Somehow a friend asked me to look and repair a home-made speed controller for the electric motor of the stove from his “penny”. He praised the regulator as it was possible to smoothly change the engine speed, but something broke in it.
The dimensions of the regulator case immediately alerted me, it was painfully 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 circuit assembled by soldering leg to leg from which wires went to a variable resistor and to power transistors. Power transistors were broken. Since the engine consumed not a small current, the power transistors, especially at low speeds, got quite hot. Considering such an adjustment scheme outdated, I decided to assemble a PWM (pulse-width modulation) regulator with a powerful field-effect transistor as a key element.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, which was developed more than 30 years ago. Nevertheless, the range of applications of the 555 timer (our analogue KR1006VI1) is practically unlimited. The use of the main operating modes and their modified versions allows the timer to be used in a variety of devices. It is known that the following main functional devices can be assembled on microcircuits of the 555 and 556 families:
- - monostable generator (single vibrator);
- - generator - multivibrator;
- - time delay generator;
- - pulse-width modulator;
- - pulse detector;
- - frequency divider.
The circuit of the motor speed controller turned out to be simple, with a minimum of external piping:
I didn’t poison the printed circuit board for the speed controller of the electric motor, I just cut the contact areas for the timer with a cutter:
I soldered the timer and assembled the body 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 fixed it on a small radiator - we choose the dimensions based on the operating current of the electric motor. If it is small, then the transistor may not need cooling at all.
A high-quality and reliable rotation speed controller for single-phase collector motors can be made on common parts in just 1 evening. This circuit has a built-in overload detection module, provides a soft start to the controlled motor and a motor speed stabilizer. Such a unit works with a voltage of both 220 and 110 volts.
Regulator technical parameters
- supply voltage: 230 volts AC
- control range: 5…99%
- load voltage: 230 V / 12 A (2.5 kW with heatsink)
- maximum power without heat sink 300 W
- low noise
- speed stabilization
- soft start
- board dimensions: 50×60 mm
circuit diagram
Scheme of the motor controller on the triac and U2008 The circuit of the control system module is based on a PWM pulse generator and a motor control triac - a classic circuit design for such devices. Elements D1 and R1 ensure that the supply voltage is limited to the value of the generator microcircuit that is safe for power supply. Capacitor C1 is responsible for filtering the supply voltage. Elements R3, R5 and P1 are a voltage divider with the possibility of its regulation, which is used to set the amount of power supplied to the load. Thanks to the use of resistor R2, which is directly included in the input circuit to the m / s phase, the indoor units are synchronized with the VT139 triac.
Printed circuit board The following figure shows the layout of the elements on the printed circuit board. During installation and start-up, attention should be paid to ensuring safe operation conditions - the regulator is powered by a 220V network and its elements are directly connected to the phase.
Regulator power increase
In the test case, a triac BT138/800 with a maximum current of 12 A was used, which makes it possible to control a load of more than 2 kW. If it is necessary to control even higher load currents, we recommend installing the thyristor outside the board on a large radiator. You should also remember about right choice FUSE fuse depending on the load.
In addition to controlling the speed of electric motors, you can use the circuit to adjust the brightness of the lamps without any alterations.
The regulator circuit, with the help of which the engine or fan speed is changed, is designed to operate from an alternating current main for a voltage of 220 volts.
The motor, together with the power thyristor VS2, is connected to the diagonal of the diode bridge VD3, while the other is supplied with an AC mains voltage of 220 volts. In addition, this thyristor controls with sufficiently wide pulses, due to which, short circuit breaks, with which all collector motors work, do not affect the stable operation of the circuit.
The transistor VT1, connected according to the pulse generator circuit, controls the first thyristor. As soon as the voltage across the capacitor becomes sufficient to open the first transistor, a positive pulse will be sent to the control output of the thyristor. The thyristor will open and now a long control pulse will appear on the second thyristor. And already from it, the voltage, which actually affects the speed, is supplied to the engine.
The rotational speed of the electric motor is adjusted by the variable resistance R1. Since an inductive load is connected to the circuit of the second thyristor, spontaneous opening of the thyristor is possible, even in the absence of a control signal. Therefore, to block this, a VD2 diode is included in the circuit, which is connected in parallel with the motor winding L1.
When setting up the engine speed controller circuit, it is advisable to use, which can measure the speed of the electric motor or a conventional pointer voltmeter for alternating current, which is connected in parallel to the engine.
By selecting the resistance R3, the voltage range is set from 90 to 220 volts. If the engine does not work correctly at minimum speed, then it is necessary to reduce the value of the resistor R2.
This circuit is well suited for adjusting the fan speed depending on the temperature.
It is used as a sensitive element. As a result of its heating, its resistance decreases, and therefore, at the output of the operational amplifier, on the contrary, the voltage increases and controls the fan speed through the field-effect transistor.
Variable resistance P1 - you can set the lowest fan speed at the lowest temperature, and variable resistance P2 regulate the highest speed at maximum temperature.
Under normal conditions, we set the minimum engine speed with the resistor P1. Then the sensor is heated and the required fan speed is set with resistance P2.
The circuit controls the fan speed based on temperature readings, using a conventional NTC.
The circuit is so simple that there are only three radio components in it: an adjustable voltage regulator LM317T and two resistors forming a voltage divider. One of the resistances is a NTC thermistor and the other is a conventional resistor. For ease of assembly drawing printed circuit board I bring below.
In order to save money, you can equip a typical angle grinder with a speed controller. Such a regulator for grinding cases of various electronic equipment is an indispensable tool in the arsenal of a radio amateur
The U2008B chip is a PWM speed controller for AC collector motors. Manufactured by TELEFUNKEN, most often it can be seen in the control circuit of an electric drill, step saw, electric jigsaw, etc., and also works with motors from vacuum cleaners, allowing you to adjust the traction. The built-in soft start circuit significantly extends the life of the motors. Control circuits based on this chip can also be used to control power, such as heaters.
All modern drills are produced with built-in engine speed controllers, but for sure, in the arsenal of every radio amateur there is an old Soviet drill, in which the change in speed was not conceived, which drastically reduces performance.
You can control the speed of rotation of an asynchronous brushless motor by setting the frequency of the AC supply voltage. This scheme allows you to adjust the rotation speed in a fairly wide range - from 1000 to 4000 rpm.
Collector motors can often be found in household electrical appliances and power tools: a washing machine, grinder, drill, vacuum cleaner, etc. Which is not at all surprising, because collector motors allow you to get both high speeds and high torque (including high starting torque ) - which is what is needed for most power tools.
At the same time, collector motors can be powered by both direct current (in particular, rectified current) and alternating current from a household network. To control the speed of rotation of the rotor of the collector motor, speed controllers are used, and they will be discussed in this article.
First, let's recall the device and the principle of operation of the collector engine. The commutator motor necessarily includes the following parts: a rotor, a stator and a brush-collector switching unit. When power is applied to the stator and rotor, they magnetic fields begin to interact, the rotor begins to rotate as a result.
Power is supplied to the rotor through graphite brushes that are tightly attached to the collector (to the collector 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 may be fed from different sources, or may be connected in parallel or in series with each other. This is how collector motors of parallel and series excitation differ. It is collector motors of series excitation that can be found in most household electrical appliances, since such inclusion makes it possible to obtain an overload-resistant motor.
Speaking of 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 working in AC circuits (especially from a household network).
This circuit works quite unpretentiously: 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 key (triac), after which it opens and passes current to the load (to the collector 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 the usual one, there is no feedback in it. In order for current feedback to appear, for example, to maintain acceptable power and prevent overloads, additional electronics are needed. But if we consider options from simple and unpretentious circuits, then a triac circuit is followed by a rheostat circuit.
The rheostat circuit allows you to effectively control the speed, but leads to the dissipation of a large amount of heat. It requires a radiator and efficient heat dissipation, and this is energy loss and low efficiency in the end.
More efficient controller circuits on special thyristor control circuits or at least on an integrated timer. The switching of the load (collector 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 mains 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 damping circuit. Such schemes are suitable for controlling powerful motors.
The principle of regulation with microcircuits at direct current is of course. A transistor, for example, opens at a strictly specified frequency of a few kilohertz, but the duration of the open state is adjustable. So, by turning the knob of the variable resistor, the speed of rotation of the rotor of the collector motor is set. This method is useful for keeping low speeds of the commutator motor under load.
Better control is precisely DC regulation. When the PWM operates at a frequency of about 15 kHz, by adjusting the pulse width, the voltage is controlled at approximately the same current. Say, by adjusting the constant voltage in the range from 10 to 30 volts, they get different revolutions at a current of about 80 amperes, achieving the required average power.
If you want to make a simple regulator for a collector 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 better regulator with the ability to maintain stable speed under a dynamic load, take a closer look at the regulators on microcircuits with feedback that can process the signal from the tachogenerator (speed sensor) of the collector motor, as is implemented, for example, in washing machines.
Andrey Povny
Based on the powerful triac BT138-600, you can assemble an AC motor speed controller circuit. This circuit is designed to control the speed of rotation of the electric motors of drilling machines, fans, vacuum cleaners, angle grinders, etc. The motor speed can be adjusted by changing the resistance of the potentiometer P1. Parameter P1 determines the phase of the trigger pulse that opens the triac. The circuit also performs a stabilization function that maintains the speed of the motor even when it is heavily loaded.
For example, when the motor of a drilling machine slows down due to increased metal resistance, the EMF of the motor also decreases. This leads to an increase in voltage in R2-P1 and C3 causing the triac to open longer and the speed increases accordingly.
Regulator for DC motor
The simplest and most popular method for adjusting the speed of rotation of a DC motor is based on the use of pulse width modulation ( PWM or PWM ). In this case, the supply voltage is applied to the motor in the form of pulses. The pulse repetition rate remains constant, and their duration can change - this is how the speed (power) changes.
To generate a PWM signal, you can take a circuit based on the NE555 chip. The most simple circuit DC motor speed controller is shown in the figure:
Here VT1 is an n-type field effect transistor capable of withstanding the maximum motor current at a given voltage and load on the shaft. VCC1 is 5 to 16V, VCC2 is greater than or equal to VCC1. The frequency of the PWM signal can be calculated using the formula:
F = 1.44/(R1*C1), [Hz]
Where R1 is in ohms, C1 is in farads.
With the ratings indicated in the diagram above, the PWM signal frequency will be equal to:
F = 1.44/(50000*0.0000001) = 290 Hz.
It is worth noting that even modern devices, including high-power control, are based on just such schemes. Naturally, using more powerful elements that can withstand high currents.
