Detailed soft start diagram for power tools. We make a smooth start of a power tool with our own hands

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.

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.

The prototype design in the figure below was used to adjust the filament of lamps, that is, to operate a purely active load.

The basis of the design is the K1182PM1R microcircuit. It is highly specialized, and as strange as it may sound today, it is domestically produced. If necessary, the start time can be increased by installing a larger capacitance of capacitor C3. While this capacitor is charging, the electric motor smoothly increases speed to maximum. A 68 kOhm resistor is optimally chosen for our circuit. If you want to make a power regulator, then you need to replace resistance R1 with a variable one. Resistance is 100 kOhm or more.

A standard junction box is suitable as an excellent housing made of insulating material. A socket is screwed onto it and a cable with a plug is connected, which makes this design very similar to a DIY extension cord.

If you want, you can assemble a slightly more complex soft start circuit. It is typical for the XS–12 module. It is installed in power tools during factory production by many companies.

If you want to regulate the speed of the connected electric motor, then the design becomes a little more complicated: because a trimming resistor of 100 kOhm and an adjusting resistance of 50 kOhm are installed.

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.

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Smooth starting of an angle grinder with your own hands will extend the life of your tool and save money

When choosing an angle grinder, a person thinks about the long service life of the tool. It is believed that the more expensive the tool, the longer it will last. But sometimes there is not enough money for an expensive purchase and you have to purchase an inexpensive model. Inexpensive models of angle grinders do not have a speed regulator. Other devices, such as drills, screwdrivers and hammer drills, have a speed control. And the angle grinder only has a power button. Thus, the angle grinder breaks faster, because under the influence of a sharp start, the gearbox and winding wires of the armature fail.

The following situations are possible:

• The action of a high load on the gearbox axis causes an inertial jump, leading in some cases to the tool falling out of the hands.
• The amount of torque during the start-up period contributes to wear of the gearbox gears.
• Destruction of the circle due to overload.

You can upgrade the tool and end up with a grinder with soft start. You can do the modernization yourself. A soft start for an angle grinder can be made with your own hands in two ways. The first method involves purchasing a ready-made device, which already has a speed controller and slows down the start of the engine at startup. This device is placed inside the device. The second method is to make a circuit that will make the start smoother. If the power cord breaks, the circuit is connected to the break.

Circuit manufacturing plan

The angle grinder's soft start circuit involves the use of the well-known KR118PM1 microcircuit for phase adjustment. The design contains semistors. Multiplying the operating frequency is achieved by installing resistors that pass current in one direction. The advantage of this scheme is its simplicity and the absence of special adjustments after assembly. This method can be used by anyone who does not have special skills, but works with a soldering iron.

Basic principles for designing a circuit:

• When choosing capacitor C3, the acceleration time can be increased;
• The installed resistor R1 with a resistance of 68 kOhm does not require replacement with a variable resistance, as it ensures smooth starting of models of various powers (0.6–1.5 kW);
• If you want to equip it with a power regulator, resistor R1 is replaced with a variable resistance. A value of more than 100 kOhm does not help reduce the output voltage. The angle grinder switches off when the microcircuit legs are shorted;
• When using a semistor of the TS-122-25 type, models with a power of 0.6–2.7 kW start smoothly. And also in this case there is a power reserve in case of jamming. For models up to 1500 W, less powerful semi-sectors (VT139 and W140) will be sufficient.

Circuit operation process

When the start buttons are closed, current flows to the microcircuit. The voltage across the main capacitor begins to increase. It reaches the operating value as it charges. Depending on the charge of the capacitor, the thyristors open. The opening of the VS1 semistor is also carried out with delay. A separate half-cycle of alternating voltage is characterized by a decrease in delay. As a result, the voltage at the input to the tool increases smoothly. Based on this, the engine starts smoothly. As a result, the speed does not increase quickly and the gearbox does not receive inertial surges.

The installed capacitor C2 facilitates starting within 2 seconds. This time is enough to start functioning, and a quick start does not increase the load. Turning off the tool leads to the discharge of capacitor C2 through resistance R1. With a capacity of 68 kOhm, the discharge period lasts 3 seconds. After this, you can start the device again.

The value of the current moving through the input of the semistor VS1 is regulated by resistor R2. Capacitor C1 is considered a control part of the microcircuit. Resistors and capacitors are attached to the legs of the microcircuit by soldering.

Connecting the soft start function

This microcircuit is comparable to any device that provides a voltage of 220 V. Power is supplied to the XP1 connector.

The assembled circuit is placed in a plastic container. A junction box is suitable as it. A socket and a wire with a plug are connected to the block. The device resembles an extension cord. The socket accepts the angle grinder plug. The functionality is checked using a tester. First, negative resistance is determined.

Complicated collection method

If you have certain skills or experience, you can make a complicated smooth launch scheme. This serves as a typical circuit for the XS-12 module. This circuit is installed in many models of power tools, even at the manufacturer. If you want to adjust the speed, you need to install a trimming and adjusting resistor with a capacity of 100 kOhm and 50 kOhm, respectively. But there is another way - to place an alternating voltage of 470 kOhm in the middle of the resistor-diode section. The resistor capacity is 47 kOhm.

The microcircuit is powered from a voltage of 5–35 V. An auxiliary semiconductor diode DZ is not required, since the power circuit produces no more than 25 V. It is recommended to connect a 1 MΩ resistor simultaneously with capacitor C2.

It should be remembered that when turning on a tool connected to the circuit, the load must be removed. Otherwise the soft start may burn out. First you need to wait until full promotion is achieved, and then start working.

To extend the life of an angle grinder, sometimes you don’t need to spend money on an expensive model. It will be enough to develop a smooth start of the angle grinder with your own hands. Then your tool will have reliability and a long service life. Moreover, the above scheme has been repeatedly used by many craftsmen.

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Home > Repair > DIY soft start for power tools

A smooth start for any power tool is very important for the following reasons. First, it helps protect your electrical device from breakdowns, which means fewer trips to the repair shop, which means virtually no downtime and increased productivity. Secondly, having a soft start for the electric motor saves you money that could otherwise be spent on paying repairmen or buying a new tool.

This article will look at making a soft start for an electric motor with your own hands using the example of an angle grinder or, in other words, an angle grinder.

Why do you need a soft start unit?

Due to some design features, launching an angle grinder leads to the appearance of dynamic loads on the device. Since the mass of the disk with which useful work is carried out is quite high, powerful inertial forces act on the commutator motor and gearbox of the device, which leads to the following negative factors:

1. During the start, which is especially sharp for an angle grinder, inertial forces very strongly affect the body of the device, which can lead to injury: you simply cannot hold the tool and release it. Therefore, when starting the electric motor of the angle grinder, always hold it with both hands.
2. During start-up, the electric motor is subject to an overload caused by the supply of high voltage. What does this lead to? First of all, the motor winding suffers and accelerated wear of the brushes occurs, which will not happen if you make a block for a soft start. Otherwise, be prepared for the fact that one not very wonderful day a short circuit will occur in the motor caused by complete wear of the brushes. This, in turn, will force you to shell out money for repairs or buy a new sander.
3. Rapidly applying torque to the gearbox during startup will cause accelerated wear on the gears in your grinder's gearbox.
4. Also keep in mind that jumping the angle grinder can destroy the blade, the fragments of which can cause serious harm to you, so never work without a cover for protection.

To make it more clear to you which elements of the grinding machine suffer most from a sudden start, look at the diagram below.

Of course, some companies that produce grinding machines equip their devices with a soft start block at the factory. However, equipping with a soft start is an unaffordable luxury for angle grinders in the budget price segment, so if you do not want to buy an expensive power tool, then you are in danger of encountering the problems described above.

However, there is a way out and it is quite simple: make your own device for a soft start according to one of the possible schemes. If there is free space in the body of your device, then you can use a ready-made device for a soft start and put it in an angle grinder.

Making a soft start for an angle grinder with your own hands

One of the most commonly used circuits for the manufacture of a starting device is based on the KR118PM1 microcircuit and triacs that make up the power section. Using this scheme, you can make a soft start unit without having specialized skills and without deep knowledge of electrical engineering. The only important thing is that you know how to solder.

Graphically, this diagram looks like this.

You can connect a self-made device to absolutely any power tool designed for a voltage of two hundred and twenty volts. The soft start unit, created on the basis of this circuit, does not have to be turned on with a separate button, but can be connected to the standard button of the grinding machine. If your angle grinder has free space inside the case, you can install the unit in it or make a separate case for it and connect it to the power tool through a gap in the power cable.

The best option for connecting the soft starter unit and your grinder is the following: you apply voltage to the input of the unit (connector XS1) from a power source with a voltage of two hundred and twenty volts. A plug from an angle grinder is connected to the output of the block (connector XP1).

Operating principle of the soft starter

1. After you press the power button on the grinder, voltage appears in the circuit, which is initially sent to the microcircuit, which is designated DA1 in the diagram above. The capacitor, which regulates the voltage, gradually increases it until the operating value is reached. Due to the operation of the capacitor, the thyristors in the microcircuit open with some delay and slowly transmit voltage to the power section in triacs VS1.
2. The process described above occurs in periods that become shorter and shorter if you count them from the moment of startup. As a result, the voltage supplied to the grinding machine increases slowly, and not abruptly, which determines the smooth start of the electric motor.
3. The time during which the engine reaches operating speed depends on the capacity of the capacitor C2 used. As a rule, a capacity equal to forty-seven microfarads is enough for the angle grinder to start smoothly in two seconds. Usually this period of time is enough to remove the overload from the electric motor and gearbox.
4. After you finish work and turn off your device, resistor R1 discharges capacitor C1 with its resistance. If the value of resistor R1 is sixty-eight kilo-ohms, then the discharge takes only three seconds. You can then use the soft starter again as it is ready to start the sander again.

If you want to upgrade the unit to a device that regulates the speed of the electric motor, then replace the constant resistor R1 with a variable one. In this case, you can adjust its resistance, and therefore influence the engine speed.

The VS1 triac in your block must meet the following characteristics:

• The minimum current it allows is twenty-five amperes.
• The maximum voltage for which it is designed is four hundred volts.

This circuit, tested by many craftsmen, was tested on a grinder with a power equal to two kilowatts, and has a power safety margin of up to five kilowatts, which is made possible thanks to the KR118PM1 microcircuit.

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Smooth start of the grinder

Schematic diagram:

In this form, the circuit ensures a smooth start and reaching the rated speed. The acceleration time depends on the capacity of capacitor C3. To adjust the speed, resistor R2 must be variable, preferably group A, or solder the variable in parallel with R2. In the latter case, it is desirable that their total resistance be close to the nominal value (the maximum voltage on the motor depends on this). If desired, the regulator can be built into the handle of the tool, although this is a more complex modification and, in my opinion, completely unjustified. In this case, it is easier to buy in a store. But if you decide to make such a modification, it makes sense to replace the standard power switch with a low-current one, which will lead to increased reliability. To do this, you need to turn on a microswitch in parallel with resistor R2 and capacitor C3 using normally closed contacts. I have this device assembled in a junction box, which can be easily purchased at any electrical goods store. In principle, this option suits me quite well. The last time I successfully used my drill as a screwdriver, without reverse, of course. In principle, it is not difficult to reverse, just switch the ends of one of the windings, but this fuss with the wires and the switch is a waste of time for me... I have a triac TC 122-25-5, you can install almost any one with a voltage of at least class 4 and current not lower than 1.5-2 denominations (in case of jamming).

Attention! The design has a galvanic connection to the network, which is unsafe for your life and health! Parts and fastening elements must be insulated!

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