How to power a cordless electric screwdriver from the mains

How to turn a cordless electric screwdriver into a mains one

There are two ways to make an adapter: Use an old battery pack, because it already has a connector that fits under the screwdriver, or connect the wires directly into the handle.

Connecting the old battery pack

Connecting the old unit is done as follows:

First, you’ll need to disassemble the battery pack by removing the screws as shown in the figure.

To take out used nickel-cadmium batteries.

Next, separate them from the connector pins.

Connecting the wires directly

To connect the wires directly to the screwdriver, proceed as follows:

To connect the wires directly, you must first disassemble the screwdriver, that is, unscrew the screws that fasten the two halves of the housing.

Consider the connections, find the plus and minus, remember the polarity of the connection. For convenience, it was decided to remove the bottom wide part of the handle.

Next, you need to connect the wires, this can be done with a soldering iron or good old duct tape.

And the final touch is to wrap the wires at the exit of the handle for extra security and insulation.

Want to know how to make a screwdriver directly from a charger?

Congratulations! Now that you have learned how to convert the screwdriver into a corded machine, you can apply this knowledge in practice

And it doesn’t matter if your screwdriver is charged or not. You don’t have to worry about how long the battery will last

Rebuild instructions

Let’s take a closer look, step by step, at how you can convert a cordless electric screwdriver to a mains powered one.

Disassemble the battery

In order to convert the tool to a corded tool that receives voltage from the native charger or computer power supply, you need to follow simple steps.

First disassemble the old battery pack. Remove the screws. It is important to keep all terminals.

Pull out the innards

Remove the batteries and carefully release the terminals. Then a wire with a cross section that can handle the operating current is soldered to these terminals. Select a wire with a cross section of at least 2.5 mm² and the length you need for comfortable use of the electric screwdriver. Remember which color wire you solder the minus and plus terminals to.

Connect the wires

Disassembling the computer power supply case. Remove the board and solder the wires on the power cable. To the wires coming out of the power supply, instead of the yellow and black wires, solder the wires with terminals from the battery. The black wire is the minus contact, the yellow one is the plus contact.

You can increase the power delivered by connecting black wire to black wire and yellow wire to yellow wire. This will improve the performance of the electric screwdriver because there will be less loss.

To start the computer power supply you must connect the green wire from the 20-pin connector to the black wire. This can be done directly on the PSU board. For convenience, you can connect a switch to the green and free black wire.

For ease of use you can solder a special connector to the wires, allowing them to disconnect. It is necessary to observe the polarity, otherwise you can damage the electric screwdriver. To do it you need to have a connector with a key (a special ledge on the housing, which prevents it from being connected incorrectly).

Put everything back together and connect the electric screwdriver to 220V

It is necessary to assemble a “modified” battery. Insert the terminals with wires and lead them out through the drilled hole. Inside the body of the former battery, it is recommended to put a capacitor with a capacity of 10000 uF at 16 V or 25 V and connect it to the terminals in parallel. Choose a voltage capacitor that is 1.5 or 2 times the nominal voltage of the tool.

Such a capacitor will compensate a large inrush current. If it is not placed inside the tool the probability of tripping of the power unit by the built-in safety device will increase considerably. It’s also recommended that a weight be placed inside the tool to balance it out. This will reduce the load on the hand while working.

Put the computer power supply together and connect the electric screwdriver to the 220 V mains. If the test shows that the tool does not have enough power, you can replace the low-voltage power cord.

Other ways to upgrade

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

  • Power adapter for the laptop.
  • Connecting a computer switching power supply (power supply).
  • Using a 12 V car battery.
  • Assembling a home-made power supply.

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

When using the switching power supply (power from 350W and above) for the PC (form factor AT) it is necessary to find the voltage of 12V on the connectors which supply the hard disk drive or CD-ROM drive. Take out the wires, and the rest neatly cut and insulate. 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 starting 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 energy. Nothing has changed when upgrading a model other than connecting a different battery. A big disadvantage is its weight. In addition, you need to assemble a battery charger or buy one in a specialized store.

Assembling your own PSU is the best solution for those who maintain the quality. The previous versions are good, but they do not allow for flexibility. For example, they are only applicable to 12 volt screwdrivers, not 18 volt. There are chargers designed for 19 V. Obtaining 18 V is achieved by connecting rechargeable batteries, for example, 12 and 6 V in series. Note that the characteristics of the batteries should differ only in terms of voltage. This is why it is often necessary to assemble a power supply yourself.

Schematics and their description

Option of assembling PSU by yourself should be made on the condition of 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.

The simple variant of 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 300W or more, voltage on the II winding must be in the range from 20 to 24V and the current more than 15A. For the diode bridge use powerful diodes, 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 the capacity of 2000 uF (you can limit the capacitance to 470) and voltage of 25V or higher. Parts should be selected afresh in terms of current and voltage. All radio elements are mounted on a gethinax board, which is attached to the housing.

power, cordless, electric, screwdriver

Universal power adapter

The suggested variant of the universal PSU has excellent characteristics and can carry a load current of up to 10A. The output voltage is 18 V, although you can do the math 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 the mains is off (Scheme 2).

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The adapter is assembled on a voltage regulator, consisting of a transistor VT3 and VD2-VD5 (Stabilizators). Power is switched on with the help of the tumbler SB1 and closes its contacts of the relay K1. Power goes to a transformer that converts alternating current to the required rating. The output current from the transformer goes to the rectifier. Then the rectified voltage goes to the stabilizer. There is a current amplifier in the scheme, assembled on the transistors VT1 and VT2. This amplifier is connected to the load. Battery charging mode (standby power supply) is realized through VD6 and limiter in the form of resistor R4. By means of SB2 it is possible to disconnect charging of the battery.

Scheme 2. Universal PSU for electric screwdriver and battery charging

In the absence of supply voltage of 220 V the relay is de-energized, and voltage from the battery is fed to other contacts of the relay (power directly from the battery). Fuses are used for short circuit current and overload protection. The system can be used without backup power supply. No additional adjustment required.

The list of parts is shown in the corresponding diagram 2, but you can also replace them with counterparts, for example:

  • VT1 and VT2 can be replaced with KT808 or KT819 with the same parameters. The transistors must be cooled and a heat sink is therefore mandatory. Transistors can be sealed with thermal paste to improve heat dissipation. Analogous to VT3 are KT815 or KT817. Any alpha indices are acceptable.
  • Transformer should be used with output power more than 150 W and with load voltage on the II winding of 14-16 V. Battery is standard 12V.
  • Relay K1 must be used AC voltage from 220V and current of 3A.
  • FU1 fuse for 3A, FU2 must be 10A.
  • The rectifier is used as ready-made (KTs405A, in extreme case. KTs407A) or assembled on the diodes D231 and D242 (any letter index). Diode VD6 can be replaced with analogous diode, referring to the reference book or the Internet.
  • Stabilitrons are desirable to leave the same: the output voltage parameters depend on them, although it is possible to connect them in series for the necessary U.
  • Capacitors can be replaced with any analogs according to the reference documents. Note the U in the circuit to which the capacitor is connected.
  • Resistors R2 and R3 (MLT-0,5), R1 and R4 (type ПЭВ-10 or ВЗР-10).

After assembling the device is assembled and adjusted to the appropriate form, the design is chosen by yourself.

12 V adapter

The adapter is assembled on the chip 7912 and is a linear regulator. The transistor increases the PSU power (circuit 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 12 V electric screwdriver

The secondary power supply is a transformer, the output of which is 16 V (for 12 V DC powered model) or 22 V (for 18 V powered electric screwdriver). Rectifier is assembled from common diodes with reverse voltage over 50V (it is possible to use readymade variants). The smoothing filter is a high capacitor with a capacity of about 10000 uF, but the higher this value, the better.

The microcircuit 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. A radio element 2N3055 is a p-n-p transistor and it can be replaced by any (you have to pick up an analog from the 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 of making printed circuit board by laser-utilization technology (LUT) on the Internet.

Adjustable modification

Regulated PSU is very convenient in use and is versatile. Thanks to the adjustable voltage values it is possible to power any equipment, use it to charge the battery. The basic element is an LM317 type chip. The amplification is done with two transistors like 2N3055, but you can use more powerful, because this increases the power of the PSU and allows you to get current up to 20A. The transistors are mounted on a heat sink, and it is desirable to apply in the design also a fan for cooling (cooler from a personal computer at 12 V).

    A double winding transformer for 15 volts and 10 amps.

  • Diodes D1-D4 (diode bridge): MR750 or other analog.
  • Fuse links for 1A and 10A. The second parameter 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 analogs): D5 (1N4148, 1N4448 or 1N4151), D6 (1N4001), D10 (1N5401), D7, D8 and D9 (1N4001).
  • Circuit: LM317.
  • Transistors: 2N3055.
  • Variable resistors: P1 (5k), P2 (47 or 230W), P3 (10k).

PSU for an electric screwdriver with their own hands

In order to perform the conversion of a cordless electric screwdriver into a network, you must first make a step-down transformer. It is made on the basis of the one used in TV sets of older models. When powering an electric screwdriver from an electronic transformer, the latter must be designed for a power equal to 160 W. In order to prepare one, which is necessary for a screwdriver, you need to do the following:

  • Prepared transformer must be disassembled.
  • The secondary winding has to be completely removed.
  • Wind ten turns on the transformer.
  • Now the transformer is ready, now we have to assemble it.
  • Next, you need to make measurements. It is now connected to the mains and the voltage measured on the secondary winding. Now divide the number of turns, which in this case is ten, by the voltage now measured. Multiply this value by the voltage required by the tool, and you get the number of turns you need.
  • Now disconnect the transformer from the network, take it apart again and wind the required number of turns. Then it needs to be assembled.

For winding a wire, the cross section of which is equal to 1 sq. mm.

After the current has passed through the transformer, the output will be an alternating voltage. The circuit of the power supply for an electric screwdriver provides that in order to get the DC from it, it will be necessary to make a diode bridge. It is made using diodes on heat sinks designed for 20V and 10A.

The transducer made in this way is placed in a housing. Its output will produce the voltage that is necessary to operate the screwdriver. The input will be 220 V mains voltage.

Wires coming from PSU are connected to pins, through which the tool is powered.

Such a power supply for an electric mains-powered screwdriver is usually mounted in the housing where the battery cell used to be.

How to convert a cordless screwdriver to 220 volt power

Craftsmen have come up with several ways to convert the screwdriver to run on mains power. They are all about providing the motor with the required voltage by means of an intermediate power supply or converter.

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Table: Power supply options for mains screwdriver

  • An uncomplicated conversion.
  • Uses your existing battery charger.
  • No need to adjust the voltage of the power supply.
  • No need for any intervention in the electric circuitry of the screwdriver.
  • An uncomplicated conversion.
  • Nice engineering. only the power cord comes out of the screwdriver.
  • no cable losses in the low-voltage cable.
  • No need to interfere with the electric circuitry of the screwdriver.
  • Find a ready-made compact power supply for the voltage you need.
  • Power supply gets warm in the closed box, you need to take breaks in work.
  • Beautiful engineering. only the power cord comes out of the screwdriver.
  • No loss in low-voltage cable.
  • No need to tamper with the electric circuitry of the screwdriver.
  • You have to pick up the circuit and find the radio components.
  • Master must have experience in soldering, assembling and debugging electrical circuits.
  • Requires disassembly of the screwdriver and connection to its circuitry.
  • Power supply takes up space on the table.
  • You need to find the right power supply.
  • Simple remodeling.
  • Computer power supply easy to find.
  • Any power supply of 300 W or more will do.
  • You have to disassemble the screwdriver and connect to its circuitry.
  • Power supply takes up a lot of space on your desk.

Household or professional

Professional screwdrivers are known to be more expensive, but this is not a coincidence. They are made with a large margin of safety, for which higher quality and more expensive materials are used. In addition, they have more power, which makes it possible to screw in longer screws and/or work with tougher materials.

The difference between a professional and domestic electric screwdriver in life

To decide whether you need a domestic or professional electric screwdriver, estimate the amount of work you will need to perform. If you are starting a 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 domestic more than enough. With this kind of work, the resource of the pro tool simply won’t be in demand. So it is not very difficult to choose an electric screwdriver by this criterion.

Types of battery cells

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

These devices use cells of different types and voltages, each of which has its own advantages and disadvantages.

The most common are 1.2V nickel-cadmium (Ni. Cd).

The more advanced 1.2V nickel-metal hydride (Ni-MH).

The most advanced lithium-ion (Li-Ion) 3.6V.

  • no memory effect;
  • Very low self-discharge current;
  • high specific capacity, which allows you to reduce the weight and size of the device;
  • many times higher number of charge/discharge cycles than other types of accumulators.

Device design

The screwdriver consists of several basic elements:

  • Cylindrical electric motor powered by current. There are permanent magnets inside the body, which allow the design to gain sufficient torque. They are also handy when repairs are needed. The motor shaft contains a planetary reduction gear.
  • Torque limiter. Necessary to limit the gain when working with a screwdriver. Transmits torque through hinges pressed by an internal spring.
  • Planetary Gearbox. Named after the solar system, which is similar in assembly. Located in a separate housing and consisting of several gears and other parts. Acts as a force on the load controller. Operates harder in drill mode.
  • Speed regulator with reversing function. It is activated by reversing the polarity of the connection.
  • The battery of the device. Represents several separate nutrients in a single sheath. The voltage varies from 9 to 25V.

Device in disassembled condition Source stroy-podskazka.When the battery pack malfunctions, there are options for replacement or repair. It is usually expensive to change such batteries, because in a cheap device, the replacement will be about equal to the full cost of the screwdriver. Repair is not always possible, in addition, as in the first option, its cost will be close to the full price of the device. But there is also a third option, such as converting the screwdriver to mains operation, which will allow you to use the tool further without much cost or effort.

Tips for Using an Electric Screwdriver

When the 12-18 volt power supply is assembled, the electric screwdriver becomes a mains. It should be used according to the rules:

  • Every 20 minutes of operation, take a break for 3-5 minutes to allow the block element to cool down;
  • If operating an external unit, keep it clean. It should not be dusty, dirty. This way the unit will heat up faster and work less efficiently;
  • Renewed tool is forbidden to use at a height of more than 200 centimeters;
  • equip the element with a protective disconnection device. If there are problems with the network RCD will save the equipment from breakdown;
  • All wires must be reliably soldered.

Device mobility

When converting battery-powered equipment to mains power, one of its main distinctive properties is lost. mobility. Therefore, if you decide to make a power conversion of a 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:

  • The power supply (PSU) will be external. This version of the design provides for 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. According to Ohm’s law, 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 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 it is necessary to install a transformer of high power in the battery housing of the screwdriver. But the modern radio industry allows us 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 on how to convert the screwdriver to work from the mains. The task is to power the electric motor of the device with an intermediate source.

Using the laptop charger

To make a 12 V power supply for a screwdriver with your own hands is possible, even without technical knowledge. You only need to find an unnecessary charger from a laptop, which has specifications similar to those for powering the 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.
  • We cut off the output plug, expose and tin the ends of the wires.
  • Strip wires and solder to the battery input wires.
  • Insulate the soldering points to avoid short circuits.
  • Make a hole in the box so that the wire is not compressed, and assemble the construction.

The basis. a power supply from a computer

To make such a device you will need a block from a personal computer of format A. Т. It’s not hard to find, this is an old model of the power supply, which is easy to buy at any market for radio components. It is important to know that you can use a 300-350 W unit with a current of 12 V at least 16 A.

It is the AT format blocks meet these parameters. On the body of this device there is a power button, which is very convenient for work. There is a cooling fan inside and an overload protection circuit.

The order of rewiring the unit:

  • Remove 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 big square connector.
  • Connect this wire to the black wire in 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 case.
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Then we find the smaller connector (MOLEX) in the output bundle and do the following operations with it:

  • We leave the black and yellow wire and cut the other two short.
  • For convenient PSU positioning during work, 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. It should be done by soldering, you can make a good twist, and it is necessary to observe strictly the polarity.
  • Make a hole in the housing, so as not to squeeze the wire during assembly. The device is ready.

If you have the desire to refine your design, i.e. е. If you want to put it in a different 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 modification you only need to connect the power terminals of the battery charger output to the power supply of the electric motor.

If you have a battery charger with continuously variable output voltage, you can use it as an 18 volt power supply for a screwdriver.

Safety precautions

After converting the appliance to mains power, safety and operating rules must be followed:

  • Observe breaks every 30 minutes to extend the life of the unit and avoid malfunctions.
  • It is not recommended to work higher than two meters.
  • It is important to periodically clean the power supply of the device from dust.
  • Check the condition of the power cord. It should not be pinched or subject to moisture and other negative factors. Ignoring this rule can lead to a short circuit of the device.

Following these simple guidelines will allow an old screwdriver to last longer than a new one, while still retaining its power and ease of use.

Preventive maintenance

Batteries are made of several elements stacked together, which do not malfunction all at once, but piecemeal. To identify the broken part of the battery, fully charge it and let it run at full capacity before discharging. After that, disassemble and measure the voltage of each individual element. The parts where the voltage will be missing or inferior to other elements must be completely replaced. Repair is done with a soldering tool. All of the battery cells are soldered together with the same wire strip that was used to connect the parts originally.

The following video shows the step-by-step process of repairing the appliance:

Electric screwdriver powered from 220 V mains

I have finally started to implement my long-time idea, namely, to provide power for an electric screwdriver from 220 volts. No doubt some of you also have a screwdriver, with a worn out, unusable battery that no longer takes a charge. In my location, there were two instances of.

The first (black) has a working voltage of 18 volts. It was him that I originally wanted to power from the mains, t.к. Comfortable in the hand and quite powerful. But there is no button. Perhaps in the future I will cut off the handle and make it like a drill. The second one was made for 12 volt. Served for quite a long time. The battery can, of course, be purchased new or, as a last resort, replaced by a bank. But all the same I want to have always a ready tool at hand, especially that an electric drill is not always convenient to use.к. it is heavy. The power transformer will help us to realize this idea.

We used a step-down transformer TS-250-36. “250”. This is its rated power and the number 36 means that the output voltage will be 36V. It has an O-shaped magnetic core. The windings are arranged so that half of the primary is wound on the left side and the other half on the right. Similarly wound the secondary winding, which is located on top of the primary. It is not difficult to distinguish the windings of a step-down transformer from each other, t.к. The secondary is made of a thicker wire, and the one to which the mains voltage is applied is made of a thinner wire. That’s because it carries less current.

The windings have a symmetrical arrangement and the two 18 volt halves are connected with a wire (the connection point is clearly visible in the bottom photo). I’m going to use one half.

But before I rewound the transformer I have to measure. I urge you to be careful when dealing with current, not to touch live parts, and always check if the multimeter has the right measurement limit.

On the right you measure the voltage at half of the secondary. As you can see, the voltage is a little higher than the rating, i.e.к. Here no load is connected.

So I removed one half and now let’s disassemble the transformer. Between the layers of paper there was a large amount of paraffin.

The secondary winding in my case is wound in two layers, separated by a layer of paper. To reduce the secondary voltage from 18 volts I had to remove almost half of the turns.

When determining the required voltage, you must take into account that after the transformer will be a diode bridge, which will reduce the voltage by about a couple of volts. But adding a smoothing capacitor will increase the voltage by about 1.4 times. Т.е. with no load, the rectified voltage on the capacitor will be equal to the amplitude value.

As we unwind the secondary, we measure. Soon, I settled on a value of 11.2 volts, t.к. I was afraid of a drawdown when connecting the load.

When the transformer is prepared (although some may use a ready made one with the right parameters), now it’s time to get to know the circuit.

A diode bridge (VDS) must be soldered to the output of the transformer to convert the AC current into a DC pulsating. The diode bridge can be assembled from separate diodes or you can use a ready-made. In its selection should take into account how many amps consumes your electric screwdriver (the bridge to pick up with a reserve).

Wires from the secondary winding solder to the diode bridge leads, where the letters AC (alternating current).

Well, after the bridge you need to solder a capacitor to smooth out the ripple. Its voltage should be at least twice as high as the voltage of the electric screwdriver. And capacity from 470 uF to 2200 uF.

If you want, you can add a switch and fuse in the circuit before the transformer.

So after connecting the circuit I measured. Idle voltage at the output of the power supply (when the load is not connected) is 15 volts. When you start the electric screwdriver, it sags to 11.5 volts, which is the norm, so it’s not a big deal. Fully charged new battery gave 13 volts.

This is what the tool looks like from the inside. Here you can find the limit of the pushbutton and you can see that the motor is controlled by a high powered transistor.

To be able to connect to the power supply, I disassembled the battery. From it we need the contacts. This part needs to be tinned. I did solder with rosin, but in some cases you may need flux for soldering aluminum.

Of course when soldering the wires from the power supply do not forget about polarity, usually it is specified on the body of the battery. The compartment is now very light. The wire was sealed with thermal adhesive.

The tests showed that the electric screwdriver performed well when operated from the power supply.

This article has a video that shows in detail the process of building the power supply, rewinding the transformer, wiring and test.