A smooth start for any power tool is very important. the following reasons. Firstly, it helps protect electrical device from breakdowns, which contributes to fewer trips to repairmen, which means almost complete absence of downtime and increased productivity. Secondly, having a soft start for the electric motor saves you money that could otherwise be spent on paying repairmen or buying a new tool.
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This article will consider making a soft start for an electric motor with your own hands using the example of an angle grinder or, in other words, an angular grinding machine.
Why do you need a soft start unit?
Due to some design features, starting the grinder leads to the appearance of dynamic loads to the device. Since the mass of the disk with which it is carried out useful work, is quite high, then the commutator motor and gearbox of the device are affected by powerful inertial forces, which leads to the following negative factors:
- During the start, which is especially sharp, inertial forces very strongly influence the body of the device, which may cause injury: You simply don't 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 electric motor is subject to an overload caused by the supply high voltage current What does this lead to? First of all, the motor winding suffers and accelerated wear of the brushes occurs, which will not happen if you make a block for a soft start. Otherwise, be prepared for the fact that one not very wonderful day something will happen in the engine. short circuit caused by complete wear of the brushes. This, in turn, will force you to shell out money for repairs or buy a new sander.
- Rapidly applying torque to the gearbox during startup will cause accelerated wear on the gears in your grinder's gearbox.
- Also keep in mind that jumping the angle grinder can destroy the blade, the fragments of which can cause serious harm to you, so never work without a cover for protection.
To make it more clear to you which elements of the grinding machine suffer most from a sudden start, look at the diagram below.
Of course, some companies that produce grinding machines equip their devices with a soft start block at the factory. However, equipment with a soft start is an unaffordable luxury for angle 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 encountering the problems that were described above.
However, there is a way out and it is quite simple: make your own device for a soft start according to one of possible schemes. If there is free space in the body of your device, then you can use a ready-made soft start device and put it in the grinder.
Making a soft start for an angle grinder with your own hands
One of the most commonly used schemes for manufacturing starting device based on chip KR118PM1 and triacs that make up the power section. Using this scheme, you can make a soft start unit without having specialized skills and without deep knowledge of electrical engineering. The only important thing is that you know how to solder.
Graphically, this diagram looks like this.
DIY device you can connect to absolutely any power tool, designed for a voltage of two hundred and twenty volts. Soft start block, created on the basis of this scheme, does not need to be turned on with a separate button, but can be connected to the standard button of the grinding machine. If your angle grinder has free space inside the case, you can install the unit in it or make a separate case for it and connect it to the power tool through a gap in the power cable.
The best option for connecting a soft starter unit and your grinder will be as follows: you apply voltage to the input of the block (connector XS1) from a power source with a voltage of two hundred and twenty volts. A plug from an angle grinder is connected to the output of the block (connector XP1).
Operating principle 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 designated DA1 in the diagram above. The capacitor, which regulates the voltage, gradually increases it until the operating value is reached. Due to the operation of the capacitor, the thyristors in the microcircuit open with some delay and slowly transmit voltage to the power part in triacs VS1.
- The process described above occurs in periods that become shorter and shorter if you count them from the moment of startup. As a result, the voltage supplied to the grinding machine increases slowly, and not abruptly, which determines the smooth start of the electric motor.
- The time during which the engine reaches operating speed is depends on the capacity of the capacitor used C2. As a rule, a capacity equal to forty-seven microfarads is enough for the angle grinder to start smoothly in two seconds. Usually this period of time is enough to remove the overload from the electric motor and gearbox.
- After you finish work and turn off your device, resistor R1 discharges capacitor C1 with its resistance. If the value of resistor R1 is sixty-eight kilo-ohms, then the discharge takes only three seconds. You can then use the soft starter again as it is ready to start the sander again.
If you want to upgrade the unit to a device regulating the speed of the electric motor, then replace the constant resistor R1 with a variable one. In this case, you can adjust its resistance, and therefore influence the engine speed.
Triac VS1 in your block must meet the following characteristics:
- The minimum current it allows is twenty-five amperes.
- The maximum voltage for which it is designed is four hundred volts.
This circuit, tested by many craftsmen, was tested on a grinder with a power equal to two kilowatts, and has a power safety margin of up to five kilowatts, which is made possible thanks to the KR118PM1 microcircuit.
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 number of electricity. 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 voluminous work V industrial scale you should use an angle grinder that is approximately twice as powerful. More to the main indicators except technical characteristics, refers to 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. Pay attention and pay attention to safety when selecting tools and when further work it's very important with him.
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 upgrade an angle grinder with established scheme. The electrical circuit is assembled quite simply. It’s not difficult to do, and ready-made diagram You can, if desired, connect not only an angle grinder, but any other tool. However, the tool must have brushed motor, not asynchronous.
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 controller boards sewing machine or a 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 a 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 comes the sizing epoxy resin for fastening. 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 firm grinders Bosch electronics sets 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.
Everyone who has been using an angle grinder for more than one year has had it break. At first, every master tried to repair grinder sparkling on its own, hoping that it will work after replacing the brushes. Usually, after such an attempt, the broken instrument remains lying on the shelf with burnt windings. And to replace it, a new grinder is bought.
Drills, screwdrivers, hammer drills, and milling cutters are necessarily equipped with a speed control. Some so-called calibration grinders are also equipped with a regulator, while ordinary grinders only have a power button.
Manufacturers do not deliberately complicate low-power grinders with additional circuits, because such a power tool should be cheap. It is clear, of course, that the service life of an inexpensive tool is always shorter than that of a more expensive professional one.
The simplest angle grinder can be upgraded so that its gearbox and armature winding wires will no longer be damaged. These troubles mainly occur during a sharp, in other words, shock start of the angle grinder.
All modernization is just a matter of assembly electronic circuit and securing it in the box. In a separate box, because there is very little space in the handle of the sander.
Verified, working diagram posted below. It was originally intended to regulate the intensity of lamps, that is, to operate on an active load. Her main advantage? simplicity.
- The highlight of the soft starter, the circuit diagram of which you see, is the K1182PM1R microcircuit. This microcircuit is highly specialized, domestically produced.
- The acceleration time can be increased by choosing a larger capacitor C3. While this capacitor is charging, the electric motor accelerates to maximum speed.
- There is no need to replace resistor R1 with a variable resistance. A 68 kOhm resistor is optimally selected for this circuit. With this setting, you can smoothly start the angle grinder with a power of 600 to 1500 W.
- If you are going to assemble a power regulator, then you need to replace resistor R1 with a variable resistance. A resistance of 100 kOhm or more does not reduce the output voltage. By short-circuiting the pins of the microcircuit, you can completely turn off the connected grinder.
- By inserting a VS1 semistor of type TS-122-25 into the power circuit, that is, 25A, you can smoothly start up almost any commercially available grinder with a power from 600 to 2700 W. And there remains a large reserve of power in case the grinder jams. To connect angle grinders with a power of up to 1500 W, imported semi-sectors BT139, BT140 are sufficient. These are less powerful electronic keys cheaper.
The semisistor in the above circuit does not open completely; it cuts off about 15V of the mains voltage. This voltage drop does not affect the operation of the grinder in any way. But when the semistor heats up, the speed of the connected instrument decreases greatly. This problem can be solved by installing a radiator.
This simple circuit has one more drawback - it is incompatible with the speed controller installed in the tool.
The assembled circuit must be hidden in a plastic box. Housing made of insulating material important, because you need to protect yourself from mains voltage. You can buy a junction box at an electrical supply store.
A socket is screwed to the box and a cable with a plug is connected, which makes this design look like an extension cord.
If experience allows and there is a desire, you can collect more complex circuit smooth start. Below circuit diagram is standard for the XS–12 module. This module is installed in the power tool during factory production.
If you need to change the speed of the connected electric motor, then the circuit becomes more complicated: a 100 kOhm trimmer and a 50 kOhm adjustment resistor are installed. Or you can simply and roughly introduce a 470 kOhm variable between the 47 kOhm resistor and the diode.
It is advisable to connect a 1 MΩ resistor in parallel with capacitor C2 (it is not shown in the diagram below).
The supply voltage of the LM358 microcircuit ranges from 5 to 35V. The voltage in the power circuit does not exceed 25V. Therefore, you can do without an additional zener diode DZ.
Whatever soft start circuit you assemble, never turn on the tool connected to it under load. Any soft start can be burned if you rush. Wait until the grinder unwinds, and then work.
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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 the commutator motor is located. For asynchronous motors the circuit will not work, it requires a frequency converter.
First I drew printed circuit board for soft start system, without speed control components. 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.
Associated with high dynamic loads. Due to the mass of the working disk, at the beginning of rotation, inertial forces act on the gearbox axis. This entails some negative aspects:
- Loads on the axle during a sharp start create an inertial jerk, which, when large diameter and the weight of the disk can tear the power tool out of your hands;
- When the operating voltage is suddenly applied to the motor, a current overload occurs, which disappears after reaching the rated speed;
- High torque with a sharp increase in speed prematurely wears out the gears of the angle grinder gearbox;
- The overloads experienced by the working disk can destroy it when the engine starts.
IMPORTANT! When starting the grinder, always hold the tool with both hands and be prepared to hold it. Otherwise, you may get injured. This warning is especially relevant for heavy diamond or steel blades.
As a result, the brushes wear out and both windings of the electric motor overheat. If you constantly turn the power tool on and off, overheating can melt the insulation of the windings and lead to short circuit, followed by expensive repairs.
In some cases, the teeth may break off and the gearbox may jam.
Therefore, the presence of a protective casing is mandatory.
IMPORTANT! When starting the angle grinder, the open sector of the casing should be directed in the direction opposite to the operator.
To better understand the mechanics of work, consider the structure of the angle grinder in the drawing. All elements experiencing overload during a sudden start are clearly visible.
Schematic drawing of the location of the working bodies and control systems in the angle grinder
To reduce the harmful effects of a sudden start, manufacturers produce angle grinders with speed control and soft start.
The speed control is located on the tool handle
But only medium and high models are equipped with such a device. price category. Many home craftsmen purchase angle grinders without a regulator and slowing down the starting speed. This is especially true for powerful specimens with a cutting disc diameter of more than 200 mm. Not only is such an angle grinder difficult to hold in your hands during startup, but the mechanical and electrical parts wear out much faster.
There is only one way out - to install a soft start of the angle grinder yourself. There are ready-made factory devices with a speed controller and engine start retardation when starting.
Ready-made device for adjusting soft start
Such blocks are installed inside the case, if there is free space. However, most angle grinder users prefer to make a circuit for smooth starting of the angle grinder themselves, and connect it to the break in the power cable.
How to make a soft start circuit for an angle grinder with your own hands
The popular circuit is implemented on the basis of the KR118PM1 phase control control microcircuit, and the power part is made of triacs. This device is quite easy to install and does not require additional settings after assembly, and therefore, it can be made by a master without specialized education; it is enough to be able to hold a soldering iron in his hands.
Electrical circuit for adjusting soft start for an angle grinder
The proposed unit can be connected to any power tool designed for an alternating voltage of 220 volts. A separate remote power button is not required; the modified power tool is turned on with a standard key. The circuit can be installed either inside the body of the angle grinder or in the break of the power cable in a separate case.
The most practical thing is to connect the soft starter to the socket from which the power tool is powered. The input (XP1 connector) is supplied with power from a 220 volt network. A consumable socket is connected to the output (connector XS1), into which the angle grinder plug is plugged.
When the start button of the angle grinder is closed, voltage is supplied to the DA1 chip via the common power circuit. There is a smooth increase in voltage across the control capacitor. As it charges, it reaches a working value. Due to this, the thyristors in the microcircuit do not open immediately, but with a delay, the time of which is determined by the charge of the capacitor. Triac VS1, controlled by thyristors, opens with the same pause.
Watch the video with a detailed explanation of how to do it and what scheme to use
In every half cycle AC voltage, the delay decreases in an arithmetic progression, as a result of which the voltage at the input to the power tool gradually increases. This effect determines the smooth start of the angle grinder engine. Consequently, the disk speed increases gradually, and the gearbox shaft does not experience inertial shock.
The time it takes for the speed to reach the operating value is determined by the capacitance of capacitor C2. The value of 47 uF ensures a smooth start in 2 seconds. With such a delay, there is no particular discomfort when starting to work with the tool, and at the same time, the power tool itself is not subject to excessive loads from a sudden start.
After turning off the angle grinder, capacitor C2 is discharged by resistor R1. At a nominal 68 kOhm, the discharge time is 3 seconds. After which the soft starter is ready for a new start cycle of the angle grinder.
With a little modification, the circuit can be upgraded to an engine speed controller. To do this, resistor R1 is replaced with a variable one. By adjusting the resistance, we control the engine power by changing its speed.
Thus, in one housing it is possible to make an engine speed controller and a soft start device for a power tool.
The remaining details of the circuit work as follows:
- Resistor R2 controls the amount of current flowing through the control input of triac VS1;
- Capacitors C1 and C2 are control components of the KR118PM1 microcircuit used in standard scheme inclusions.
For simplicity and compactness of installation, resistors and capacitors are soldered directly to the legs of the microcircuit.
The VS1 triac can be anything with the following characteristics: maximum voltage up to 400 volts, minimum throughput current 25 amperes. The amount of current depends on the power of the angle grinder.
Due to the smooth start of the angle grinder, the current will not exceed the rated operating value for the selected power tool. For emergency cases, for example, a jammed angle grinder disk, a current reserve is required. Therefore, the nominal value in amperes should be doubled.
The ratings of the radio components used in the proposed electrical circuit were tested on an angle grinder with a power of 2 kW. There is a power reserve of up to 5 kW, this is due to the peculiarity of the operation of the KR118PM1 microcircuit.
The scheme is working, executed many times by home craftsmen.