Charging for an electric screwdriver 18 volts with their own hands

How to make a power supply for an electric screwdriver 18v with their own hands. instructions and diagrams

Any household tool that can function autonomously has a significant disadvantage. Maintain the battery in good condition is troublesome, while working, it requires regular charging, storage life is limited, and the cost of such a power source is such that the acquisition of a new one quite strongly “hits the

And it is not always possible to find it, especially if the electric screwdriver of an old modification. The conclusion is simple. make a power supply for an electric screwdriver for 18 volts with your own hands.

The most rational solution. to pick up components or remake the existing power supply from any technical device. It can be done with your own hands, without any help.

What to pay attention to:

After acquiring a unit, you will only need to remake the “box” in which the battery was placed. This is the only thing that even an amateur can do with his own hands.

• First. Drill a hole in the plastic (the easiest), put the power wire (cord) inside the body and connect (solder) to the PSU terminals. The best variant.
• Second. In the conductor “” install the n / n diode of the appropriate power, the cathode which. in the direction of the el / motor of an electric screwdriver.

Those who have skills with a soldering iron and multimeter, “folk craftsmen” offer so many circuits that it is easy to choose something suitable. These are just a few of the many things that are not difficult to find:

• Universal power supplies.
• Based on two- and three-pole resistors.
• Impulse.
• With filters.
• Units with a gain circuit and some others.

What the vast majority of them have in common? Except for pulse modifications. step-down transformer, as it is a secondary (power supply for an electric screwdriver) voltage of 18 V. That’s the difficulty. You can choose a transformer, but, unfortunately, not all parameters of radio components are shown in the schemes. If resistance value is indicated, power is not; not all types of semiconductors are indicated, etc. And there is almost no information about the transformer: wire cross section, number of turns, and so on. So you have to do the calculations yourself.

But even a transformer can be made with your own hands, if you have the skill and desire. For example, take it from the power supply of an old PC. The main thing is to meet the basic requirements listed above. Depending on the modification of the computer, there may be some differences. You can use part of the circuit and dimmer LED lamp. There are other options.

But all this is time experience independent design theoretical knowledge. It turns out that buying a power supply and / or remake it, adapting it to work with an electric screwdriver, much easier and faster. All other options are unlikely to be acceptable to a person who is with electricity / electronics on “you”, even if there is a diagram and its description. After all, you will also have to “etch” the board to place all the radio components. many people know how to do this?

On sale there are ready-made PSU (pulsed) at 18 V, just for screwdrivers. Their Who are not sure that they can assemble the power supply with their own hands, it is worth considering.

It remains to add that the decision to switch to a PSU has a significant disadvantage. “binding” to the socket. But how relevant is it for a domestic electric screwdriver? And the advantages are plenty. torque stability, the ability to breathe “second life” into a tool for which no batteries can be found, and no care for the power source. And from what it can be made, what options are described in quite some detail.

Charging a faulty battery

Sometimes it happens that the electric screwdriver itself works, but the battery is broken. There are several options for solving the problem:

• Buying a new one.
• Repair of an old one. If you do it yourself, you will need special knowledge of. Not everybody wants to work with harmful substances.
• Connection via power supply. For example, if you have a widespread “Chinese” at 14.4 V, suitable car battery. You can build your own from a transformer for 15-17 V. You will need a diode bridge (rectifier) and a thermostat to combat overheating. Other components. only for controlling input and output voltages. No regulator needed.
• The “native” battery or its substitutes can be excluded from the design at all. The electric screwdriver will be powered directly from the mains.

Different voltage models

It is not enough to know the type of battery charger and brand of manufacturer, you also need to know the voltage of your electric screwdriver. The most common choices are 12, 14 and 18 V.

12 volt chargers

Circuits can be made up of transistors up to 4.4 pF. This can be seen in the diagram of the charger for an electric screwdriver 12 volts. Circuit conductivity is 9 microns. Capacitors are needed to control the clock jumps. The resistors used are usually field resistors. Tetrodes-based chargers have an additional phase resistor. It protects against electromagnetic oscillations.

12 volt chargers work with up to 30 ohms resistance. It is not uncommon to find them on 10 mAh batteries. Among well-known manufacturers, Makita is the most common.

14 volt chargers

The schematic shows that five transistors are needed for a 14 volt charger. Other circuit features:

• The microcircuit is suitable only for four channels;
• Capacitors are pulse capacitors;
• tetrodes are needed to work with 12 mAh batteries;
• two diodes;
• The conductivity is about 5 µm;
• The average capacitance of the resistor is no more than 6.3 pF.

Circuit-built devices can handle currents up to 3.3A. Triggers are included in the circuit rarely. The exception is Bosch products. With Makita products, triggers are successfully replaced by wave resistors.

Chargers for 18V

An 18 volt electric screwdriver charger uses only transient transistors in the circuit. Other features of the products include:

• three capacitors;
• tetrode and diode bridge;
• a grid trigger;
• The current conductivity is about 5.4 µm, sometimes chromatic resistors are used to increase it.

The use of transceivers with increased conductivity is a feature of the domestic company “Interskol”. Current draw can be up to 6A. Makita often uses high quality dipole transistors in its models.

Whichever manufacturer of an electric screwdriver you choose, the problem of replacing the charger can easily be solved. You only need to know a few things about your tool to know that.

Power supply

We will not consider buying any units or transformers, if only to buy a new battery! We will consider using what we have on hand. I should say at once. the charger from the same electric screwdriver is only good for drilling over-ripe bananas, its power is too low.

Ideally a step-down, powerful 12 V transformer will do, for example from a computer uninterruptible power supply. The power of such transformer is usually 350-500 watts. But I didn’t have such a transformer in stock, but I had a lot of computer power supplies. I am sure that if someone has some electronic junk, there must be some ATX computer power supplies lying around.

This is one of the first representatives of computer ATX power supplies.

Computer ATX-block is quite suitable for an electric screwdriver, the load capacity of the 12 volt bus allows you to remove a current of 10-20 amps. I want to dispel a small myth. it is impossible to stuff a block into a battery case of an electric screwdriver, ATX board is too big. I have to make a separate case for it or leave it in its original metal case. The disadvantage of the native case is sensitivity to dust, and in fact even the smallest repair is a lot of dust.

Pretty weak unit, the 12V bus load is only 10A. If possible you had better choose units with more powerful twelve volt bus.

Varieties of batteries

The charger for an electric screwdriver is created with the features of a self-contained power source in mind. The following sections discuss popular battery packs. When examining the compatibility of the functional components of an electric screwdriver, it is advisable to pay particular attention to the charge recovery modes.

Nickel-cadmium

Lithium battery charger

These batteries are different:

Unfortunately, big problems arise at the disposal stage. Harmful chemical compounds in Ni-Cd batteries are very harmful to the environment. For this reason, the use of such products is being phased out in many countries.

Unless otherwise specified by the manufacturer, select the mode of operation together with a suitable electrical circuit charger for an electric screwdriver according to the following data:

• to extend the service life it is recommended to “train” 2-6 full work cycles before you start and then every 6-8 months thereafter;
• prolonged storage in discharged state is allowed;
• pre-discharge voltage. from 0.9 to 1 V;
• nominal capacity is retained only at positive temperature;
• overheating is not permissible during the reconditioning process (not exceeding 40°C);
• the completion of the cycle is indicated by a slight decrease in voltage;
• Charging current is calculated by formula:

Important! The letter “C” is for capacity, indicated in the certificate of the battery. If C=2.5 Ah, a charge with 5A = 22.5.

Sulfuric acid batteries for electric screwdriver

Products of this category are created on the basis of lead cells with gel electrolyte of acid type. Advantages:

The main disadvantages of sulfuric acid batteries are their considerable size and high weight. Cells are charged at 1.8-2 V while maintaining a current of 0.1-0.15C.

Lithium-ion batteries for electric screwdriver

This is the most common modern solution. Similarly designed batteries are used in smartphones and laptops, other household and professional appliances. Pros:

• better performance, compared to the above analogues in terms of energy storage per unit volume (weight);
• wide operating temperature range;
• long-term maintenance of good operating parameters;
• No excessive disposal requirements.

One standard cell charges at 3.6V to 4.2V. Exceeding the threshold set by the manufacturer shortens the battery life. Low level limits storage capability. Energy potential of batteries is restored with careful temperature control.

Charger for electric screwdriver converted to lithium

Another dizzying hands 🙂 Watch out for traffic! Many pictures! And a lot of letters 🙂 If you remember, I converted my electric screwdriver battery to lithium quite a long time ago. But here with normal charger for it all pulled. And now you have to charge it once a month instead of every few days 🙂 When I was not too lazy. I used a lab-charger with limited voltage and current, when I was too lazy. I plugged it into an old motherboard charger, which wasn’t designed for lithium and gave out about 18 volts and about three amps. Hoped for a protection circuit board inside the battery. But the thought of a normal charger did not leave me. And even a power supply with a voltage and current regulator I bought long ago:. PSU. www.aliexpress.com/item/Power-Supply-Module-AC-110v-220v-to-DC-24V-6A-AC-DC-Switching-Power-Supply-Board/32827334983.html. regulator. www.aliexpress.com/item/DC-Step-Down-Adjustable-Constant-Voltage-Current-Power-Supply-Module-Drop-shipping/32787533675.html I chose the regulator with power reserve and with the expectation to give 20-24 volts and limit it to 16.7 volts and up to 1 amp. Going forward there was a little problem with the PSU, but more about that in the review.

Besides that, all fasteners are for bolts (stainless steel) and screws, which I also bought on Ali a long time ago. I bought them in several diameters, from M1 to M3.) Screws. www.aliexpress.com/item/500pcs-lot-DIN7985-Stainless-Steel-304-M2-Phillips-Pan-Round-Head-Machine-Screw-kit-m2x4-5/32765362652.html and many other sizes from the same seller Screws. www.aliexpress.com/item/400pcs-M2-Cross-pan-Head-Self-Tapping-Screws-Black-Oxide-Assortment-Kit-M2-4-5-6/32580525848.html and also the same seller has other sizes. It has already come in handy many times 🙂

This is what the native electric screwdriver charger and the battery itself looked like:

The battery was inserted upside down into it:

There are three contacts inside the socket. two power and one for the thermal fuse inside the battery: (here the contacts are already taken out)

The charger has a transformer and a board with simple analog electronics:

The power supply and the regulator just wouldn’t fit into the original charger case, so I had to make a new one. At first I thought to make a separate “cap” with contacts to put on the battery, and separately the charger itself. But then I thought, there’s no gain, only extra wires will get tangled underfoot. And I decided to repeat the original charger design. PSU with a regulator inside and a slot for the battery right there in the case.

Lately, everything I’m going to do, I model first. Especially things that have to be combined with ready-made ones, like the battery of an electric screwdriver. And to have something to build the case on, I started with a model of the battery socket. The form is not complicated, it was enough only a caliper to remove all the dimensions, the first printed model is perfectly compatible with the original: Well, or so it seemed to me 🙂 After that I proceeded to model the socket, based on the already made model of the stem. Printed out the socket. the previously printed foot fits perfectly:

But the foot of the real battery somehow does not feel very snug in the printed socket: I recheck all the sizes. everything is correct, but the contacts are a little bit out of place, a little loose and somehow awkwardly sits. Finally I saw that the stem was not tapered on all sides. The flat leading edge fits straight, no constriction. I reprinted the stem and the socket taking that into account and everything fell into place 🙂 Then I changed it a few more times and printed the socket, trying to get the size right. And several times it was my inattention. in the model I changed one size. external, and after printing I looked at the other. internal. And was surprised that somehow nothing changes 🙂

After trying two legs and four sockets I was completely satisfied with the result. I added the top surface to the socket, the stiffening ribs and the mounting for the board with contacts: And went on to the next step. the modeling of the body itself. I decided right away that the case will consist of upper and lower halves, but it was just necessary to decide how to place PSU and regulator inside. For this I spent another half an evening and made models of them. And started virtually putting them to each other and to the socket in different ways. In the end I decided on this layout:

And when you understand the layout, you get a more or less clear idea of the size of the hull, so you can start drawing it in final. Started with the top cover. Nothing complicated. extend the top plane to the size of the case, raise the walls, add posts to mount the stabilizer. To small vertical elements. props, for example, for 3D printing, it is better to add ribs for reinforcement. And to the base of all the vertical elements. especially the thin ones, like the walls. it is useful to add chamfers to increase the base area, this will give additional strength. I didn’t forget about cooling. on the upper side I made two rows of narrow slots, just above the regulator radiators. I rounded the corners of the case, making it a little rounder near the socket for design purposes 🙂 I added holes for two indicator LEDs. And I did the lip around the perimeter. On the bottom half will be a mating edge so that the halves slightly fit into each other. I tried on the regulator and the board with the pins: And the other side with the inserted LEDs:

By the way, I made the model of the contact.) Later I added a small cutout for the power cord and mounts to tighten the two halves of the housings:

With the lower half of the case everything was even easier. to copy the contour of the upper half, stretch the walls, add posts for PSU, mounting to tighten the halves, ventilation holes and trailing edge: Trying on the PSU: And you can see how it all feels in height: feels great 🙂

Battery varieties

The charger for an electric screwdriver is created taking into account the peculiarities of the autonomous power source. The following sections describe popular rechargeable batteries

When examining the compatibility of the functional components of an electric screwdriver, it is advisable to pay special attention to the charge recovery modes

Ni-Cd batteries

Unfortunately, big problems arise at the disposal stage. The harmful chemical compounds in Ni-Cd batteries are very harmful to the environment. For this reason, the use of such products is being phased out in many countries.

Unless otherwise specified by the manufacturer, select the operating mode along with a suitable charger circuit for the electric screwdriver according to the following data:

• To extend service life, it is recommended to “train” with 2-6 full cycles before starting operation and every 6-8 months thereafter;
• long storage time in discharged state is acceptable;
• Pre-discharge voltage. from 0.9 to 1 V;
• the nominal capacity is only maintained at positive temperature;
• Overheating is not allowed during the reconditioning process (not exceeding 40°C);
• The completion of the cycle is indicated by a slight decrease in voltage;
• the charging current is calculated according to the formula:

Important! The letter “C” is used to denote the capacity given in the battery datasheet. If C=2.5 Ah, you can charge with a current of 5A = 22.5

Sulfuric acid batteries for electric screwdriver

Products in this category are created on the basis of lead cells with an acid type gel electrolyte. Advantages:

The main disadvantages of sulfuric acid batteries are their large size and weight. The cells are charged at 1.8-2 V while maintaining a current of 0.1-0.15C.

Lithium-ion batteries for electric screwdrivers

It is the most common modern solution. Similarly designed batteries are used in smartphones and laptops, other household and professional appliances. Pros:

• better performance in terms of energy storage per unit volume (weight) in comparison with the analogues discussed above;
• wide working temperature range;
• long-term maintenance of good operating parameters;
• no excessive disposal requirements.

One standard cell charges at 3.6V to 4.2V. Exceeding the threshold set by the manufacturer reduces service life. Low level limits storage capability. The energy potential of accumulators is restored with careful temperature control.

How a storage device works

When a storage device fails it makes sense to try to restore it first. For repair it is desirable to have a schematic diagram of the charger and a multimeter. The circuitry of many charge devices is based on the HCF4060BE chip. Its switching circuitry forms the holding time interval of the charge. It includes a quartz oscillator circuit and a 14-bit binary counter, which makes it easy to implement a timer.

It is easier to disassemble the principle of the charger circuit on the real example. This is what it looks like in an Interskol screwdriver:

This circuit is designed to charge 14.4 volt batteries. It has a LED indicating the connection to the network, LED2 is on, and the charging process, LED1 is on. As a counter chip U1 HCF4060BE or its analogues are used: TC4060, CD4060. Rectifier is assembled on the power diodes VD1-VD4 type 1N5408. Transistor PNP type Q1 operates in the key mode, to its outputs are connected the control contacts of relay S3-12A. The key operation is controlled by the U1 controller.

When you turn on a battery charger AC voltage of 220 volts through a fuse goes to the step-down transformer, at the output of which its value is 18 volts. Then it goes through the diode bridge, is rectified and comes to the smoothing capacitor C1 with the capacity of 330 uF. It has a voltage of 24 volts. When the battery is connected, the contact group of the relay is in an open position. Microcircuit U1 is energized through the stabilitron VD6 by constant signal equal to 12 volt.

The button SK1 used works without latching. When it is released all the power comes through the circuit VD7, VD6 and the limiting resistor R6. LED1 is also powered via resistor R1. The LED lights up, indicating that the charging process has begun. The runtime of the chip U1 is set for one hour of operation, after which the power is removed from the transistor Q1 and, accordingly, from the relay. Its contact group opens and the charging current disappears. LED1 goes out.

This charger is equipped with overheat protection circuit. This protection is realized with a temperature sensor. thermocouple SA1. If during the process, the temperature reaches more than 45 degrees Celsius, the thermocouple will be triggered, the chip will receive a signal and the charge circuit will break. After the process, the voltage on the battery terminals reaches 16.8 volts.

This way of charging is not considered intelligent, the charger can not determine what state the battery is in. Due to what the duration of operation of the screwdriver on battery power will be reduced due to the development of its memory effect. That is, the capacity of the battery each time after charging decreases.

Device mobility

When converting cordless equipment to power from the mains one of its main characteristics. mobility. is lost. Therefore, if you have decided to make a redesign of the power supply of the screwdriver, it is necessary to determine exactly what device you want to use in the future.

There are two concepts for how to convert battery-type equipment to mains power:

• The power supply (PSU) will be external. This variant of performance provides the presence of a separate device. But don’t let this scare you, even a heavy and large rectifier can just be near the power outlet. You will still be limited by the length of the power cable either to the outlet or to the power supply unit. According to Ohm’s law, reducing the voltage for the same wattage increases the amperage. Therefore, the power cord of the device for 12-19 volts should have a larger cross-section than the mains cable for 220 volts.
• The power supply is built into the battery case. In such a device mobility is almost completely preserved, only the length of the mains cable can limit the movement of the operator. One problem may arise when you need to install a high-power transformer in the battery housing of your screwdriver. But the modern radio industry allows to solve this problem, there are a large number of compact rectifiers on the radio equipment markets.

Each method finds supporters, as it has a certain set of characteristics.

Options for making a power supply

There are several options for converting a screwdriver to mains power. The task is to power the electric motor of the device with an intermediate source.

Let’s use the charger from a laptop

To make a 12V power supply for a screwdriver with your own hands is possible, even without technical knowledge. You should only find a useless charger from a laptop, which has specifications similar to the parameters to power a screwdriver. The main thing is that the output voltage corresponds to the desired one (12-14 volts).

To achieve this goal, you must first disassemble the battery and remove the defective elements. This is followed by the following manipulation:

• Take the battery charger from a laptop.
• Cut off the output plug, bare and tin the ends of wires.
• Strip wires and solder to the battery input wires.
• Insulate the soldering points to avoid short circuits.
• We make a hole in the body, so as not to squeeze the wire, and make the assembly of the construction.

The base is a power supply from a computer

To make this device you will need a PC block of format A. Т. It is not difficult to find it, it is an old model of the power supply, which is easy to buy at any radio parts market. It is important to know that you can use a 300-350 W block with a current of 12 V at least 16 A.

The AT format blocks have the following parameters. On the case of this device is a power button, which is very convenient when working. There is a cooling fan and overload protection circuit mounted inside.

The order of the rearrangement of the unit:

• Removing the lid of the B housing. П. Inside we will see a board with a lot of wires going to the connectors, as well as a fan.
• The next step is to disable the power protection. Find the green wire on the square large connector.
• Connect this wire to the black wire from the same connector. You can make a jumper from another piece of wire, or you can just cut it short and leave it in the body.

Then in the outputs bunch find the smaller connector (MOLEX) and do with it the following operations:

• We leave the black and yellow wire, and cut the other two short.
• For the convenience of the PSU location during operation, solder an extension wire to the black and yellow wires.
• Attach the other end of the extension cord to the contacts of the empty battery compartment. This should be done by soldering, you can make a good twist, it is necessary to strictly observe the polarity.
• We make a hole in the case, so as not to squeeze the wire during assembly. The device is ready.

If you have the desire to ennoble your design, t. е. to hide it in another case, drill holes for air intake to prevent the PSU from overheating.

Power from the car charger

With a car battery charger, it’s pretty easy to make a device to power a screwdriver. To make the conversion, you only need to connect the power terminals of the charger output to the power supply of the electric motor.

If there is a charging device with a continuously variable output voltage, you can use it as an 18-volt power supply for a screwdriver.

The mobility of the device

When converting cordless equipment to power from the mains one of the main distinguishing features is lost. mobility. Therefore, if you decide to make a power conversion of the screwdriver, you need to determine exactly what kind of device you want to use in the future.

There are two concepts on how to convert battery-type equipment to mains power:

• Power supply unit (PSU) will be external. This design has a separate device. But do not let this scare you, even a heavy and large rectifier can simply be near the power outlet. You will still be limited by the length of the power cable either to the outlet or to the power supply unit. Ohm’s law says that reducing the voltage for the same power increases the amperage. Therefore, the power cord of the 12-19 volt device must have a larger cross-section than the 220 volt power cord.
• The power supply is built into the battery housing. In such a device mobility is almost completely preserved, only the length of the mains cable can limit the movement of the operator. One problem may arise when it is necessary to install a transformer of high power in the battery housing of the screwdriver. But the modern radio industry allows you to solve this problem, there are a large number of compact rectifiers on the radio equipment markets.

Each method finds supporters, because it has a certain set of characteristics.

Power pack variants

There are several options for converting a screwdriver to mains power. The task is to power the electric motor of the device with an intermediate source.

Using a laptop charger

To make a 12 V power supply for a screwdriver with your own hands is possible, even without technical knowledge. It is only necessary to find an unnecessary charger from a laptop, which has specifications similar to those for powering a screwdriver. The main thing is that the output voltage corresponds to what we are looking for (12-14 volts).

To achieve this goal, you must first disassemble the battery and remove the defective elements. Then follow these manipulations:

• Take the laptop charger.
• Cut the output connector, bare and tin the ends of wires.
• We solder the stripped wires to the battery input wires.
• Insulate the soldering points to avoid short circuits.
• Make a hole in the housing, so as not to squeeze the wire, and assemble the construction.

The base. a power supply from a computer

To make such a device you will need a block from a personal computer A-format. Т. It is easy to find, this is an old model of the power supply, and you can easily buy it at any hardware market. It is important to know that you can use a 300-350W unit with a current of 12 V at least 16 A.

It is the AT format blocks that correspond to these parameters. On this case is a power button, which is very handy when working. Inside there is a cooling fan and an overload protection circuit.

Procedure for rebuilding the unit:

• Let’s remove the B housing cover. П. Inside we will see a board with many wires going to the connectors, as well as a fan.
• The next step is to disconnect the power protection. Find the green wire on the square socket.
• Connect this wire with the black one from the same socket. You can make a jumper from another piece of wire, or you can just cut it short and leave it in the case.

Then in the bundle of outputs find a smaller connector (MOLEX) and do with it the following operations:

• Leave the black and yellow wires, and cut the other two short.
• For the convenience of the PSU when working solder to the black and yellow wires extension cord.
• Attach the other end of the extension cord to the contacts of the empty battery compartment. It should be done by soldering, you can make a good twist, it is necessary to observe the polarity.
• Make a hole in the case, so as not to squeeze the wire during assembly. The device is ready.

If you feel like refining your design, t. е. to hide it in another case, drill holes for air intake to prevent the PSU from overheating.

Power from the car charger

Having a car battery charger, it is quite easy to make a device to power a screwdriver. To make the conversion, you only need to connect the power terminals of the charger output to the power supply of the electric motor.

If you have a device for charging with stepless regulation of the output voltage, you can use it as a power supply of 18 volts for a screwdriver.

Power supply for cordless screwdriver

A friend asked me to build an external power supply for a screwdriver. Together with the screwdriver (Fig.1) brought a power transformer from an old Soviet burner-grinder “Ornament-1” (fig.2). see if it is impossible to use it?

At first, of course, we disassembled the battery compartment, looked at the “banks” (Fig.3 and Fig.4). Have checked every “bank” by means of the charger with several charge-discharge cycles. out of 10 pieces only 1 good and 3 more or less normal, and the rest are completely “dead”. So, for sure we will have to make an external power supply.

To assemble the power supply, you need to know what kind of current the screwdriver consumes when it is working. Having connected it to the lab source, we find out that the motor starts to rotate at 3.5 V, and at 5-6 V there is considerable power on the shaft. If we press the start button when 12V is fed into it, the power supply unit protection will go off, which means that the current consumption exceeds 4A (the protection is set for this value). If you start the screwdriver on a low voltage, and then increase it to 12 V, it works fine, the current consumption is about 2 A, but at the moment when the screw goes halfway into the board, the power supply unit protection triggers again.

To get the full picture of current consumption, we connected the screwdriver to the car battery by putting a 0,1 ohm resistor in the positive wire gap (fig.5). The voltage drop from it was fed into a computer sound card with an open input, SpectraPLUS software was used for viewing. The resulting graph is shown in Figure 6.

The first pulse on the left is the start pulse when turning on. You can see that the maximum value reaches 1.8 V and this indicates a current of 18 A flowing (I=U/R). Then, as the motor is revving up, the current drops to 2 amps. In the middle of the second second, the head of the screwdriver is clamped by hand until the “ratchet” is triggered. The current at this time rises to about 17 A, then drops to 10-11 A. At the end of the 3rd second the start button is released. It turns out that the screwdriver requires a power supply with a capacity of 200 W and a current of up to 20 A. But given that the battery compartment says it’s 1.3Ah (Fig.7), it’s probably not as bad as it seems at first glance.

Open the burner power supply, measure the output voltages. Maximum is about 8,2 V. Not much, of course. Given the voltage drop across the rectifier diodes, the output voltage across the filter capacitor will be about 10-11 V. But there is no way out, let’s try to assemble the circuit according to the figure 8. Diodes KD2998B (Imax=30A, Umax=25V) were used. The mounting of diodes VD1-VD4 is done by hinged mounting on the paddles of burner contact sockets (fig.9 and Fig.10). As a high-capacitance capacitor we used a parallel connection of 19 smaller capacitors. The whole “battery” is wrapped with masking tape and the capacitors are chosen such sizes that the whole bunch with a slight effort fit into the battery compartment of the screwdriver (Fig.11 and Fig.12).

The fuse block is very uncomfortable in the burner, so it was removed, and the fuse was tucked “directly” between one of the leads of 220V and the lead of the interference suppression capacitor C1 (Fig.13). When closing the housing, the mains lead is tightly crimped by a rubber ring and this prevents the lead from dangling inside when bending it from outside.

Checking the capability of the screwdriver showed that everything is working fine, the transformer after half an hour of drilling and screwing screws heats up to about 50 degrees Celsius, the diodes are heated to the same temperature and do not need radiators. The screwdriver with such a power supply has less power compared to powering it from a car battery, but this is understandable. the voltage at the capacitors does not exceed 10.1 V, and during the increase of the load on the shaft even further decreases. By the way, a decent “loss” on the supply wire length of about 2 meters, even using its cross section of 1.77 sq.mm. To check the drop on the wire, a circuit was assembled according to Figure 14, in which the voltage across the capacitors and the drop voltage on one conductor of the supply wire were monitored. The results in the form of graphs at different loads are shown in Figure 15. Here in the left channel is the voltage at the capacitors, and in the right channel. the drop on the “minus” wire, going from the rectifying bridge to the capacitors. It can be seen that when the screwdriver head is stopped by hand, the supply voltage drops to below 5 V. At the same time about 2,5 V drops on the power cord (2 times 1,25 V), the current is pulsed and is connected to the rectifier bridge (Fig.16). Replacing the power cord with another one, with a cross section of about 3 sq.mm resulted in the increased heating of the diodes and the transformer, so we returned the old wire.

Looked at the current between the capacitors and the screwdriver itself, assembling the circuit in Figure 17. The resulting graph is in Figure 18, “chunky”. is 100 Hz ripple (the same as in the previous two figures). You can see that the inrush pulse exceeds the value of 20 A. most likely this is due to the lower internal resistance of the power supply due to the use of parallel connection of capacitors.

List of radio elements

Nameplate Type Nominal Quantity NoteMy Notebook ShopVD1-VD4

C1

C2

C3

C4

C5

F1

Tr1

Figure
Diode	KD2998B	4	Search in the Otron store	Notepad
Capacitor	1.0 μF	1	400 В	Search in the Otron store	To the pad
Capacitor	0.47 uF	1	160 В	Search for in-store Otron	Notebook
Electrolytic capacitor	2200 uF	15	16 В	Search in Otron store	Notepad
Electrolytic capacitor	1000 uF	4	16 В	Search in Otron store	Notepad
Capacitor	1.0 μF	1	160 В	Search in the store Otron	Notepad
Fuse	3.16 А	1	see. Text	Search in the Otron store	To the notebook
Transformer	220/8 В	1	See. Text	Search the Otron store	Notepad
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