12v power supply for an electric screwdriver with their own hands

Power supply for an electric screwdriver 12-18c. how to make their own hands?

The weakest place in household screwdrivers is the battery. Like any galvanic element, it has its own service life. Electric screwdriver battery lasts on average 3-4 years and then has to be discarded. By the way, claims that with proper care and maintenance it will last 10 years are clearly exaggerated.

How to give a screwdriver a second life if the battery fails?

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Easy tool repair

The main advantage of a cordless electric screwdriver is its mobility. Used in these tools is a lithium-ion battery, which is protected from overload and complete discharge. There is also protection against overcharging in the form of a separate circuit built into the cell itself. The main source of power (primary) is 220 V, and recharging of the battery is also performed.

Depending on the model of an electric screwdriver, the battery receives charging voltage of 14 V to 21 V. The output of the battery produces a supply voltage of 12 to 18 V. this type of battery lasts a long time, but if you do not use it for a long time, the built-in battery discharge protection does not help either: the discharge is permanent.

You need to constantly discharge and charge the battery to extend its life. If for some reason it is not possible to “keep track” of the tool, a particular battery cell often fails. There are basic ways to solve this problem:

When replacing the battery, you must consider that a new one is quite difficult to find. Tools are made so that it is difficult to find parts for them. It is not profitable for the firm to produce their product with a high repairability, because they need the income from the purchase of the product. It is only possible to find a new battery from dealers. It is also possible to disassemble the battery and change the defective cell.

When buying a new tool, the user tends to buy a higher quality model, forgetting about the rules for using lithium-ion batteries. The main rules which will help to keep the life of the tool for a long time:

• It is strictly forbidden to “start” the tool at once when you buy it in winter. You need to wait about an hour until it “warms up” to room temperature.
• Putting the battery on charge.
• The cycle of charging and discharging the battery perform about 3 times.

If none of the options for solving the problem is not suitable, you need to proceed to the redesign of the electric screwdriver on the mains with your own hands. It is easy to do. There are many simple and complicated ways to. Changing the model of the tool has several positive aspects:

• No need to recharge the battery.
• Reduces the load on the mechanical part.
• Many options for power supply units.
• Increased quality characteristics of the product.

In addition, mobility can be maintained by converting the charger in the block version to charge almost any battery.

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Other ways to upgrade

Radio amateurs offer many options for upgrading the tool. Some of them are very simple and are reduced to the use of ready-made power supplies, while others require knowledge in electrical engineering and give the device versatility. Classification of methods:

• Laptop power adapter.
• Connecting a computer switching power supply (power supply unit).
• Using a 12-volt car battery.
• Assembling a homemade power supply.

Using a laptop charger is the best solution to the problem. In addition, it is necessary to know the parameters of an electric screwdriver and charger (there are 12 V and 19 V), as well as to take into account the size of the latter (for installation in the battery compartment). You need to solder the output of the laptop power adapter, to the terminals to which the battery is connected.

When using a switching power supply (power from 350 watts and above) for a personal computer (form factor AT) it is necessary to find the voltage of 12V on the connectors which are feeding a hard drive or CD-ROM drive. Take the wires out and neatly cut and insulate the rest. You can assemble the case for the PSU, which will allow you to get current up to 16A. In addition, it is necessary to remove the startup protection. To do this, you need to connect the green wire with the black wire from this connector. These two methods are very simple and need no further description.

The car battery is the best source of electrical power. Nothing has changed when you upgrade the model except for connecting a different battery. A significant disadvantage is its weight. In addition, you need to build a battery charger or buy it in a specialized store.

Building your own PSU is the best solution for those who maintain quality. The previous options are good, but do not allow for application flexibility. For example, they apply only to screwdrivers with a voltage of 12 V, not 18 V. There are chargers, designed for voltage of 19 V. To get 18 volts is achieved by connecting rechargeable batteries, for example, 12 and 6 volts in series. It should be noted that the characteristics of the batteries should differ only in terms of voltage. That’s why it is often necessary to assemble the power supply yourself.

Schemes and their description

Option of assembling PSU by yourself should be made with the knowledge in the field of radio engineering. In addition, before assembling you need to think carefully about everything, find a case for mounting and the appropriate radio elements.

A simple version of a PSU

A simple circuit 1 PSU (electric screwdriver from 220 volts), consisting of a power transformer (diode bridge input), rectifier and capacitor filter.

Diagram 1. Power Supply for an 18 V Electric Screwdriver

Transformer must be chosen with power of 300W or more, the voltage on the II winding must be in the range of 20 to 24V and current over 15A. For the diode bridge powerful diodes must be used, matched to the current of the secondary winding. It is more difficult to find the right power supply for an electric screwdriver. At the output of the rectifier you must put a capacitor with a capacity of 2000 uF (you can limit the capacity to 470 uF) and voltage of 25 V or higher. Parts must be selected with extra capacity in terms of current and voltage. All radio elements are mounted on a gethinax board, which is fixed in the case.

Universal power adapter

The suggested variant of universal PSU has excellent characteristics and can withstand up to 10A load current. The output voltage is 18 V, although you can make calculations and make a power supply for an electric screwdriver 12 V. This PSU can be used as a battery charger (battery charger) and as a backup power supply when mains power is off (Scheme 2).

The adapter is assembled on the voltage regulator, consisting of transistor VT3 and VD2-VD5 (Stabilizators). Power is switched on with the help of the tumbler SB1 and closes its contacts of relay K1. Power is supplied to the transformer which transforms the alternating current to the desired rating. The output current from the transformer flows to the rectifier. Then the rectified voltage is fed to the regulator. There is also a current amplifier in the circuit, assembled on transistors VT1 and VT2. The load is connected to this amplifier. Battery charging mode (reserve power supply) is realized through VD6 and limiter in the form of resistor R4. With the help of SB2 you can turn off the charging of the battery.

Scheme 2. Universal power supply for electric screwdriver and battery charging

When there is no supply voltage of 220 V, the relay is de-energized, and the voltage from the battery is fed to the other relay contacts (power directly from the battery). Fuses are used for short circuit current and overload protection. Such system can be used without backup power supply. No further adjustment is necessary.

The list of radio components is shown in the corresponding schematic 2, however substitutes with analogs are possible, for example:

• VT1 and VT2 can be replaced with KT808 or KT819 with the same parameters. Transistors need to be cooled, and therefore a heat sink is a must. The transistors can be sealed with thermal paste to improve heat dissipation. Analogues for VT3 are KT815 or KT817. Any alpha indices are acceptable.
• Transformer should be used with more than 150W output power and 14-16V load voltage on II winding. The battery is standard 12V.
• Relay K1 must be used with AC voltage from 220V and current of 3A.
• FU1 fuse must be 3A, FU2 must be 10A.
• The rectifier is used as ready-made rectifier (KTs405A, in extreme case. KTs407A) or assembled on the diodes D231 and D242 (any letter index). The diode VD6 can be replaced with a similar one, guided by the reference book or the Internet.
• Stabilitrons are desirable to leave the same ones: they determine the output voltage parameters, though serial connection for the necessary U value is also possible.
• The capacitors can be replaced with any analogs according to the reference documents. The U in the circuit to which the capacitor is connected must be considered.
• Resistors R2 and R3 (MLT-0,5), R1 and R4 (type ПЭВ-10 or ВЗР-10).

After assembling the device is assembled and brought to an appropriate appearance, the design is chosen by oneself.

12 V power adapter

The adapter is assembled on the microcircuit 7912 and represents a linear regulator. A transistor increases the power of the PSU (Diagram 3). This home-made device can also power an electric screwdriver for 18 V, for which you need to calculate the transformer.

Scheme 3. Power supply for electric screwdriver 12 V

The secondary power supply is a transformer with an output of 16 V (for 12 V DC powered models) or 22 V (for 18 V powered electric screwdrivers). The rectifier is assembled from common diodes with a reverse voltage over 50V (you can use readymade alternatives). The smoothing filter is a high capacity capacitor of about 10000 uF, but the higher this value is, the better.

The chip must be purchased at a specialized hardware store. In addition the circuit uses LED’s that allow to make diagnostics in case of PSU failure. The 2N3055 is a p-n-p transistor and it can be replaced with any (similar device should be chosen from reference books with a voltage of about 50 V and current of more than 5 A). It is possible to use LUT to make the circuit board. There is a detailed description on the Internet about how to make a printed circuit board using laser cutting technology (LUT).

Adjustable modification

Regulated PSU is very convenient in use and universal. Thanks to the adjustable voltage values, you can power any technique, use it to charge the battery. The main element is a chip of LM317 type. The amplification is done with the help of two transistors, type 2N3055, but you can use a more powerful, because it increases the power of the PSU and allows you to get current up to 20A. The transistors are mounted on a radiator, and it is desirable to apply in the design is also a fan for cooling (cooler from a PC at 12 V).

Two-winding transformer with 15V and 10A current.
• Diodes D1-D4 (diode bridge): MR750 or equivalent.
• 1 A and 10 A fuse links. The second value is chosen according to the real load (current consumption).
• Resistors: R1 (2.2k for 2.5w), R2 (240), R3 and R4 (0.1 for 10w), R7 (6.8k), R8 (10k), R9 (47 for 0.5w), R10 (8.2k).
• Capacitors: C1, C7 and C9 (47n), C11 (22n), C2 (4700µ at 50V), C3 and C5 (10µ at 50V), C4 and C6 (100n), C8 (330µ at 50V), C10 (1µ at 25V).
• Diodes (you can use analogues): D5 (1N4148, 1N4448 or 1N4151), D6 (1N4001), D10 (1N5401), D7, D8 and D9 (1N4001).
• Circuit: LM317.
• Transistors: 2N3055.
• Variable resistance: P1 (5k), P2 (47 or 230 W), P3 (10k).

The electric screwdriver battery design

Electric screwdriver conversion to lithium 18650 batteries

Battery design is brand-independent. In all devices, the battery design is similar and differs in appearance, housing and contacts.

Battery construction

The battery case contains several cells connected in series. Their number depends on the voltage of each cell and the battery as a whole. Using the most common, nickel-cadmium cells with a voltage of 1.2 volts, to supply a device rated 12 volts you need 10. The capacity of the battery is specified in ampere hours.

Interesting. When connected in series the output voltage increases, but the capacity does not change and is equal to the capacity of the individual cells.

Household or professional

As you know, professional screwdrivers have a higher price, but this is no accident. They are made with more durability, for which better and more expensive materials are used. They also have more power, which makes it possible to screw in longer screws and/or work on tougher materials.

The difference between a professional and a professional electric screwdriver is in the life span

To decide whether you need a domestic or professional electric screwdriver, assess the amount of work that will need to be done. If you start construction or major repairs, you probably need a professional or semi-professional model. If the tool will be needed periodically. to unscrew/screw something from time to time, a household tool is more than enough. In such work, the resource of a pro tool will simply not be in demand. So it is not very difficult to choose an electric screwdriver according to this criterion.

Conversion from a computer power supply

Standard power supplies AT is suitable for the conversion. The average output voltage is 14 V, and the average power is less than 400 W. These values are ideal for a 14-volt power supply for an electric screwdriver. Can be adapted from an old computer. Computer PSU comes with a built-in fuse, cooler. The main disadvantage is the size of the component PC.

ATX standard computer power supplies are not suitable. They are arranged more complicated and creation from them of the power supply for an electric screwdriver requires thorough knowledge of electronics. PSUs of the ATX standard require fundamental intervention in the design, so they can be built into an electric screwdriver. To remake a power supply of the AT standard should:

• Disassemble the computer system unit.
• Disconnect the power supply, for which the green wire is responsible.
• Unsolder black and green wire.
• Connect the black wire to the black wire and the green wire to the yellow wire.
• Solder one end of the green wire to the black wire socket.
• Connect the other end of the green wire to the contacts of the power supply of an electric screwdriver.

If your computer power supply has a red wire, then unsolder that wire. This is needed to monitor the load on the 5V rail. Next, check the voltage of the incoming current. If there is a value of 14 volts, the reworked power supply unit is assembled. After that the black and yellow wire is connected. The electric screwdriver will be connected to it. When soldering it is important to observe the polarity. The black wire to “-” and the yellow wire to “-“.

It is important to make sure that the power cord and wires are not twisted during rewiring.

How to make an 18V power supply instead of a battery

Power supplies for an electric screwdriver for 18 volts is not easy to make with their own hands from improvised means and old electrical appliances. For example, the option to convert from a car battery to 12V, the computer PSU is not suitable. Professionals in radio engineering suggest assembling the unit by yourself.

Consider the dimensions of the charger so that it can be mounted in the battery compartment of the electric screwdriver. Also before remaking you should compare the input power parameters of the charger and the power supply. At a lack of voltage the electric screwdriver will not work with the necessary efficiency, and at overvoltage. overvoltage and failure of elements of the electric circuit will occur.

To put the power supply for a cordless electric screwdriver for 18V instead of the battery in the case should:

• Unscrew the battery cover.
• Clean the case of all parts.
• Remove the printed circuit board from the power supply of an electric screwdriver.
• Install the board in the case in which the battery was located.
• Solder the wires at the output according to the pins.
• Drill a hole that is designed for the input wires in the housing.

A collapsible mains transformer will do. The power of the part should not exceed 250 watts, otherwise the construction will not work. You should disassemble the transformer, wind the secondary windings except for the mains. Then the wire is wound onto 1 secondary winding and the desired number of turns is obtained, producing the appropriate voltage and amperage.

You will also need a non-polar paper capacitor. Approximate capacity = 1 uF, and the voltage. not exceeding 400 volts (optional). As diodes, any rectifier models that carry 10-20 amps of current will do. The minimum voltage in the return path must be at least 30 volts.

How to make a power supply for 18V instead of the battery

Power supplies for an electric screwdriver for 18 volts is not easy to make with their own hands from improvised means and old electrical appliances. For example, the option to convert from a car battery to 12V, computer PSU is not suitable. Professionals in radio engineering suggest assembling the unit yourself.

Consider the dimensions of the battery charger so that it can be mounted in the battery compartment of the electric screwdriver. Also before remaking you need to compare the input power parameters of the battery charger and the power supply. If there is a lack of voltage, the electric screwdriver will not work with the necessary efficiency, and if there is too much. overvoltage and failure of elements of the electric circuit will occur.

To put the power supply for a cordless electric screwdriver for 18V instead of the battery in the case should:

• Unscrew the battery cover.
• Clean the case of all parts.
• Remove the circuit board from the power supply of the electric screwdriver.
• Place the board in the case that contained the battery.
• Solder the wires at the output according to the pins.
• Drill a hole that is designed for the input wires in the housing.

A collapsible line transformer is fine. The power of the part must not exceed 250 W, otherwise the construction will not work. You should disassemble the transformer, wind the secondary windings except for the mains. Then a wire is wound onto 1 secondary winding and the desired number of turns is obtained, producing the appropriate voltage and amperage.

You also need a non-polar paper capacitor. Approximate capacitance = 1 uF, and a voltage not to exceed 400 volts (optional). Any rectifier model with 10-20 Amps of current will work as a diode. The minimum voltage on the return path must be at least 30 volts.

Impulse power supply for an electric screwdriver

In pulse units, the input voltage is converted into high-frequency pulses after passing through a rectifier. The schematics for self-assembly of the device is enough. You need to have knowledge in radio engineering and electronics to create.

The circuit of the switched-mode power supply for a cordless electric screwdriver is a bridge-type rectifier. In the diagram below there are field analog transistors instead of diodes. It monitors the operation of the transistors and compares the voltage at the capacitor and the transformer output. As current flows through the transistor diodes, the rectifier begins to work. This occurs at startup when the rectifier capacitor receives a voltage of about 5 volts.

A thermostat can be built into the circuit. It is for emergency shutdown in case of overheating. The thermostat is optional, but it protects the ballast resistor.

When the capacitor receives 10 volts current the comparator in D1 will start. The relay contacts are connected by shunts to bypass the ballast resistor. The voltage is supplied from the triac in the T1 cell, which is opened by the comparator when the capacitor is charging. LEDs are built into the circuit, indicating the functionality of the charger.

This switched mode PSU is for 18 volts, but the voltage is adjustable. For this you need to make more or fewer turns of the transformer.

The sequence of operations when assembling the switching-mode power supply circuit:

• Put a thermistor on the input and mount a diode bridge.
• Solder the transistors.
• Solder the capacitors.
• Install diodes on the output.

Field-effect transistors are synchronized by installing drivers. Do not short-circuit the flanges of the transistors. They are fastened by means of insulation washers.

Impulse power supply for an electric screwdriver

In pulse units, the input voltage is converted into high-frequency pulses after passing through a rectifier. There are enough circuit diagrams to assemble your own device. You need to have knowledge of radio engineering and electronics to build it.

Schematic diagram of a switching power supply for a cordless electric screwdriver. bridge-type rectifier. In the figure below instead of diodes there are field analog transistors. The comparator is used to track the operation of the transistors and to compare the capacitor voltage and the transformer output. As current flows through the transistor diodes, the rectifier begins to work. This occurs at startup when the rectifier capacitor receives a voltage of about 5 volts.

A thermostat can be built into the circuit. It is needed for emergency shutdown of the device in case of overheating. A thermostat is optional, but it protects the ballast resistor.

When the capacitor receives a voltage of 10 volts, the comparator in D1 will start. The relay contacts are connected by shunts to bypass the ballast resistor. The voltage is applied from the triac in cell T1, which is opened by the comparator when the capacitor is charging. LED’s are built into the circuit, indicating that the charger is working.

This pulse PSU is designed for 18 volts, but the voltage is adjustable. To do this, make more or fewer turns of the transformer.

The sequence of operations when assembling the switching-mode power supply circuit:

• Put a thermistor at the input and mount a diode bridge.
• Solder the transistors.
• Solder the capacitors.
• Install diodes on the output.

Field effect transistors are synchronized by installing drivers. Do not short-circuit the flanges of the transistors. Mounted with washers for insulation.

Power supply operating rules

The case in which you build the power supply must have ventilation holes so that overheating does not occur. Also if there is no cooling system, you need to put a fan.

To make your homemade power supply for an electric screwdriver work long, you should let it cool down every 30-40 minutes of work. It is necessary to monitor the temperature of the housing, the condition of the cable, and periodically check the contacts in the circuitry if you suspect. Improper soldering or incorrect polarities can cause circuit failure or short circuits.

The origin of the parts should not be neglected when redesigning a homemade device. They must be matched to the input power, voltage, current flow and resistance. Diode bridges and transformers. the basis for the entire circuit, their selection affects the performance of the PSU of an electric screwdriver.

Power supply for an electric screwdriver

In order to your own hands to power an electric screwdriver from a household electrical outlet, you will need a failed battery, battery charger, laminated wire, electrical tape, solder, soldering iron and acid. The first step is to solder the plug wire to the pins of the charger. Since the unit uses brass terminals and the wire has copper conductors, in order to solder them, you should use acid as a connector. The quality of this connection directly affects the functioning of the entire device. In the second step, work is carried out with the defective battery of the tool. It is necessary to disassemble the battery and remove the internal parts from it. During this operation it is necessary to use personal protective equipment, and it is recommended not to throw the inner filling into the household garbage, but to dispose of in a safe place for people. In the final step, it is necessary to solder the wires of the charger with the battery terminals, which are located in the inner part of the housing.

When homemade power supply for an electric screwdriver, it is necessary to carefully observe the safety precautions when working with electricity. Before you start, you need to carefully weigh the pros and cons (how much time it will take, what the cost of materials and spare parts will be), sometimes it will be easier and cheaper to take the charger to a specialized workshop or buy a new unit.

How to make a power supply for a 12 volt electric screwdriver

It is not difficult to create a 12-volt PSU, because fewer parts are used inside the circuit. You can not re-solder resistors, transformers.

Replace the battery with the assembled PSU

A suitable way is to put the voltage rectifier from another device into the battery case or connect them. In this way, the electric screwdriver becomes a mains powered screwdriver.

The following instructions must be followed to perform the conversion:

• Unscrew the 4 screws on the battery cover.
• Remove all the radio components from the case.
• Remove the PCB from the PSU of another device. It must match the power, voltage.
• Put the board in the battery case.
• Solder the wires.
• Drill a hole to be used for the input wires in the case.

Screw the cover in place. The PSU can be powered by a 220V mains supply, the voltage when charging will depend on the model of voltage rectifier.

Conversion from a transformer with rectifier

The toroidal core transformer is most effective for the power supply of an electric screwdriver. Such a transformer retains a specific power, while maintaining a small size and simple design.

Toroidal transformer

The complexity of the redesign lies in the coils, it is important to match the voltage with the number of turns. One coil equals 2 volts, provided that the wire diameter of the transformer is 4 mm.

The different layers of coils must be insulated from each other. To make a rectifier for a cordless electric screwdriver with your own hands from a transformer, you need to have a basic knowledge of radio engineering and instrumentation.

You can make a transformer from a defective or unwanted apparatus, like an old tube TV. The second winding must have a voltage in the region of 24-30 volts, it is necessary to exceed the battery input voltage by 4-5 volts. If the parameters of the input voltage fit the standards for creating a power supply for a cordless electric screwdriver for 12 volts with his hands, then you can start soldering rectifier bridge.

It is important the quality and origin of the transformer itself. It determines 90% of the success, the first encountered or broken transformer ring is not suitable.

Example of a poor-quality transformer It is correct to take transformers from computer power supplies, TVs. The transformer ferrite ring should have a capacity in the region of 200-250 W. powerful battery rings have dimensions that may interfere with the mounting of the assembled PSU in the case. The electrical circuit should be protected against short circuits during assembly with fuses and transformer winding.

Precautions

There are a few precautions you should familiarize yourself with before using a cordless power tool:

• Store the device at a temperature not below 0 degrees;
• Do not let any liquid get on the battery;
• charge the battery only at a temperature of 10-50 degrees Celsius;
• Do not charge a damaged battery.

Quite often the owners of cordless screwdrivers are faced with situations where the battery stops working. In such cases, it will be necessary to connect the device to the mains. However, before this, it is necessary to know how to transfer an electric screwdriver to 220V power and what to do for this purpose.

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