How to make a soft start and speed controller for an angle grinder. Repair of drill speed controller. Case study: Can an electric drill be connected via a dimmer?

In the eighties of the last century, the magazine “Radio” published a schematic diagram of a drill speed controller, reprinted from a Bulgarian magazine on radio electronics. The parts in this diagram were made abroad. In 1985, I made this drill speed controller from domestic parts and still works properly.

Currently, imported and domestic drills are produced with speed controllers, but there are many early production drills that do not provide for changing the speed, which, of course, reduces the operational capabilities of the drill.

In Fig. Figure 1 shows a diagram of a drill speed controller, manufactured as a separate unit and, as tests have shown, suitable for any drills with a power of up to 1.8 kW, as well as for any devices that use a collective

AC motor, for example, in angle grinders, so-called grinders. I selected domestic regulator parts for my drill brand S480B (n=650 rpm, power 270 W, voltage 220 V).

Resistors:

R, - 7 kOhm (assembled from two parallel-connected resistors with a nominal value of 12 kOhm and 18 kOhm, type MLT2, power 2 W each\

R 2 - 2.2 kOhm type SP variable, power 1 W;

R 3 - 51 Ohm MLT type, power 0.125 W;

Capacitor C, - 2 μF (actually assembled from two series-connected capacitors with a capacity of 4 μF, type MBGO-2, operating voltage 160 V).

Diodes: VD1 and VD2 - type D7Zh (forward current 300 mA and reverse voltage U^p = 400 V). Diodes D226, D237B, KD-221V, MD226 have similar parameters.

Thyristor VT1 - type KU202N (reverse voltage U^ = 400 V, open current J oc = 10 A). Thyristors 2U202M, 2U202N, KU202M have the same parameters.

(angle grinders), commonly known among Bulgarians, have a speed regulator.

The speed regulator is located on the body of the angle grinder

Consideration of various adjustments should begin with an analysis of the electrical circuit of the angle grinder.

simple representation of the electrical circuit of a grinding machine

More advanced models automatically maintain rotation speed regardless of the load, but tools with a manual disk are more common. If a trigger-type regulator is used on a drill or electric screwdriver, then such a regulation principle is impossible on an angle grinder. Firstly, the features of the tool require a different grip when working. Secondly, adjustment during operation is unacceptable, so the speed value is set with the engine turned off.

Why adjust the rotation speed of the grinder disc at all?

1. When cutting metal of different thicknesses, the quality of work greatly depends on the speed of rotation of the disk.
   If you are cutting hard and thick material, you must maintain maximum rotation speed. When processing thin sheet metal or soft metal (for example, aluminum), high speeds will lead to melting of the edge or rapid blurring of the working surface of the disk;
2. Cutting and sawing stone and tile at high speed can be dangerous.
   In addition, the disk, which rotates at high speeds, knocks small pieces out of the material, making the cutting surface chipped. Moreover, different speeds are selected for different types of stone. Some minerals are processed at high speeds;
3. Grinding and polishing work is in principle impossible without adjusting the rotation speed.
   By setting the speed incorrectly, you can damage the surface, especially if it is a paint coating on a car or a material with a low melting point;
4. The use of discs of different diameters automatically implies the presence of a regulator.
   Changing a disk Ø115 mm to Ø230 mm, the rotation speed must be reduced by almost half. And it’s almost impossible to hold a 230 mm disc rotating at 10,000 rpm in your hands;
5. Polishing of stone and concrete surfaces, depending on the type of crowns used, is carried out at different speeds. Moreover, when the rotation speed decreases, the torque should not decrease;
6. When using diamond discs, it is necessary to reduce the number of revolutions, since their surface quickly fails due to overheating.
   Of course, if your grinder works only as a cutter for pipes, angles and profiles, you won’t need a speed controller. And with the universal and versatile use of angle grinders, it is vital.

From a drill, with the help of additional devices, you can make various devices that will replace various machines, such as drilling, lathe, grinding and others. But if drill machines do not have the ability to regulate the rotation speed, then working on them will not be very convenient.

Modern drills are often equipped with a speed regulator in the form of a trigger. In this case, the rotation speed depends on the degree of pressure. At the same time, the trigger lock does not fix the trigger at the selected rotation speed in all models of drills, but only locks the trigger when the maximum pressure is applied, that is, at maximum speed, which can negate such a speed controller. Another disadvantage of the built-in regulator is that when the drill is inserted into any device, it may be in a position in which it is inconvenient to use the speed regulator, even if it has no other disadvantages.

For drill machines, it is more convenient to use an external regulator, which eliminates the disadvantages described above. You can make such a regulator from a dimmer (lighting regulator) and a socket. The schematic diagram of such a regulator is as follows:

The implementation of this scheme may vary. We will present two options that are not the best from a security point of view. Of course, the regulator must be made so that the inside is closed on all sides, and not as it is done in the pictures.

It is very convenient to use such a speed regulator; the regulator plug is inserted into the mains socket, and the drill plug into the regulator socket. The drill trigger is fixed in the fully pressed position, and the rotation speed is controlled by turning the dimmer knob. It is only necessary that the power of the drill does not exceed the power of the dimmer. Such a regulator can be used not only to regulate the rotation speed, but also to control the heating of a soldering iron or boiler.

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Today it is impossible to find a person who does not know about the existence of an electric drill. Many people have had to use this tool. But not everyone knows how this irreplaceable household thing works.

Inside the drill body there is an electric motor, its cooling system, a gearbox, and a drill speed controller. It’s worth talking about the operation of the drill speed controller in a little more detail. All parts wear out during operation, the drill power button is especially susceptible to this process. And the speed control system is directly connected to it.

Purpose of the speed controller

The speed control of a modern electric drill is located inside the power button of the device. The microfilm technology used to assemble it makes it possible to achieve such small sizes. All parts and the board itself on which these parts are located are small in size. The main part of the regulator is a triac. The principle of its operation is to change the moment of closing the circuit and turning on the triac. It happens like this:

1. After turning on the button, the triac receives a sinusoidal voltage to its control electrode.
2. The triac opens and current begins to flow through the load.

With a larger amplitude of the control voltage, the triac turns on earlier. The amplitude is controlled using a variable resistor, which is connected to the trigger of the drill. The button connection diagram may be slightly different in different models. Just don’t confuse the speed controller with the reverse control device. These are completely different things. Sometimes they can be located in different buildings. The speed controller may provide for connecting a capacitor and both wires from the outlet.

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Using a drill as a machine tool

Figure 1. Typical diagram of a drill speed controller.

A hand drill can be used in non-standard ways. A variety of machines are made on its basis: drilling, grinding, circular and others. In such machines, the speed control function is very important. For most household drills, the speed is regulated by the device's start button. The harder it is pressed, the higher the speed. But they are fixed only at maximum values. In most cases this can be a significant drawback.

You can get out of this situation by making your own remote version of the speed controller. As a regulator, it is quite possible to use a dimmer, which is usually used to regulate lighting. The regulator circuit is quite simple and is shown in Fig. 1. To make it, you need to connect wires of different lengths to the socket. The other end of the long wire is connected to the plug. The rest is assembled according to the scheme. It is recommended to use an additional circuit breaker that will turn off the device in the event of an emergency.

The homemade speed controller is ready. You can perform a test run. If it works normally, you can place it in a suitable sized box and attach it to the frame of the future machine in a convenient place.

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Repair of a button with speed control

Figure 2. Diagram of a speed controller for a microdrill.

Repairing a button is a rather complicated process that requires certain skills. When opening the case, some parts may simply fall out and get lost. Therefore, caution is needed in work. In case of problems, the triac usually fails. This part is very cheap. Disassembly and repair occur in the following order:

1. Disassemble the button housing.
2. Rinse and clean the insides.
3. Remove the board with the circuit on it.
4. Remove the burnt part.
5. Solder a new part.

It is very easy to disassemble the case. You need to bend the sides and remove the cover from the latches. Everything must be done carefully and carefully so as not to lose 2 springs that may jump out. It is recommended to clean and wipe the insides with alcohol. Clip-contacts in the shape of copper squares slide out of the grooves, and the board is easily removed. A burnt triac is usually clearly visible. All that remains is to unsolder it and solder a new part in its place. The regulator is reassembled in the reverse order.

You can repair a drill yourself, the main thing is to know the causes of breakdowns and methods of “treating” them. Today we will talk about what the drill button connection diagram looks like, and we will not ignore other faults, thanks to which you will be the happy owner of a working tool.

If your tool begins to work worse, or even stops performing its direct duties, it’s time to diagnose the problems and try to deal with them. First, we check the wire for damage and the voltage in the outlet, for which you can plug in any other device - a TV or a kettle.

If you are inspecting battery-powered devices, they should be checked using a tester - in this case, the voltage indicated on the case should have a similar value to the battery voltage.

If the voltage is less, you will have to replace the batteries with new ones. If the battery is working normally, the power supply is normal, look for hardware problems. The most common breakdowns are:

• Problems with engine operation;
• Brush wear;
• Problems with the button operation.

Knowing how the electric drill button is connected, you can quickly solve the problem. In addition, a problem with the operation of the drill can also arise due to the dustiness of the tool, because the drill “takes” wood, brick, and other materials. This means that you should take care to clean the device after each use - this is the only way to reduce the risk of malfunctions due to contamination of the tool. That is why, after you have carried out, immediately clean the drill.

Unfortunately, to check the functionality of the tool, a tester will not be enough for you, which is due to the fact that most of the device’s buttons are equipped with smooth speed control, and therefore a regular tester may give you incorrect data. In this case, you will need a special connection diagram for the drill button. Often in instruments one wire is connected to a terminal, and therefore pressing the button simultaneously leads to ringing of the terminals. If the light comes on, everything is fine with the button, but if you notice a malfunction, it’s time to replace the button.

When making a replacement, keep in mind that the circuit can be either simple or with reverse. Due to this, all work on replacing the button must be carried out exclusively according to the diagram, without adding anything “on your own”. So, the part must be suitable in size and match the power of the tool. At the same time, calculating power is a fairly simple task. We use the formula P=U*I (taking into account that the drill power is 650 W), I = 2.94 A (650/220), which means the button should be at 2.95 A.

Despite the fact that this process is quite complicated, you can do all the work yourself, following some important rules. For example, remember that opening the case may cause all parts and loose parts to simply fall out of the case. Naturally, this should be avoided, because then it will be quite difficult to assemble the device together. To do this, you can smoothly lift the lid, noting the exact location of the spare parts on paper.

The button is repaired as follows:

1. First, the clamps for the casing are hooked, after which it is carefully pulled together;
2. All rusted and darkened terminals are cleaned of carbon deposits, for which you can use alcohol or sandpaper;
3. We reassemble the tool, making sure that all parts of the device are in place, and check the functionality of the drill - if nothing has changed, we change the part;
4. We fill the speed regulator with a compound, and therefore if a part fails, we simply replace it;
5. A frequent breakdown is the abrasion of the working layer under the rheostat - it’s better not to repair it, it’s just a waste of time, it’s better to buy a new one and replace it.

Many people are interested in where to get such a scheme? First of all, it should come with the instrument when you purchase it, but if there is no diagram or you have lost it, you will have to look on the Internet. After all, only with its help will you be able to carry out repairs competently, without errors. By the way, the speed control button and the reverse control button are located in different places, and therefore you will have to check them separately.

There are several reasons for damage to the armature or stator of a drill. First of all, this is illiterate operation of the device. For example, many users simply overload the tool, working without interruption. This leads to the fact that the drill motor does not have time to “rest”. The second reason lies in poor coil wire, which is often found in cheap models. That is why breakdowns of cheap tools are much more common. In this case, repairs must be carried out using specialized tools. And it will be better if you entrust this work to professional specialists.

However, if you decided to carry out the repairs on your own, you will definitely have a question - how to do everything right? As you already understand, it “suffers” from armature and stator breakdowns, and this can be checked with several signs, for example, when the tool suddenly sparks during operation. If there are no “bright” signs, you can use an ohmmeter.

The stator is changed like this:

1. First, carefully disassemble the device body;
2. Remove the wires and all internal parts;
3. After finding out the causes of the breakdown, we replace the spare part with a new one and close the housing again.

But the drill may not work due to trivial faults - for example, due to brushes inside the motor. This means that you can’t do without repairing brushes, and this work is quite simple - you don’t even need to have special knowledge and tools. To do this, we disassemble the device, remove the brush holders from it and replace parts that are broken. By the way, there are models whose body does not need to be disassembled - you just need to remove special plugs through the installation window, after which we change the brushes.

You can purchase these parts at any hardware store; there are also some models that are sold along with a set of additional brushes. It is important that you do not wait until the brushes are completely worn out - check them from time to time. And all due to the fact that there is a risk of a gap forming between the bristles and the collector. As a result, this part will begin to overheat and eventually fall off - which means you will have to change the entire anchor, which will be much more expensive and more difficult, and it is not a fact that you will be able to solve this issue yourself.

As you can see, there are a variety of breakdowns, many of which will be within your control, others will only be possible for specialists in service centers. And to reduce the risk of such breakdowns, you need to take care of your tool, clean it after work, check the condition of the parts and brushes in order to replace them with new ones in time. However, if you see that you can’t handle it yourself, take the device to a workshop.