An angle grinder, which received the nickname “Bulgarian” in the post-Soviet space, was something every owner wanted to have in his home workshop 3-4 decades ago. Then for most people it really was a dream, since only one plant produced this electric tool - “Eltos-Bulgarka” in the Bulgarian city of Plovdiv (hence the popular name). And although over the past time the number and range of grinders have grown incredibly, the main components of the tool’s design have not changed.

Grinders are used not only for grinding and polishing surfaces, but also for processing metal and concrete (using diamond or abrasive wheels).

Electrical equipment for an angle grinder

Over 40 years, the appearance of the angle grinder has remained virtually unchanged: an oblong body with a motor and gearbox mounted inside, a handle screwed to the side and a protective casing.

A grinder, like any tool, sooner or later refuses to work. But there are situations when a simple repair of electrical equipment is sufficient to eliminate a malfunction. To perform these minor repairs, you need to have an understanding of how such equipment works internally and be able to read its electrical diagram.

The electrical circuit of the grinding machine consists of the following elements:

• anchor;
• collector;
• electric brushes;
• gearbox;
• stator;
• handle holders;
• power cable with plug.

Each of these elements performs its own functions in the electrical circuit; a malfunction of each leads to a stop in the operation of the tool. For example, the armature, being a rotating element of the chain, is responsible for the rotation of the grinding disc. To make the disk rotate, the armature must spin at an even higher speed. Therefore, the higher the rotation speed of the armature, the greater the power of the tool.

The collector is the area on the anchor where all the power and control cables exit. Its task is to translate the signals passing through the windings into a language understandable to the engine and control unit. If you remove the case cover, its polished plates immediately catch your eye, especially since they are relatively large in size.

The purpose of electric brushes is to provide current supply to the commutator from the power cable. If they are in normal working condition, then an even glow will be visible through the ventilation hole. If the glow is not noticeable or it pulsates, then this is a sign that there are problems with the brushes.

The gearbox is a very important part not only of the electrical circuit, but also of the entire design of the angle grinder. Its purpose is to supply energy from the rotating armature to the grinding disc, thus ensuring its rotation. In fact, it is the gearbox that is responsible for the speed and power of rotation of the grinding disc of the grinder.

The stator is the most technically complex component in the electrical circuit of an angle grinder. All the windings of the armature and rotor are pressed into it, determining their rotation. The coil windings located in the stator are designed up to the last turn. If the stator fails, successfully rewinding it by a non-professional is a very rare case. Therefore, if the stator in an angle grinder breaks down, it is better not to risk it and have it repaired in a workshop.

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Reading an Electrical Diagram

But knowing the purpose of the main elements of the instrument’s electrical circuit is not enough; you also need to be able to read this circuit. And although the electrical circuit of an angle grinder is not the most complex that you can come across among electrical circuits, even it can be difficult for a person far from electricity to understand without outside help.

The grinder circuit is designed like this: two stator windings are connected in series via a cable to a network with a voltage of 220 V and are not electrically connected to each other. They are turned on/off using a switch mechanically connected to the start button of the angle grinder. Each winding is connected through a contact to a graphite brush.

Then the electrical circuit, through two windings connected in parallel to the graphite brushes, goes to the rotor, where it closes at the contacts of its commutator. It is noteworthy that the armature winding consists of many windings, but only two are directly connected to the graphite brushes. In 9 cases out of 10, the failure of a grinding machine, like any power tool, occurs due to a break in the electrical circuit.

To diagnose a circuit and detect faults in it, a special device is used - a multimeter. This portable tester is useful not only for diagnosing an angle grinder, but also any other power tool, including electrical wiring in the house.

Testing should always begin at the electrical current input site and sequentially test all elements of the electrical circuit with a multimeter. To check the conductivity of electricity, the multimeter should be set to the minimum resistance position.

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Troubleshooting minor problems

If the grinder does not start when you press the “Start” button, it is quite possible that the cause of the breakdown is not too serious and the machine can be repaired on your own. There is a rule for repairing any power tool - move from simple to complex.

In the above situation, in 9 cases out of 10, the cause of the malfunction will be a break in the electrical circuit in the area from the power source to the graphite brushes. The first step is to remove the casing and check with a tester whether electricity is supplied to the “Start” button. If electric current does not flow to the button terminals, then it is enough to replace the old electrical wire with a new one to repair the tool.

If current flows to the trigger, but does not go further, then the problem is in the start button itself. It needs to be replaced, but this should be done slowly. First you need to carefully disassemble the trigger mechanism, and do not be too lazy to mark the contacts to be removed. To replace a button that has become unusable, any button that is suitable in size and with similar parameters will do. You need to be especially careful when reconnecting the contacts, since their incorrect installation will most likely result in a burnt winding or a jammed armature.

If both the electrical wire and the start button are in full working order, but current does not flow to the graphite brushes, you first need to clean the contact plates of the brush holders attached to the commutator. If, even after performing this procedure, the grinder does not turn on, then the brushes themselves should be changed.

An angle grinder is called an angle grinder, which at home allows you to clean surfaces, sand, cut tiles and saw wood. Every craftsman wants to own a reliable and functional tool, without failures or breakdowns. Factory versions of angle grinders can be slightly modified for this purpose - assemble a speed controller for an angle grinder with your own hands. This will increase the working life of the machine and allow you to work without unpleasant surprises.

Why does an angle grinder have a soft start and a speed controller?

The most common surprise at work is the failure of the electric motor winding. This can happen after just a few runs of the new tool. The problem occurs due to very high rotation speed. When the machine is turned on, several sequential actions occur at once:

• the current increases sharply:
• the electric motor starts;
• The speed increases to operating values.

All this happens in a very short period of time, which puts a huge load on each angle grinder unit, especially on the electrical winding. As a result, it breaks off.

Many models are initially equipped with soft start devices and speed controllers, but they are not very popular due to their high cost. On more budget ones, it is quite possible to assemble a speed controller for an angle grinder yourself, and the smooth start is assembled on the same chip. One action solves two main problems of a much-needed tool.

Those who have worked with an angle grinder with tiles, stone and similar materials know that the quality of cutting and the appearance of the edge suffer greatly from high speeds, and the tool itself is literally “killed” by such work. The same problem applies to metal parts: aluminum and other soft alloys need to be cut at minimum speeds, and thick and hard blades need to be cut at maximum speeds. Processes of grinding and polishing surfaces at high speeds will damage the material.

Installing a speed controller will significantly expand the existing functionality and allow you not to worry about performance. And preventing breakdowns has never bothered anyone.

The simplest regulator circuit

The electrical circuit of the speed controller for the angle grinder is assembled on a printed circuit board or mounted. Moreover, a printed circuit board can also be made independently using PCB and ferric chloride for etching. Instead of iron, you can use a mixture of hydrogen peroxide, salt and citric acid.

Electrical circuit configuration

To make the diagram you will need:

• resistor R1(4.7 kOhm);
• symmetrical thyristor DIAC(DB3);
• symmetrical thyristor TRIAC(VT-136/138);
• trim resistor VR1(500kOhm);
• capacitor C1 (0.1 µF*400V).

Principle of operation

The operating principle of the circuit is constructed as follows. VR1 is responsible for counting the charging time of C1. When voltage is applied to the circuit, the thyristors are closed, the output is 0. As the capacitor charges, the voltage in it increases and opens the DIAC, which supplies voltage to the TRIAC. It also opens and allows current to pass through. Then both thyristors close and remain in this position until C1 is completely recharged. As a result, a complex wave signal is formed at the output with an amplitude that directly depends on the operating time of the C1-VR1-R1 circuit.

Final assembly and testing of the regulator

The circuit is assembled on a printed circuit board or a copper (aluminum) radiator. When mounted on an assembly, the location of the thyristors is especially important (strictly on the radiator, it plays the role of a heat sink). Then a mandatory check of the circuit’s functionality is carried out using a regular light bulb. The smoothness of the change in heat will be the same as in the finished speed controller for an angle grinder after final assembly.

Factory models are equipped with a plastic adjustment wheel; if desired, it can also be purchased separately and included in the homemade regulator kit. If the testing was successful, the regulator is attached to the angle grinder and fits into the power supply circuit of the tool.

Installing the regulator on an angle grinder

The do-it-yourself speed controller for an angle grinder can be mounted in four options:

• into the pen;
• in an outer box, which is mounted in a convenient place on the instrument body;
• into the cavity for cooling (manufacturers use this option);
• to the network cable.

Installing an additional box does not require cutting the housing to output the regulator, but the location should be chosen very pickily so that the innovation does not interfere with the comfortable holding of the instrument. Installation into a handle or cavity for cooling will require cutting a hole for the adjustment wheel to come out; the main thing here is not to lose the rigidity of the protective casing and to clean the edges well so as not to injure your hands during operation.

Often the best option is to mount it on a wire. In this case, the regulator is easy to test; there is no need to think about the location and method of fastening (insulating tape and a plastic case are quite suitable). If desired, you can always remove it and redo it.

The intricacies of working an angle grinder with a homemade regulator

A limitation in the operation of the modified instrument will be strict adherence to the “work/rest” mode. This is necessary to preserve the collector winding. When operating at low speeds, the brushed motor gets very hot and can cause trouble.

The next factor is the moment of switching on. The speed must be reduced when the tool is running. When turned on at minimum speed, the voltage may not be enough to spin the rotor, the commutator lamellas will remain closed, and the winding will begin to overheat and may burn out.

It should be understood that installing a regulator will not increase the power of the tool in any way. If the specification indicates a maximum number of 3000 rpm, then the angle grinder will produce a range from 0 to 3000 rpm.

If you have an old angle grinder in your arsenal, don’t rush to write it off. Using a simple electrical circuit, the device can be easily upgraded by adding the function of changing the speed. Thanks to a simple regulator that you can actually assemble with your own hands in a few hours, the functionality of the device will increase significantly. By reducing the rotation speed, the grinder can be used as a grinding and sharpening machine for various types of materials. New opportunities are emerging for the use of additional attachments and accessories.

Why does the grinder need low speeds?

The built-in disc speed control function allows you to delicately process materials such as plastic or wood. At low speeds, operating comfort and safety increases. 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 move the additional service stuffing outside the power unit. In this situation, equipment repair is greatly simplified. Therefore, some companies specially produce remote, separate electronic regulators that connect to the machine’s power cord.

Speed ​​controller and soft start - what are they for?

Modern grinders use two important functions 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 circuit that ensures a slow increase in engine speed from zero to maximum when the device is turned on.

They are used in electromechanical tools that use a commutator motor in their design. Helps reduce wear on the mechanical part of the unit during switching on. They reduce the load on the electrical elements of the mechanism by putting them into operation gradually.

As studies of the properties of materials have shown, the most intense production of friction units 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 to 700 km of mileage in terms of wear on the piston group.

When the power is turned on, an abrupt transition occurs 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 simply “rips out of your hands.” It is at this moment that the overwhelming number of breakdowns associated with the mechanical part of the unit occur.

The stator and rotor windings experience no less load. The commutator motor starts in short circuit mode, the electromotive force is already pushing the shaft forward, but inertia does not yet allow it to rotate. A jump in starting current occurs in the coils of the electric motor. And although they are structurally designed for such work, sooner or later a moment comes (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 voltage “dip” in the general network at the moment of starting a hand tool is solved. This means that the refrigerator, TV or computer will not be at risk of “burning out”. And the safety circuit breakers on the meter will not operate and cut 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 models of angle grinders.

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.

Additional electrical circuits 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 an angle grinder, soldering iron or light bulb, is easy to assemble with your own hands.

Electrical circuit diagram

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

• R1 - resistor, resistance 4.7 kOhm;
• VR1 - trimming resistor, 500 kOhm;
• C1 - capacitor 0.1 µF x 400 V;
• DIAC - triac (symmetrical 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), triacs DB3 and TRIAC are closed. The output voltage is zero. Capacitor C1 charges and the voltage across it increases. At a certain point in time, specified 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. Current begins to flow through the open triac. At the beginning of the second half-cycle of the sinusoid, the triacs are closed until capacitor C1 is recharged in the opposite direction. Thus, the output produces a pulse signal of complex shape, the amplitude of which depends on the operating time of the C1-VR1-R1 circuit.

Assembly order

Assembling this circuit will not be difficult even for a novice radio amateur. Spare parts are available and can be purchased at any store. Including desoldering from old boards. The procedure for assembling the regulator using thyristors is as follows:

How to connect the device to an angle grinder, options

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

Installing a homemade board

There are no ready-made installation recipes. Anyone who decides to equip an angle grinder with a regulator places it in accordance with their goals and model of the tool. Some people insert the device into the handle of the holder, others into a special additional box on the body.

In different models, the space inside the angle grinder body may be different. Some have enough free space to install a control unit. In others, you have to take it to the surface and attach 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.

This is usually where the factory speed controller is located. A DIY diagram can be placed in this space. To prevent the regulator from burning out, the thyristors should be installed on the radiator.

Video: soft start plus and engine speed adjustment

Features of installation of the finished block

When purchasing and installing a factory regulator inside an angle grinder, most often you have to modify the body - cut a hole in it to allow the adjustment wheel to come out. But this may adversely affect the rigidity of the casing. Therefore, it is preferable to install the device outside.

The numbers on the adjustment wheel indicate the number of spindle revolutions. This value is not absolute, but conditional. “1” - minimum speed, “9” - maximum. The remaining numbers serve as a guide for regulation. The location of the wheel on the body varies. For example, on the Bosch PWS 1300–125 CE, Wortex AG 1213–1 E or Watt WWS-900 angle grinders, it is located at the base of the handle. On other models, such as the Makita 9565 CVL, the adjustment wheel is located at the end of the housing.

The connection diagram of the regulator to the angle grinder is not complicated, but sometimes it is not so easy to stretch the cables to the button, which is located at the other end of the device body. The problem can be solved by selecting the optimal wire cross-section or by placing it on 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 everything always works out on the first try; sometimes the device has to be tested and then some adjustments made. And this is easier to do when access to its elements is open.

Important! If you have no experience working with electrical circuits, it is more advisable to purchase a ready-made factory regulator or angle grinder equipped with this function.

Device Instruction Manual

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

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

Following the correct order of activation and adjustment will allow you to operate the angle grinder for an unlimited period of time.

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

Attention! If the angle grinder already contains electronic circuits, for example, it 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 angle grinder with a circuit for adjusting engine speed will increase the efficiency of using the device. and expand its functional range. This will also save the technological resource of the grinding machine and increase its service life.

Power tools occupy one of the main places in our workshop. Each electrical device performs all functions according to technical specifications. What else would you like? I really want the tool to last longer or not break at all. Just as a person gets used to a friend - a dog, so he gets used to an instrument.

One of the main tools is an angle grinder, which we call an angle grinder. This is a universal tool that can cut, grind, clean surfaces, saw boards, and can be adapted to many other operations.

Smooth start and rotation speed adjustment + (Video)

Smooth starting of a power tool is the main guarantee of its longevity. Remember when a light bulb burns out? Most often at the moment of switching on. Because after connecting to the electrical network, the load increases sharply. The damaged parts of the spiral cannot withstand it and it burns out.

The same processes occur in the grinder. At the moment of switching on, the current increases sharply, because the driving forces need to not only move the armature, but also quickly gain the required speed. The effect of such a hard start can be the most deplorable - winding breakage.

To reduce the likelihood of tool failure due to a hard start, it is necessary to modify the angle grinder and equip it with a small built-in soft start device.

Another modification is the rotation regulator. From personal experience, everyone knows how inconvenient it is to work with a tool that does not have rotation adjustment. If an electric drill does not have such a device, then it is difficult to select the rotation speed and feed of the drill. This leads to either jamming of the drill or its breakage.

A lathe works similarly, in which there is a whole set of special gears to adjust the rotation of the spindle. Not only the safety of the cutter, but also the quality of material processing largely depends on this.

You can combine two advantages - soft start and adjustment of shaft speed using an electronic circuit. It is quite possible to assemble it yourself and install it directly into the car body. With such a circuit, it will start smoothly without creating overloads in the windings and network. And with the same scheme, it will be possible to regulate the speed in order to select the mode of operation with any material.

If you cut metal with significant thickness and hardness, then it is necessary to maintain high speeds. But when processing surfaces of low-melting materials, high speed will do more harm than help. It needs to be reduced. It is dangerous to work with stone or tiles at high speed. And here it needs to be reduced.

Even when grinding the disk, the rotation speed must be proportionally changed, because the linear speed of the disk edge will decrease. You cannot do without a speed controller when working with a diamond-cut disk, because at high temperatures it is destroyed very quickly.

Everything suggests that if the grinder does not have a speed controller, then one must be made and installed in the car.

How to make a speed controller with your own hands + (Video)

In order not to complicate the perception of the operating principle with complex terms, the fundamental operation of the circuit can be explained simply. It has a sensitive element that reads the load value. Depending on the read value, this element controls the locking device.

The operating principle is similar to that of a water tap. In this case, you are the sensing element that controls the water tap. The flow of water, depending on the need, becomes more or less. The same process occurs with current.

It is necessary to correctly understand the point that we cannot in any way increase the rotation speed beyond that indicated in the characteristics of the angle grinder. We can only lower the speed. If the maximum rpm is 3000, then the range in which we can adjust the rpm will be below this value.

In the simplest version, you can use a thyristor regulator circuit. He will both feel and regulate. Two in one. This circuit has only five parts. It is very compact and easily fits into the case. Such a regulator will not operate from zero speed, but this is not necessary for an angle grinder.

If lower speeds are needed in operation, then it is necessary to use another circuit on an integrated circuit, where the locking element will be a triac. Such a circuit will be able to regulate the speed from almost zero to the desired value.

In both schemes, the main load falls on the locking element. It must be designed for voltages up to 600 V and currents up to 12 A. If your grinder is more powerful than 1 kW, then the locking element must withstand a load of up to 20 A.

All parts of the thyristor circuit can be placed on a printed circuit board or simply mounted. According to the second option, the parts are soldered on a printed circuit board. A printed circuit board can be manufactured using different methods. It can be etched from foil PCB, you can even cut it out with a cutter, but it will turn out very roughly. In principle, you can ask a radio amateur you know to make it for a very modest reward.

Radio-electronic elements are inserted into the manufactured printed circuit board. They can be purchased in specialized stores or at radio markets. The ratings of each should not differ in rating and rated power. It is advisable to install a thyristor or triac on a heat sink - an aluminum or copper radiator.

When the finished board is ready, you need to choose a convenient place in the grinder body to install it. It is advisable to install it so that it is convenient to use and so that it does not interfere with the work process.

Before installing the circuit in the car, it must be checked. To do this, instead of an angle grinder, you need to connect a regular incandescent lamp to the output. An example with a power of 60 - 40 W at 220 V is suitable. The performance will be obvious by the change in the glow of the light bulb.

Now all that remains is to mount the device in the chosen location and perform a test run of the angle grinder. It will stop breaking out of your hands during startup, and the speed will be smoothly adjusted by rotating the regulator.