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 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.
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.
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 a soft start. Over time, owners of such grinders begin to understand that their absence sharply reduces the functionality of the tool. In this case, you can modify the angle grinder by installing homemade devices on it.
When power is applied to the grinder motor, sudden increase in speed from zero to 10 thousand or more. Those who have worked with an angle grinder know well that it is sometimes difficult to hold it in your hands when starting, especially if a large diameter diamond disc is installed.
It is precisely because of such abrupt increases in engine speed that the mechanics of the device most often fail.
Also, during startup, a huge load is applied to the rotor and stator windings of the electric motor. Since a commutator 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 force of inertia prevents this from happening. As a result, the starting current in the motor coils sharply increases. Despite the fact that the manufacturer has invested a certain safety margin for the coils, taking into account overloads at start, sooner or later the insulation cannot withstand it, which leads to an interturn short circuit.
In addition to starting problems, the lack of speed control causes some discomfort. For example, an angle grinder's speed regulator may come in handy for certain types of work:
In addition, when roughing with wire brushes, there is a high probability of wire jamming in any gap. If the spindle speed was high, then the angle grinder may simply be torn out of your hands.
If you connect a power (speed) regulator with a soft start module to the angle grinder, then all the problems described above will disappear, the service life of the device will increase and the safety of its use will increase.
One of the most popular schemes for smoothly 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 circuit, 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.
The processes described above occur in periods that become shorter each time. Therefore, the voltage supplied to the motor windings does not increase abruptly, but slowly, resulting in a smooth start of the angle grinder.
The time it takes for the electric motor to reach full speed depends on the capacitance of capacitor C2. The capacitor capacity of 47 uF allows you to start the engine in 2 seconds. When the angle grinder is turned off, capacitor C1 is discharged using 60 kOhm resistor R1 for 3 seconds, after which this electronic module is again ready to start.
If resistor R1 is replaced with a variable one, then you will get a speed controller that will allow you to reduce engine speed.
It is important that triac VS1 has the following characteristics:
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 a speed controller for an 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 simpler:
A regulator soldered in this way will take up less space and can be easily placed in the body of the angle grinder.
To connect a homemade power regulator, no special knowledge is required, and any home craftsman can cope with this task. The module is being installed into a break in one wire, through which power goes to the grinder. That is, one wire remains intact, and a regulator is soldered into the gap of the second.
In the same way, you can connect a factory power regulator that costs 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 instrument, as shown in the following photo.
Also, the regulator can be placed in a socket and used to reduce the speed not only of an angle grinder, but also of other electrical appliances (drill, sharpener, wood milling or lathe, etc.). This is done as follows.
The regulator is connected as described above - at a break in one of the wires of the power cable.
The following photos show what a finished socket will look like, having a built-in speed controller for an angle grinder, which can also be used for other electrical appliances.
Instead of a junction box, you can use any plastic case suitable size. You can also make the box yourself by gluing pieces of plastic together with a glue gun.
The disadvantage of small cheap angle grinders is the lack of soft start and speed control. Anyone who has plugged in a powerful electrical appliance has noticed how the brightness of the network lighting drops at that moment. This is due to the fact that powerful electrical appliances consume enormous current at the moment of startup, and accordingly, the voltage in the network sags. The tool itself may fail, especially a Chinese one with unreliable windings.
The soft start system will protect both the network and the tool. There will also be no strong kickback (shock) at the moment of switching on. And the speed regulator will allow you to work for a long time without overloading the tool.
The presented circuit is copied from an industrial design, installed on expensive devices. It can be used not only for an angle grinder, but also for a drill, milling machine, etc., where there is a commutator motor. The circuit is not suitable for asynchronous motors; a frequency converter is required.
First, I drew a printed circuit board for the soft start system, without components for adjusting the speed. This was done on purpose, because... In any case, the regulator must be wired out. Having a diagram, everyone can figure out what to connect where.
In the circuit, the regulating element is a dual operational amplifier LM358, which controls the power triac BTA20-600 through transistor VD1. I didn't get it from the store and installed BTA28 (more powerful). For a tool up to 1 kW, any triac with a voltage of more than 600V and a current of 10-12A is suitable. Because Since the circuit has a soft start, the starting currents will not burn such a triac. During operation, the triac heats up and should be installed on a radiator.
The phenomenon of self-induction is known, which is observed when a circuit with an inductive load is opened. In our circuit, circuit R1-C1 dampens self-induction when the grinder is turned off and protects the triac from breakdown. R1 from 47 to 68 Ohm, power 1-2W. Film capacitor 400V.
Resistor R2 provides current limitation for the low voltage part of the control circuit. This part itself is both a load and, to some extent, a stabilizing link. Thanks to this, after the resistor it is possible not to stabilize the power supply. Although there is a variant of the same circuit with an additional zener diode. I didn't install it because... The supply voltage of the microcircuit is within normal limits.
Possible replacements for low-power transistors are indicated below the diagram.
The regulator is adjusted using multi-turn resistor R14, and the main adjustment is done using resistor R5. The circuit does not allow power adjustment from 0, but only from 30 to 100%. If you need a simpler, powerful regulator from 0, then you can assemble a version that has been proven over the years. True, for an angle grinder, obtaining the minimum power is pointless.
All budget angle grinder options have several disadvantages. Firstly, there is no soft start system. This is a very important option. Surely all of you have plugged this powerful power tool into the network, and when you start it, you have observed how the intensity of the light bulb, which is also connected to this network, drops.
This phenomenon occurs due to the fact that powerful electric motors consume huge currents at the moment of starting, due to which the network voltage sags. This can damage the tool itself, especially those made in China with unreliable windings that may one day burn out during startup.
That is, the soft start system will protect both the network and the tool. In addition, at the moment of starting the tool, a powerful kickback or push occurs, and if a soft start system is implemented, this, of course, will not happen.
Secondly, there is no speed regulator, which will allow you to work with the tool for a long time without loading it.
The diagram presented below is from an industrial design:
It is introduced by the manufacturer into expensive devices.
You can connect not only a grinder to the circuit, but also, in principle, any devices - drills, milling machines and lathes. But taking into account the fact that the tool must have a commutator motor.
This will not work with asynchronous motors. A frequency converter is required there.
So, you need to make a printed circuit board and start assembling.
A dual operational amplifier LM358 is used as a regulating element, which, using transistor VT1, controls the power triac.
So, the power link in this circuit is a powerful triac of the BTA20-600 type.
There was no such triac in the store and I had to buy a BTA28. It is a little more powerful than what is shown in the diagram. In general, for motors with a power of up to 1 kW, you can use any triac with a voltage of at least 600 V and a current of 10-12 A. But it is better to have some reserve and take 20 A triacs, they still cost a penny.
During operation, the triac will heat up, so it is necessary to install a heat sink on it.
To avoid any questions about the fact that the engine, when starting, can consume currents that significantly exceed the maximum current of the triac, and the latter can simply burn out, remember that the circuit has a soft start, and starting currents can be ignored.
Surely everyone is familiar with the phenomenon of self-induction. This effect occurs when a circuit to which an inductive load is connected is opened.
It's the same in this scheme. When the power supply to the motor suddenly stops, the self-induction current from it can burn the triac. And the snubber circuit dampens self-induction.
The resistor in this circuit has a resistance of 47 to 68 ohms, and a power of 1 to 2 W. Film capacitor for 400 V. In this embodiment, self-induction is a side effect.
Resistor R2 provides current suppression for the low-voltage control circuit.
The circuit itself, to some extent, is both a load and a stabilizing link. Thanks to this, after the resistor it is possible not to stabilize the power supply. Although the network has the same circuits with an additional zener diode, it is pointless to use it, since the voltage at the power pins of the operational amplifier is within normal limits.
Possible replacement options for low-power transistors can be seen in the following picture:
The PCB that was mentioned earlier is only a soft starter board and does not have any speed control components. This was done on purpose, since in any case the regulator must be output via wires.
The regulator is adjusted using a 100 kOhm multi-turn trimmer resistor.
If you need a more powerful regulator, it can be assembled according to the following scheme:
If everything is in order, then after disconnecting from the network, you immediately need to check the triac by touch - it should be cold.
If everything works fine - the grinder starts smoothly and the speed is regulated - then it’s time to start testing under load.
Attached files:
Scheme for connecting an analogue CCTV camera to a TV or computer Connecting a digital CCTV camera
A grinder, or grinding machine, is often simply necessary on the farm to perform metal work. In addition, it can be used to clean both wooden and stone materials. It is difficult to imagine performing industrial work without an angle grinder. This is a tool that is suitable for both a professional in his work and an amateur in household work.
When doing work with your own hands, it is important that the power tool has a smooth start. This is especially true if you often have to work, and the network cannot withstand the voltage of the tool.
Budget options for angle grinders - angle grinders - have a number of disadvantages:
Therefore, when choosing a tool, it is very important to pay attention to such parameters as speed control and the presence of a soft start. In addition, when choosing an angle grinder, you should pay attention to power. The main indicator here is the volume of work performed.
If the work is not large-scale and not frequent at the household level, then a power tool with an adjustment of 125 mm and a power of between 600-900 W is suitable.
For large-scale work on an industrial scale, you should use an angle grinder that is approximately twice as powerful. In addition to technical characteristics, one of the main indicators is safety. The grinder must be safe. What does it mean? Firstly, as already mentioned, the presence of a soft start, which prevents voltage surges during switching on. Automatic fuses necessary for emergency stop of the motor during a system failure. The fuses serve as a regulator when the circle jams. Provides protection from dust. It is necessary when using an angle grinder frequently to prevent dust from accumulating in the tool.
The heat dissipation function is important. The heat sink protects against overheating. During operation, especially if the work is prolonged, the machine body is subject to strong heating so that there is no overheating and heat removal is necessary. When overloaded, the angle grinder stops - this happens during heating, approaching 200 o C. Well, balancing the disk serves to reduce unpleasant vibration and beating of the tool during operation, old worn disks are especially susceptible to this effect. Paying attention and paying attention to safety when choosing a tool and when further working with it is very important.
When choosing a tool, it is worth noting that there are grinders with one and two handles. Here you should rely solely on convenience. Two-handed models will most likely be more comfortable to hold, however, such tools are heavier in weight; one-handed models will also have to be held with two hands, but such angle grinders are smaller in size and weight.
Bosch is the leader in the power tools market. The tools of this company have all the necessary characteristics from convenience to safety. Another advantage of Bosch tools is that there is good ventilation.
Manufacturers do not burden cheap angle grinders that do not have sufficient power with voltage control switching circuits, otherwise such angle grinders would no longer be cheap. When starting the grinder, if it is smooth, the process is carried out through an adapter connected by contacts to the rectifier block. The rectifier block converts the current.
But sometimes it makes sense to modernize an angle grinder using an established scheme. The electrical circuit is assembled quite simply. It is not difficult to make, and you can, if desired, connect not only an angle grinder, but any other tool to the finished circuit. However, the tool must have a commutator motor, not an asynchronous one.
A homemade approach to creating a circuit would be as follows:
If the board is connected correctly, the triac and resistors of the angle grinder should start smoothly, and the use of the rotation speed should be regulated. After this, you can test the grinder in action. Such knowledge may be needed when repairing electric motor faults. For example, when voltage increases or improper balancing occurs.
If you use your ingenuity to create a speed controller with your own hands, you can use soldered control boards from a sewing machine or vacuum cleaner. In addition, the components for the regulator are inexpensive and can be easily purchased if possible. It is worth noting that the device requires a gearbox to support a certain number of revolutions and speed. If the speeds are high, then the reason is most likely in the stator. The stator requires repair. Repairing the stator is possible at home.
The operation of the commutator motor is ensured by any type of electrical voltage. When changing the voltage power, you need to reduce or increase the number of revolutions. The thyristor speed controller helps to change this number.
Regulator assembly steps:
Finally, it is glued with epoxy resin to secure it. A homemade device can work for years. There are cases when the device accelerates at higher speeds after switching on - this means the stator winding is short-circuited. In this case, a turn short circuit occurred. The stator requires repair, most often it requires rewinding.
What are the typical malfunctions: the winding breaks or burns, a short circuit occurs, the insulating surface breaks through.
An electric angle grinder is impossible without a speed controller, so that it is possible to reduce the speed.
The regulator circuit from a physics point of view looks like this:
The electronic regulator can be not only built-in, but also remote for convenience. In Bosch angle grinders, the electronics set the speed from almost 3 thousand to 11.5 thousand. There is no load on the meter's power, all indicators are taken into account. Reducing the number of revolutions and increasing them is not difficult for the tool. Adjustable rotation speeds are simply necessary when working with an angle grinder.
Only at first glance, it seems that an angle grinder may never be needed in life, that situations when it will come in handy, much less when it will have to be repaired, will not arise. Of course, you can turn to professionals, or you can identify the problem yourself and try to fix it.
