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 disk 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:
- when grinding or polishing any surfaces;
- when installing large diameter tools;
- for cutting certain materials.
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.
Homemade regulator circuit
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.
- After pressing the unit start button, electric current begins to flow, first of all, to the microcircuit (DA1).
- The control capacitor begins to charge smoothly and after a while reaches the required voltage. Thanks to this, the opening of the thyristors in the microcircuit occurs with some delay. It depends on the time it takes to fully charge the capacitor.
- Since the VS1 triac is controlled by the microcircuit’s theristors, it opens just as smoothly.
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:
- the minimum current for which it is designed must be 25 A;
- The triac must be designed for a maximum voltage of 400 V.
This circuit and the regulators made according to it have been repeatedly tested by many craftsmen on grinders with power up to 2000 Watt. It is worth noting that this device, thanks to the KR118PM1 microcircuit, is designed for power up to 5000 W. So he has a considerable margin of safety.
Ideally, to solder 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:
- solder all the parts of the circuit by weight, that is, leg to leg;
- Attach a radiator to the triac (can be made from sheet aluminum).
A regulator soldered in this way will take up less space and can be easily placed in the body of the angle grinder.
How to connect a regulator to an 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.
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:
- The power tool does not have the ability to have a smooth, soft start. This can lead to power outages, since the angle grinder consumes a large amount of electricity in the first seconds after switching on. There is also a huge probability of damage to the electric motor and breakage of the tool after not a soft start, but a sharp, jerky one.
- Power tools, especially simple Chinese ones, do not have a speed regulator (by adjusting the speed you can ensure long operation of the tool without putting a load on it).
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.
Bt136 600E: voltage regulation switching circuit
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:
- To get started, you should download the board if you don’t have it;
- The Bt136 600E triac is used as the power link;
- During operation, the triac will heat up; to avoid this, a heat sink is installed;
- The resistors used provide resistance to current, providing current suppression;
- The regulator is adjusted using a multi-turn trimmer resistor;
- To check, you should connect a light bulb;
- After connecting, the light bulb must be turned off - the triac must be cold;
- Connecting the resulting circuit to the grinder.
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.
Do-it-yourself speed controller for an angle grinder
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:
- First, you need to unscrew the handle of the grinder, evaluate the place and figure out where to place the elements of the circuit (if there is no space, then you can make the device in a separate box);
- The resistor can be made of aluminum;
- Provided the triac does not heat up too much, a small radiator is sufficient;
- Next, the structure is soldered.
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.
Making a speed controller
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:
- Resistor – R1;
- Trimmer resistor – VR1;
- Capacitor – C10;
- Triac - DIAC;
- Triac - TRIAC.
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.
Making a soft start for a power tool with your own hands (video)
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.
The speed regulator for an angle grinder is a useful mechanism that expands the functionality and extends the service life of the power tool.
Soft start and speed controller are mandatory devices
One of the main places in the home workshop of any self-taught craftsman is occupied by an angle grinder - an angle grinder, which is popularly called an angle grinder. With its help, you can efficiently clean a variety of surfaces, sand them, cut and saw wood products. At the same time, every fan of doing such work on his own wants to make his own (or imported) more reliable and functional. This is quite real.
The key to long-term use of the angle machine is its smooth start function. When the tool is turned on, the electrical current increases. The grinder needs not only to start the electric motor, but also to quickly gain the required speed for operation. Naturally, such a sudden load negatively affects the angle grinder components, in particular, its electrical winding. The latter often breaks off. For this reason, many grinders fail after several starts. It is possible to prevent such a problem on your own. It is necessary to modify the grinder by equipping it with a built-in soft start and speed controller. It is assembled on one chip.
Many advanced (and, of course, expensive) angle grinders are initially equipped with a function for adjusting the rotation of the working disk. In cheap models of angle grinders, as well as in older devices, such a device is not provided. And its necessity among home craftsmen is not even discussed. Why? More on this later.
Why control the speed of the disk?
If the grinder is used for cutting and cutting tiles and natural stone products, the high rotation speed of the tool literally kills the power tool. In addition, with such processing, small particles begin to crumble from the material. This significantly deteriorates the quality and appearance of the tiled or stone surface. If there is a function for selecting the required speed, processing proceeds without a hitch. And the electric tool itself is completely protected from damage.
Rotation speed is also important when working with metal products. For example, aluminum or tin blanks should be cut at minimum speed. But thick and hard metal, on the contrary, is processed at high speeds. Polishing and grinding work using an angle grinder cannot be performed effectively if the saw does not allow you to select the required speed. You will simply ruin the surface being treated. Try sanding wood or the paintwork of a car body at high speed and you will understand what we are talking about.
As you can see, modifications to the angle grinder make the device many times more functional. It becomes possible to work with any soft materials and delicate surfaces. And most importantly, the grinder becomes almost eternal. It will function for decades!
An elementary and very reliable speed controller for an angle grinder is made with your own hands from inexpensive electrical parts. Below is a diagram that shows all the necessary elements for assembling the mechanism we are interested in on a printed circuit board.
We see that we will need:
- symmetrical thyristor DIAC (DB3);
- resistor R1 (its resistance should be 4.7 kOhm);
- another symmetrical thyristor VT136/138 (TRIAC);
- capacitor C1 (400 V, 0.1 µF);
- additional resistor VR1 of 500 kOhm.
This scheme works according to the following principle. The charging time of the capacitor is changed by an additional resistor (it is called a tuning resistor). When voltage arrives at the circuit, the symmetrical thyristors are in the closed position, and zero voltage is noted at the output. When charging the capacitor, an increase in the voltage across it is observed, which leads to the opening of thyristor DB3. After which the voltage is supplied to VT136/138. This thyristor also opens, and an electric current passes through it. Then the symmetrical elements close again and remain in this state until the capacitor is completely recharged in the opposite direction. As a result, at the output we receive a pulse-type signal that is complex in shape. Its specific amplitude is determined by the operating time of the circuit capacitor - additional resistor - resistor R1.
Thyristors are usually placed on a printed circuit board. It is easy to make from PCB (foil material is used). Some craftsmen cut out the board with a cutter. It is allowed to place circuit elements using the surface-mounted method. Symmetrical thyristors are installed strictly on a copper or aluminum radiator. It plays the role of an effective heat sink. The assembled mechanism is checked using a conventional incandescent lamp of 40–60 W. Connect it to the circuit and begin adjusting the brightness of the light. If the intensity changes, it means you did everything right. Now you can mount the regulator into the body of the angle grinder. This may not be so easy to do. After all, you need to ensure that the additional mechanism does not interfere with you when using the angle grinder.
You will have to determine the installation location of the homemade regulator yourself, focusing on the design features of the angle grinder. Installation of the circuit in most cases is performed:
- in an additional box installed on the device body;
- into the handle of the holder;
- into a small cavity (designed for cooling and air circulation) in the back of the angle grinder.
The connection of the circuit to the device is carried out by mounting it into the power supply channel of the angle grinder. I don't think you'll have any difficulties with this.
Operating an angle grinder with a homemade regulator
When using a grinder with a self-assembled circuit to select the speed of movement of the disk, you must strictly adhere to the recommended operating modes of the device. He should be given frequent breaks. This is especially important when processing any products at low speeds. This precaution is due to the strong heating of the angle grinder operating on a modified voltage. If you use an angle grinder without breaks, the collector will not withstand it, its windings will burn out.
Another important point. It is not advisable to start the grinder with the speed controller set to the minimum value. In such a situation, the rotor will not have enough voltage (it will not spin). This will lead to overheating of the electrical windings due to the fact that the collector lamellas will not exit the short-circuit mode (remain short-circuited). It will be right:
- set the regulator to the maximum value;
- connect the angle grinder to the network;
- reduce the disk rotation speed by the amount necessary to complete the work.
The need for a regulator arose due to the need to clean various kinds of rusty pieces of iron in the country before painting them. This can be conveniently done using a metal cord brush installed instead of a cutting wheel. However, since the grinder operates at maximum speeds around 10,000 rpm, the body vibrates quite strongly, and your hands get tired quickly.
The brush itself tries to catch on various irregularities and tear the grinder out of your hands, which is very dangerous. There is also an electric sharpener, which overheats sharpened chisels and thin drills at maximum speed. And the electric stove, despite the fact that it has a thermostat, strives to turn the heated food into coal.
To resolve the issue, Ali purchased an assembled 2000W network power regulator board for 100 rubles.
After successful testing of the regulator “on the snot”, the question of design of the device arose.
These boards have already been described several times on mysku, but the appearance of the assembled devices laid out for public display forced us to look for a more beautiful solution. I wanted to have a ready-made design that was as compact as possible. In Leroy Merlin, with a preliminary estimate of 30 rubles, I purchased a TDM junction box 65x65x50 mm. 
At the moment, these junction boxes are not available in Leroy, I will explain why the choice fell on this one:
- hinged non-removable lid
- one blank side wall
- suitable base size
- the height is sufficient to accommodate the radiator.
To accommodate the board, the bosses protruding from the bottom were trimmed and a hole was drilled in the side wall for the regulator slide. In fact, the board is secured in the box only by the regulator body and the standard reinforcing corner of the board. The socket is attached to the box cover with two M4 screws.
The network cable is threaded through a hole in an insulating sleeve inserted into the box body “in reverse”. This installation of the coupling prevents it from being pulled out along with the power cable during careless movements. Since the conductors of the power cable touch the radiator, an additional piece of PVC tube cut and tied with electrical tape was placed on it.
I made marks on the body of the extreme positions of the regulator.
As episodic operation for more than a year with different consumers has shown, the radiator does not get particularly hot and remains warm in a closed box during long-term operation with powerful consumers.
As for cleaning rusty pieces of iron with a cord brush for an angle grinder, such work at lower speeds has definitely become more comfortable and less dangerous. The gyroscope effect is noticeably reduced. A couple of times the cord brush got snagged in the corner, but thanks to the reduced power on the shaft, the angle grinder was able to be held in my hands without injury. And the grinder itself heats up significantly less.
PS Grinder model BLACK&DECKER (B&D) CD 115, I’ve had it for 7 years now.
