The smooth start on the grinder does not work. Do-it-yourself smooth start for a grinder: a diagram. Grinder soft starter, connection. Video: homemade angle grinder

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

Drills, screwdrivers, hammer drills, milling cutters are necessarily equipped with a speed controller. Some so-called calibration grinders are also equipped with a regulator, while conventional grinders only have a power button.

Manufacturers do not deliberately complicate low-power 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 grinder can be upgraded, so that the gearbox and armature winding wires will no longer be damaged. These troubles mainly occur with a sharp, in other words, shock start of the grinder.

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

A proven, working diagram is laid out below. It was originally intended to adjust the incandescence of lamps, that is, to work on an active load. Its main advantage? simplicity.

The highlight of the soft starter, the schematic diagram of which you see, is the K1182PM1R microcircuit. This microcircuit is highly specialized, of domestic production.
The acceleration time can be increased by choosing a larger capacitor C3. While charging this capacitor, the electric motor picks up speed to the maximum.
There is no need to replace the resistor R1 with a variable resistance. The 68 kΩ resistor is optimally matched to this circuit. With this setting, you can smoothly start a 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 grinder.
By inserting a semiconductor VS1 of the TC-122-25 type, that is, at 25A, into the power circuit, you can smoothly start almost any commercially available grinder with a power from 600 to 2700 W. And there is a large margin of power in the event of a grinding machine jamming. To connect grinders with a power of up to 1500 W, the imported semistors BT139, BT140 are enough. These less powerful electronic keys are cheaper.

The semiconductor in the above circuit does not open completely, it cuts off about 15V of the mains voltage. Such a voltage drop does not affect the operation of the grinder in any way. But when the semicistor heats up, the revolutions of the connected instrument are greatly reduced. This problem is solved by installing a radiator.

This simple circuit has another drawback - its incompatibility with the speed control installed in the instrument.

The assembled circuit must be hidden in a plastic box. An insulating housing is important, because you need to protect yourself from mains voltage. You can buy a junction box at an electrical 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. Given below circuit diagram is standard for 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 trimmer is installed at 100 kOhm, and an adjusting resistor at 50 kOhm. Or you can simply and roughly introduce a 470 kOhm variable between the 47 kOhm resistor and the diode.

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

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

Whichever softstarter you build, never run a connected tool under load. Any soft start can be burned if you hurry. Wait for the grinder to unwind, and then work.

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Smooth starting an induction motor is always a difficult task because it takes a lot of current and torque to start an induction motor, which can burn out the winding of an electric motor. Engineers are constantly proposing and implementing interesting technical solutions to overcome this problem, for example, using a switching circuit, an autotransformer, etc.

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

The principle of operation of an induction electric motor is known from physics, 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 rotor magnetic field, trying to catch up with the stator magnetic field, contributes to the excitation of a large starting current. The motor runs at full speed and the torque value also increases following the current. As a result, the winding of the unit can be damaged due to overheating.

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

The advantageous features of using a circuit with a soft starter (SCP):

decrease in starting current;
reduction in energy costs;
increased efficiency;
relatively low cost;
reaching maximum speed without affecting the unit.

How to start the engine smoothly?

There are five basic soft start methods.

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

By including an automatic transformer in the circuit, it is possible to maintain the starting current and torque by reducing the initial voltage. See the picture below.

Direct start is the easiest and most cheap waybecause the induction motor is connected directly to the power supply.
Connections according to a special configuration of windings - the method is applicable for 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.

Regulator of turns of the collector motor

Most schemes household appliances and electric tools created on the basis of a 220 V collector motor. Such demand is explained by its versatility. The units can be powered from DC or AC 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 governors are used.

Do-it-yourself start-up of an electric motor can be done, for example, in this way.

As a rule, budget angle grinders (angle grinders), popularly called a grinder, do not have adjustable electronic modules in their design, which include an engine speed controller and a soft start. The owners of such grinders over time begin to understand that their absence dramatically 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 or more. Those who worked with the angle grinder know well 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 starting, a huge load is applied to the rotor and stator windings of the electric motor. Since a collector motor is installed in the grinder, it starts in short-circuit mode: the electromagnetic field is already “trying” to turn the rotor, but it remains stationary for some time, since the inertia force does not allow it to be done. As a result, the starting current in the motor coils rises sharply. Despite the fact that the manufacturer has invested a certain margin of safety for the coils, taking into account the overload at start, sooner or later the insulation does not withstand, which leads to an interturn short circuit.

In addition to starting problems, the lack of speed control causes some discomfort. For example, a grinder's 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 roughing with tines, there is a high probability of wire jamming in any gap. If the spindle speed was high, then the grinder can simply be pulled out of the hands.

If you connect a power (speed) regulator 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.

Homemade regulator circuit

One of the most popular schemes for smooth starting a 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 electronics. The main thing is that you know how to use a soldering iron.

This block works as follows.

After pressing the start button of the unit electricity begins to flow, first of all, to the microcircuit (DA1).
The control capacitor starts to charge smoothly and after a while gains the required 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 VS1 triac 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 grow abruptly, but slowly, as a result of which the grinder starts smoothly.

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

If you replace the resistor R1 with a variable, then you get a speed regulator, which will reduce the engine speed.

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

the minimum current strength for which it is designed should be 25 A;
the triac must be rated 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 the speed controller for the grinder, you will need to draw a printed circuit board, etch the contacts with acid and then plow them, drill holes and solder the radio components. But everything can be made easier:

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

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

How to connect a regulator to a grinder

No special knowledge is required to connect a homemade power regulator, and any house master will cope with this task. The module is installed break one wirethrough which the 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 the instrumentas shown in the following photo.

Also, the regulator can be placed in an outlet 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 as follows.

The regulator is connected as described above - at a break in 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 regulator, which can be used for other electrical appliances.

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

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

Are motors and loads a problem?

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

Probably the most significant load on the engine at the time of start-up is the 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 its normal level. To ensure the required power supply have to increase the capacity of electrical equipment and conductive lines, which leads to their rise in price.

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

In the event of abnormal situations resulting in engine burnout or severe overheating, properties of transformer steel may change so much so that after repair the engine will lose up to thirty percent of its power. Under such circumstances, it is already unusable for further use 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 of them:

at the time of starting the electric motor, the supply current can exceed the nominal four and a half to five times, which leads to significant heating of the windings, which is not very good;
starting the motor by direct switching leads to jerks, which primarily affect the density of the same windings, increasing the friction of the conductors during operation, accelerating 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 machine. This is already completely unhealthy, because can damage 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;
you should also not forget about the products that may be on the production line. They can fall, crumble or break due to such a jerk;
well, and probably the last of the points worthy of 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 consumed electricity.

It would seem that all of the above operational difficulties are inherent only in powerful and bulky industrial equipment, however, this is not the case. All this can be a headache for any average layman. This primarily applies to the power tool.

The specificity of the use of such units as jigsaws, drills, grinders and the like, imply multiple start and stop cycles over a relatively short period of time. Such a mode of operation affects their durability and energy consumption to the same extent as their industrial counterparts. With all this, do not forget that soft start systems cannot regulate the operating speed of the motor or reverse their direction. It is also impossible to increase the starting torque or reduce the current lower than is required to start the rotation of the rotor of the electric motor.

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

Options for soft start systems for electric motors

Star-delta system

One of the most widely used industrial induction motor starting systems. Its main advantage is simplicity. The engine starts when the star system windings are commuted, after which, when the nominal speed is set, it automatically switches to the delta commutation. This start option allows you to achieve a current almost a third lowerthan when starting the electric motor directly.

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

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

Electronic system of soft start of the electric motor

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

With the help of such 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 helps to increase the life of the electric motors. Due to the fact that the engine start-up is controlled by reducing the voltage, the rotor acceleration is carried out smoothly, and not abruptly, like with other circuits.

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

main - lowering the starting current to three or four rated;
reduction of the motor supply voltage, if appropriate capacities and wiring are available;
improving the parameters of starting and braking;
emergency network protection against overcurrent.

Single-phase starting circuit

This circuit is designed to start electric motors with a capacity of no more than eleven kilowatts. This option is used in the event that it is required to soften the shock 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 reduction in the cost of production of semiconductors, including triacs, they are discontinued and are rarely found;

Two-phase starting scheme

This circuit is designed to regulate and start motors up to two hundred and fifty watts. Such soft starters sometimes equipped with a bypass contactor to reduce the cost of the device, however, this does not solve the problem of phase asymmetry, which can lead to overheating;

Three-phase starting scheme

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 temperature and electrical endurance of the triacs used. His versatility allows you to implement a lot of functionssuch as: dynamic brake, retraction catch or balancing of magnetic field and current limitation.

An important element of the last mentioned circuit is the bypass contactor, which was mentioned earlier. He allows you to ensure the correct thermal mode of the soft start system of the electric motor, after the engine reaches its normal operating speed, preventing its overheating.

The existing soft starters of electric motors, 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 by command of the operator or the global control system Under such circumstances, at the moment the loads are switched on, interference may appear that can lead to malfunctions in the operation of the automation, and therefore, it is worth taking care of the protection systems. The use of soft start schemes can significantly reduce their impact.

Do-it-yourself smooth start

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

There are many schemes for smooth engine start devices. 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 starterwhich will prolong the life of your power tool and household appliances for years to come.

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 the function of changing the frequency of revolutions. Thanks to a simple regulator, which can be assembled with your own hands in a few hours, the functionality of the device will increase significantly. By reducing the speed, the grinder can be used as a grinding and sharpening machine for different types materials. There are new possibilities for the use of additional attachments and accessories.

Why does the Bulgarian have low revs?

The built-in disc speed control allows you to delicately handle materials such as plastics or wood. Comfort and safety of work is increased at low revs. This function is especially useful in electrical and radio installation practice, in car services and restoration workshops.

In addition, there is a strong belief among professional users of power tools that the simpler the device is, the more reliable it is. And the additional service "stuffing" is better to take out outside the power unit. In this situation, the repair of equipment is greatly simplified. Therefore, some companies specifically produce remote individual electronic controls that are connected to the machine's power cord.

Speed \u200b\u200bcontroller and soft start - what are you needed for

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

speed regulator - a device designed to change the number of engine revolutions in different 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 wear on the mechanical part of the unit during switching on. They reduce the load on the electrical elements of the mechanism, starting them up 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 equal to the wear of the piston group to 700 km.

When the power is turned on, there is an abrupt transition from the rest state to the rotation of the disk at a speed of 2.5-10 thousand rpm. Those who have worked with a grinder are well aware of the feeling that the machine is simply "being pulled out of hand". It is at this moment that the overwhelming number of breakdowns associated with the mechanical part of the unit occurs.

The stator and rotor windings are equally stressed. Collector motor starts in short-circuit mode, the electromotive force is already pushing the shaft forward, but the inertia still does not allow it to rotate. There is a jump in the starting current in the coils of the electric motor. And although structurally they are designed for such work, sooner or later a moment comes (for example, with a voltage surge in the network) when the winding insulation does not withstand and an interturn short circuit occurs.

When you include soft start circuits and changes in engine speed into the electrical circuit of the instrument, all of the above problems automatically disappear. Among other things, the problem of voltage "dip" in the common network at the time of startup is solved hand tool... This means that the refrigerator, TV or computer will not be exposed to the danger of "burnout". And the safety devices on the meter will not work and turn off the current in the house or apartment.

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

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

Additional wiring diagrams increase the cost of the tool, but increase the service life and the 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.

Basic electrical diagram

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

R1 - resistor, 4.7 kOhm;
VR1 - trimmer resistor, 500 kOhm;
C1 - capacitor 0.1 μF x 400 V;
DIAC - triac (symmetrical thyristor) DB3;
TRIAC - BT-136/138 triac.

Circuit operation

The trimmer VR1 changes the charging time of the capacitor C1. When voltage is applied to the circuit, at the first moment of time (the first half-cycle of the input sinusoid), the DB3 and TRIAC triacs are closed. The output voltage is zero. Capacitor C1 is charging, the voltage across it increases. At a certain moment in time, set by the R1-VR1 chain, the voltage across the capacitor exceeds the opening threshold of the DB3 triac, the triac opens. The voltage from the capacitor is transmitted to the control electrode of the TRIAC triac, which also opens. Current begins to flow through the open triac. At the beginning of the second half-cycle, the triac sine waves close until the capacitor C1 is recharged in the opposite direction. Thus, a complex pulse signal is obtained at the output, the amplitude of which depends on the operating time of the C1-VR1-R1 circuit.

Assembly order

The assembly of this circuit will not complicate even a novice radio amateur. Spare parts are available, you can buy them at any store. Including soldering from old boards. The assembly procedure for the thyristor regulator is as follows:

How to connect the device to a grinder, options

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

Installing a homemade board

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

IN different models the space inside the grinder's body can be different. Some have enough free space to install a 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 DIY scheme can be placed in this space. To prevent the regulator from burning out, the thyristors should be installed on the radiator.

Video: smooth start plus and engine speed control

Features of mounting a finished block

When buying and installing a factory regulator inside the grinder, most often you have to modify the body - cut a hole in it to output the adjusting wheel. However, 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 spindle revolutions. The meaning is not absolute, but conditional. "1" - minimum speed, "9" - maximum. The rest of the numbers are for guidance when regulating. The location of the wheel on the body is different. For example, on a Bosch angle grinder 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 the Makita 9565 CVL, the adjusting wheel is located at the end of the casing.

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

A good option is to install the regulator on the surface of the device or fasten it to a power cable. Everything does not always work out on the first try, sometimes the device has to be tested, after which some adjustments are 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 advisable to purchase a ready-made factory regulator or angle grinder equipped with this function.

Device manual

The basic rule when operating a grinder with a homemade speed controller is to observe the work and rest mode. The fact is that the engine operating at the "regulated" voltage is especially hot. When sanding at reduced 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 controller is set to a minimum - the undervoltage is not enough to spin the rotor, the collector lamellas will remain in short circuit mode, and 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.

Observance of the correct order of inclusion and adjustment will allow you to operate the grinder for an unlimited time.

In addition, it should be understood that the speed control on the grinder is based on 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 grinder will operate 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 regulator, then the thyristor regulator will not work. The internal circuits of the device simply won't turn on.

Video: homemade angle grinder

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