
The slider is designed for video shooting on cameras and video cameras. It is analogous to the rail system used in wide-format cinema. With its help, a smooth movement of the camera around the object being photographed is created. Another very powerful effect that can be used when working with a slider is the ability to move closer or further from the subject. The next photo shows the engine that was chosen to make the slider.
The slider is driven by a 12-volt DC motor. A diagram of a regulator for the motor that moves the slider carriage was found on the Internet. The next photo shows the power indicator on the LED, the toggle switch that controls the reverse and the power switch.
When operating such a device, it is important that there is smooth speed control, plus easy inclusion of engine reverse. The speed of rotation of the motor shaft, in the case of using our regulator, is smoothly adjusted by rotating the knob of a 5 kOhm variable resistor. Perhaps I am not the only one of the users of this site who is interested in photography, and someone else will want to replicate this device; those who wish can download an archive with a circuit diagram and printed circuit board of the regulator at the end of the article. The following figure shows a schematic diagram of a regulator for an engine:
Regulator circuit
The circuit is very simple and can be easily assembled even by novice radio amateurs. Among the advantages of assembling this device, I can name its low cost and the ability to customize it to meet your needs. The figure shows the controller's printed circuit board:
But the scope of application of this regulator is not limited to sliders alone; it can easily be used as a speed regulator, for example, a machine drill, a homemade Dremel powered by 12 volts, or a computer cooler, for example, with dimensions of 80 x 80 or 120 x 120 mm. I also developed a scheme for reversing the engine, or in other words, quickly changing the rotation of the shaft in the other direction. To do this, I used a six-pin toggle switch with 2 positions. The following figure shows its connection diagram:
The middle contacts of the toggle switch, marked (+) and (-), are connected to the contacts on the board marked M1.1 and M1.2, the polarity does not matter. Everyone knows that computer coolers, when the supply voltage and, accordingly, the speed are reduced, make much less noise during operation. In the next photo, the KT805AM transistor is on the radiator:
Almost any medium and high power n-p-n structure transistor can be used in the circuit. The diode can also be replaced with analogues suitable for current, for example 1N4001, 1N4007 and others. The motor terminals are shunted by a diode in reverse connection; this was done to protect the transistor during switching on and off moments of the circuit, since our motor has an inductive load. Also, the circuit provides an indication that the slider is turned on on an LED connected in series with a resistor.
When using an engine of greater power than shown in the photo, the transistor must be attached to the radiator to improve cooling. A photo of the resulting board is shown below:
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