How to increase the engine speed of an electric screwdriver.

The schematic diagram of the electric screwdriver RPM regulator

The 555 timer is widely used in control devices, e.g. PWM controllers for DC motors. Everyone who has ever. ever used a cordless electric screwdriver, probably heard the squeak coming from within. This whistles the motor windings due to the pulse voltage generated by the PWM system. It is simply unseemly to regulate the RPM of an engine connected to a battery in any other way, although it is quite possible. For example, simply connect a powerful rheostat in series with the motor, or use an adjustable linear voltage regulator with a large heat sink.

The PWM regulator based on the 555 timer is shown in figure 1.

The scheme is simple enough and based on the multivibrator, albeit altered into a pulse generator with an adjustable duty cycle which depends on the ratio of charging and discharging rate of the capacitor C1.

The capacitor is charged by the circuit: 12V, R1, D1, left-hand resistor P1, C1, GND. And the capacitor is discharged by the following circuit: top cover of C1, right side of resistor P1, diode D2, pin 7 of timer, bottom cover of C1. By turning the slider of the resistor P1 we can change the ratio of its left and right resistances, and therefore the charging and discharging time of the capacitor C1, and as a consequence the pulse frequency.

Scheme of the PWM-regulator on a 555 timer

This circuit is so popular that it is available as a set as shown in the following figures.

Schematic diagram of a PWM regulator kit.

The timing diagrams are also shown here, but unfortunately no part ratings are shown. These can be seen in figure 1, which is why it’s actually shown here. Instead of bipolar transistor TR1 without circuit modification you can use powerful field device which will allow to increase load power.

By the way, this circuit has one more element. the diode D4. Its purpose is to prevent the discharge of the C1 time-charging capacitor through the power supply and the motor load. The PWM frequency stabilization is thereby achieved.

By the way, with similar circuits you can control not only the speed of the DC motor, but just an active load. an incandescent lamp or some heating element.

The printed circuit board of a PWM regulator kit.

If you do a little bit of work, it is quite possible to recreate such a circuit, using one of the programs for drawing printed circuit boards. Although, given the small number of parts, it will be easier to assemble one piece by hinged assembly.

The appearance of a set of PWM. controller.

However, already assembled branded kit, looks nice enough.

Here’s where someone might ask: “The load in these regulators is connected between 12V and the collector of the output transistor. And what to do, for example, in a car, because there everything is already connected to the mass, the body, the car?”

Yes, the weight is a contradiction. The only recommendation is to put a transistor switch in the middle of the plus wire. A possible variant of such a scheme is shown in picture 5.

Figure 6 shows the output cascade on a MOSFET transistor separately. The drain of the transistor is connected to 12V battery, the gate just “hangs” in the air (which is not recommended), in the circuit of the source is the load, in our case the light bulb. This figure is shown just to explain how a MOSFET transistor works.

In order to open the MOSFET transistor, it is enough to apply a positive voltage to the gate relative to the source. In this case the bulb will be turned on full power and will continue to shine until the transistor is closed.

The easiest way to close the transistor in this diagram is to short-circuit the gate to the source. And this manual short circuit is quite suitable for testing of the transistor, but in a real circuit, especially a pulse circuit, you’ll have to add some more details, as shown in Fig. 5.

As we said above, you need an additional voltage source to open the MOSFET transistor. In our circuit its role is done by the capacitor C1, which is charged through the circuit 12V, R2, VD1, C1, LA1, GND.

To open transistor VT1, you need to apply a positive voltage from charged capacitor C2 to its gate. It is obvious that this will only happen if transistor VT2 is open. And this is only possible if the OP1 transistor is closed. Then the positive voltage from the positive terminal of capacitor C2 through resistors R4 and R1 will open transistor VT2.

At this point, the PWM input signal must be low and bypass the optocoupler LED (often called the inverse LED switching), therefore, the optocoupler LED is off and the transistor is closed.

To close the output transistor, you have to connect its gate to the source. In our circuit this happens when the transistor VT3 opens and for this you need the output transistor OP1.

PWM signal at this time has a high level, so the LED is not bypassed and emits its proper infrared rays, the optocoupler transistor OP1 is open, resulting in the load. the bulb is turned off.

As one of the options for the use of such a circuit in the car, this daytime running lights. In this case, motorists claim the use of high beam lamps, turned on half-light. Most of them are based on microcontroller, there are a lot of them on the internet, but it’s much easier to make one on the NE555.

The engraver grinder from an electric screwdriver with my own hands

In this article I want to show you how I made an interesting thing out of an old, unnecessary electric screwdriver. Of course you can buy a ready-made graver on aliexpress from 1000, but we’re not gathered at this site for that, right?

Chisel, engraver, dremel analogy. in other words, a universal hand tool that allows you to drill, saw, chisel, grind and perform many other tasks. The device will have not only a smooth regulation, but also an automatic increase in speed when there is load on the shaft.

For many years I had lying around this electric screwdriver for 18 volts.

Button burned out, the batteries are also outdated. Why not give it a second life. Also one of the reasons I wanted to get rid of it is that it’s very heavy and uncomfortable in the hand. The battery slides forward, and I think that’s a terrible design. Takes off very hard, often jams.

To find a new battery like this or at least replace the banks would cost half the price of a new electric screwdriver, so I have no regrets about disassembling it.

So, I’ve got the main parts. The RS550 motor is mounted here, the idle consumption is about 1.5 amps and it spins up to almost 20,000 rpm./minute., naturally without load.

Between the motor and the chuck there is a two-stage planetary reduction gear, it reduces the speed, if I am not mistaken, by 12 times.

The motor shaft drives the first stage, which consists of plastic satellite gears. In the middle of the second stage there is an intermediate piece that turns the second stage, where the steel satellites are already in place, t.к. the torque increases here. The biggest part. The crown gear has a knoll on its face and the housing has balls in special holes. When the torque regulator is turned, these balls extend or fall back, thus blocking the crown gear or allowing it to slip with a characteristic crackle. That’s why the mechanism was nicknamed “the ratchet”. This I told briefly, and in fact half of the details I do not need.

Next, I simplified the design and to do this, I had to remove the chuck. There is a screw inside. This screw is not standard and unscrew clockwise. But the chuck will not come off just like that.к. It itself also has a thread, already a classic thread. After unscrewing the screw, any L-type wrench is clamped into the chuck and you need to hit it sharply, counterclockwise (gear lock). Note: some of the steps described in the article will be more understandable from the video on Soldering iron TV.

I will now explain what the conversion is all about. If any chuck is fastened directly to the motor, it would be wrong.к. the motor has no bearings as such, just brass bushings. If you attach any chuck directly to the motor, it will not be correct, i.e. if it is loaded from the front, e.g. by drilling, these bushes will wear out and then play. The use of a gearbox is therefore compulsory. All the load will be applied to it, or rather to its bearing. My simplification is that the gear on the motor shaft will only rotate one group of satellites, t.е. I will leave only one step. Also have to shorten the width of the crown gear.

So everything is ready and the parts are cleaned. The crown gear was sawed with an angle grinder and ground. Now it will not protrude.

Instead of the second half of the body, which was screwed to the motor, I prepared the adapter plate. It was hand filed out of stainless steel.

A washer was made of fluoroplastic to prevent the gears from catching on the screws. Also secured the crown gear from spinning.

Because I left only one gear stage in the gearbox, the rpm went up and the torque went down, but that’s okay, because the drill is not used for screwdriving. The revised gearbox has 6 motor revolutions per one chuck revolution, i.e.е. It has six times less torque than the other half of the housing. The speed of the chuck will be high enough to drill, saw, and grind. I think it’s a plus, because the gearbox reduces engine rpm a bit.к. the load on the motor is reduced and its service life is not affected. The whole “ratchet” mechanism is completely removed from the design, it is not needed.

I will make the body from 50 mm plastic pipe. On the adapter plate I made ears to attach this tube. They will have to be bent. Originally it was just an idea to cut off the handle from the original body, but it is too thick and there is no room for the electronic stuff.

Perhaps I have paid too much attention to mechanics, but some information will help those, who decided to repair an electric screwdriver. Now let’s move on to the electronic part.

Many different motor control circuits were tried. All of this has been assembled and tested over a long period of time. I used pulse width modulation to control the motor. There’s no point in going into too much detail about PWM, it’s a pretty well covered topic. In short, this is a power control, by changing the pulse duty cycle.

Roughly speaking, there is a rectangular signal in which we increase or decrease the length of the pulses, by the same amount the pause between them changes. The frequency in this case is constant. The result is a smooth speed control from zero to 100%.

Circuit diagram. Press to increase.

I decided to build the motor control circuit on the LM324. All 4 operational amplifiers from the microcircuit are involved here. On the elements of DA1.1, DA1.2 assembled a triangular oscillator. It is easy to change the frequency of this generator by adjusting the capacitor C3. In my case the capacitance is 2.2 nF, which sets the PWM frequency to about 1.5 kHz. This triangular signal from the output of the second element, it’s pin number 7, goes to the non-inverting input of the element DA1.3. At its other input we see a group of resistors that set the voltage, in particular variable resistor R3 is just for PWM changes. But how do we get this PWM signal? The point is that the element DA1.3 is connected as a comparator and it compares the triangular signal with the voltage that we set with the variable resistor R3. When the signal on pin 10 is higher than the voltage on pin 9, the output of this comparator is high, and vice versa.

How to make a power supply for an electric screwdriver from energy-saving bulbs?

Modern power tools are popular because they are not connected to the mains during operation, which extends the possibilities of their operation, even in the field.

The presence of a battery greatly limits the duration of active work, so the screwdrivers and drills require constant access to a power source.

Unfortunately, in modern tools (often made in China), the power battery has little reliability and often fails quickly, so craftsmen have to make do with improvised materials, not only to assemble a switching power supply, but also to save money on this.An example of such a handmade is a switched-mode power supply (UPS) for a cordless electric screwdriver for 18 V, assembled from elements of a non-working energy-saving lamp, which can be useful even after its “death”.

The structure and principle of operation of the energy-saving bulb

To understand what can be useful energy-saving bulb, consider its structure.The lamp construction consists of the following components:

• A sealed glass tube (bulb) inside coated with a phosphor composition. The bulb is filled with inert gas (argon) and mercury vapor.
• Plastic housing made of non-flammable material.
• A small electronic board (electronic ballast) with a ballast that is responsible for starting and eliminating flicker. Ballasts of modern devices are equipped with a filter that protects the lamp against line disturbances.
• The fuse, which protects the board components from voltage surges, which can cause fire of the device.
• Housing. it “packs” the control gear, fuse, and connecting wires. Markings are placed on the body, which contain information about the voltage, wattage and color temperature.
• The socket that provides the contact between the lamp and the power supply (the most common sockets are E14, E27, GU10, G5).3).

Two spirals (electrodes) are connected to the bulb, which are heated by current and emit electrons from their surface. As a result of the interaction of electrons with mercury vapor in the bulb is a glow charge that “gives birth” to UV radiation. Affecting the phosphor, ultraviolet light “makes” the lamp glow. The color temperature of an energy-saving bulb is determined by the chemical composition of the phosphor.

Types of breakage of energy-saving bulbs

The energy-saving lamp can fail in two cases:

• Lamp bulb breaks;
• The electronic ballast (EB) (high frequency voltage converter), responsible for converting alternating current to direct current, gradually heating the electrodes and preventing flickering of the appliance during power-on, has failed.

If the bulb breaks, the lamp can simply be thrown away, and if the electronic ballast breaks, it can be repaired or used for its own purposes, such as using it to make a UPS by adding an isolation transformer and rectifier to the circuit.

The electronic ballast of an energy-saving lampThe majority of EB lamps are high-frequency voltage converters, assembled on semiconductor triodes (transistors). expensive devices are equipped with a complex circuit of EB, respectively, cheaper. simplified.

The electronic ballast is “complete” with the following electrical elements:

• Bipolar transistor, operating at voltages up to 700 V and currents up to 4A;
• Protective diodes (they are mainly D4126L type elements or similar);
• a pulse transformer;
• choke;
• by a bidirectional dynistor, similar to the twin KH102;
• 10/50V capacitor
• Some EB circuits are complete with field-effect transistors.

The following diagram shows the electronic ballast for a lamp with a functional description of each part.

Some EB circuits of energy-saving bulbs can almost completely replace the circuit of a homemade pulse source, adding a few elements and making small changes.

Individual transducer circuits run on electrolytic capacitors or contain a specialized chip. It is better not to use such circuits of EB, because they are often the source of failure of many electronic devices.

What do the wiring diagrams of econo and UPS have in common?

Below is one of the common wiring diagrams of a lamp augmented with an A-A’ jumper replacing the missing parts and the lamp, a pulse transformer and a rectifier. The elements of the circuit highlighted in red can be removed.

As a result of some changes and necessary additions, as you can see in the diagram below, you can assemble the impulse power unit, where the added elements are marked in red.

What kind of BP power settings can be achieved from an energy-saving bulb?

“Second” life “econo” is often used by modern radio amateurs.

After all, their hand-made often requires a power transformer, the availability of which presents certain difficulties, starting with its purchase and ending with the consumption of a large amount of wire for the winding and the dimensions of the final product.

Therefore, folk craftsmen have learned to replace the transformer with a switching power supply. Especially if you use the electronic ballast of a faulty lighting fixture for this purpose, it will save you money, especially for a transformer with more than 100 watts of power.

You can make a small switching power supply by winding the secondary side of an existing inductance coil. To get a higher wattage power supply you will need an additional transformer.

Switching power supply for 100 W or more can be made on the basis of EB lamps power 20-30 W, the scheme of which will have to change a little, adding to it a rectifying diode bridge VD1-VD4 and changing towards an increase in the cross section of the winding of choke L0.

If you can not increase the gain of the transistors, you have to increase their base current, changing the ratings of resistors R5-R6 to smaller. In addition, you will have to increase the power parameters of the base and emitter circuit resistors.If the generation frequency is low, you have to replace the capacitors C4, C6 with elements of higher capacity.

Breaking myths about batteries: everything you should know about the battery of your smartphone

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A lot of myths related to the work of the battery, only confusing. We checked out the most popular misconceptions and found out what affects the life of any battery and how to properly charge your gadgets.

How to increase battery life? Why smartphone discharges so quickly? We will check the popular myths that you can find on the Internet and tell the whole truth about modern gadgets.

Myth: Charging at night shortens battery life

Charging at night will not shorten battery life

Should you charge your phone at night?? Let’s find out.

• This myth is based on the danger of overcharging the battery. But this problem is not relevant for modern smartphones.
• Even old lithium-ion batteries very rarely overheat if they are connected to a charger for too long. Today’s batteries, however, are smart enough to withstand overnight charging with no problem.
• Unfortunately, there is some truth in this myth: the battery does lose its charge capacity if you leave it charging overnight. But these losses are so minimal that you won’t notice them.
• Consequently, you don’t need to worry if you want to put your smartphone charging overnight. The consequences will be far from those feared by owners of phones with old batteries.

Tip: The battery will last longer if it constantly balances between 40 and 80 percent of its charge.

Myth: Ending an app increases battery life

Closing apps will not increase battery life

Many smartphone owners believe that they can extend the battery life of their gadget if they close unused apps. But this is a myth, today’s cell phones are designed for multitasking.

• For example, if you quit an app in iOS, it will be frozen. This means that the program will stop doing anything and will not consume power.
• Closing an app completely deletes its data from the RAM of your gadget. When you choose to open it again, the app will need to be reloaded into the smartphone’s memory. And this process will consume much more battery resources than reopening it.

Tip: Don’t quit an app if you are going to use it again soon.

• Instead of constantly closing applications, you can extend the battery life of your gadgets in other ways. For example, turn off notifications or background program updates.

Myth: Only use original chargers

In certain circumstances, you can also use “non-native” chargers

Logically, most manufacturers want you to use only original chargers. “Native” accessories are quite expensive, but the fact that they are better for the battery is a myth. You can use other chargers for many gadgets, and we’ll prove why.

• Modern smartphone chargers are standardized. Generally, the recharge time from a “non-native” device is slightly longer, but it doesn’t affect battery performance.
• You can charge your smartphone with almost any charger, but we do not advise you to use only cheap accessories bought on famous Chinese sites.
• Third-party chargers are a budget alternative that you can safely use as long as they are certified and charge the battery to the required level.

Myth: Bluetooth, Wi-Fi, and geolocation services drain your battery faster

Turning off Bluetooth hardly saves you a big percentage of your battery life

Some applications quickly drain the battery of the smartphone. But that’s not the case for functions like Bluetooth, Wi-Fi, and location detection.

• Bluetooth and Wi-Fi don’t drain your battery as quickly as many people think. When we tested smartphones, the activity of these features on average reduced the total battery life of the gadget by only 30 minutes. You should agree that this is a small loss if your smartphone is running for 24 hours a day.
• But things used to be different: Wi-Fi and Bluetooth used other modules that required much more power than their modern counterparts. Progress has been made, and now these services do not consume as much power.
• Turning off location detection will not increase overall battery life. But if you do not use this feature, it is better to turn it off.

Tip: The display backlight uses the most energy. Turn off the screen when you are not using your smartphone. Reducing the brightness of the display can save a lot of battery power.

Myth: Always fully discharge the battery before you charge it

The battery does not need to be fully discharged

Many people think that the battery must always be fully discharged before it should be plugged in. But we’re ready to dispel that myth as well.

• This rule of thumb was true in the days of nickel-cadmium or nickel-metal hydride batteries. They were the ones with the so-called “memory effect”, which decreases the total capacity of the battery and it does not charge above a certain level.
• Smartphones today have only lithium-ion or lithium-polymer batteries, which no longer have a “memory effect. However, some manufacturers still recommend calibrating the battery if the gadget starts discharging quickly or shuts down altogether at a certain battery level.

Tool chuck

Types of chucks for electric screwdrivers.

Screw or drill bits are used with the tool. The standard bits shank is in the form of a hexagon. The chuck is designed for fastening the bits and transmitting the rotary motion to them. It is inserted into the threaded end of the spindle and secured against loosening by means of a screw.

The most common is the three-jaw, self-centering, self-clamping chuck. Inside it has a hexagonal recess for inserting the shank of the bit. It is fastened between the cams by turning the coupling. The socket is fitted with a locking mechanism that enables the bit to be clamped without turning the spindle.

Disassembly of the screwdriver

In most cases, in order to find and repair the device, it must be disassembled. Since all devices are similar in appearance, resembling the shape of a gun, their disassembly can be presented in the form of recommendations given on the repair of the Interskol screwdriver:

• First of all, the battery pack is disconnected. To do this, you need to press the latch and unfasten the module.
• All screws around the perimeter of the device are unscrewed using a Phillips screwdriver.
• After unscrewing the screws, the two halves of the housing are separated, while holding the structural parts installed in the grooves.
• The speed switch, the start button and the reversing mechanism are carefully disconnected.
• The gearbox is extracted from the removed half. To remove it, you will need to turn the gearbox in its seat.

Electric screwdriver speed regulator with their own hands. Metals, equipment, instructions

Like any other tool, an electric screwdriver sometimes needs repair. In such situations, some craftsmen replace this tool with a drill.

But it should be understood that screwing or unscrewing bolts and screws with a drill is quite inconvenient and has to be done with a lot of force. Therefore, it is very important for the home handyman to learn how to troubleshoot an electric screwdriver with their own hands.

To help home handymen in this matter, in this article we will tell about the device of an electric screwdriver, what malfunctions can occur in the work of this tool, as well as what ways they can be eliminated.

• How an electric screwdriver is constructed
• What is needed for repair
• What is the order of disassembly
• What kinds of troubleshooting can occur and how to fix them

How an electric screwdriver works

Before we get into the question of tool malfunctions, first of all, it is worth knowing what structural elements the tool consists of.

To illustrate the construction of an electric screwdriver, you can use the following image.

As can be seen from the figure, the tool consists of the following structural elements:

• electric motor;
• Gear mechanism;
• Reverse and its switch button;
• The force regulator is in the form of a ratchet;
• chuck for fixing bits and drills;
• Start button;
• The speed regulator, in other words, the speed of rotation of the working shaft.

It is also worth understanding, the basic scheme of the device of screwdrivers of such popular brands as Makita (Makita),Bosch (Bosch),Hitachi (Hitachi),Aeg has no significant differences.

What is needed for repair

In order to qualitatively perform the repair of an electric screwdriver, it is necessary to prepare the following materials and tools in advance:

• multimeter;
• Phillips screwdriver;
• hair dryer;
• sandpaper;
• used toothbrush;
• technical alcohol;
• lithium-based grease.

What is the order of disassembly

To disassemble an electric screwdriver, you should perform a number of the following sequential operations:

• disconnect the unit in which the battery is located;
• using a Phillips screwdriver to remove all the screws which connect the two parts of the tool case;
• The electric motor, gearbox and all other constructional parts are removed;
• the reversing switch button is removed;
• The force regulator is dismantled;
• the gearbox is disconnected from the motor.

Diagram of electric screwdriver disassembly, click on the picture to enlarge

After following the above procedure, it is safe to say that the electric screwdriver is disassembled.

What malfunctions occur and how to rectify them

The main breakdowns of an electric screwdriver, which can be repaired with your own hands, are the following important aspects:

The causes of this malfunction may be as follows:

• the switch is broken;
• burned out one of the wires of the electrical circuit;
• failed battery;
• Wear of the graphite brushes;
• burnout of the electric motor windings.

To remove the above-described faults, it is necessary to perform the following actions:

• replace the switch;
• to find a break in the circuit and level out the problem;
• to purchase a new battery;
• Replace the brushes of the collector of the electric motor;
• rewind the motor windings.

• Reverse stops working.

As a rule, the causes of failure of this type are the following facts:

It is important to know: in the case of a reverse fault, first of all, it is worth cleaning the contacts of the conductive wires, or replacing the whole switch.

When there is no adjustment of the power of rotation of an electric screwdriver, the following reasons may be:

The following operations are worthwhile for troubleshooting:

• check the contact group of the power button, clean all connections, and in some cases. replace this entire assembly;
• if the cause of malfunction is a transistor, it must be replaced.

Causes of malfunction of this type are as follows:

• the main shaft has failed;
• Working surfaces and gear teeth have considerable wear;
• the pin of the main pinion is worn out.

As a rule, in the situations described above, the worn out structural element of the gearbox is replaced.

So, in this article, we’ve listed all the typical screwdriver malfunctions, as well as provided recommendations on how to properly repair the tool.

We hope that the information presented in the article, will become a practical guide for you in the repair of electric screwdriver of different brands.

From this video you will learn how to repair and clean an electric screwdriver:

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How to repair a screwdriver

An electric screwdriver can be safely attributed to the tool, which often have to use not only in everyday life, but also to work on construction sites. But like any complex technical accessory, the product can break. How to repair an electric screwdriver yourself we will consider in this text.

Equipment in the construction market, where the screwdrivers occupy a special place, is quite large. Many models have individual criteria, assembly quality and cost. However, most models are characterized by basic principles of operation and internal design.

The basic elements of any electric screwdriver can include:

• the presence of an electric motor;
• planetary gearbox;
• The adjustable function button “Start”;
• reverse switch;
• force regulator;
• power supply.

The electric motor is powered by DC power, structurally represented by a cylindrical shape. an armature with brushes and magnets is located inside. The peculiarity of the electric circuit of the motor implies that the direction of the supply voltage flow will be directed to the brushes. When changing the polarity to be supplied the motor is reversed.

The main faults of screwdrivers

All malfunctions of this instrument can be conditionally divided into 2 groups:

Faulty electrical parts

The main signs of failure of the electric part of an electric screwdriver are:

Electric screwdriver battery circuit diagram.

The first thing to pay attention to when there is no power on an electric screwdriver is the battery. Maybe it just ran out of power? Therefore, the first thing to do is to put it on charge. If this does not help, then use an ordinary tester to measure the voltage on the power supply terminals. At the same time, the meter must show a voltage no lower than the value indicated on the battery case. If the indicator is understated, you should determine what is the cause of the malfunction: in the breakdown of the battery or the charger.

To diagnose the charge, plug it in and measure the voltage at the output terminals with the same tester. It should be slightly higher than the nominal voltage (indicated in the passport of the charging unit). If there is no voltage you can conclude that the battery is broken. If you know a lot about electronics you can try to repair the battery charger with your own hands by checking all the electrical elements and their connections with a multimeter. Otherwise you will need to seek help from a specialist or buy a new charger.

If the problem is in the battery, you will first need to disassemble the battery. Then you need to visually inspect all connections and check the quality of soldering. If everything is normal, take the tester and measure the voltage separately on each battery cell The meter should show a voltage of at least 0.9V. If any element has a lower voltage, you will need to replace it with a new one. When replacing, it must be ensured that the capacity and type of supply element are the same.

The Battery Electric Screwdriver Gearbox Diagram.

If the battery is good, then the next point is to check the power button. To do this, disassemble the electric screwdriver and measure the voltage across the terminals of the button. The battery should be installed. If the tester shows normal voltage, the battery is removed and the leads from the power source are shorted. After that the button is pressed as far as it will go and the resistance of its output is measured. The multimeter should show a small resistance (about zero). If the resistance is too high, it is necessary to replace the button with a new one. It can be connected with burn-out of the contacts, which happens very often. If the button is normal, the problem may be in the brushes or other parts of the electric motor. Check the reversing switch the same way.

If the electric motor runs at maximum power and the speed regulator does not function, the problem may be a broken switch or failure of the control transistor. These elements are also checked with a multimeter and replaced with new ones if necessary.

It is not uncommon for the brushes to be worn out. They should be changed when the wear is more than 45-50%, because otherwise the armature will wear out. If there is nothing wrong with the brushes, you need to check the motor itself. To do this, they are disconnected and the resistance of the windings is checked with a multimeter. If it is small, then you have a short circuit, and if there is no short circuit at all, then look for a breakage. In that case you need to rewind the winding.

Mechanical faults of screwdrivers

Over time, many of the mechanical parts of the screwdriver wear out and fall into disrepair. This is manifested by unstable operation of the tool and specific sounds, which can be used to judge the bad condition of the bearings or the bush. If such elements are found, they should be removed and replaced with new ones. If during the work of an electric screwdriver there is periodic jamming of the motor, then this is a clear sign of failure of the planetary gearbox.

If the chuck runs out, it is necessary to inspect the gearbox shaft. There is a high probability that it will be bent. The gearbox consists of toothed gears. which over time wear out their teeth. This will cause the gears to slip, affecting the efficiency of the tool. In this case, the worn elements will need to be replaced.If your household fails electric screwdriver, do not panic and immediately carry the tool to an expensive handyman. Repair of electric screwdriver with their own hands can perform each self-respecting owner. The main thing. it is to understand the essence of the problem and carefully think through your actions when carrying out repairs.

PWM speed controller for a Bosch 18 volt screwdriver

Creator: Radio Amateur

Circuit board, schematic. The button on the working screw meowed, autopsy revealed that the motor is alive, the button is also alive together with the integrated resistor. But the PWM itself died in an unequal struggle with the endless loads on the screwdriver. But the best part is, the power transistors are still intact, and the PWM is in a different world. Since the scheme could not be found and the board with the double-sided arrangement of SMD parts mass was abundantly varnished on both sides, I saw no chance for resuscitation. And use a screwdriver without speed control is not very comfortable. I remembered a simple PWM regulator for 40W Zhiguli heater, and with the help of a knife, rathole and some mom attached all this stuff to Hermanz. And the effort was not in vain. WORKING.I had to put up with a little squeak at low speed, if you increase the PWM frequency squeak is not audible, but under a critical load begins to heat the transistor. I made a compromise. a little squeak for the transistor’s thermal. And the longevity of the circuit.

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Electric motor speed regulation in modern electronic equipment is achieved not by changing the supply voltage, as it was done before, but by supplying the electric motor with current pulses of different duration. PWM (pulse width modulated) regulators, which have recently become very popular, serve these purposes. The circuit is universal. it also controls the speed of the motor, the brightness of the lights and the current in the charger.

The circuit shown works perfectly, and a printed circuit board is included.

Without circuit modification the voltage can be raised up to 16 volts. The transistor to put depending on the power of the load.

It is also possible to assemble a PWM regulator using this circuit, with an ordinary bipolar transistor:

And if necessary, instead of compound transistor KT827 put field IRFZ44N, with resistor R1. 47k. The poleswitch without heat sink, with a load up to 7 amperes, does not heat up.

A timer on the NE555 chip monitors the voltage at capacitor C1, which is taken from pin THR. When it reaches the maximum the internal transistor opens. Which shorts the DIS pin to ground. At the same time on the output OUT appears logical zero. The capacitor begins to discharge through DIS and when the voltage on it becomes equal to zero. the system switches to the opposite state. on the output 1, the transistor is closed. The capacitor starts charging again and everything repeats.

The charge of capacitor C1 follows the path: “R2-up lever R1.D2” and the discharge along the path: D1. lower arm R1. DIS. When we turn the variable resistor R1 we change the ratio of the resistance of the upper and lower arm. Which consequently changes the pulse length to pause ratio. The frequency is mainly set by the capacitor C1 and depends some more on the resistor R1. By changing the charge/discharge resistance ratio, we change the duty cycle. The R3 resistor provides the output pull-up to a high level. so there’s an open collector output. Which is not capable of setting a high level on its own.

Assembly and tuning recommendations

You can put any diodes, capacitors about the same rating as in the diagram. Variations within the same order of magnitude do not significantly affect the operation of the device. At 4.If you put 7 nanofarads in C1, for example, the frequency goes down to 18kHz, but you almost don’t hear it.

If after completing the circuit, the control transistor is getting warm, most likely it is not fully opened. That is transistor has a big voltage drop (it is partially open) and current is flowing through it. As a result, a lot of power is dissipated, for heating. It is desirable to parallel the circuit output with capacitors of high capacity, otherwise it will sing and regulate badly. To keep it whistle free, just match C1, it is often the cause of whistling. In general, the scope of very broad, especially promising will be its use as a dimmer for high-power LED lamps, LED strips and spotlights, but about it next time. This article was written with the support of ear, ur5rnp, stalker68.

The SPARK-3 battery charger is designed for charging 6 to 24 volt batteries with a current of 0.5 to 9.9 ampere to a given voltage or time.