The soft start does not work on the grinder. Soft start for a grinder with your own hands: a diagram. Bulgarian soft starter, connection. Video: homemade angle grinder speed controller

For everyone who has been using the grinder for more than one year, it broke. At first, each master tried to repair the sparkling grinder on his own, hoping that it would work after replacing the brushes. Usually, after such an attempt, a broken tool remains lying on a shelf with burned-out windings. And a new grinder is bought to replace it.

Drills, screwdrivers, rotary hammers, milling cutters are necessarily equipped with a speed dial regulator. Some so-called calibration grinders are also equipped with a regulator, and ordinary grinders have only a power button.

Manufacturers do not deliberately complicate low-power angle grinders with additional circuits, because such a power tool should be cheap. It is clear, of course, that the service life of an inexpensive tool is always shorter than that of a more expensive professional one.

The simplest angle grinder can be upgraded so that the gearbox and armature winding wires will no longer be damaged. These troubles mainly occur during a sharp, in other words, shock start of the grinder.

All modernization consists only in assembling the electronic circuit and fixing it in the box. In a separate box, because there is very little space in the handle of the grinder.

A tested, working circuit is laid out below. It was originally intended to adjust the incandescence of lamps, that is, to work on an active load. Her main asset? simplicity.

The highlight of the soft starter, the schematic diagram of which you see, is the K1182PM1R chip. This microcircuit is highly specialized, of domestic production.
The acceleration time can be increased by choosing a larger capacitor C3. While this capacitor is being charged, the electric motor speeds up to maximum.
No need to replace the resistor R1 variable resistance. The 68 kΩ resistor is optimally matched for this circuit. With this setting, you can smoothly start the grinder with a power of 600 to 1500 watts.
If you are going to assemble a power regulator, then you need to replace the resistor R1 with a variable resistance. A resistance of 100 kΩ or more does not lower the output voltage. By short-circuiting the legs of the microcircuit, you can completely turn off the connected angle grinder.
By inserting a TS-122-25 semistor VS1 into the power circuit, that is, at 25A, you can smoothly start almost any grinder available for sale, with power from 600 to 2700 watts. And there is a large margin of power in case the grinder jams. To connect grinders with a power of up to 1500 W, imported seven-stores BT139, BT140 are enough. These less powerful electronic keys are cheaper.

The triac in the above circuit does not fully open, it cuts off about 15V of the mains voltage. Such a voltage drop does not affect the work of the grinder. But when the sevenstor is heated, the speed of the connected tool is greatly reduced. This problem is solved by installing a radiator.

This simple circuit has another drawback - its incompatibility with the speed controller installed in the tool.

The assembled circuit must be hidden in plastic boxes. The housing made of insulating material is important, because you need to protect yourself from mains voltage. You can buy a junction box at an electrical supply store.

A socket is screwed to the box and a cable with a plug is connected, which makes this design look like an extension cord.

If experience allows and there is a desire, you can assemble a more complex soft start circuit. Below circuit diagram is standard on the XS-12 module. This module is installed in the power tool at the factory.

If you need to change the speed of the connected electric motor, then the circuit becomes more complicated: a tuning resistor of 100 kOhm is installed, and a control resistor of 50 kOhm is installed. Or you can simply and roughly introduce a 470 kΩ variable between a 47 kΩ resistor and a diode.

In parallel with capacitor C2, it is desirable to connect a resistor with a resistance of 1 MΩ (it is not shown in the diagram below).

The supply voltage of the LM358 chip is in the range from 5 to 35V. The voltage in the power circuit does not exceed 25V. Therefore, you can do without an additional zener diode DZ.

Whatever soft starter you build, never turn on the tool connected to it under load. Any soft start can be burned if you rush. Wait for the grinder to unwind, and then work.

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Smooth start an induction motor is always a difficult task, because starting an induction motor requires a lot of current and torque, which can burn the motor winding. Engineers constantly propose and implement interesting technical solutions to overcome this problem, such as using an incorporation circuit, an autotransformer, etc.

Currently, such methods are used in various industrial installations for the smooth operation of electric motors.

From physics, the principle of operation of an induction electric motor is known, the whole essence of which is to use the difference between the frequencies of rotation of the magnetic fields of the stator and rotor. The magnetic field of the rotor, trying to catch up with the magnetic field of the stator, contributes to the excitation of a large starting current. The motor runs at full speed, while the torque value also increases following the current. As a result, the winding of the unit may be damaged due to overheating.

Thus, it becomes necessary to install a soft starter. Soft starters for three-phase asynchronous motors help to protect the units from the initial high current and torque resulting from the slip effect of the induction motor.

Advantageous features of using a circuit with a soft starter (SCD):

reduction of starting current;
reduction of energy costs;
improving efficiency;
relatively low cost;
achievement top speed without damage to the unit.

How to smoothly start the engine?

There are five basic soft start methods.

High torque can be created by adding external resistance to the rotor circuit as shown in the figure.

By including an automatic transformer in the circuit, the starting current and torque can be maintained by reducing the initial voltage. See the picture below.

Direct start is the easiest and cheap way because the induction motor is connected directly to the power supply.
Connections on a special winding configuration - the method is applicable to motors intended for operation under normal conditions.

The use of SCP is the most advanced of all the methods listed. Here, semiconductor devices such as thyristors or SCRs that regulate the speed of an induction motor successfully replace mechanical components.

Collector motor speed controller

Most schemes household appliances and electric tools was created on the basis of a 220 V collector electric motor. This demand is explained by its versatility. The units can be powered by direct or alternating voltage. The advantage of the circuit is due to the provision of an effective starting torque.

To achieve a smoother start and have the ability to adjust the speed, speed controllers are used.

Starting an electric motor with your own hands can be done, for example, in this way.

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 soft start. The owners of such grinders eventually begin to understand that their absence drastically reduces the functionality of the tool. In this case, you can refine the angle grinder by installing home-made devices on it.

When power is applied to the grinder motor, abrupt increase in speed from zero to 10 thousand and more. Those who worked with angle grinders are well aware that it is sometimes difficult to hold it in their hands at startup, especially if it is installed diamond disc large diameter.

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

Also during start-up, a huge load is applied to the rotor and stator windings of the electric motor. Since a collector 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 inertia force does not allow it to be done. As a result, the starting current in the motor coils increases sharply. Despite the fact that the manufacturer has invested a certain margin of safety for the coils, taking into account the overloads at the start, sooner or later the insulation does not withstand, which leads to an interturn short circuit.

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

when grinding or polishing any surfaces;
when installing a large diameter tool;
for cutting some materials.

In addition, when peeling with brushes, there is a high probability of wire jamming in any slot. If the spindle speed was high, then the grinder can simply be pulled out of the hands.

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

Scheme of a homemade regulator

One of the most popular schemes for soft 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 scheme, 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.

After pressing the start button electricity begins to flow, first of all, to the microcircuit (DA1).
The control capacitor begins to charge smoothly and after a while gains the desired voltage value. Due 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.
Since the triac VS1 is controlled by the thermistors of the microcircuit, it opens just as smoothly.

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

The capacitance of the capacitor C2 determines the time for the electric motor to reach full speed. The capacitance of 47 microfarads allows you to start the engine in 2 seconds. When the angle grinder is turned off, the discharge of the capacitor C1 is carried out using a 60 kΩ resistor R1 for 3 seconds, after which this electronic module is again ready to start.

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

It is important that the VS1 triac has the following characteristics:

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

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

Ideally, in order to solder the speed controller for the 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 easier:

solder all the details of the circuit on weight, that is, leg to leg;
attach a radiator to the triac (can be made from sheet aluminum).

The regulator soldered in this way will take up less space, and it can be easily placed in the grinder body.

How to connect a regulator to an angle grinder

To connect a homemade power regulator does not require special knowledge, and any House master cope with this task. The module is installed in the break of one wire, through which food goes to the grinder. That is, one wire remains intact, and the regulator is soldered into the gap of the second.

In the same way, you can connect a factory power regulator worth 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 of the tool as shown in the following photo.

Also, the regulator can be placed in a socket and used to reduce the speed not only of the grinder, but also of other electrical appliances (drills, sharpeners, milling or lathe on wood, etc.). This is done in the following way.

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

The following photos show how the finished outlet will look like, which has a built-in grinder speed controller, which can be used for other electrical appliances.

Instead of a junction box, you can use any plastic case right size. Also, the box can be made independently by gluing pieces of plastic with a glue gun.

Who wants to strain, spend their money and time on the re-equipment of devices and mechanisms that already work perfectly? As practice shows - many. Although not everyone in life encounters industrial equipment equipped with powerful electric motors, they constantly meet, albeit not so voracious and powerful, electric motors in everyday life. Well, everyone used the elevator, for sure.

Are motors and loads a problem?

The fact is that virtually any electric motors, at the moment of starting or stopping the rotor, experience huge loads. The more powerful the engine and the equipment it drives, the greater the cost of running it.

Probably, the most significant load that falls on the engine at the time of start-up is a multiple, albeit short-term, excess of the rated operating current of the unit. After a few seconds of operation, when the electric motor reaches its nominal speed, the current consumed by it will also return to normal levels. To ensure the necessary power supply have to increase the capacity of electrical equipment and conductive lines which drives up their prices.

At startup powerful electric motor, due to its high consumption, there is a "drawdown" of the supply voltage, which can lead to failures or failure of equipment powered with it from the same line. In addition, the service life of power supply equipment is reduced.

In the event of emergency situations that caused the engine to burn out or its severe overheating, properties of transformer steel may change so much so that after repair the engine will lose up to thirty percent of power. Under such circumstances, it is no longer suitable for further operation and requires replacement, which is also not cheap.

What is a soft start for?

It would seem that everything is correct, and the equipment is designed for this. But there is always a "but". In our case, there are several:

at the moment of starting the electric motor, the supply current can exceed the rated one by four and a half to five times, which leads to significant heating of the windings, and this is not very good;
starting the engine by direct connection leads to jerks, which primarily affect the density of the same windings, increasing the friction of the conductors during operation, accelerates the destruction of their insulation and, over time, can lead to an interturn short circuit;
the aforementioned jerks and vibrations are transmitted to the entire driven unit. It's not healthy at all, because may cause damage to its moving parts: gear systems, drive belts, conveyor belts, or just imagine yourself riding in a twitching elevator. In the case of pumps and fans, this is the risk of deformation and destruction of turbines and blades;
do not forget about products that may be on the production line. They may fall, crumble or break due to such a jerk;
Well, and probably the last of the points that deserve attention is the cost of operating such equipment. We are talking not only about expensive repairs associated with frequent critical loads, but also about a tangible amount of inefficiently spent electricity.

It would seem that all of the above operating difficulties are inherent only in powerful and bulky industrial equipment, however, this is not so. All this can become a headache for any average layman. First of all, this applies to power tools.

The specifics of the use of such units as electric jigsaws, drills, grinders and the like involve multiple start and stop cycles within a relatively short period of time. This mode of operation, to the same extent, affects their durability and energy consumption, as well as their industrial counterparts. With all this, one should not forget that soft start systems unable to control engine speed or reverse their direction. It is also impossible to increase the starting torque or reduce the current below what is required to start the rotation of the motor rotor.

Video: Soft start, adjustment and protection of the collector. engine

Options for soft start systems for electric motors

Star-delta system

One of the most widely used starting systems for industrial asynchronous motors. Its main advantage is simplicity. The engine starts when the windings of the star system are switched, after which, when the nominal speed is set, it automatically switches to delta switching. This kind of start allows you to achieve a current almost a third lower than with direct start of the electric motor.

However, this method is not suitable for mechanisms with small rotational inertia. These include, for example, fans and small pumps due to the small size and weight of their turbines. At the time of the transition from the "star" to the "delta" configuration, they will sharply reduce speed or stop altogether. As a result, after switching, the electric motor essentially restarts. That is, in the end, you will not only achieve savings on the engine resource, but, most likely, you will get an overrun of electricity.

Video: Connecting a three-phase asynchronous motor with a star or delta

Electronic motor soft starter

Soft start of the engine can be performed using triacs included in the control circuit. There are three schemes for such inclusion: single-phase, two-phase and three-phase. Each of them differs in its functionality and final cost, respectively.

These schemes usually it is possible to reduce the starting current up to two or three nominal. In addition, it is possible to reduce the significant heating inherent in the aforementioned star-delta system, which contributes to an increase in the service life of electric motors. Due to the fact that the engine start is controlled by reducing the voltage, the acceleration of the rotor is carried out smoothly, and not abruptly, like in other schemes.

In general, several key tasks are assigned to engine soft start systems:

the main one - lowering the starting current to three or four nominal;
reduction of the motor supply voltage, in the presence of appropriate capacities and wiring;
improvement of starting and braking parameters;
emergency protection of the network against current overloads.

Single-phase starting circuit

This scheme is designed to start electric motors with a power of not more than eleven kilowatts. This option is used if it is necessary to soften the impact at start-up, and braking, soft start and lowering the starting current do not matter. First of all, because of the impossibility of organizing the latter in such a scheme. But due to the cheaper production of semiconductors, including triacs, they are discontinued and rarely found;

Two-phase starting circuit

Such a scheme is designed to regulate and start engines with a power of up to two hundred and fifty watts. Such soft start systems sometimes equipped with a bypass contactor to reduce the cost of the device, however, this does not solve the problem of asymmetric power supply of the phases, which can lead to overheating;

Three-phase starting circuit

This circuit is the most reliable and versatile soft start system for electric motors. The maximum power of the motors controlled by such a device is limited exclusively by the maximum thermal and electrical endurance of the triacs used. His versatility allows you to implement a lot of functions such as: dynamic brake, flyback or magnetic field and current limiting balancing.

An important element of the last of the mentioned circuits is the bypass contactor, which was mentioned earlier. He allows to ensure the correct thermal regime of the soft start system of the electric motor, after the engine has reached its normal operating speed, preventing it from overheating.

The soft starters of electric motors that exist today, in addition to the above properties, are designed for their joint operation with various controllers and automation systems. They have the ability to turn on at the command of the operator or the global control system. Under such circumstances, at the time of switching on the loads, interference may occur that can lead to malfunctions in the automation, and therefore, it is worth taking care of protection systems. The use of soft start circuits can significantly reduce their impact.

DIY soft start

Most of the systems listed above are actually inapplicable in domestic conditions. First of all, for the reason that at home we rarely use three-phase asynchronous motors. But collector single-phase motors - more than enough.

There are many schemes for the smooth start of engines. The choice of a specific one depends solely on you, but in principle, having certain knowledge of radio engineering, skillful hands and desire, it is quite you can assemble a decent homemade starter which will prolong the life of your power tool and household appliances for many years.

If you have an old angle grinder in your arsenal, do not rush to write it off. Using a simple electrical circuit, the device can be easily upgraded by adding a speed change function to it. Thanks to a simple regulator, which you can really assemble with your own hands in a few hours, the functionality of the device will increase significantly. By reducing the rotational speed, the grinder can be used as a grinding and grinding machine For various kinds materials. There are new opportunities for the use of additional nozzles and equipment.

Why grinder low speed?

The built-in disc speed control function allows you to delicately process materials such as plastic or wood. At low speeds, the comfort and safety of work is increased. This function is especially useful in electrical and radio installation practice, in car services and restoration workshops.

In addition, among professional users of power tools there is a strong opinion that the simpler the device is, the more reliable it is. And it is better to take the additional service “minced meat” outside the power unit. In this scenario, the repair of equipment is greatly simplified. Therefore, some companies specifically produce remote separate electronic regulators that connect to the power cord of the machine.

Speed controller and soft start - what are you for?

In modern angle grinders, two important functions are used that increase the reliability and safety of the tool:

speed controller - a device designed to change the number of engine revolutions in various operating modes;
soft start - a scheme that provides a slow increase in engine speed from zero to maximum when the device is turned on.

They are used in electromechanical tools, in the design of which a collector motor is used. They help to reduce the wear of the mechanical part of the unit during switching on. Reduce the load on the electrical elements of the mechanism, starting them into operation gradually.

As studies of the properties of materials have shown, the most intensive development of rubbing nodes occurs during a sharp transition from a state of rest to a mode of rapid movement. For example, one start of an internal combustion engine in a car is equivalent in terms of piston group wear to 700 km of run.

When the power is turned on, there is an abrupt transition from a state of rest to rotation of the disk at a speed of 2.5-10 thousand revolutions per minute. Those who have worked with an angle grinder are well aware of the feeling that the machine is simply “pulling out of their hands”. It is at this moment that the vast majority of breakdowns associated with the mechanical part of the unit occur.

The stator and rotor windings also experience no less load. Collector motor starts in short circuit mode, the electromotive force is already pushing the shaft forward, but the inertia does not yet allow it to rotate. There is a jump in the starting current in the coils of the electric motor. And although they are structurally designed for such work, sooner or later there comes a moment (for example, during a power surge in the network) when the winding insulation cannot withstand and an interturn short circuit occurs.

When soft start circuits and changes in engine speed are included in the electrical circuit of the tool, all of the above problems automatically disappear. Among other things, the problem of the “failure” of voltage in the general network at the time of launch is solved. hand tool. And this means that the refrigerator, TV or computer will not be at risk of "burnout". And the safety circuit breakers on the meter will not work and turn off the current in the house or apartment.

The soft start circuit is used in angle grinders of medium and high price categories, the speed control unit is used mainly in professional angle grinder models.

Adjusting the speed allows you to process soft materials with a grinder, perform fine grinding and polishing - at high speed, wood or paint will simply burn out.

Additional wiring diagrams increase the cost of the tool, but increase the service life and level of safety during operation.

How to assemble a regulator circuit with your own hands

The simplest power regulator, suitable for a grinder, soldering iron or light bulb, is easy to assemble with your own hands.

Circuit diagram

In order to assemble the simplest speed controller for a grinder, you need to purchase the parts shown in this diagram.

R1 - resistor, with a resistance of 4.7 kOhm;
VR1 - tuning resistor, 500 kOhm;
C1 - capacitor 0.1 uF x 400 V;
DIAC - triac (symmetric thyristor) DB3;
TRIAC - triac BT-136/138.

Circuit operation

Trimmer resistor VR1 changes the charging time of capacitor C1. When voltage is applied to the circuit, at the first moment of time (the first half-cycle of the input sinusoid), the triacs DB3 and TRIAC are closed. The output voltage is zero. Capacitor C1 is charged, the voltage across it rises. At a certain point in time, set by the R1-VR1 chain, the voltage on the capacitor exceeds the opening threshold of the triac DB3, the triac opens. The voltage from the capacitor is transmitted to the control electrode of the TRIAC triac, which also opens. A current begins to flow through an open triac. At the beginning of the second half-cycle of the sinusoid, the triacs close until the capacitor C1 recharges in the opposite direction. Thus, the output is a pulsed signal of complex shape, the amplitude of which depends on the operating time of the circuit C1-VR1-R1.

Assembly order

The assembly of this circuit will not make it difficult even for a beginner radio amateur. Spare parts are available, you can buy them at any store. Including soldering from old boards. The order of assembly of the regulator on thyristors is as follows:

How to connect the device to the angle grinder, options

The connection of the regulator depends on which type of device is selected. If used simple circuit, it is enough to mount it in the power supply channel of the power tool.

Installing a homemade board

There are no ready-made recipes for installation. Everyone who decides to equip the angle grinder with a regulator has it according to their goals and tool model. Someone inserts the device into the handle of the holder, someone into a special additional box on the case.

IN various models the space inside the body of the angle grinder can be different. In some, there is enough free space to install the control unit. In others, you have to bring it to the surface and fix it in a different way. But the trick is that, as a rule, there is always a certain cavity in the back of the instrument. It is designed for air circulation and cooling.

Usually this is where the factory speed controller is located. A hand-made circuit can be placed in this space. So that the regulator does not burn out, thyristors should be installed on a radiator.

Video: soft start plus and engine speed control

Features of mounting the finished block

When buying and installing a factory regulator inside a grinder, most often you have to modify the case - cut a hole in it to bring out the adjusting wheel. But this can adversely affect the rigidity of the casing. Therefore, it is preferable to install the device outside.

The numbers on the adjusting wheel indicate the number of revolutions of the spindle. The value is not absolute, but conditional. "1" - minimum speed, "9" - maximum. The rest of the figures serve as a guide for adjustment. The location of the wheel on the body is different. For example, on the angle grinder Bosch PWS 1300-125 CE, Wortex AG 1213-1 E or Watt WWS-900, it is located at the base of the handle. In other models, such as Makita 9565 CVL, the adjusting wheel is located at the end of the casing.

The connection diagram of the regulator to the angle grinder is not complicated, but sometimes it is not so easy to run the cables to the button, which is located on the other end of the device case. The problem can be solved by selecting the optimal wire section or bringing it to the surface of the casing.

A good option is to install the regulator on the surface of the device or attach it to a network cable. Not always everything works out on the first try, sometimes the device has to be tested, after which some adjustments must be made. And this is easier to do when access to its elements is open.

Important! If there is no experience with electrical circuits, it is more expedient to purchase a ready-made factory regulator or an angle grinder equipped with this function.

Device instruction manual

The basic rule when operating a grinder with a homemade speed controller is compliance with the regime of work and rest. The fact is that an engine running on a “regulated” voltage is especially hot. When grinding at low speeds, it is important to take frequent breaks so that the collector windings do not burn out.

It is also highly discouraged to turn on the tool if the speed control is set to a minimum - the reduced voltage will not be enough to scroll the rotor, the collector lamellas will remain in short circuit mode, the windings will start to overheat. Unscrew the variable resistor to the maximum, then, turning on the angle grinder, reduce the speed to the desired value.

Compliance with the correct order of switching on and adjustment will allow you to operate the angle grinder indefinitely.

In addition, it should be understood that the adjustment of the speed of rotation on the angle grinder occurs according to the principle of a water tap. The device does not increase the number of revolutions, it can only lower them. It follows from this that if the maximum passport speed is 3000 rpm, then when the speed controller is connected, the angle grinder will work in a range lower than the maximum speed.

Attention! If the angle grinder already contains electronic circuits, for example, is already equipped with a speed controller, then the thyristor controller will not work. The internal circuits of the device simply will not turn on.

Video: homemade angle grinder speed controller

Equipping the grinder with an engine speed control circuit will increase the efficiency of using the device. and expand its functional range. It will also save the technological resource of the grinding machine and increase its service life.