Power tool engine speed controller - diagram and principle of operation. Speed ​​controller for a commutator motor: design and DIY production Scheme for smoothly adjusting the speed of an electric motor

Not every modern drill or grinder is equipped with a factory speed regulator, and most often speed control is not provided at all. However, both angle grinders and drills are built on the basis of commutator motors, which allows each of their owners, who has the slightest ability to handle a soldering iron, to make their own speed controller from available electronic components, either domestic or imported.

In this article we will look at the diagram and principle of operation of the simplest engine speed controller for a power tool, and the only condition is that the engine must be a commutator type - with characteristic lamellas on the rotor and brushes (which sometimes spark).

The above diagram contains a minimum of parts and is suitable for power tools up to 1.8 kW and above, for a drill or grinder. A similar circuit is used to regulate speed in automatic washing machines that have commutator high-speed motors, as well as in dimmers for incandescent lamps. Such circuits, in principle, will allow you to regulate the heating temperature of a soldering iron tip, an electric heater based on heating elements, etc.

The following electronic components will be required:

Constant resistor R1 - 6.8 kOhm, 5 W.

Variable resistor R2 - 2.2 kOhm, 2 W.

Constant resistor R3 - 51 Ohm, 0.125 W.

Film capacitor C1 - 2 µF 400 V.

Film capacitor C2 - 0.047 uF 400 volts.

Diodes VD1 and VD2 - for voltage up to 400 V, for current up to 1 A.

Thyristor VT1 - for the required current, for a reverse voltage of at least 400 volts.

The circuit is based on a thyristor. A thyristor is a semiconductor element with three terminals: anode, cathode, and control electrode. After a short pulse of positive polarity is applied to the control electrode of the thyristor, the thyristor turns into a diode and begins to conduct current until this current in its circuit is interrupted or changes direction.

After the current stops or when its direction changes, the thyristor will close and stop conducting current until the next short pulse is applied to the control electrode. Well, since the voltage in the household network is alternating sinusoidal, then each period of the network sinusoid the thyristor (as part of this circuit) will work strictly starting from the set moment (in the set phase), and the less the thyristor is open during each period, the lower the speed will be power tool, and the longer the thyristor is open, the higher the speed will be.

As you can see, the principle is simple. But when applied to a power tool with a commutator motor, the circuit works more cleverly, and we will talk about this later.

So, the network here includes in parallel: a measuring control circuit and a power circuit. The measuring circuit consists of constant and variable resistors R1 and R2, capacitor C1, and diode VD1. What is this chain for? This is a voltage divider. The voltage from the divider, and what is important, the back-EMF from the motor rotor, add up in antiphase, and form a pulse to open the thyristor. When the load is constant, then the open time of the thyristor is constant, therefore the speed is stabilized and constant.

As soon as the load on the tool, and therefore on the engine, increases, the value of the back-EMF decreases, since the speed decreases, which means the signal to the control electrode of the thyristor increases, and opening occurs with less delay, that is, the power supplied to the engine increases, increasing the dropped speed . This way the speed remains constant even under load.

As a result of the combined action of signals from the back-EMF and from the resistive divider, the load does not greatly affect the speed, but without a regulator this influence would be significant. Thus, using this circuit, stable speed control is achievable in each positive half-cycle of the network sinusoid. At medium and low rotation speeds this effect is more pronounced.

However, with increasing speed, that is, with increasing voltage removed from the variable resistor R2, the stability of maintaining a constant speed decreases.

In this case, it is better to provide a shunt button SA1 parallel to the thyristor. The function of diodes VD1 and VD2 is to ensure half-wave operation of the regulator, since the voltages from the divider and the rotor are compared only in the absence of current through the motor.

Capacitor C1 expands the control zone at low speeds, and capacitor C2 reduces sensitivity to interference from brush sparking. The thyristor needs to be highly sensitive so that a current of less than 100 μA can open it.

The regulator circuit, which is used to change the speed of rotation of the engine or fan, is designed to operate from an alternating current network at 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 receives an AC mains voltage of 220 volts. In addition, this thyristor carries out control with sufficiently wide pulses, due to which short circuit breaks, with which all commutator motors operate, do not affect the stable operation of the circuit.

The first thyristor is controlled by transistor VT1, connected according to a pulse generator circuit. As soon as the voltage on the capacitor becomes sufficient to open the first transistor, a positive pulse will be sent to the control terminal of the thyristor. The thyristor will open and now a long control pulse will appear on the second thyristor. And from it the voltage, which actually affects the speed, goes to the engine.

The rotational speed of the electric motor is adjusted by 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 diode VD2 is included in the circuit, which is connected in parallel to the L1 winding of the motor.

When setting up the engine speed controller circuit, it is advisable to use one, which can be used to measure the rotational speed of the electric motor, or a regular pointer voltmeter for alternating current, which is connected in parallel with the engine.

By selecting resistance R3, the voltage range is set from 90 to 220 volts. If the engine does not operate correctly at minimum speed, then it is necessary to reduce the value of resistor R2.

This circuit is well suited for adjusting fan speed depending on 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 a field-effect transistor.

With variable resistance P1, you can set the lowest fan rotation speed at the lowest temperature, and with variable resistance P2, you can control the highest rotation speed at maximum temperature.

Under normal conditions, we set resistor P1 to the minimum engine speed. Then the sensor is heated and the desired fan speed is set with resistance P2.

The circuit controls the fan speed depending on the temperature readings, using a conventional negative temperature coefficient.

The circuit is so simple that it contains only three radio components: an adjustable voltage regulator LM317T and two resistances forming a voltage divider. One of the resistances is a negative TCR thermistor, and the other is a regular resistor. To simplify assembly, I provide a drawing of the printed circuit board below.

In order to save money, you can equip a standard angle grinder with a speed controller. Such a regulator for grinding housings of various electronic equipment is an indispensable tool in the arsenal of a radio amateur.

The U2008B microcircuit is a PWM speed controller for AC commutator motors. Manufactured by TELEFUNKEN, it can most often be seen in the control circuit of an electric drill, step saw, 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 engines. Control circuits based on this chip can also be used to regulate power, for example, heaters.

All modern drills are produced with engine speed regulators built into them, but for sure, in the arsenal of every radio amateur there is an old Soviet drill, in which the change in speed was not intended, which sharply reduces the performance characteristics.

You can regulate the rotation speed of an asynchronous brushless motor by adjusting the frequency of the AC supply voltage. This circuit allows you to adjust the rotation speed in a fairly wide range - from 1000 to 4000 rpm.

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.

When using an electric motor in tools, one of the serious problems is adjusting the speed of their rotation. If the speed is not high enough, then the tool is not effective enough.

If it is too high, then this leads not only to a significant waste of electrical energy, but also to possible burnout of the tool. If the rotation speed is too high, the operation of the tool may also become less predictable. How to fix this? For this purpose, it is customary to use a special rotation speed controller.

The motor for power tools and household appliances is usually one of 2 main types:

1. Commutator motors.
2. Asynchronous motors.

In the past, the second of these categories was most widespread. Nowadays, approximately 85% of motors used in electric tools, household or kitchen appliances are of the commutator type. This is explained by the fact that they are more compact, they are more powerful and the process of managing them is simpler.

The operation of any electric motor is based on a very simple principle: If you place a rectangular frame between the poles of a magnet, which can rotate around its axis, and pass a direct current through it, the frame will begin to rotate. The direction of rotation is determined according to the “right hand rule”.

This pattern can be used to operate a commutator motor.

The important point here is connecting the current to this frame. Since it rotates, special sliding contacts are used for this. After the frame rotates 180 degrees, the current through these contacts will flow in the opposite direction. Thus, the direction of rotation will remain the same. At the same time, smooth rotation will not work. To achieve this effect, it is customary to use several dozen frames.

Device

A commutator motor usually consists of a rotor (armature), stator, brushes and tachogenerator:

1. Rotor- this is the rotating part, the stator is an external magnet.
2. Brushes made of graphite- this is the main part of the sliding contacts, through which voltage is supplied to the rotating armature.
3. Tachogenerator is a device that monitors rotation characteristics. In the event of a violation of the uniformity of movement, it adjusts the voltage supplied to the engine, thereby making it smoother.
4. Stator may contain not one magnet, but, for example, 2 (2 pairs of poles). Also, instead of static magnets, electromagnet coils can be used here. Such a motor can operate on both direct and alternating current.

The ease of adjusting the speed of a commutator motor is determined by the fact that the rotation speed directly depends on the magnitude of the applied voltage.

In addition, an important feature is that the rotation axis can be directly attached to a rotating tool without the use of intermediate mechanisms.

If we talk about their classification, we can talk about:

1. Brushed motors DC.
2. Brushed motors AC.

In this case, we are talking about what kind of current is used to power the electric motors.

Classification can also be made according to the principle of motor excitation. In a brushed motor design, electrical power is supplied to both the rotor and stator of the motor (if it uses electromagnets).

The difference lies in how these connections are organized.

Here it is customary to distinguish:

• Parallel excitation.
• Consistent excitation.
• Parallel-sequential excitation.

Adjustment

Now let's talk about how you can regulate the speed of commutator motors. Due to the fact that the rotation speed of the motor simply depends on the amount of voltage supplied, any means of adjustment that are capable of performing this function are quite suitable for this.

Let's list a few of these options as examples:

1. Laboratory autotransformer(LATR).
2. Factory adjustment boards, used in household appliances (you can use in particular those used in mixers or vacuum cleaners).
3. Buttons, used in the design of power tools.
4. Household regulators lighting with smooth action.

However, all of the above methods have a very important flaw. Along with the decrease in speed, the engine power also decreases. In some cases, it can be stopped even just with your hand. In some cases, this may be acceptable, but in most cases, it is a serious obstacle.

A good option is to adjust the speed using a tachogenerator. It is usually installed at the factory. If there are deviations in the motor rotation speed, an already adjusted power supply corresponding to the required rotation speed is transmitted to the motor. If you integrate motor rotation control into this circuit, then there will be no loss of power.

How does this look constructively? The most common are rheostatic rotation control, and those made using semiconductors.

In the first case, we are talking about variable resistance with mechanical adjustment. It is connected in series to the commutator motor. The disadvantage is the additional heat generation and additional waste of battery life. With this adjustment method, there is a loss of engine rotation power. Is a cheap solution. Not applicable for sufficiently powerful motors for the reasons mentioned.

In the second case, when using semiconductors, the motor is controlled by applying certain pulses. The circuit can change the duration of such pulses, which in turn changes the rotation speed without loss of power.

How to make it yourself?

There are various options for adjustment schemes. Let us present one of them in more detail.

Here is how it works:

Initially, this device was developed to adjust the commutator motor in electric vehicles. We were talking about one where the supply voltage is 24 V, but this design is also applicable to other engines.

The weak point of the circuit, which was identified during testing of its operation, is its poor suitability at very high current values. This is due to some slowdown in the operation of the transistor elements of the circuit.

It is recommended that the current be no more than 70 A. There is no current or temperature protection in this circuit, so it is recommended to build in an ammeter and monitor the current visually. The switching frequency will be 5 kHz, it is determined by capacitor C2 with a capacity of 20 nf.

As the current changes, this frequency can change between 3 kHz and 5 kHz. Variable resistor R2 is used to regulate the current. When using an electric motor at home, it is recommended to use a standard type regulator.

At the same time, it is recommended to select the value of R1 in such a way as to correctly configure the operation of the regulator. From the output of the microcircuit, the control pulse goes to a push-pull amplifier using transistors KT815 and KT816, and then goes to the transistors.

The printed circuit board has a size of 50 by 50 mm and is made of single-sided fiberglass:

This diagram additionally shows 2 45 ohm resistors. This is done for the possible connection of a regular computer fan to cool the device. When using an electric motor as a load, it is necessary to block the circuit with a blocking (damper) diode, which in its characteristics corresponds to twice the load current and twice the supply voltage.

Operating the device in the absence of such a diode may lead to failure due to possible overheating. In this case, the diode will need to be placed on the heat sink. To do this, you can use a metal plate that has an area of ​​30 cm2.

Regulating switches work in such a way that the power losses on them are quite small. IN In the original design, a standard computer fan was used. To connect it, a limiting resistance of 100 Ohms and a supply voltage of 24 V were used.

The assembled device looks like this:

When manufacturing a power unit (in the lower figure), the wires must be connected in such a way that there is a minimum of bending of those conductors through which large currents pass. We see that the manufacture of such a device requires certain professional knowledge and skills. Perhaps in some cases it makes sense to use a purchased device.

Selection criteria and cost

In order to correctly choose the most suitable type of regulator, you need to have a good idea of ​​what types of such devices there are:

1. Various types of control. Can be a vector or scalar control system. The former are used more often, while the latter are considered more reliable.
2. Regulator power must correspond to the maximum possible engine power.
3. By voltage It is convenient to choose a device that has the most universal properties.
4. Frequency characteristics. The regulator that suits you should match the highest frequency that the motor uses.
5. Other characteristics. Here we are talking about the length of the warranty period, dimensions and other characteristics.

Depending on the purpose and consumer properties, prices for regulators can vary significantly.

For the most part, they range from approximately 3.5 thousand rubles to 9 thousand:

1. Speed ​​controller KA-18 ESC, designed for 1:10 scale models. Costs 6890 rubles.
2. MEGA speed controller collector (moisture-proof). Costs 3605 rubles.
3. Speed ​​controller for LaTrax 1:18 models. Its price is 5690 rubles.

Based on the powerful triac BT138-600, you can assemble a circuit for an AC motor speed controller. This circuit is designed to regulate the rotation speed of electric motors of drilling machines, fans, vacuum cleaners, grinders, etc. The motor speed can be adjusted by changing the resistance of potentiometer P1. Parameter P1 determines the phase of the trigger pulse, which opens the triac. The circuit also performs a stabilization function, which maintains engine speed even under heavy load.

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 for a longer time, and the speed increases accordingly.

Regulator for DC motor

The simplest and most popular method of adjusting the rotation speed of a DC motor is based on the use of pulse width modulation ( PWM or PWM ). In this case, the supply voltage is supplied to the motor in the form of pulses. The repetition rate of the pulses remains constant, but their duration can change - so the speed (power) also changes.

To generate a PWM signal, you can take a circuit based on the NE555 chip. The simplest circuit of a 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 shaft load. VCC1 is from 5 to 16 V, 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 values ​​indicated in the diagram above, the frequency of the PWM signal will be equal to:

F = 1.44/(50000*0.0000001) = 290 Hz.

It is worth noting that even modern devices, including those with high control power, are based on precisely such circuits. Naturally, using more powerful elements that can withstand high currents.