Not every modern drill or grinder is equipped with a factory speed regulator, and most often speed control is not provided at all. However, both angle grinders and drills are built on the basis of commutator motors, which allows each of their owners, even if they know how to handle a soldering iron, to make their own speed controller from available electronic components, either domestic or imported.
In this article we will look at the diagram and principle of operation of the simplest engine speed controller for a power tool, and the only condition is that the engine must be a commutator type - with characteristic lamellas on the rotor and brushes (which sometimes spark).
The above diagram contains a minimum of parts and is suitable for power tools up to 1.8 kW and above, for a drill or grinder. A similar circuit is used to regulate speed in automatic washing machines that have commutator high-speed motors, as well as in dimmers for incandescent lamps. Such circuits, in principle, will allow you to regulate the heating temperature of a soldering iron tip, an electric heater based on heating elements, etc.
The following electronic components will be required:
Constant resistor R1 - 6.8 kOhm, 5 W.
Variable resistor R2 - 2.2 kOhm, 2 W.
Constant resistor R3 - 51 Ohm, 0.125 W.
Film capacitor C1 - 2 µF 400 V.
Film capacitor C2 - 0.047 uF 400 volts.
Diodes VD1 and VD2 - for voltage up to 400 V, for current up to 1 A.
Thyristor VT1 - for the required current, for a reverse voltage of at least 400 volts.
The circuit is based on a thyristor. A thyristor is a semiconductor element with three terminals: anode, cathode, and control electrode. After a short pulse of positive polarity is applied to the control electrode of the thyristor, the thyristor turns into a diode and begins to conduct current until this current in its circuit is interrupted or changes direction.
After the current stops or when its direction changes, the thyristor will close and stop conducting current until the next short pulse is applied to the control electrode. Well, since the voltage in the household network is alternating sinusoidal, then each period of the network sinusoid the thyristor (as part of this circuit) will work strictly starting from the set moment (in the set phase), and the less the thyristor is open during each period, the lower the speed will be power tool, and the longer the thyristor is open, the higher the speed will be.
As you can see, the principle is simple. But when applied to a power tool with a commutator motor, the circuit works more cleverly, and we will talk about this later.
So, the network here includes in parallel: a measuring control circuit and a power circuit. The measuring circuit consists of constant and variable resistors R1 and R2, capacitor C1, and diode VD1. What is this chain for? This is a voltage divider. The voltage from the divider, and what is important, the back-EMF from the motor rotor, add up in antiphase, and form a pulse to open the thyristor. When the load is constant, then the open time of the thyristor is constant, therefore the speed is stabilized and constant.
As soon as the load on the tool, and therefore on the engine, increases, the value of the back-EMF decreases, since the speed decreases, which means the signal to the control electrode of the thyristor increases, and opening occurs with less delay, that is, the power supplied to the engine increases, increasing the dropped speed . This way the speed remains constant even under load.
As a result of the combined action of signals from the back-EMF and from the resistive divider, the load does not greatly affect the speed, but without a regulator this influence would be significant. Thus, using this circuit, stable speed control is achievable in each positive half-cycle of the network sinusoid. At medium and low rotation speeds this effect is more pronounced.
However, with increasing speed, that is, with increasing voltage removed from the variable resistor R2, the stability of maintaining a constant speed decreases.
In this case, it is better to provide a shunt button SA1 parallel to the thyristor. The function of diodes VD1 and VD2 is to ensure half-wave operation of the regulator, since the voltages from the divider and the rotor are compared only in the absence of current through the motor.
Capacitor C1 expands the control zone at low speeds, and capacitor C2 reduces sensitivity to interference from brush sparking. The thyristor needs to be highly sensitive so that a current of less than 100 μA can open it.
For high-quality drilling of board holes, it is necessary to use an electric drill with a torque and speed stabilizer. The transistor stabilized unit has large power losses on the regulated transistor. The large weight and dimensions of the transformer and radiators do not allow for a portable version of the device.
Thyristor regulators voltages are distinguished by their low weight and technical capabilities for stabilizing the speed and torque of the electric motor. The voltage drop across the power thyristor in pulse mode is insignificant and at low power there is no need for a radiator.
Characteristics:
Mains voltage 220V
Power 300 Watt
Load current 10 Amps
Stabilization 86.7%
Regulator circuit speed of the electric drill stabilizes the torque by introducing positive feedback from the electric motor M1 through the RC circuit R12C2 VD2R6R1C1 to the emitter of the unijunction double-base transistor VT1
Diode VD2 allows you to supply only pulses of positive polarity from the brushes of the electric motor of the drill M1 to the emitter of transistor VT1. Variable resistor R6 works as a speed regulator, and at the same time stabilizes them when the load changes:
Without Feedback 0.6A 22.2 V 13 watts 260 rev. min
With Feedback 2.8 A 21 V 58.8 watts 520 rpm
With feedback, the speed drops slightly, at an idle speed of 600 rpm.
Characteristics of dual-base transistors:
|
Iе max, mA |
UB1B2 max, B |
UB2E max, B |
Pmax, mW |
RB1B2, kOm |
fmax, kHz |
||
Single-junction double-base transistors designed for operation in generators of periodic and single pulses. The resistance between the terminals of the transistors depends on the current of the control emitter junction. On the input current-voltage characteristic of unijunction transistors there is a section with a negative differential resistance. At a certain voltage at the emitter, the transistor is unlocked and the current through the base quickly increases. The process occurs like an avalanche.
The unijunction transistor belongs to the thyristor family. The unijunction transistor is included in the KU106A-G transistor-thyristor assembly and is a hybrid device consisting of a unijunction transistor and a triode thyristor.
Scheme:
The unlocking pulse from the unijunction transistor VT1 arrives at the control electrode of the thyristor VS1, which goes into a conducting state and remains in it as long as the forward current flowing through the thyristor VS1 is greater than the holding current.
The voltage from resistor R3 of the cathode circuit VS1 through resistors R7R9 is supplied to the control electrode of the powerful thyristor VS2 and brings it into the open state.
The switching threshold of thyristor VS2 is set by resistor R9. due to the wide spread of input characteristics. The anode of the power thyristor is directly connected to the electric motor of the M1 electric drill.
Pulses of negative polarity that occur during rotation of the electric motor are eliminated by diode VD3.
Part of the voltage from the motor collector is supplied to stabilize rotation - to the emitter of the dual-base transistor VT1.
The HL1 LED indicates the voltage on the electric drill motor and reduces impulse noise with voltages of more than 300 Volts.
Diode VD3 ensures the flow of reverse current to the armature of the electric motor while the thyristor is locked. At the beginning of each half-cycle, the rectifier voltage through diode VD2 and resistors R1, R6 is supplied to charge capacitor C1; there is still no back emf at this moment. Next, the voltage at the anode of the thyristor VS2 will be equal to the difference in the voltage of the diode bridge VD4-VD7 and the back emf of the armature, that is, from the rotation speed.
Reducing the speed with increasing load torque on the shaft reduces the back-emf and speeds up the charging of capacitor C1, reduces the delay angle of the thyristor unlocking - the decrease in speed is almost completely compensated.
Voltage pulses from resistor R3 are supplied to the control electrode of low-power thyristor VS1 for pre-amplification, then through resistors for setting the switching threshold R7, R9
to the control electrode of the powerful power thyristor VS2. Circuit VD1, R9 reduces the influence of mains voltage and load on the operation of the relaxation generator on transistor VT1.
The current of thyristor VS1 is limited by the value of resistor R4; it is not recommended to reduce its value, since the restoration of controllability will be impaired, that is, the interval between the transition of the thyristor current and voltage through zero to negative polarity and back to positive will decrease.
The recovery time depends on many factors: forward and reverse current, the amplitude of the switched-off voltage and the voltage on the control electrode.
By the way, radio interference is created by a reverse current, which almost instantly drops at the stage of turning off the thyristor at a very high speed and can cause overvoltages.
Forced switching is created by installing a diode VD3 and allows you to interrupt the current in the thyristor VS2 for a time sufficient for blocking.
Practical tests of the electric drill speed controller in different modes with changes in the ratings of radio components confirmed the theoretical justification for using positive feedback to stabilize the speed and speed of the electric motor:
Idle speed did not exceed 600 rpm,
the load on the electric motor shaft in both cases was about 4 kg of force, electric motor type DPR 72-F6-06 DC, body length 80 mm, diameter 40 mm.
The torque increased in the presence of feedback, the speed dropped slightly.
Radio components in the circuit not scarce:
resistors for a power of 0.25 watts of the MLT type, the double-base transistor VT1 and the thyristor VS1 can be replaced by the KU106V-G assembly, the type of power thyristor and transformer depends on the voltage and power of the electric motor used. Transformers of the TN-54 type with four windings of 6.3 volts and a current of more than three amperes, connected in a series circuit, work well in the circuit.
The silicon diode assembly type PBL405 has a low voltage drop and does not require a heatsink.
Install a small radiator 60*40*50 on the flat thyristor VS2.
Circuit adjustment The speed controller of an electric drill is as follows: at the minimum value of the resistance of resistor R6 (revolutions), set the threshold for turning on thyristor VS2 by changing the value of resistor R9, then by increasing the resistance of resistor R6, set the required electric motor speed.
In the printed wiring diagram, almost all radio components are located except for the switching circuits, power transformer and diode bridge, the speed controller and LED indicator HL1 are installed on the top cover of the case, fuse FU1, switch SA1 and the power cord output are attached to the side.
Literature:
1. Thyristors. Technical reference 1971 Translation from English. Publishing house "Energy".
2. Electric drill speed regulator. V. Novikov. "Radiomir" No. 5 2006 p. 19
3. Resistors, capacitors, transformers, chokes, switching devices for electronic devices. Directory. Minsk "Belarus" 1994
List of radioelements
| Designation | Type | Denomination | Quantity | Note | Shop | My notepad |
|---|---|---|---|---|---|---|
| VT1 | Transistor | KT117B | 1 | To notepad | ||
| VS1 | Thyristor & Triac | KU101E | 1 | To notepad | ||
| VS2 | Thyristor & Triac | KU202E | 1 | To notepad | ||
| VD1 | Zener diode | D818B | 1 | To notepad | ||
| VD2 | Diode | KD503B | 1 | To notepad | ||
| VD3 | Rectifier diode | 1N4005 | 1 | To notepad | ||
| VD4-VD7 | Diode | PBL405 | 4 | To notepad | ||
| C1-C4 | Capacitor | 0.1 µF | 4 | To notepad | ||
| C5 | Capacitor | 0.05 µF 630 V | 1 | To notepad | ||
| R1 | Resistor | 4.7 kOhm | 1 | To notepad | ||
| R2 | Resistor | 910 Ohm | 1 | To notepad | ||
| R3, R12 | Resistor | 100 Ohm | 2 | To notepad | ||
| R4 | Resistor | 1.2 kOhm | 1 | To notepad | ||
| R5 | Resistor | 360 Ohm | 1 | To notepad | ||
| R6 | Variable resistor | 100 kOhm | 1 | To notepad | ||
| R7 | Resistor | 1.5 kOhm | 1 | To notepad | ||
| R8 | Resistor | 1 kOhm | 1 |
So, the article by Alexey Sidorkin:
I think every person has had more than one event or incident in their life for which they could not find a suitable explanation, remaining a secret for a long time. This happened with my drill.
My son-in-law Dmitry acquired this Bosch PSB 500 RE drill in May 1998 to furnish his newly acquired apartment. At that time, not everyone had such a prestigious tool (power 500 W, speed control, reverse rotation, impact mode - “hammer”) on the household. The purchase aroused quiet envy - I had a simple Soviet drill without any bells and whistles. My daughter gave the Bosch drill later after the tragic death of her son-in-law during an accident in 2002.
Of course, my use of the tool was not “every day from morning to evening”; the drill was used for everyday needs, as in most ordinary families, plus the summer season at the dacha.
Fig.1. General view of the BoschPSB 500 RE drill.
The drill worked properly, successfully performing all its options and functions... and suddenly 5-6 years ago the speed regulator stopped “obeying” - no matter the position/setting of the regulator wheel/handwheel, when you press the trigger, the drill immediately made full revolutions without any smoothness. The first thing that came to mind as to why there were no low speeds was that the drill’s speed control circuit had burned out. But by that time, other tools appeared on the farm, including a screwdriver and another drill in the village, and the operation of the Bosch drill in low speed mode was not so relevant, and we never got around to fixing the problem.
Subscribe! It will be interesting.
Just recently I had to carefully work with a drill, and its high speed turned out to be very inappropriate, and there were no other tools with a chuck at hand. Not far from the house there is a workshop for repairing household appliances. They told me that the speed controller (hereinafter referred to as RO) for the Bosch drill is only “made to order”, wait at least 2 months, the cost of work is 500 rubles.
I decided to figure it out on my own, after all, I am a power equipment technician, albeit retired.
He's an adjuster himself, but he went to the workshop? If it’s urgent, and for a couple of hundred (previously it was called “per bottle”), then there’s no point in “uncovering your rifle,” others should also be allowed to live.
I opened the drill, disconnected the RO (two detachable electrical contacts of the knife type, two “for screws” and one screw securing the power wire - Fig. 2).
Rice. 2. Connecting the speed controller in the drill.
The drill speed controller is a separate unit. In Fig. 3, almost life-size, there are two halves (lid and body) of an already opened RO, the material is plastic, the halves are fixed between each other “with latches.”
Rice. 3. Drill speed controller with cover removed
Figure 3 shows: 1 – contact group; 2 – sliding contacts; 3 – resistor strips; 4 – adjusting screw handwheel; 5 – trigger return spring.
The housing of the speed controller for the drill contains a contact group 1 and sliding contacts 2 in the form of two spring plates, driven by pressing the trigger and returning to their original position under the influence of the return spring 5.
The cover contains a capacitor (bottom) and a board (top) with electronic elements and two resistor strips 3, along which, when the trigger is pressed, contacts 2 slide to smoothly change the speed of the tool. A special lubricant is applied to the resistor strips to protect the strips, reduce friction and prevent sparking of the sliding contacts.
An adjusting screw with a handwheel 4 on the trigger limits the depth of the trigger press and the distance/length of sliding of the contacts 2 along the resistor strips 3, thereby determining the range of regulation and the maximum speed of the drill. If the adjusting screw is turned out completely, then the trigger, when fully pressed, closes the contact group to directly turn on the drill motor, bypassing the electronic adjusting elements, and the engine runs at the highest possible speed (3000 rpm).
The drill speed controller circuit is almost identical. The only differences are in design and dimensions.
The scope of my work included checking the precise operation of the trigger when pressed, the interaction of the parts of the contact group, the rotation of the adjusting screw, leveling the distribution of lubricant on the resistor strips, and cleaning accessible areas from accumulated dust and dirt. No malfunctions, malfunctions or suspicious aspects were found. In other words, I carried out a small inspection, after which I assembled the drill, turned it on and... the speed controller is working , as if nothing had happened!
Thus, repairing the Bosch drill speed controller was reduced to simple cleaning!
Many assumptions could be made regarding the reasons for the temporary malfunction of the drill - from a blow or an unnoticed fall of the tool to problems with electronic components. However, an analysis of the situation still tends to disrupt the operation of the “sliding contacts - resistor strips” pair for some unknown reason; it is enough for a speck (particle) to simply get under one of the sliding contacts - and that’s it, there will be no adjustment. This is also evidenced by turning on the tool immediately at full speed, which is only possible when the contact group is triggered.
What's new in the VK group? SamElectric.ru ?
Subscribe and read the article further:
But, whatever you say, it turns out that the instrument turned out to be electrician himself and repaired himself!
Question from a reader
Reader Alexander contacted me by email with the following request:
Good evening. I came across your blog where you repair a Bosch drill. I have a similar problem, but I have almost nothing to do with electronics. Stupidly I disassembled the trigger of a Bosch GSB 1600 RE drill. Everything worked great before, I put it together somehow, but now the soft start doesn’t work. Perhaps I’m putting the parts in the wrong order and in the wrong place. I am attaching a photo of the disassembled one. I hope this helps, the drill is good.
Photo of a disassembled Bosch drill button:
Bosch drill repair. The disassembled trigger is a button with a speed control.
Bosch drill repair. Disassembled trigger - button
I don't know how to help the reader. Maybe someone can share their experience?
One of the visitors from the Republic of Bashkortostan wrote to me about two weeks ago. He liked the circuit of an electronic speed controller for a micro drill on Radiokot, but it has several disadvantages: greater heat generation LM317 and a low maximum current of 1.5A. He suggested using the LM2596 module instead of LM317 to increase the output current to 3A.
The idea is good in concept, but I’ll tell you about how to adapt the module to the control circuit.
To begin with, I will propose a modified circuit by Alexander Savov on LM317
The meaning of this circuit is that when there is no load on the drill shaft, the engine speed is minimal, but as soon as it is loaded a little, the speed jumps to the maximum possible. All this is implemented using a current sensor on R6 and a comparing comporator with a threshold slightly higher than the drop on the shunt
I decided to try this scheme with a canopy and the scheme works quite well. The engine under load was used from a 12V screwdriver 
Using the same method on the current sensor, I redesigned the circuit for LM2596, slightly reworking the module and adding a Savov circuit to it. Here's what I got
I connected the module with the motor to 12V, set the trimmer resistor on the module to the minimum engine speed, approximate resistance 5kOhm. After the changeover, I unsoldered and installed a 5.1 kOhm resistor; in the diagram this resistor is indicated as R11. Now I installed a key on the fourth leg, shunting it to the ground. I connected a current detector to the key and began testing. I measured the drop on the R8R9 shunt, set the voltage on the 2nd leg with the R7 trimmer to a few millivolts more than on the 3rd leg. The circuit worked rather sluggishly, it took a long time to turn on, then it took a long time to turn off. By selecting a resistor in the feedback and C8, we were able to achieve stable operation.
This is what a mounted drill speed controller looks like 
In principle, the circuit turned out to be quite working and has the right to life, but we must take into account that LM358 must be powered from a stabilized voltage, so it is recommended to set it to .
I’m not going to implement a drill speed controller on a printed circuit board, I already have a machine, but I’ll print it for you a little later, I don’t have time right now
I would also like to note that the LM2596 module used was provided by a friend from Bashkortostan, he has a website SolBatCompany.Ru, selling solar panels and various electronic modules, I recommend checking it out. You can buy such a module in China for only 50 rubles, here is the link
Using the assembled speed controller, I made a short video of its operation.
DIY electric drill repair
If you have certain skills, repairing a drill at home is quite simple. From the numerous cases of drill breakdowns, several characteristic malfunctions can be identified, which are caused by improper operation of the power tool or defective elements from the manufacturer. Such typical breakdowns include:
- failure of engine elements (stator, armature).
- wear of the brushes or their burning.
- failure of the regulator and reverse switch.
- wear of support bearings.
- poor quality clamp in the tool chuck.
Electric drill device
The structure of an electric drill (the simplest Chinese electric drill):
1 - speed regulator, 2 - reverse, 3 - brush holder with brush, 4 - motor stator, 5 - impeller for cooling the electric motor, 6 - gearbox.
Electric motor.
The commutator electric motor of a drill contains three main elements - a stator, an armature and carbon brushes. The stator is made of electrical steel with high magnetic permeability. It has a cylindrical shape and grooves for laying stator windings. There are two stator windings and they are located opposite each other. The stator is rigidly mounted in the drill body.
Electric drill device:
1 - stator, 2 - stator winding (second winding under the rotor), 3 - rotor, 4 - rotor commutator plates, 5 - brush holder with brush, 6 - reverse, 7 - speed controller.
The rotor is a shaft onto which an electrical steel core is pressed. Along the entire length of the core, grooves are machined at equal distances for laying armature windings. The windings are wound with a solid wire with taps for attachment to the collector plates. Thus, an anchor is formed, divided into segments. The collector is located on the shaft shank and is rigidly mounted on it. During operation, the rotor rotates inside the stator on bearings located at the beginning and end of the shaft.
Spring-loaded brushes move along the plates during operation. By the way, when repairing a drill, special attention should be paid to them. The brushes are pressed from graphite and have the shape of a parallelepiped with built-in flexible electrodes.
Replacing brushes.
The most common type of breakdown is wear of the motor brushes, which can be replaced yourself at home. Sometimes, brushes can be replaced without disassembling the drill body. For some models, it is enough to unscrew the plugs from the installation windows and install new brushes. For other models, replacement requires disassembling the housing; in this case, you must carefully remove the brush holders and remove the worn brushes from them.
Brushes are sold at all normal power tool stores, and often an extra pair of brushes is included with a new electric drill.
New brushes
Don't wait for the brushes to wear down to their minimum size. This risks increasing the gap between the brush and the collector plates. As a result, increased sparking occurs, the collector plates become very hot and may “move away” from the base of the collector, which will lead to the need to replace the armature.
You can determine the need to replace brushes by increased sparking, which can be seen in the ventilation slots of the housing. The second way to determine this is the chaotic “jerking” of the drill during operation.
Electric motor diagnostics.
In second place, in terms of the number of drill breakdowns, can be placed the malfunction of engine components and, most often, the armature. Failure of an armature or stator occurs for two reasons - improper operation and poor-quality winding wire. World-famous manufacturers use expensive coil wire with double insulation with heat-resistant varnish, which significantly increases the reliability of engines. Accordingly, in cheap models the quality of insulation of the winding wire leaves much to be desired. Improper operation comes down to frequent overloading of the drill or prolonged operation without breaks to cool the engine. Repairing a drill with your own hands by rewinding the armature or stator, in this case, is impossible without special tools. Only complete replacement of the element (exclusively experienced repairmen will be able to rewind the armature or stator with their own hands).
To replace the rotor or stator, it is necessary to disassemble the housing, disconnect the wires, brushes, remove the drive gear if necessary, and remove the entire motor along with the support bearings. Replace the faulty element and install the engine in place.
An armature malfunction can be determined by a characteristic smell, an increase in sparking, and the sparks have a circular motion in the direction of movement of the armature. Pronounced “burnt” windings can be seen during visual inspection. But if the engine power has dropped, but there are no signs described above, then you should resort to the help of measuring instruments - an ohmmeter and a megohmmeter.
The windings (stator and armature) are subject to only three damages - interturn electrical breakdown, breakdown to the “case” (magnetic circuit) and winding breakage. A breakdown to the housing is determined quite simply; it is enough to touch any winding output and magnetic circuit with the probes of a megohmmeter. A resistance of more than 500 MΩ indicates no breakdown. It should be taken into account that measurements should be carried out with a megger with a measuring voltage of at least 100 volts. By taking measurements with a simple multimeter, it is impossible to accurately determine that there is definitely no breakdown, but you can determine that there is definitely a breakdown.
It is quite difficult to determine the interturn breakdown of the armature, unless, of course, it is visible visually. To do this, you can use a special transformer, which has only a primary winding and a break in the magnetic circuit in the form of a trench for installing an armature into it. In this case, the armature with its core becomes a secondary winding. Rotating the armature so that the windings alternate in operation, we apply a thin metal plate to the armature core. If the winding is short-circuited, the plate begins to rattle strongly, and the winding heats up noticeably.
Often, an interturn short circuit is detected in visible areas of the wire or armature bar: the turns may be bent, crumpled (i.e., pressed against each other), or there may be some conductive particles between them. If so, then it is necessary to eliminate these short circuits by correcting bruises in the tire or removing foreign bodies, respectively. Also, a short circuit can be detected between adjacent collector plates.
You can determine whether the armature winding is broken if you connect a milliammeter to the adjacent armature plates and gradually turn the armature. In whole windings a certain identical current will appear; a broken winding will show either an increase in current or its complete absence.
A break in the stator windings is determined by connecting an ohmmeter to the disconnected ends of the windings; the absence of resistance indicates a complete break.
Speed regulator.
The drill speed is controlled by a triac regulator located in the power button. It should be noted that there is a simple adjustment scheme and a small number of parts. This regulator is assembled in a button body on a PCB substrate using microfilm technology. The board itself has miniature dimensions, which made it possible to place it in the trigger body. The key point is that in the drill regulator (in the triac) the circuit opens and closes in milliseconds. And the regulator does not change the voltage that comes from the outlet in any way (however, the root mean square value of the voltage changes, which is shown by all voltmeters that measure alternating voltage). More precisely, pulse-phase control occurs. If the button is pressed lightly, then the time when the circuit is closed is the shortest. As you press, the time the circuit is closed increases. When the button is pressed to the limit, the time the circuit is closed is maximum or the circuit does not open at all.
More scientifically it looks like this. The principle of operation of the regulator is based on changing the moment (phase) of turning on the triac (circuit closure) relative to the transition of the mains voltage through zero (the beginning of the positive or negative half-wave of the supply voltage).
Voltage diagrams: in the network (at the regulator input), at the control electrode of the triac, at the load (at the regulator output).
To make it easier to understand the operation of the regulator, we will construct three time diagrams of voltages: mains voltage, at the control electrode of the triac, and at the load. After turning on the drill, an alternating voltage is supplied to the regulator input (top diagram). At the same time, a sinusoidal voltage is applied to the control electrode of the triac (middle diagram). At the moment when its value exceeds the switching voltage of the triac, the triac will open (the circuit will close) and the mains current will flow through the load. After the control voltage drops below the threshold, the triac remains open due to the fact that the load current exceeds the holding current. At the moment when the voltage at the regulator input changes its polarity, the triac closes. Then the process is repeated. Thus, the voltage across the load will have the shape as in the bottom diagram.
The greater the amplitude of the control voltage, the earlier the triac will turn on, and therefore, the longer the duration of the current pulse in the load. And vice versa, the smaller the amplitude of the control signal, the shorter the duration of this pulse will be. The amplitude of the control voltage is controlled by a variable resistor connected to the drill trigger. The diagram shows that if the control voltage is not phase-shifted, the control range will be from 50 to 100%. Therefore, in order to expand the range, the control voltage is shifted in phase, and then during the processes of pressing the trigger, the voltage at the output of the regulator will change as shown in the figure below.
It is shown how the voltage at the output of the regulator will change if the drill trigger is pulled.
Speed controller repair.
The presence of voltage at the input terminals of the power button and absence at the output terminals indicates a malfunction of the contacts or components of the speed controller circuit. You can disassemble the button by carefully picking up the latches of the protective casing and pulling it off the button body. A visual inspection of the terminals will allow you to judge their performance. Blackened terminals are cleaned of carbon deposits with alcohol or fine sandpaper. Then the button is reassembled and checked for contact; if nothing has changed, then the button with the regulator must be replaced. The speed controller is made on a substrate and is completely filled with an insulating compound, so it cannot be repaired. Another typical malfunction of the button is the erasure of the working layer under the rheostat slider. The easiest way out is to replace the entire button.
Repairing a drill button with your own hands is only possible if you have certain skills. It is important to understand that after opening the case, many switching parts will simply fall out of the case. This can be prevented only by smoothly lifting the cover initially and sketching the location of the contacts and springs.
Reverse device(if it is not located in the button body) has its own changeover contacts, therefore it is also susceptible to contact loss. The disassembly and cleaning mechanism is the same as the buttons.
When purchasing a new speed controller, you should make sure that it is designed for the power of the drill, so with a drill power of 750W, the regulator must be designed for a current of more than 3.4A (750W/220V=3.4A).
The wiring diagram, and in particular the drill button connection diagram, may differ in different models. The simplest diagram, and best demonstrating the principle of operation, is the following. One lead from the power cord is connected to the speed controller.
Electrical diagram of a drill.
"reg. rev."- electric drill speed controller, "1st st.obm."- first stator winding, "2nd st.obm."- second stator winding, "1st brush."- first brush, "2nd brush."- second brush.
Reverse repair.
To avoid confusion, it is important to understand that the speed controller and the reverse control device are two different parts that often have different housings.
The speed controller and reverse are located in separate housings. The photo shows that only two wires are connected to the speed controller.
The only wire coming out of the speed controller is connected to the beginning of the first stator winding. If there were no reversing device, the end of the first winding would be connected to one of the rotor brushes, and the second rotor brush would be connected to the beginning of the second stator winding. The end of the second stator winding leads to the second wire of the power cord. That's the whole scheme.
A change in the direction of rotation of the rotor occurs when the end of the first stator winding is connected not to the first, but to the second brush, while the first brush is connected to the beginning of the second stator winding.
Drill reverse circuit.
This switching occurs in the reverse device, so the rotor brushes are connected to the stator windings through it. This device may have a diagram showing which wires are connected internally.
Reverse diagram of an electric drill
(in the photo the reverse is disconnected from the speed controller).
Electric drill reverse connection diagram.
Black wires lead to the rotor brushes (let the 5th contact be the first brush, and let the 6th contact be the second brush), gray wires lead to the end of the first stator winding (let there be the 4th contact) and the beginning of the second (let there be 7- th contact). When the switch is in the position shown in the photo, the end of the first stator winding with the first rotor brush (4th with 5th), and the beginning of the second stator winding with the second rotor brush (7th with 6th) are closed. When switching the reverse to the second position, the 4th is connected to the 6th, and the 7th to the 5th.
The design of the electric drill speed controller provides for connecting a capacitor and connecting both wires coming from the outlet to the controller. The diagram in the figure below, for better understanding, is slightly simplified: there is no reverse device, the stator windings to which the wires from the regulator are connected are not yet shown (see diagrams above).
Connection diagram for the button (speed control) of the drill.
In the case of the described electric drill, only two lower contacts are used: the far left and the far right. There is no capacitor, and the second wire of the power cord is connected directly to the stator winding.
Connecting an electric drill button.
Gearbox.
The drill gearbox is designed to reduce drill speed and increase torque. A gear reducer with one gear is more common. There are drills with several gears, for example two, and the mechanism itself is somewhat reminiscent of a car gearbox.
The presence of extraneous sounds, grinding and jamming of the cartridge indicates a malfunction of the gearbox or gear shift mechanism, if any. In this case, it is necessary to inspect all gears and bearings. If worn splines or broken teeth are found on the gears, then a complete replacement of these elements is necessary.
Bearings are checked for suitability after removing them from the armature axis or drill body using special pullers. While holding the inner race with two fingers, you need to rotate the outer race. Uneven slipping of the race or “rustling” when turning indicates the need to replace the bearing. A bearing replaced at the wrong time will lead to jamming of the armature, or, in the best case, the bearing will simply turn in the seat.
Impact action of the drill.
Some drills have an impact mode for making holes in concrete walls. To do this, a wavy “washer” is placed on the side of the large gear, and the same “washer” is placed opposite.
A large gear with a wavy side.
When drilling with the impact mode turned on, when the drill rests, for example, on a concrete wall, the wavy “washers” come into contact and, due to their waviness, imitate impacts. The “washers” wear out over time and require replacement.
The wavy surfaces do not touch thanks to the spring.
Touching wavy surfaces. The spring is stretched.
Replacing the drill chuck.
The chuck is subject to wear, namely the clamping jaws, due to dirt and abrasive residues of building materials getting into it. If the cartridge needs to be replaced, it is necessary to unscrew the locking screw inside the cartridge (left-hand thread) and unscrew it from the shaft.
Power cord.
The cord is checked with an ohmmeter, one probe is connected to the contact of the power plug, the other to the core of the cord. Lack of resistance indicates a break. In this case, repairing the drill comes down to replacing the power cord.
In custody I would like to add: when assembling the drill after repairing it, make sure that the wires are not pinched by the top cover. If everything is in order, the two halves will collapse without a gap. Otherwise, when tightening the screws, the wires may become flattened or cut.
Flattened wire.