We make a smooth start of a power tool with our own hands. Do-it-yourself speed controller and soft start on an angle grinder Do-it-yourself soft start of an electric motor 220V

Many power tools fail due to wear and tear on the motor. Modern models of angle grinders have a soft start device. Thanks to it, they are able to work for a long time. The operating principle of the element is based on changing the operating frequency. In order to learn more about the starter device, it is worth considering the diagram of the standard model.

Soft starter

The standard soft start circuit for an angle grinder consists of a triac, a rectifier unit and a set of capacitors. To increase the operating frequency, resistors are used that allow current to pass in one direction. The starter is protected by a compact filter. models maintain low. However, in this case, much depends on the maximum power of the motor installed in the angle grinder.

How to connect the model?

The soft start of the angle grinder is connected via an adapter. Its input contacts are connected to the rectifier block. In this case, it is important to determine the zero phase in the device. To secure the contacts you will need to check the functionality of the starter using a tester. First of all, negative resistance is determined. When installing a starter, it is important to remember the threshold voltage that the device can withstand.

Device diagram for an angle grinder with a 10 A triac

The do-it-yourself soft start circuit for an angle grinder involves the use of contact resistors. The polarity coefficient of modifications, as a rule, does not exceed 55%. Many models are produced with interlocks. A wired filter is responsible for protecting the device. Low frequency transceivers are used to pass current. The process of lowering the threshold voltage is carried out on a transistor. The triac in this case acts as a stabilizer. When connecting the model, the output resistance at an overload of 10 A should be about 55 Ohms. Covers for starters are suitable on a semiconductor basis. In some cases, magnetic transceivers are installed. They handle low speeds well and can maintain the rated frequency.

Model for grinders with a 15 A triac

Soft start for an angle grinder with 15 A triacs is universal and is often found in low-power models. The difference between the devices is their low conductivity. The soft start circuit (device) of an angle grinder involves the use of contact-type transceivers that operate at a frequency of 40 Hz. Many models use comparators. These elements are installed with filters. The rated voltage of starters starts from 200 V.

Starters for angle grinders with a 20 A triac

Devices with 20 A triacs are suitable for professional grinders. Many models use contactor resistors. First of all, they are able to operate at high frequencies. The maximum temperature of the starters is 55 degrees. Most models have a well-protected case. The standard device circuit involves the use of three contactors with a capacity of 30 pF or more. Experts say that the devices stand out for their conductivity.

The minimum frequency for starters is 35 Hz. They are capable of operating in a DC network. Modifications are connected via adapters. Such devices are well suited for 200 W motors. Filters are quite often installed with triodes. Their sensitivity indicator is no more than 300 mV. Quite often there are wired comparators with a protection system. If we consider imported models, they have an integrated converter that is installed with insulators. Current conductivity is ensured at around 5 microns. With a resistance of 40 Ohms, the model is capable of stably maintaining high speeds.

Models for angle grinder 600 W

For 600 W angle grinders, starters with contact triacs are used, in which the overload does not exceed 10 A. It is also worth noting that there are many devices with plates. They are distinguished by their security and are not afraid of elevated temperatures. The minimum frequency for 600 W angle grinders is 30 Hz. In this case, the resistance depends on the installed triode. If it is used of the linear type, then the above parameter does not exceed 50 Ohms.

If we talk about duplex triodes, then the resistance at high speeds can reach up to 80 Ohms. Very rarely, models have stabilizers that operate from comparators. Most often they are attached directly to the modules. Some modifications are made with wired transistors. Their minimum frequency starts from 5 Hz. They are afraid of overloads, but are able to maintain high speeds at

Devices for angle grinders 800 W

800 W grinders work with low frequency starters. Triacs are quite often used at 15 A. If we talk about the circuit of the models, it is worth noting that they use expansion transistors, whose current carrying capacity starts from 45 microns. Capacitors are used with and without filters, and the capacitance of the elements is no more than 3 pF. It is also worth noting that starters differ in sensitivity.

If we consider professional grinders, then modifications of 400 mV are suitable for them. In this case, the current conductivity may be low. There are also devices with variable transistors. They warm up quickly, but are not able to maintain high speeds of the grinder, and their current conductivity is about 4 microns. If we talk about other parameters, the rated voltage starts from 230 V. The minimum frequency for models with wideband triacs is 55 Hz.

Starters for angle grinders 1000 W

Starters for these angle grinders are made using triacs with an overload of 20 A. The standard device circuit includes a triode, a stabilizer plate and three transistors. The rectifier unit is most often installed on a wire base. Capacitors can be used with or without a filter. The minimum frequency of the conventional model is 30 Hz. With a resistance of 40 ohms, starters are capable of supporting large overloads. However, problems may arise at low speeds of the angle grinder.

How to make a starter using a triac TS-122-25?

Making a soft start for an angle grinder with a triac TS-122-25 with your own hands is quite simple. First of all, it is recommended to prepare a contactor resistor. Capacitors will be required of the single-pole type. A total of three elements are installed in the starter. The capacitance of one capacitor should not exceed 5 pF. To increase the operating frequency, a contactor is soldered on the plate. Some experts say that filters can increase conductivity.

The rectifier block is used with a conductivity of 50 microns. It is capable of withstanding large overloads and will be able to provide high speeds. Next, to assemble a soft start on an angle grinder with your own hands, install a thyristor. At the end of the work, the model is connected via an adapter.

Assembling a model with VS1 series triacs

You can assemble a soft start for an angle grinder using a VS1 triac with your own hands using several rectifier blocks. The capacitors for the device are suitable for the linear type with a capacity of 40 pF or more. You should start assembling the modification by soldering the resistors. Capacitors are installed in series order between insulators. The rated voltage of a high-quality starter is 200 V.

Next, to make a smooth start for the angle grinder with your own hands, take a prepared triac and solder it at the beginning of the circuit. Its minimum operating frequency should be 30 Hz. In this case, the tester must display a value of 50 ohms. If problems arise with overheating of the capacitors, then you need to use dipole filters.

Model for angle grinders with regulator KR1182PM1

To assemble a soft start for an angle grinder with the KR1182PM1 regulator with your own hands, you need a contact thyristor and a rectifier unit. It is more expedient to use a triode for two filters. It is also worth noting that to assemble the starter you will need three capacitors with a capacity of at least 40 pF.

The sensitivity indicator of the elements must be 300 mV. Experts say that the triac can be installed behind the lining. You also need to remember that the threshold voltage should not fall below 200 V. Otherwise, the model will not be able to operate at lower speeds of the angle grinder.

As a rule, budget angle grinders (angle grinders), popularly called grinders, do not have adjustable electronic modules in their design, which include an engine speed controller and a soft start. Over time, owners of such grinders begin to understand that their absence sharply reduces the functionality of the tool. In this case, you can modify the angle grinder by installing homemade devices on it.

When power is applied to the grinder motor, sudden increase in speed from zero to 10 thousand or more. Those who have worked with an angle grinder know well that it is sometimes difficult to hold it in your hands when starting, especially if a large diameter diamond disk is installed.

It is precisely because of such abrupt increases in engine speed that the mechanics of the device most often fail.

Also, during startup, a huge load is applied to the rotor and stator windings of the electric motor. Since a commutator motor is installed in the angle grinder, it starts in short circuit mode: the electromagnetic field is already “trying” to turn the rotor, but it remains motionless for some time, since the force of inertia prevents this from happening. As a result, the starting current in the motor coils sharply increases. Despite the fact that the manufacturer has invested a certain safety margin for the coils, taking into account overloads at start, sooner or later the insulation cannot withstand it, which leads to an interturn short circuit.

In addition to starting problems, the lack of speed control causes some discomfort. For example, an angle grinder's speed regulator may come in handy for certain types of work:

• when grinding or polishing any surfaces;
• when installing large diameter tools;
• for cutting certain materials.

In addition, when roughing with wire brushes, there is a high probability of wire jamming in any gap. If the spindle speed was high, then the angle grinder may simply be torn out of your hands.

If you connect a power (speed) regulator with a soft start module to the angle grinder, then all the problems described above will disappear, the service life of the device will increase and the safety of its use will increase.

Homemade regulator circuit

One of the most popular schemes for smoothly starting an angle grinder engine with the ability to adjust the speed is presented below.

The basis of this regulator is the KR118PM1 microcircuit, as well as triacs, which are the power part of the device. Using this circuit, you can make a power regulator with your own hands, even without special knowledge in radio electronics. The main thing is that you know how to use a soldering iron.

This block works as follows.

1. After pressing the unit start button, electric current begins to flow, first of all, to the microcircuit (DA1).
2. The control capacitor begins to charge smoothly and after a while reaches the required voltage. Thanks to this, the opening of the thyristors in the microcircuit occurs with some delay. It depends on the time it takes to fully charge the capacitor.
3. Since the VS1 triac is controlled by the microcircuit’s theristors, it opens just as smoothly.

The processes described above occur in periods that become shorter each time. Therefore, the voltage supplied to the motor windings does not increase abruptly, but slowly, resulting in a smooth start of the angle grinder.

The time it takes for the electric motor to reach full speed depends on the capacitance of capacitor C2. The capacitor capacity of 47 uF allows you to start the engine in 2 seconds. When the angle grinder is turned off, capacitor C1 is discharged using 60 kOhm resistor R1 for 3 seconds, after which this electronic module is again ready to start.

If resistor R1 is replaced with a variable one, then you will get a speed controller that will allow you to reduce engine speed.

It is important that triac VS1 has the following characteristics:

• the minimum current for which it is designed must be 25 A;
• The triac must be designed for a maximum voltage of 400 V.

This circuit and the regulators made according to it have been repeatedly tested by many craftsmen on grinders with power up to 2000 Watt. It is worth noting that this device, thanks to the KR118PM1 microcircuit, is designed for power up to 5000 W. So he has a considerable margin of safety.

Ideally, to solder a speed controller for an angle grinder, you will need to draw a printed circuit board, etch the contacts with acid and then tin them, drill holes and solder the radio components. But everything can be made simpler:

• solder all the parts of the circuit by weight, that is, leg to leg;
• Attach a radiator to the triac (can be made from sheet aluminum).

A regulator soldered in this way will take up less space and can be easily placed in the body of the angle grinder.

How to connect a regulator to an angle grinder

To connect a homemade power regulator, no special knowledge is required, and any home craftsman can cope with this task. The module is being installed into a break in one wire, through which power goes to the grinder. That is, one wire remains intact, and a regulator is soldered into the gap of the second.

In the same way, you can connect a factory power regulator that costs about 150 rubles, which is often purchased by craftsmen in China.

If there is very little space in the grinder, then the regulator can be placed outside the instrument, as shown in the following photo.

Also, the regulator can be placed in a socket and used to reduce the speed not only of an angle grinder, but also of other electrical appliances (drill, sharpener, wood milling or lathe, etc.). This is done as follows.

The regulator is connected as described above - at a break in one of the wires of the power cable.

The following photos show what a finished socket will look like, having a built-in speed controller for an angle grinder, which can also be used for other electrical appliances.

Instead of a junction box, you can use any plastic case suitable size. You can also make the box yourself by gluing pieces of plastic together with a glue gun.

Smooth start of the grinder the circuit, which is built on the KR1182PM1 microcircuit (phase control microcircuit), allows you to smoothly and safely start not only the angle grinder, but also any powerful power tool. The soft start circuit is quite simple and does not require any configuration.

It is possible to connect to the circuit without any changes any power tool that operates on a 220-volt power supply. Starting and turning off the electric motor of the angle grinder is carried out by an electric button on the power tool itself.

The soft start circuit for an angle grinder is shown in the figure below. Connector XP1 is connected to a 220 volt power outlet, and a grinder plug is plugged into XS1 (socket). It is possible to install and connect in parallel several sockets for power tools that operate alternately.

When you press the power tool button, the circuit closes and power supply is supplied to DA1 (phase regulator). In this case, capacitor C2 begins to charge, which leads to a smooth increase in voltage across it. The result of this is a delay in the opening of the thyristors (inside) the regulator, and with them the VSI triac. The delay decreases in each half-cycle of the mains voltage, as a result of which the voltage flowing through the electric motor of the angle grinder gradually increases and, consequently, its speed gradually increases.

With the capacitance value of capacitor C2 indicated in this diagram, a smooth increase in speed from the minimum amount to the nominal one takes about 2 seconds, which is quite enough to protect the power tool from dynamic and thermal shock, and at the same time ensure comfortable work with the angle grinder.

After turning off the electric motor of the angle grinder, capacitance C2 is discharged through resistance R1 and after 3 seconds the soft start circuit of the angle grinder is ready for a new start. By replacing the constant resistance R1 with a variable one, it is possible to smoothly change the power supplied to the electric motor. Resistance R2 reduces the current flowing through the control electrode of the triac, and capacitances C1 and SZ are radio components of a typical connection circuit for the KR1182PM1 microcircuit.
All resistances and capacitances are soldered directly to the terminals of the KR1182PM1 microcircuit.

It is possible to use any triac, with a maximum operating voltage of more than 400 V and a maximum current of at least 25 amperes (depending on the power of the grinder). Due to the smooth start of the electric motor of the angle grinder, its starting current is not more than the rated current. The current reserve is needed only in case of jamming of the power tool.
The soft start circuit has been tested with tools with power up to 2.2 kW. Since the KR1182PM1 microcircuit guarantees the flow of current in the circuit of the electrode (control) triac VS1 during the entire active phase of the half-cycle, there are no restrictions on the minimum power of the connected load.

Associated with high dynamic loads. Due to the mass of the working disk, at the beginning of rotation, inertial forces act on the gearbox axis. This entails some negative aspects:

1. Loads on the axle during a sharp start create an inertial jerk, which, with a large diameter and mass of the disk, can tear the power tool out of your hands;

IMPORTANT! When starting the grinder, always hold the tool with both hands and be prepared to hold it. Otherwise, you may get injured. This warning is especially relevant for heavy diamond or steel blades.

2. When the operating voltage is suddenly applied to the motor, a current overload occurs, which disappears after reaching the rated speed;

As a result, the brushes wear out and both windings of the electric motor overheat. When constantly turning a power tool on and off, overheating can melt the insulation of the windings and lead to a short circuit, followed by costly repairs.

3. High torque with a sharp increase in speed prematurely wears out the gears of the angle grinder gearbox;

In some cases, the teeth may break off and the gearbox may jam.

4. The overloads experienced by the working disk can destroy it when the engine starts.

Therefore, the presence of a protective casing is mandatory.

IMPORTANT! When starting the angle grinder, the open sector of the casing should be directed in the direction opposite to the operator.

To better understand the mechanics of work, consider the structure of the angle grinder in the drawing. All elements experiencing overload during a sudden start are clearly visible.

Schematic drawing of the location of the working bodies and control systems in the angle grinder

To reduce the harmful effects of a sudden start, manufacturers produce angle grinders with speed control and soft start.

The speed control is located on the tool handle

But only models of the middle and high price categories are equipped with such a device. Many home craftsmen purchase angle grinders without a regulator and slowing down the starting speed. This is especially true for powerful specimens with a cutting disc diameter of more than 200 mm. Not only is such an angle grinder difficult to hold in your hands during startup, but the mechanical and electrical parts wear out much faster.
There is only one way out - to install a soft start of the angle grinder yourself. There are ready-made factory devices with a speed controller and engine start retardation when starting.

Ready-made device for adjusting soft start

Such blocks are installed inside the case, if there is free space. However, most angle grinder users prefer to make a circuit for smooth starting of the angle grinder themselves, and connect it to the break in the power cable.

How to make a soft start circuit for an angle grinder with your own hands

The popular circuit is implemented on the basis of the KR118PM1 phase control control microcircuit, and the power part is made of triacs. Such a device is quite easy to install, does not require additional settings after assembly, and therefore, it can be made by a master without specialized education, just be able to hold a soldering iron in his hands.

Electrical circuit for adjusting soft start for an angle grinder

The proposed unit can be connected to any power tool designed for an alternating voltage of 220 volts. A separate remote power button is not required; the modified power tool is turned on with a standard key. The circuit can be installed either inside the body of the angle grinder or in the break of the power cable in a separate case.

The most practical thing is to connect the soft starter to the socket from which the power tool is powered. The input (XP1 connector) is supplied with power from a 220 volt network. A consumable socket is connected to the output (connector XS1), into which the angle grinder plug is plugged.

When the start button of the angle grinder is closed, voltage is supplied to the DA1 chip via the common power circuit. There is a smooth increase in voltage across the control capacitor. As it charges, it reaches a working value. Due to this, the thyristors in the microcircuit do not open immediately, but with a delay, the time of which is determined by the charge of the capacitor. Triac VS1, controlled by thyristors, opens with the same pause.

Watch the video with a detailed explanation of how to do it and what scheme to use

In each half-cycle of alternating voltage, the delay decreases in an arithmetic progression, as a result of which the voltage at the input to the power tool gradually increases. This effect determines the smooth start of the angle grinder engine. Consequently, the disk speed increases gradually, and the gearbox shaft does not experience inertial shock.

The time it takes for the speed to reach the operating value is determined by the capacitance of capacitor C2. The value of 47 uF ensures a smooth start in 2 seconds. With such a delay, there is no particular discomfort when starting to work with the tool, and at the same time, the power tool itself is not subject to excessive loads from a sudden start.

After turning off the angle grinder, capacitor C2 is discharged by resistor R1. At a nominal 68 kOhm, the discharge time is 3 seconds. After which the soft starter is ready for a new start cycle of the angle grinder.
With a little modification, the circuit can be upgraded to an engine speed controller. To do this, resistor R1 is replaced with a variable one. By adjusting the resistance, we control the engine power by changing its speed.

Thus, in one housing it is possible to make an engine speed controller and a soft start device for a power tool.

The remaining details of the circuit work as follows:

• Resistor R2 controls the amount of current flowing through the control input of triac VS1;
• Capacitors C1 and C2 are control components of the KR118PM1 microcircuit, used in a typical switching circuit.

For simplicity and compactness of installation, resistors and capacitors are soldered directly to the legs of the microcircuit.

The VS1 triac can be anything with the following characteristics: maximum voltage up to 400 volts, minimum throughput current 25 amperes. The amount of current depends on the power of the angle grinder.

Due to the smooth start of the angle grinder, the current will not exceed the rated operating value for the selected power tool. For emergency cases, for example, a jammed angle grinder disk, a current reserve is required. Therefore, the nominal value in amperes should be doubled.

The ratings of the radio components used in the proposed electrical circuit were tested on an angle grinder with a power of 2 kW. There is a power reserve of up to 5 kW, this is due to the peculiarity of the operation of the KR118PM1 microcircuit.
The scheme is working, executed many times by home craftsmen.

Soft starting is widely used in the safe starting of electric motors. When starting the engine, the rated current (In) is exceeded by 7 times. As a result of this process, there is a reduction in the operating period of the motor, namely the stator windings and a significant load on the bearings. It is for this reason that it is recommended to make a soft start for a power tool with your own hands, where it is not provided.

General information

The stator of an electric motor is an inductance coil; therefore, there are resistances with an active and reactive component.

When electric current flows through radioelements having resistance with an active component, losses occur due to the conversion of part of the power into thermal energy. For example, a resistor and the stator windings of an electric motor have a resistance with an active component. Calculating active resistance is not difficult, since the phases of the current (I) and voltage (U) coincide. Using Ohm's law for a section of a circuit, you can calculate the active resistance: R = U/I. It depends on the material, cross-sectional area, length and its temperature.

If the current passes through a reactive type of element (with capacitive and inductive characteristics), then, in this case, a reactive R appears. An inductor that has practically no active resistance (the calculations do not take into account the R of its windings). This type of R is created due to the Electromotive Force (EMF) of self-induction, which is directly proportional to the inductance and frequency I passing through its turns: Xl = wL, where w is the angular frequency of the alternating current (w = 2*Pi*f, and f - network current frequency) and L - inductance (L = n * n / Rm, n - number of turns and Rm - magnetic resistance).

When the electric motor is turned on, the starting current is 7 times greater than the rated current (the current consumed during operation of the tool) and the stator windings heat up. If the stator coil is old, then an interturn short circuit may occur, which will lead to failure of the power tool. To do this, you need to use a soft starter for a power tool.

One of the methods for reducing the inrush current (Ip) is to switch windings. To implement it, 2 types of relays (time and load) and the presence of three contactors are required.

Starting an electric motor with windings connected in a star type is possible only with 2 contactors not simultaneously closed. After a certain time interval, which is set by a time relay, one of the contactors is turned off and another one, not previously used, is turned on. Thanks to this alternation of switching on the windings, the inrush current decreases. This method has a significant drawback, since when two contactors are simultaneously closed, a short-circuit current occurs. However, when using this method, the windings continue to heat up.

Another way to reduce the starting current is to control the frequency of starting the electric motor. The principle of this approach is the frequency change of the supply U. The main element of this type of soft starter is a frequency converter, consisting of the following elements:

1. Rectifier.
2. Intermediate chain.
3. Inverter.
4. Electronic control circuit.

The rectifier is made of powerful diodes or thyristors, acting as a converter U of the network power supply into a direct pulsating current. The intermediate circuit smoothes out the pulsating direct current at the output of the rectifier, which is collected on large capacitors. An inverter is necessary to directly convert the signal at the output of the intermediate circuit into a signal of the amplitude and frequency of the variable component. An electronic control circuit is needed to generate the signals necessary to control the rectifier or inverter.

Operating principle

During the start-up of a commutator-type electric motor, a significant short-term increase in current consumption occurs, which causes premature failure of the power tool and requires it to be repaired. Electrical parts wear out (current exceeds 7 times) and mechanical parts (sharp start). To organize a “soft” start, soft start devices (hereinafter referred to as soft starters) should be used. These devices must meet the basic requirements:

The most widely used are triac soft starters, the operating principle of which is smooth regulation of U by adjusting the opening angle of the triac junction. The triac must be connected directly to the motor windings and this allows you to reduce the starting current from 2 to 5 times (depending on the triac and control circuit). The main disadvantages of triac soft starters are the following:

1. Complex schemes.
2. Overheating of windings during prolonged startup.
3. Problems with starting the engine (leads to significant heating of the stator windings).

The circuits become more complicated when using powerful engines, however, with light loads and idle speed, simple circuits can be used.

Soft starters with regulators without feedback (1 or 3 phases) have become widespread. In models of this type, it becomes possible to pre-set the start time and U value before starting the engine. However, in this case it is impossible to regulate the amount of torque under load. With this model, a special device is used to reduce the starting current, protect against phase loss and imbalance, as well as against overloads. Factory models have a function for monitoring the condition of the electric motor.

The simplest single-phase control circuits are executed on a single triac and are used for instruments with a power of up to 12 kW. There are more complex circuits that allow you to adjust the power parameters of an engine with a power of up to 260 kW. When choosing a factory-made soft starter, it is necessary to take into account the following parameters: power, possible operating modes, equality of permissible currents and the number of starts in a certain period of time.

Application in an angle grinder

When starting an angle grinder (angle grinder), high dynamic loads appear on the tool parts.

Expensive models are equipped with a soft starter, but not ordinary varieties, for example, angle grinders from the Interskol company. An inertial jerk can tear an angle grinder out of your hands, and this poses a threat to life and health. In addition, when starting the electric motor of the tool, an overcurrent occurs and, as a result, wear of the brushes and significant heating of the stator windings, wear out of the gearbox and possible destruction of the cutting disk, which can crack at any time and cause harm to health, and maybe even life. The tool needs to be secured and for this you should make an angle grinder with speed control and soft start with your own hands.

Homemade options

There are many schemes for modernizing power tools using soft starters. Among all varieties, devices based on triacs are widely used. A triac is a semiconductor element that allows you to smoothly regulate power parameters. There are simple and complex circuits that differ in design options, as well as in the supported power of the connected power tool. The design includes internal ones, which allow them to be built inside the case, and external ones, manufactured in the form of a separate module, which acts as a speed limiter and starting current when starting the angle grinder directly.

The simplest scheme

A soft starter with speed control on a thyristor KU 202 is widely used due to its very simple design (diagram 1). Connecting it does not require any special skills. Radio elements for it are very easy to obtain. This regulator model consists of a diode bridge, a variable resistor (acts as a U regulator) and a thyristor tuning circuit (supplying U to the control output with a nominal value of 6.3 volts) from a domestic manufacturer.

Scheme 1. Electrical diagram of the indoor unit with speed control and soft start (electrical circuit diagram)

Due to the size and number of parts, this type of regulator can be built into the body of a power tool. In addition, the variable resistor knob should be removed and the speed controller itself can be modified by integrating a button in front of the diode bridge.

The basic principle of operation is to regulate the speed of the electric motor of the tool by limiting the power in manual mode. This circuit allows you to use power tools with a power of up to 1.5 kW. To increase this indicator, it is necessary to replace the thyristor with a more powerful one (information about this can be found on the Internet or in a reference book). In addition, you need to take into account the fact that the thyristor control circuit will differ from the original one. KU 202 is an excellent thyristor, but its significant drawback is its configuration (selection of parts for the control circuit). To implement a soft start in automatic mode, scheme 2 is used (soft starter on a microcircuit).

Soft start on a chip

The best option for manufacturing a soft starter is a soft starter circuit with one triac and a microcircuit that controls the smooth opening of a p-n type junction. The device is powered from a 220 V network and is easy to assemble yourself. A very simple and universal soft start circuit for an electric motor also allows you to regulate the speed (diagram 2). The triac can be replaced with the same one or with characteristics exceeding the original ones, according to the reference book of semiconductor-type radioelements.

Scheme 2. Scheme for soft start of a power tool

The device is implemented on the basis of the KR118PM1 microcircuit and a triac. Due to the versatility of the device, it can be used for any tool. It does not require configuration and is installed into the power cable.

When the electric motor starts, U is supplied to KR118PM1 and the charge of capacitor C2 gradually increases. The thyristor opens gradually with a delay depending on the capacitance of the control capacitor C2. With a capacitance of C2 = 47 μF, there is a delay at startup of about 2 seconds. It depends in direct proportion to the capacitance of the capacitor (with a larger capacitance, the startup time increases). When the angle grinder is turned off, capacitor C2 is discharged using resistor R2, the resistance of which is 68 k, and the discharge time is about 4 seconds.

To regulate the speed, you need to replace R1 with a variable resistor. When changing the parameter of the variable resistor, the power of the electric motor changes. R2 changes the amount of current flowing through the triac input. The triac needs cooling and, therefore, a fan can be built into the module housing.

The main function of capacitors C1 and C3 is to protect and control the chip. The triac should be selected based on the following characteristics: direct U should be 400..500 V and direct current should be at least 25 A. With such ratings of radio elements, it is possible to connect a tool with a power from 2 kW to 5 kW to the soft starter.

Thus, to start electric motors of various tools, it is necessary to use factory-made or home-made soft starters. Soft starters are used to increase the service life of the tool. When starting the engine, there is a sharp increase in current consumption by 7 times. Because of this, the stator windings may burn out and the mechanical part may wear out. Soft starters can significantly reduce the starting current. When making a soft starter yourself, you need to follow safety rules when working with electricity.