Schematic diagram of the USM soft starter. Soft start for an angle grinder with your own hands - saving you money and protecting power tools
When starting an electric motor, a starting torque occurs, which sags the voltage due to the occurrence of starting currents. They are 9 times higher than the operating currents. This has a bad effect on the stable operation of electrical appliances, reduces the life of the engine. This is because the start of the engine begins to be delayed and its windings overheat. Experts advise adding devices to the motor network that can make it start smoothly. Home craftsmen also learned how to make do-it-yourself devices for soft starting an electric motor.
Overloads at start of electric motors
The moment of starting is the beginning of the movement of the motor shaft connected to the transmission devices. At this point, the motion of the rotor is rather unstable. Transmission mechanisms make the shaft rotate under heavy load. Such instability will inevitably lead to impact loads, and this has a bad effect on the transmission devices. This greatly affects the key of the motor shaft and the gearbox.
The soft start device smoothes the loads at start-up. The movement of the shaft starts with very small revolutions, and the speed gradually increases. This means that there are no shocks and loads on the transmission mechanisms. This is the principle of operation of the soft start of the electric motor.
It is worth noting that soft start devices that are manufactured in factories are universal devices. They can be used for various tasks. First of all, this is a smooth start of the electric motor, its gradual braking, protection of the electrical network and devices from dangerous overloads. Anyone can find a suitable product for certain tasks. Such devices have the big disadvantage is the high cost. But you can make a soft starter for an electric motor with your own hands, spending the minimum amount on this Money and time.
DIY soft start device
It is worth considering the type of soft start device for an asynchronous electric motor using the KR1182P chip. It is necessary for a three-phase electric motor with a voltage of 380 volts.
It has some useful features that are worth describing:
- The windings in an electric motor are connected in a star.
- The output keys are powerful thyristors connected in parallel-counter circuit.
- Damping chains are included in the circuit in parallel with the thyristors. Here they are applied purposefully. Their main task is to prevent false switching of thyristors.
- Varistors are necessary to absorb the switching interference that occurs in the circuit.
present in the chain and power unit, which consists of a rectifier, capacitor and transformer. A similar block is needed to provide power to the switching relays. After rectifier bridge stands at the exit integrated stabilizer. It provides a stable voltage of 12 volts at the output. Additionally, it is able to provide protection against short circuits and various overloads.
How to make a power tool soft starter yourself
Brief description of the device
The most common circuit is made using a control phase control microcircuits KR118PM1, and its power circuit is implemented on triacs. Such a device is quite easy to assemble and does not require long settings after installation. Therefore, a person without special skills is capable of doing it. You just need to know how to use an electric soldering iron.
Such a device can be connected to all types of power tools that powered by AC. An additional removal of the power toggle switch is not needed here, since the upgraded electric tool will turn on from the factory button. This device can be placed inside the grinder or in the break of the power cord in a homemade case. The most popular is to connect the soft starter directly to the outlet that feeds the electric tool. The input connector receives power from a 220-volt network, and a socket is connected to the output connector, which will power the angle grinder.
When the start button of the angle grinder closes, then according to the power circuit, current will be supplied to the control microcircuit. The control capacitor will gradually accumulate voltage and as it charges, it will reach the required operating value. After that, the thyristors under the control of the microcircuit will not open immediately, but with a slight delay, the value of which depends on the charge of the capacitor. The thyristor-controlled triac will open after the same amount of time.
With each half-cycle of the alternating voltage, the delay time decreases according to the law arithmetic progression. As a result of this, the value of the voltage supplied to the angle grinder gradually increases. A similar effect and provides a smooth start of the motor of the power tool. Thus, its speed increases smoothly, and the gearbox shaft is not subjected to inertial loads.
The amount of time to gain speed to the required value depends on the capacitance of the input capacitor. The 46 microfarad capacitance is able to provide a smooth start in 3 seconds. With such a delay, there is no strong discomfort at the beginning of working with the grinder, and she herself will not be subject to heavy loads from a sudden start.
When the power tool is turned off, the input capacitor begins to discharge using a special resistor. Using a resistance rating of 67 kilohms, the amount of time to fully discharge is no more than 4 seconds. The soft starter is then ready again for a new start of the power tool.
With a little work, such a scheme can be improved to a high-quality motor speed controller. You need to change the discharge resistor to a variable resistance. By adjusting it, you can control the maximum power of the motor, thereby changing the speed. In other words, in a single case, it becomes possible to manufacture a soft start device for an angle grinder and a motor speed controller.
The main elements of such a device work like this:
- The resistor is able to control the value of the current that flows through the control output of the triac.
- Two capacitors help control the chip, which are used in the factory wiring diagram.
- To compactly and easily make the installation, it is necessary to solder the capacitors and resistors directly to the legs of the microcircuit.
- The triac can be installed absolutely any, but with certain technical specifications. The allowable voltage should be up to 380 volts, and the smallest throughput current must be at least 24 amperes. The value of the current directly depends on the maximum power of the grinder.
Due to the soft start of the power tool, the current value will not be higher than the nominal value for a particular tool model. In emergency situations, for example, jamming of the cutting disc of an angle grinder, a certain margin in terms of current value is simply necessary. That is why the rated current must be at least doubled.
Many electric tools, especially those from earlier years, are not equipped with a soft starter. Such tools are launched with a powerful jerk, as a result of which there is increased wear on bearings, gears and all other moving parts. Cracks appear in the varnish insulating coatings, which are directly related to the premature failure of the tool.
To eliminate this negative phenomenon, there is a not very complicated circuit on an integrated power controller, which was developed back in the Soviet Union, but it is still not difficult to buy it on the Internet. The price is from 40 rubles and above. It is called KR1182PM1. Works well in various control devices. But we will assemble a soft start system.
Soft starter diagram
Now let's look at the schema itself.As you can see, there are not very many components and they are not expensive.
It will take
- Chip - KR1182PM1.
- R1 - 470 Ohm. R2 - 68 kilo ohms.
- C1 and C2 - 1 microfarad - 10 volts.
- C3 - 47 microfarads - 10 volts.
The power of the device depends on the brand of triac that you supply.
For example, the average value of the current in the open state for different triacs:
- BT139-600 - 16 amps,
- BT138-800 - 12 amps,
- BTA41-600 - 41 amps.
Device Assembly
You can put any others that you have and that suit your power, but keep in mind that the more powerful the triac, the less it will heat up, which means it will work longer. Depending on the load, you must also use a cooling radiator for the triac.I installed the BTA41-600, you can not install a radiator for it at all, it is powerful enough and will not heat up during repeated-short-term operation, with a load of up to two kilowatts. I don't have a more powerful tool. If you plan to connect a more powerful load, then think about cooling.
Let's collect the parts for mounting the device.
We also need a “closed” socket and a power cable with a plug.
It is good to adjust the breadboard in size with large scissors. It cuts easily, simply and neatly.
Place the components on the breadboard. For a microcircuit, it is better to solder a special socket, it costs a penny, but it makes the job very easy. There is no risk that you will overheat the legs of the microcircuit, you do not need to be afraid of static electricity, and even if the microcircuit burns out, you can replace it in a couple of seconds. It is enough to take out the burnt one and insert the whole one.
We solder the parts immediately.
We place new parts on the board, referring to the diagram.
Solder carefully.
For the triac, the nests need to be slightly drilled out.
And so in order.
We insert and solder the jumper and other parts.
We solder.
We check the compliance with the diagram and insert the microcircuit into the socket, not forgetting the key.
We insert the finished circuit into the outlet.
We connect the power to the outlet and the circuit.
Please watch the test video of this device. The change in the behavior of the device at startup is clearly shown.
Good luck in your business and concerns.
This article will consider a soft start diagram for an angle grinder from available parts. Since the soft start is not installed in the entire tool, this can be corrected and self-assembly a simple circuit soft start for the grinder and do it yourself. This device will help upgrade your tool and make it less dangerous and more convenient.
If you often work with a tool, then you probably encountered the following problem: the engine, whether it be a grinder, a circular saw, a planer or other equipment, starts up very sharply. Such a sharp start is fraught with many troubles: firstly, there is a high starting current, which does not affect the wiring in the best way, secondly, a sharp start of the engine quickly wears out the mechanical parts of the tool, thirdly, ease of use decreases, when starting the grinder you have to hold on tight, she strives to break out of her hands. In expensive models, a soft start system is already built in, which easily copes with all these troubles. But what if this system does not exist? There is a way out - to assemble a soft start circuit yourself. In addition, it will be possible to use it with incandescent bulbs, because most often they burn out at the moment of switching on. A soft start will significantly reduce the possibility of a light bulb to burn out quickly.
Soft start circuit
On the Internet, there is often a soft start circuit built on a rather rare domestic K1182PM1R chip, which is not always easy to get now. That is why I propose to assemble an equally effective circuit, the key element of which is the affordable TL072 chip, you can also put the LM358 instead. The time for which the engine gains full speed is set by capacitor C1. The larger its capacity, the more time it takes to overclock, the most optimal option is 2.2 microfarads. Capacitors C1 and C2 must be rated for at least 50 volts. Capacitor C5 - at least 400 volts. Resistor R11 will dissipate a decent amount of heat, so its power must be at least 1 watt. Any low-power transistors can be used in the circuit, T1, T2, T4 have an n-p-n structure, you can use BC457 or domestic KT3102, T4 has p-n-p structure, BC557 or KT3107 will do in its place. T5 - any suitable seven-storer in terms of power and voltage, for example, BTA12 or TC-122.
Soft start manufacturing
The circuit is assembled on a 45 x 35 mm printed circuit board, the board is routed as compactly as possible so that it can be built into the body of a tool that requires a soft start. It is better to solder the power wires directly to the board, but if the load power is small, then you can install terminal blocks, as I did. The board is made by the LUT method, photos of the process are presented below.
It is advisable to tin the tracks before soldering the parts, so their conductivity will improve. The microcircuit can be installed in the socket, then it can be easily removed from the board. Resistors, diodes, small capacitors are soldered first, and then the largest components. After the assembly of the board is completed, it must be checked for correct installation, ring the tracks, wash the remaining flux.
First launch and testing
After the board is completely ready, you can check it for operability. First of all, you need to find a low-power light bulb for 5-10 watts and plug it into the board into the 220 volt network through it. Those. the board and the light bulb are connected to the network in series, and the OUT output remains unconnected. If nothing burned out on the board, and the light did not light up, you can turn on the circuit directly to the network. The same low-power light bulb can be connected to the OUT terminal for testing. When connected, it should smoothly dial up the brightness to the maximum. If the circuit is working properly, more powerful electrical appliances can be connected. With prolonged operation, the sevenistor will probably heat up slightly - there is nothing to worry about. If there is free space, it does not hurt to install it on a radiator.
Dangerous mains voltage is present on the board during operation, so safety precautions must be observed. In no case should you touch the parts of the board when it is connected to the network. Before turning on, make sure that the board is securely fixed and that no metal objects that can lead to a short circuit will fall on it. For reliability, it is recommended to fill the board with varnish or epoxy, then even moisture will not be afraid of it. Successful assembly!
Soft start video
The prototype design in the figure below was used to adjust the incandescence of the lamps, that is, to work on a purely resistive load.
The basis of the design is the K1182PM1R chip. It is highly specialized, and no matter how strange it sounds today, domestic production. If necessary, the start time can be increased by putting a larger capacitance of the capacitor C3. While this capacitor is being charged, the electric motor smoothly increases the speed to the maximum. The 68 kΩ resistor is optimally chosen for our circuit. If you want to make a power regulator, then you need to replace the resistance R1 with variables. Resistance of 100 kOhm or more.
A typical junction box will serve as an excellent insulating material case. A socket is screwed to it and a cable with a plug is connected, which makes this design very similar to a do-it-yourself extension cord.
If you want, you can assemble a slightly more complex soft start circuit. It is typical for the XS-12 module. It is installed in the power tool during the factory production of many companies.
If you want to control the speed of the connected electric motor, then the design becomes a little more complicated: because a tuning resistor is installed, by 100 kOhm, and an adjusting resistance by 50 kOhm.
In order to save money, you can equip a typical angle grinder with a speed controller. Such a regulator for grinding cases of various electronic equipment is an indispensable tool in the arsenal of a radio amateur.
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Do-it-yourself smooth start-up of an angle grinder will extend the life of your tool and save money
When choosing a grinder, a person thinks about the long service life of the tool. It is believed: the more expensive the tool, the longer it will last. But sometimes there is not enough money for an expensive purchase and you have to purchase an inexpensive model. In inexpensive models of angle grinders there is no speed dial regulator. Other devices, such as a drill, screwdriver and rotary hammer, have a speed dial control. And the angle grinder has only a power button. Thus, the angle grinder breaks faster, because under the influence of a sharp start, the gearbox and armature winding wires fail.
The following situations are possible:
- The action of a high load on the axis of the gearbox causes an inertial jump, leading in some cases to the loss of the tool from the hands.
- The amount of torque during the start-up period contributes to the wear of the gearbox gears.
- The destruction of the circle when overloaded.
You can upgrade the tool and end up with a grinder with a soft start. You can do the upgrade yourself. A soft start for a do-it-yourself grinder is made in two ways. The first method involves buying a ready-made device that already has a speed controller and slowing down the start of the engine at the time of launch. This device is placed inside the device. The second way is to make a circuit that will make the start smoother. If the power cord breaks, the circuit is connected to a break.
Circuit manufacturing plan
The soft start circuit of the grinder involves the use of the well-known KR118PM1 microcircuit for phase adjustment. The design contains sevenistors. The multiplication of the operating frequency is achieved by installing resistors that pass current in one direction. The advantage of this scheme is its simplicity and the absence of special adjustment after assembly. This method can be used by anyone who does not have special skills, but works with a soldering iron.
Basic principles of circuit design:
- When choosing capacitor C3, the acceleration time can be increased;
- The installed resistor R1 with a resistance of 68 kOhm does not require replacement with a variable resistance, as it ensures a smooth start-up of models of various strengths (0.6–1.5 kW);
- If you want to equip with a power regulator, the resistor R1 is replaced by a variable resistance. A value of more than 100 kOhm does not contribute to lowering the output voltage. The angle grinder is turned off when the microcircuit legs are closed;
- When using a semistor of the TS-122-25 type, models with a power of 0.6–2.7 kW are smoothly launched. And also in this case there is a margin of power in case of jamming. For models up to 1500 W, less powerful sevenstors (BT139 and W140) will suffice.
The process of the scheme
When the start buttons close, current flows to the microcircuit. The voltage across the main capacitor begins to rise. It reaches the working value as it is charged. Depending on the charge of the capacitor, the thyristors open. The opening of the sevenstor VS1 is also carried out with a delay. A single half-cycle of an alternating voltage is characterized by a decrease in delay. As a result, at the input, the voltage to the instrument rises smoothly. Based on this, the engine starts smoothly. As a result, the speed does not increase quickly and there are no inertial jumps to the gearbox.
The installed capacitor C2 contributes to starting within 2 seconds. This time is enough to start functioning, and a quick start does not increase the load. Turning off the tool leads to the discharge of the capacitor C2 through the resistance R1. With a capacity of 68 kOhm, the discharge period lasts 3 seconds. After that, you can restart the device.
The value of the current flowing through the input of the semistor VS1 regulates the resistor R2. Capacitor C1 is considered the control part of the microcircuit. Resistors and capacitors are attached to the legs of the microcircuit by soldering.
Connecting the soft start function
This chip is comparable to any device that provides a voltage of 220 V. Power is supplied to the XP1 connector.
The assembled circuit is placed in a plastic container. A junction box is suitable for it. A socket and a wire with a plug are attached to the unit. The device is similar to an extension cord. The socket includes an angle grinder plug. The performance check is carried out using a tester. First, the negative resistance is determined.
Complicated collection method
If you have certain skills or experience, then you can make a complicated smooth start scheme. It serves as a typical diagram for the XS-12 module. This circuit is installed in many models of power tools, even at the factory. If you want to adjust the speed, you need to install a tuning and adjusting resistor with a capacity of 100 kOhm and 50 kOhm, respectively. But there is another way - to place an alternating voltage of 470 kOhm in the middle of the resistor-diode section. Resistor capacitance 47 kOhm.
The microcircuit is powered from a voltage of 5–35 V. An auxiliary semiconductor diode DZ is not required, since the power circuit produces no more than 25 V. Simultaneously with capacitor C2, it is recommended to connect a 1 MΩ resistor.
It should be remembered that when turning on the instrument connected to the circuit, the load must be excluded. Otherwise, the soft start may burn out. First you need to wait until full promotion is reached, and then start working.
To extend the life of an angle grinder, sometimes you do not need to spend money on an expensive model. It will be enough to develop a smooth start of the grinder with your own hands. Then your tool will have reliability and a long service life. Moreover, the above scheme has been repeatedly used by many craftsmen.
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home > Repair > Do-it-yourself soft start for power tools
Soft start for any power tool is very important for the following reasons. Firstly, it helps to protect the electrical device from breakdowns, which contributes to fewer trips to the repairmen, which means almost no downtime and increased productivity. Secondly, having a soft start for an electric motor saves you money that could be spent on paying repairmen or buying a new tool.
This article will consider the manufacture of a soft start of an electric motor with your own hands using the example of a grinder or, in other words, an angle grinder.
Why you need a soft starter
Due to some design features, the launch of the grinder leads to the appearance of dynamic loads on the device. Since the mass of the disk, with which useful work is carried out, is quite high, powerful inertial forces act on the collector electric motor and gearbox of the apparatus, which leads to the following negative factors:
- During the start, which is especially sharp for the angle grinder, the forces of inertia have a very strong effect on the body of the device, which can lead to injury: you simply do not hold the tool and release it. Therefore, when starting the electric motor of the angle grinder, always hold it with both hands.
- During the start, the motor is overloaded due to the high voltage applied. What does this lead to? First of all, the motor winding suffers and accelerated brush wear occurs, which will not happen if you make a soft start unit. Otherwise, be prepared for the fact that one not very fine day, a short circuit will occur in the motor, caused by the complete wear of the brushes. This, in turn, will force you to shell out for repairs or buy a new grinder.
- The rapidly applied torque to the gearbox during start-up causes accelerated wear on the gears in the gearbox of your grinder.
- Also keep in mind that a sharp start of the grinder can destroy the disc, the fragments of which can cause you serious harm, so never work without a casing for protection.
In order to make it more clear to you which elements of the grinder are most affected by a sharp start, look at the diagram below.
Of course, some companies that produce grinders, even at the factory, complete their devices with a soft start unit. However, soft start equipment is an unaffordable luxury for grinders included in the budget price segment, so if you do not want to buy an expensive power tool, then you are in danger of running into the problems that were described above.
Nevertheless, there is a way out and it is quite simple: make a device for a soft start using one of the possible schemes with your own hands. If there is free space in the body of your device, then you can use ready device for a soft start and put it in the grinder.
We make a soft start for the grinder with our own hands
One of the most commonly used circuits for the manufacture of a starting device is based on the KR118PM1 microcircuit and triacs that make up the power part. According to this scheme, you can make a soft start unit without having specialized skills and without deep knowledge in electrical engineering. The only important thing is that you know how to solder.
Graphically, this diagram looks like this:
You can connect a device made by yourself to absolutely any power tool, designed for a voltage of two hundred and twenty volts. The soft start block created on the basis of this scheme does not have to be turned on with a separate button, but can be connected to the standard key of the grinder. If your grinder has free space inside the case, then you can install the unit in it or make a separate case for it and connect it to the power tool through a break in the power cable.
The best option connecting the soft starter unit and your grinder will be as follows: at the input of the unit (connector XS1), you supply voltage from a power supply with a voltage of two hundred and twenty volts. A plug from a grinder is connected to the block output (XP1 connector).
The principle of operation of the soft starter
- After you press the power button on the grinder, voltage appears in the circuit, which is initially sent to the microcircuit, which is indicated as DA1 in the diagram above. The capacitor, which regulates the voltage value, gradually increases it until it reaches the operating value. Due to the operation of the capacitor, the thyristors in the microcircuit open with some delay and slowly transfer voltage to the power part in the triacs VS1.
- The process described above occurs in periods that become shorter and shorter if you count them from the moment of launch. As a result, the voltage supplied to the grinder increases slowly, and not abruptly, which causes the smooth start of the electric motor.
- The time during which the engine gains operating speed depends on the capacity of the capacitor C2 used. As a rule, a capacity equal to forty-seven microfarads is enough for the grinder to start smoothly in two seconds. Usually this period of time is enough to remove the overload from the motor and gearbox.
- After you finish your work and turn off your device, resistor R1 discharges capacitor C1 with its resistance. If the value of the resistor R1 is sixty-eight kilo-ohms, then the discharge takes only three seconds. You can then use the soft starter again, as it will be ready to start the grinder again.
If you want to upgrade the unit to a device that regulates the speed of the electric motor, then instead of the constant resistor R1, put a variable one. In this case, you can adjust its resistance, and therefore influence the engine speed.
The VS1 triac in your unit must meet the following specifications:
- The current strength, the minimum passed by him, is twenty-five amperes.
- The maximum voltage for which it is designed is four hundred volts.
This circuit, tested by many masters, was tested on a grinder with a power equal to two kilowatts, and has a power margin of up to five kilowatts, which is made possible thanks to the KR118PM1 microcircuit.
techmaster.guru
Smooth start grinder
A modern power tool, made on the basis of an AC commutator motor, is almost all equipped with built-in soft starters and the ability to adjust the rotation speed. Old drills, grinders, etc., can be easily equipped with such devices, made in the form of a remote unit, or built into the tool. I offer a very simple scheme that works great and which I have been using for about two years. Even a novice radio amateur can easily assemble such a device.Schematic diagram:
In this form, the circuit provides a smooth start and reaching the rated speed. The acceleration time depends on the capacitance of the capacitor C3. To adjust the speed, the resistor R2 must be variable, preferably group A, or solder the variable in parallel with R2. In the latter case, it is desirable that their total resistance be close to the nominal value (the maximum voltage on the motor depends on this). If desired, the regulator can be built into the handle of the tool, although this is already a more complex refinement and, in my opinion, completely unjustified. In this case, it is easier to buy in the store. But if you decide on such a refinement, it makes sense to replace the standard power switch with a low-current one, which will lead to increased reliability. To do this, it is necessary to turn on the microswitch in parallel with the resistor R2 and the capacitor C3, using normally closed contacts. I have this device assembled in the case of a junction box, which can be easily bought at any electrical store. In principle, this option suits me perfectly. The last time I successfully used my drill was as a screwdriver, no reverse of course. In principle, it’s not difficult to make a reverse, it’s enough to switch the ends of one of the windings, but this fuss with wires, with a switch, I’m scrapped ... I have a triac TS 122-25-5, you can put almost any one with a voltage of at least 4th class and current not lower than 1.5-2 ratings (in case of jamming).
Attention! The design has a galvanic connection with the network, which is unsafe for your life and health! Parts and fasteners must be insulated!
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As a rule, budget angle grinders (angle grinders), popularly called grinders, do not have adjustable electronic modules in their design, which include an engine speed controller and soft start. The owners of such grinders eventually begin to understand that their absence drastically reduces the functionality of the tool. In this case, you can refine the angle grinder by installing home-made devices on it.
When power is applied to the grinder motor, abrupt increase in speed from zero to 10 thousand and more. Those who worked with angle grinders are well aware that it is sometimes difficult to hold it in their hands when starting, especially if a large-diameter diamond blade is installed.
It is because of such abrupt increases in engine speed that the mechanics of the apparatus most often fail.
Also during start-up, a huge load is applied to the rotor and stator windings of the electric motor. Since a collector motor is installed in the angle grinder, it starts in short circuit mode: the electromagnetic field is already “trying” to turn the rotor, but it remains motionless for some time, since the inertia force does not allow it to be done. As a result, the starting current in the motor coils increases sharply. Despite the fact that the manufacturer has invested a certain margin of safety for the coils, taking into account the overloads at the start, sooner or later the insulation does not withstand, which leads to an interturn short circuit.
In addition to problems with starting, the lack of speed control causes some discomfort. For example, an angle grinder speed controller can come in handy for certain types of work:
- when grinding or polishing any surfaces;
- when installing a large diameter tool;
- for cutting some materials.
In addition, when peeling with brushes, there is a high probability of wire jamming in any slot. If the spindle speed was high, then the grinder can simply be pulled out of the hands.
If you connect a power (speed) controller with a soft start module to the angle grinder, then all the above problems will disappear, the service life of the device will increase and the safety of its use will increase.
Scheme of a homemade regulator
One of the most popular schemes for soft starting an angle grinder engine with the ability to adjust the speed is presented below.
The basis of this regulator is the KR118PM1 microcircuit, as well as triacs, which are the power part of the device. Using this scheme, you can make a power regulator with your own hands, even without special knowledge in radio electronics. The main thing is that you know how to use a soldering iron.
This block works as follows.
- After pressing the start button of the unit, the electric current begins to flow, first of all, to the microcircuit (DA1).
- The control capacitor begins to charge smoothly and after a while gains the desired voltage value. Due to this, the opening of the thyristors in the microcircuit occurs with some delay. It depends on the time it takes to fully charge the capacitor.
- Since the triac VS1 is controlled by the thermistors of the microcircuit, it opens just as smoothly.
The above processes occur in periods that are reduced each time. Therefore, the voltage supplied to the motor windings does not increase abruptly, but slowly, resulting in a smooth start of the grinder.
The capacitance of the capacitor C2 determines the time for the electric motor to reach full speed. The capacitance of 47 microfarads allows you to start the engine in 2 seconds. When the angle grinder is turned off, the discharge of the capacitor C1 is carried out using a 60 kΩ resistor R1 for 3 seconds, after which this electronic module is again ready to start.
If the resistor R1 is replaced with a variable, then you will get a speed controller that will allow you to reduce the engine speed.
It is important that the VS1 triac has the following characteristics:
- the minimum current for which it is designed should be 25 A;
- the triac must be rated for a maximum voltage of 400 V.
This scheme and the regulators made according to it have been repeatedly tested by many masters on angle grinders with a power up to 2000 watts. It is worth noting that this device, thanks to the KR118PM1 chip, is designed for power up to 5000 watts. So he has a considerable margin of safety.
Ideally, in order to solder the speed controller for the angle grinder, you will need to draw a printed circuit board, etch the contacts with acid and then tin them, drill holes and solder the radio components. But everything can be made easier:
- solder all the details of the circuit on weight, that is, leg to leg;
- attach a radiator to the triac (can be made from sheet aluminum).
The regulator soldered in this way will take up less space, and it can be easily placed in the grinder body.
How to connect a regulator to an angle grinder
To connect a homemade power regulator does not require special knowledge, and any home master will cope with this task. The module is installed in the break of one wire, through which food goes to the grinder. That is, one wire remains intact, and the regulator is soldered into the gap of the second.
In the same way, you can connect a factory power regulator worth about 150 rubles, which is often purchased by craftsmen in China.
If there is very little space in the grinder, then the regulator can be placed outside of the tool as shown in the following photo.
Also, the regulator can be placed in a socket and used to reduce the speed not only of the grinder, but also of other electrical appliances (drills, sharpeners, milling or lathe on wood, etc.). This is done in the following way.
The regulator is connected as described above - at the break of one of the wires of the supply cable.
The following photos show how the finished outlet will look like, which has a built-in grinder speed controller, which can be used for other electrical appliances.
Instead of a junction box, you can use any plastic case suitable size. Also, the box can be made independently by gluing pieces of plastic with a glue gun.