# Alteration of a computer power supply for a screwdriver

### Improved performance in terms of power and stability

Let’s see how to do it. First, you need to unsolder all unnecessary wires from the circuit, leaving only the 12V line. You also need to look at the 12V output circuit from the microcircuit, perhaps there is an electrolytic capacitor of 16 Volts at the junction, it needs to be changed to at least 25 V. Since we will raise the operating voltage to 16 Volts.

To raise the voltage in the circuit, we redo the installation according to the indicated circuit on the right. Once again, you need to check the output circuit for 12V, checking that the resistance R7 is 12 kOhm and re-solder the regulating resistance R9 to a variable value of 10 kOhm. The adjustment knob can be brought out to the front panel.
Check the output voltage, for example, with a multimeter, by setting the voltage with a variable resistor to 15. 16V. This voltage is quite enough for the reliable operation of a screwdriver with an operating voltage of 12-14V.
After closing the cover, mount the terminal clamps for the cables (suitable from household power outlets or switches), an ammeter and a voltmeter can be mounted on the front panel to monitor the parameters of the circuit.

After that, we can assume that the switching power supply for the 12v screwdriver is complete.

### Power supply from an old computer

To implement the plan, almost any unit based on the tl 494 microcircuit or an analogue of the ka 7500 (domestic kr1114 EU4) is suitable. Before proceeding with the alteration, you need to make sure that the computer’s power supply is working. To do this, you need a 12 volt light bulb and a jumper wire. The power supply has three connectors with colored wires, first we take which is average in terms of the number of suitable wires, we look: red wire. 5 V; 2 black wires are negative wires; yellow wire. 12 volts.

We connect a 12V x 25W light bulb (automotive) to the 12V line by connecting contacts with a yellow and black wire. this will be a kind of indicator that the current source is working.

On the largest connector, we use the green and black wires, which need to be closed together with a wire jumper. Such a schematic snag is needed to outline the protection circuit. After supplying 220V, the fan spun, the light came on. this indicates that the unit is working and can be upgraded. The wiring of the TL494 chip must be changed as shown in the diagram, connecting the elements as shown in the diagram. This is done to remove the protection of the operation of the pulse generator, so that it works stably and does not turn off under load. After a simple alteration, it is necessary to check the operability of the device again by connecting the light bulb according to the previous scheme, while the protection is turned off and the pulse generator will work without interruption.

Soldering of the elements is quite enough for the unit to work, but it is possible to improve the performance even further. Radio magazine for 2009 (you can download at the end of the article).

### Consider the design of a block for a screwdriver from a computer

It may happen that the battery charger breaks down or the batteries fail to charge. Almost every home has old electronic equipment, including an old computer, from which the power unit can be used as a computer unit to power a 12V screwdriver. This will not harm the engine of the equipment, since the device will provide for current stabilization and can practically replace the battery assembly in terms of parameters.
From parts of already unnecessary electrical engineering, you can assemble a network rectifier by installing it directly into an empty battery box, having previously freed up space from the elements. Sources can be: power; impulse

## Charging

In order for the battery assembly to work for a long time and efficiently, it needs high-quality charging. But, even, self-respecting manufacturers, producing low-power sources for charging batteries, make them according to a simplified scheme. This is due to the fact that high-quality charging is expensive, starting from 2 thousand rubles. and more. A simplified diagram, as a rule, is: a step-down transformer; rectifier bridge from a diode assembly or individual diodes; several zener diodes and capacitors that smooth out the ripple. Yes, and the original app. parts for repair will not be easy to find. A high-quality power supply unit can be assembled from domestic parts. One of these is shown in the figure. As you can see, the alteration is quite simple, there is not even a step-down transformer, the mains voltage is extinguished by capacitors. Having passed through the diode bridge, the current becomes constant. A simple alteration provides a stabilized power supply to electronic devices at the output.

## Power supply for 12v screwdriver

One of the most important advantages and at the same time a disadvantage of a battery-powered screwdriver is the ability to work remotely without stationary power sources. To carry out work on such objects for 8. 10 hours, without being able to recharge the batteries, you need to have high-quality batteries and properly charge it. This is especially important for low-power 12V screwdriver power supplies, which do not have high energy consumption.

## Capacity or voltage

The elementary sources from which the battery for the screwdriver is assembled have different voltages, so the Ca-Ni battery has 3.2 V., Li-ion. 3, 6 V. If we connect three batteries in series, we get 12, 6V and 13.2V. A series connection is a connection in which the positive terminal is connected to the negative terminal of the next battery, and the positive terminal is connected to the negative terminal of the next one, forming a continuous chain. With this connection, the battery voltage is added. If you connect the batteries plus with a plus, and the minus terminal with a minus, then the voltage remains the same, but the capacity will double. Thus, if it is necessary to increase the voltage, we collect a serial (series) connection, if the capacitance is a parallel connection (parallel).

## Battery assemblies

a power supply for an electric hand tool may differ in the configuration of the case, group of contacts, beautiful color, but one thing is invariable. they are assembled from piece elements. Each of the manufacturing firms produces branded batteries paying great attention to quality, since the performance of the tool directly depends on the power source by which the manufacturer is judged.

Now on the market there are different batteries for sale: by the active component; size; capacity; stress.
Elements with an active Ca-Ni component appeared in devices as source of autonomous power supply from the very first. Actually, after his invention, it became possible to manufacture hand tools on batteries. These elements have a number of advantages and disadvantages.

One of the main advantages: these elements work well at temperatures close to frost down to.20 ° C and are sold at a low price.

One of the biggest problems is the so-called “memory effect”. This phenomenon is expressed in the ability of active components to oxidize with prolonged charge, i.e. if the battery remains charged for several days, then the capacity, and, accordingly, the performance will decrease several times. And, although the manufacturers in the instructions warn about the procedure for the mandatory discharge of the battery after the end of work on an additional load, for example, on an incandescent light bulb, but forgetfulness of users can damage the battery. With proper use, the number of charge-discharge cycles is up to 500. 600 times without limitation of the service life.

Metal. a hydride battery in which an oxide. nickel alloy acts as a contact plate, the active layer is made of powder with a nickel filler with the inclusion of rare earth elements.

With the correct operating mode, the discharge cycle. the charge of such batteries is brought up to 700 times. With the introduction of new active elements, the product received an additional capacity in comparison with Ca.Ni by almost one and a half times, but it also acquired a disadvantage: in the event of a controller breakdown in the battery circuit, when overcharged, the active nickel was activated and overheated. In the updated batteries, the “memory effect” was greatly reduced, but not completely ruled out. The service life was limited to three to four years of operation.

Li. ion. The Lithium Ion battery uses components with lithium ions. The very first lithium batteries were made from lithium. They had good characteristics. high operating voltage and capacitance, however, they had a problem: with a slight overvoltage or internal short circuit of the cells, lithium became active and reacted with the filler, which led to ignition or heating to high temperatures. In order to avoid battery fires, manufacturers were forced to turn the production of batteries towards the use of materials with lithium ions, such batteries received a prefix. lithium-ion. During operation, it turned out that if you systematically recharge the battery, then the active release of lithium begins and its deposition on the walls of the battery. With a certain accumulation, he could go into an active phase with the same consequences.

### Power supply from energy-saving lamps

recently, energy-saving lamps, which replaced incandescent lamps, seemed like a miracle of engineering, saving energy consumption by almost 10 times. Now we see that energy-saving lamps are being replaced by LED lamps, which are even more economical and environmentally friendly. The tubes themselves with harmful mercury vapor must be disposed of, and the lamp start-up circuits may still come in handy.

If you look at the design of an energy-saving lamp, you can see that it consists of a bulb with fluorescent gas and a threaded cartridge, between them there is a ballast. electronics for starting. A typical ballast consists of: diode input; transformer choke; two transistors; external winding feedback transformer.

Before removing the board, it is necessary to remove the wires from the filaments (there are two of them) lamps, which are attached to the board on pins.

Before reworking the ballast into a pulsed constant voltage source, it is necessary to wind an additional secondary winding on the inductor of 5.7 turns of enamel wire with a diameter of 0.5. 0.6 mm, for this it is better to evaporate the inductor and carefully wind the wire.

Now it is necessary to remove everything that is indicated in the diagram between points A. A. Since energy-saving lamps need two incandescent filaments, they have 4 output points on the board, designated P1.P2 and P3-P4, put a jumper between P1 and P4, excluding the circuit lamp start-up.

Next, checking the operation of the control circuit with a 12V 25W light bulb. Power depends on the thickness of the wound enamel wire on the choke.

When changing the cross-sectional diameter of the secondary winding on the choke from the recommended one, it is necessary to check the operation of the circuit with a test lamp. Heating of transistors is possible. In this case, it is better to install more powerful ones or install on existing radiators.

Now it remains to install an output diode bridge and a smoothing capacitor. Diodes are best installed impulse. Electrolytic capacitor 3-4 mF. The pulse rectifier is ready. Such a pulsed constant current source can be used for LED lamps, LED strips, charging battery assemblies (a small ripple at the output improves charging performance).

### Alteration of the “Chinese” under the screwdriver

This is the easiest way to get the source you need, since Chinese devices are almost universally available and inexpensive. These power supplies are rated for a higher output voltage of 24 volts. Therefore, the first task of the wizard is to lower the output voltage to the values ​​required by the tool (12-18 V).

To achieve the goal, the resistors are replaced: the native R10 is removed, and one that can be configured is inserted into the circuit. This work consists of several stages:

• First, a constant resistor is soldered, which has a permanent resistance of 2320 Ohm.
• Then a tunable resistor is inserted which is preset to 2300 ohms. If this is not done, the structure will refuse to work.
• The unit is supplied with electricity to determine the values ​​of the output parameters. The measuring device is set to a constant voltage range.
• By adjusting the resistance, an optimal voltage (12, 14, 16 or 18 volts) and a current strength not exceeding 9 amperes are achieved. Otherwise, the converted power supply for the screwdriver will soon fail due to heavy loads.

The modified design is attached to the place of the old battery. All conductive elements are insulated. For ventilation, additional holes are drilled, the case is closed. The last step is to check the operation of the screwdriver.

In much the same way, you can remodel almost any commercial power supply unit. In this case, in addition to replacing the resistor, another conversion may be required. embedding additional diodes in the circuit.

## Possible power sources

In order for any screwdriver to function from the mains, it needs to provide voltage conversion: the tool requires only 12, 16 or 18 volts. All power supplies are divided into 2 large groups: they can be pulse or transformer.

## Is mobility important?

Once the battery becomes unable to hold a charge, the screwdriver becomes a completely useless tool. Buying a new charger is impractical, as its price is often up to 50% of the cost of a new model. Therefore, the thought of reworking the instrument for the network is a completely justified decision.

It is possible to restore the characteristics of the battery, but this option is still a half measure, because in the future the situation will repeat itself. However, before choosing a solution, you need to consider what to do with the portability of the tool. Is she really needed? There are 2 options for potential screwdriver modification:

• Tool with external power supply. In this case, a separate device is made. This is not so scary, because even a bulky structure can be placed in the immediate vicinity of the outlet. However, with the limitation associated with the length of the power supply cable and power cord, you will have to put up with.
• A screwdriver with a power supply unit mounted in place of the battery. This modification method will make it possible to avoid the assembly of the overall structure, which significantly limits the use of the tool. But in this case, the length of the network cable can also create an access problem. But compact devices can be used in this capacity. They can be purchased or existing power supplies, if they are suitable for the characteristics.

The methods of “reviving” a screwdriver are very different. Nevertheless, each of these options finds supporters, since it meets the different needs of owners of cordless tools, whose operation suddenly became impossible.

### Power supply from laptop adapter

A working charger for a laptop can become a power source for the instrument. In this case, the master will have a minimal rework. Any device designed for operation with a voltage of 12-19 V is suitable for it. The output current should be as close as possible to the required.

• Prepare the input cord from the adapter. The connector is removed with pliers, and the ends of the wire are stripped of insulation.
• Disassemble the screwdriver body, then the conductors, freed from insulation, are soldered to the tool terminals.

All connections are insulated, the wire is brought out. The body is assembled, then the screwdriver is checked for operability. In this case, the work does not promise any difficulties, so almost anyone can handle it.

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### Car charger

This is another popular option for converting a cordless screwdriver to an electric one. In this case, the work takes place almost analogously to the transformation of the computer unit, however, there are several nuances. The main difference is the ability to adjust the current and voltage, which makes the car battery charger a favorite among candidates.

• Purchase two multicore cables. They should be of the same cross-section, but for convenience it is better to find wires with different colors of the winding.
• On the one hand, they are stripped of insulation by 3 cm, on the other, crocodile clips are attached.
• The ends, freed from insulation, are bent, making a kind of hooks on them. They are attached (soldered) to the terminals with which the screwdriver was attached to the battery.

All connections are carefully insulated. Holes are drilled for the wires, then they are taken out. Crocodiles connect the screwdriver to the charger, strictly observing the polarity. This simple method allows you to get a power supply suitable for all models of the instrument due to the easy adjustment of parameters.

### Power supply of a screwdriver from a computer PSU

• First of all, the computer unit is disassembled, then the green conductor is disconnected from the board, which is responsible for turning on.
• Separate all wires except black and yellow. These wires are soldered to a cable, the other end of which is connected to a screwdriver.

After isolation, the block is assembled, making sure that the cord inside is located without twisting. If we talk about the shortcomings, then there is only one minus: the maximum possible voltage is 14 V, therefore the use of this method limits the characteristics of the screwdriver.

modern computer power supplies (ATX) are not suitable for this purpose, since they already require serious alterations. The possibility of switching them on is organized differently. a special circuit located on the computer motherboard. Such drastic changes are beyond the power of an ordinary user.

## Power supply for screwdriver

In order for the tool to be able to work from the mains, you need a unit that outputs from 12 to 18 (14, 16) volts. In this case, they are guided by the screwdriver model. The mains charger can be made from an existing battery case. In this case, its dimensions are first evaluated in order to understand whether the charge will fit inside. Small power supplies are more often placed in a screwdriver body.

• First, the battery is disassembled so that all the insides can be removed. If the body has been glued, then a knife is used for this, with which the seam is opened.
• Determine the current and voltage. Since the first parameter is often not indicated, the result is found independently. they divide the power by voltage (watts by volts).
• Solder the electrical wire to the contacts of the charger: brass surfaces must be treated with acid before the operation.
• Observing the polarity, the opposite ends of the wire are connected to the output of the battery. A hole for the cable is made in the battery case.
• The wire is fixed with electrical tape. There must be a plug at the other end to connect to the network.

There are several options for obtaining a power supply. The easiest way out is to buy a ready-made device. If you plan to make a homemade power supply unit, then in this case the circuit is the first thing that becomes necessary. To avoid mistakes, you need to accurately follow the sequence of connection of all elements, as well as make a list of the necessary mini-electrical appliances.

## Do you need rework?

To redo the screwdriver or not? Before starting work, you need to evaluate the advantages and disadvantages of this solution. If we talk about the former, then as a result the owner will achieve:

• disappearance of problems with a suddenly discharged instrument;
• lack of dependence on low temperatures, because under such conditions the batteries are discharged very quickly;
• obtaining a stable torque;
• significant savings, since buying a new, rather expensive battery will not be required.

In addition, this is the only remaining option if the model has already been discontinued, when the tool is urgently needed, and there is no time to wait for the arrival of a new battery. If the screwdriver itself works flawlessly, then there are no contraindications to its alteration. The only thing he will lose is mobility, but this disadvantage is still not so significant, you can cope with it.

## Charger from a computer power supply

Hello dear friends! Today I will show you how to convert a computer power supply into a car battery charger. For alteration, a power supply assembled on TL494 or KA7500 microcircuits is suitable. Unfortunately, other power supplies cannot be altered in this way.

Each power supply has overvoltage and short-circuit protection, which must be disabled.

To turn off the protection, you need to cut the track from Vref 5v, which fits to the 13th, 14th and 15th legs of the microcircuit. After that, the power supply will start automatically when plugged into the network.

Now let’s make the power supply adjustable. Remove two resistors R1 28.7 kΩ and R2 5.6 kΩ. In place of the resistor R1, we put a variable resistor of 100 kOhm. The voltage will be steplessly adjustable from 4 to 16 volts.

Scheme for converting a computer power supply into a charger

Complete diagram of the power supply on the TL494, KA7500 microcircuit.

Scheme for converting a computer power supply unit on a TL494, KA7500 microcircuit into a charger

It remains to connect the volt ammeter according to this scheme and the charger will be completely ready.

Wiring diagram for connecting a volt ammeter to a charger

And now I will tell you how the finished device works, so that you can really appreciate all the advantages of this homemade product. The voltage of this charger is infinitely adjustable from 4 to 16 volts.

This allows you to charge six and twelve volt batteries. With the built-in volt-ammeter, you can easily determine the voltage, charging current and the end of the battery charging process.

To test the power, I decided to plug in a super bright 12 volt 55 watt halogen lamp.

The lamp burns with full glow on a 12 volt voltmeter and a current strength of 8.5 amperes and this is not the limit.

How do I charge the battery? Red crocodile plus, black minus. If the polarity is reversed or shorted, nothing terrible will happen, just a ten ampere fuse will blow.

At the moment, the voltmeter shows the battery voltage. This knob must be turned to the left as far as it will go. I turn on the power and gradually raise the voltage to 14.5 volts. The initial current strength should be no more than 10% of the battery capacity. That is, for the 60th battery, the initial charge current will be no more than 6 amperes, for the 55th, respectively, 5.5 amperes. Etc.

As the battery charges, the amperage will gradually decrease, when the amperage drops to 150 milliamperes, this will mean that the battery is fully charged. Charging time for a fully discharged battery is approximately 24 hours.

Friends, I wish you good luck and good mood! See you in new articles!

## Power supply options

Any screwdriver requires much less voltage than a regular socket gives out. Therefore, for recharge, you will definitely need a special converter, at the output of which the required voltage will be obtained. All power supplies are divided into two large groups: pulse and transformer. Let’s consider each of them separately.

## Converting a screwdriver to mains power: 5 ways

The value of a screwdriver as a home or construction tool, most often, lies in its portability. However, due to certain circumstances, portability sometimes has to be abandoned in favor of functionality. It is about converting a cordless screwdriver into a mains-powered tool. This process has a number of subtleties that it is advisable to observe.

### Pulse

The principle of operation of pulse systems is that the voltage is first rectified and then converted into a special pulse signal. In this case, it is important to achieve a stable voltage. This can be helped by a transformer winding or resistors.

Switching power supplies are quite effective and can be used in a variety of conditions. At the same time, they have a high level of protection against short circuits and similar effects. However, in terms of power, impulse systems are clearly inferior to transformer ones. In addition, such units are very capricious to the input voltage. If it is lower than the set, then the element may simply not work.

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### Alteration of purchased blocks

It can also be powered from any other commercial power supplies. The alteration process in this case will be almost the same, however, in addition to the resistor, you may need to solder additional diodes. The most important thing is to achieve the required output parameters. And this can be easily done using a combination of components.

### Computer power supply

You can make a screwdriver from the network using an unnecessary power supply from a computer. There are many types of such devices, but almost all of them are suitable for a screwdriver. The required wires can be found by colors, making inquiries on the manufacturer’s website.

Power supplies from computers are distinguished by their durability, advanced overload protection and a host of other advantages. They may not be very convenient due to their size, but a long wire will help solve this problem.

The procedure for connecting the computer power supply to the screwdriver:

• disassemble the block;
• remove the protection against switching on by disconnecting the green wire from the board;
• this wire must be connected to the black connector on the device;
• separate all wires except yellow and black;
• these two wires are soldered to the extension cable;
• the second end of the cable is directly connected to the screwdriver;
• all open contacts are isolated if possible.

Thus, a power supply unit for a 14 volt screwdriver will turn out from a computer device.

### Alteration of the power supply unit made in China

Excellent for creating a power supply for a 12 volt screwdriver with your own hands, ordinary Chinese power supplies with an output voltage of 24 V and a current of 9 A. But since the tools use a lower voltage, you need to lower it first.

To achieve the goal, you need to replace the original resistor R10 with an adjustable resistor, with which you can achieve the desired voltage. This is done in several stages:

• a constant resistor is removed;
• in its place, a previously prepared adjustable resistor is inserted, on which a resistance of 2300 ohms will be set;
• so far, the voltage is still 24 V;
• using the resistor settings, you need to achieve the required voltage on the contacts.

After all the manipulations, you need to check that the output voltage is the required value (12 V, 14 V, etc.), and also that the current exceeds 9 A.

### We use laptop charging

An excellent option is to use laptop charging. Such devices usually operate with a voltage of 12 to 19 V. This is quite enough to ensure high-quality operation of the screwdriver. But do not neglect the output current indicators. The closer it is to the required, the better.

In this case, reworking a screwdriver for mains power is reduced to an elementary soldering of wires from the charger to the board in the tool. It is advisable to isolate everything with electrical tape or other similar materials. After that, the wire is brought out and the tool can be used.

## There is a way out. reworking the screwdriver in the network

Yes, it loses one of the benefits of a cordless tool. mobility. But for work in rooms with access to a 220 volt network, this is an excellent way out. Especially since you give new life to a broken instrument.

There are two concepts of how to make a network out of a cordless screwdriver:

### Using a power supply from a personal computer

On the radio market for a small cost, you can purchase an old power supply from a personal computer. We need a version of the “AT” format, which had to be turned off with the key after exiting the operating system.

Experienced users remember such system blocks. The advantage of such a power supply is also that it indicates an honest power. If it says 300W, it means you can safely remove 15-16 amperes from the 12-volt output (again referring to Ohm’s law). This is enough to power an average screwdriver.

Such blocks have a power button in the kit. Another advantage is the presence of a cooling fan and an advanced overload protection system.

If you will hide the power supply in a beautiful case, do not forget to leave a hole for ventilation.

The connection is very simple. Black wire (-), yellow wire (12V).

Limitations. a screwdriver with a supply voltage higher than 14 volts will not work.

### External power supply

The idea is not as absurd as it might seem. Even a large and heavy buck rectifier can just stand near the outlet.

You are equally tied to the power supply, and to the stuck mains plug. And the low-voltage cord can be made to any length.

IMPORTANT! Ohm’s law says. with the same power, decreasing the voltage. we increase the current strength! Accordingly, the 12-19 volt power cord should have a larger cross section than 220 volts.

## DIY screwdriver alteration

Consider the option with a remote power supply.

### Making a homemade power supply

If you are familiar with the principles of building electrical circuits, you can make your own power supply. Scheme giving general concepts. in the illustration.

The transformer can be picked up from an old tube TV, or other household appliances. Power for 220 volts 250-350W. The main thing is the power supply. the donor should not be pulsed.

The voltage on the secondary winding is 24-30 volts. The secondary winding is made from a wire of the corresponding section.

However, if the output winding current is at least 15 amperes (see transformer specification), there is nothing to worry about.

After losses on the diode bridge (1-1.5 V on the diode), you will get the required output value.

If you have an electrical engineering education, make the calculation yourself. Or in a practical way: by connecting a 220 volt 100W incandescent lamp as a load, measure the output voltage. E

If it exceeds the needs of the screwdriver, reduce the number of turns of the secondary winding of the transformer.

To do this, you need to purchase a ready-made block with suitable characteristics and dimensions. There is enough such good on the radio markets.

Take the body with you and go to the fitting. When the desired power source is purchased, carefully separate it from the case.

We place the screwdriver in the battery box. All components must be securely fastened.

If necessary, extend the wires connecting the control board and the transformer. If the circuit touches the metal parts of the transformer during operation, a short circuit will occur.

Since the space in the case allows. separate the board and the transformer for better cooling. Whichever quality power supply you choose, the load will be high and overheating is possible.

It will not be superfluous to fix additional radiators on the power control microcircuits. Operate the screwdriver for a long time, disconnect it from the mains and touch the radio parts on the control board.

You yourself will understand which elements need heat dissipation. Holes can be made in the housing for air circulation.

Redesigning the power supply unit with your own hands will not take much time, and the cost of the purchased module is incomparable with restoring the battery’s performance.

### Battery case power supply

Mobility is preserved, you are limited only by the length of the network cable. The only problem is how to squeeze a sufficiently powerful transformer into a small case.

We recall Ohm’s law again, and we understand that a powerful 220 volt electric motor can be compact.