How to replace the battery for a 14v screwdriver


Chinese screwdrivers are notable for their low price and bad batteries, which become unusable after the first year of operation. Buying a new battery does not make sense, so the question arises of mains power. This power supply consists of accessible parts and fits completely in the battery case.

How to replace the battery for a 14v screwdriver

It is based on a board from an energy-saving lamp, a pulse transformer and an output choke from a computer power supply. I had two identical boards from 95 W lamps, but both turned out to have burned field effect transistors, so I had to change them. The lamp circuit is shown in the figure:

Parts marked in red must be removed. From the output choke from the computer power supply unit L3 (see diagram below) we remove all windings except the one that is wound with the thickest wire. We solder new parts according to the scheme:

The input chain of the fuse and thermistor can not be set. Capacitor C1 set the maximum capacity. If your energy-saving lamp is made on bipolar transistors (most often 13003, 13005), then they must be replaced with more powerful ones (13007, 13009). It may also be necessary to replace the diode bridge D1-D4 and the inductance L1. To avoid these alterations, it is necessary to take a board from the lamp as much as possible.

The Schottky output diodes D12, D13 (10A 100V) were taken with a margin, since during the tests the diodes from the mospec s20c40c computer power supply failed. The EL car lamp is used as a backlight, a power and load indicator. Field-effect transistors and schottky diodes are equipped with radiators.

The work of the screwdriver is presented in the video:

Switching Power Supply For Screwdriver

A screwdriver or cordless drill is a very convenient tool, but there is a significant drawback. with active use, the battery discharges very quickly. in a few tens of minutes, and it takes hours to charge. Even the availability of a spare battery does not save. A good way out when working in a room with a working 220V power supply network would be an external source for powering the screwdriver from the mains, which could be used instead of the battery. But, unfortunately, specialized sources for powering screwdrivers from the mains are not commercially available (only battery chargers that cannot be used as a mains source due to insufficient output current, but only as a charger).

There are suggestions in the literature and on the Internet to use car chargers based on a power transformer, as well as power supplies from personal computers and for halogen lighting lamps, as a power source for a screwdriver with a rated voltage of 13V. All these are probably good options, but without claiming to be original, I suggest making a special power supply yourself. over, on the basis of the scheme I bring, it is possible to make a power supply unit for another purpose.

And so, the source diagram is shown in the figure in the text of the article.

This is a classic flyback AC-DC converter based on the UC3842 PWM generator.

The voltage from the network goes to the bridge on the diodes VD1-VD4. A constant voltage of about 300V is released on capacitor C1. This voltage is used to power a pulse generator with a transformer T1 at the output. Initially, the starting voltage is supplied to the output terminal 7 of the integrated circuit A1 through the resistor R1. The pulse generator of the microcircuit is turned on and generates pulses at pin 6. They are fed to the gate of a powerful field-effect transistor VT1 in the drain circuit of which the primary winding of the pulse transformer T1 is turned on. The operation of the transformer begins and secondary voltages appear on the secondary windings. The voltage from the winding 7-11 is rectified by the VD6 diode and is used to power the A1 chip, which, switching to the constant generation mode, starts to consume a current that is not able to support the starting power source on the resistor R1. Therefore, when the VD6 diode malfunctions, the source pulsates. through R1, capacitor C4 is charged to the voltage required to start the chip generator, and when the generator starts, the increased current C4 discharges, and generation stops. Then the process is repeated. If VD6 is operational, the circuit immediately after start-up switches to power from the winding 11.7 of T1 transformer.

Secondary voltage 14V (idling 15V, under full load 11V) is taken from the winding 14-18. It is rectified by the VD7 diode and smoothed by the capacitor C7. In contrast to the typical circuit, the protection circuit of the output key transistor VT1 from increased drain-source current is not used here. And the input is protection. Output 3 of the microcircuit is simply connected to a common negative of the power supply. The reason for this decision is that the author does not have the necessary low-resistance resistor (nevertheless, you have to make from what is available). So the transistor here is not protected against overcurrent, which of course is not very good. However, the circuit has been working for a long time without this protection. However, if desired, protection can be easily made by following the typical UC3842 IC switching circuit.

Details Pulse transformer T1. Ready TPI-8-1 from the power supply module MP-403 of a color domestic TV of the type 3-USTST or 4-USTST. These televisions now often go to disassembly or are generally thrown away. Yes, and TPI-8-1 transformers are on sale. On the diagram, the terminal numbers of the transformer windings are shown according to the markings on it and on the circuit diagram of the MP-403 power module.

The TPI-8-1 transformer also has other secondary windings, so you can get another 14V using a 16-20 winding (or 28V turning on 16-20 and 14-18 in series), 18V from a winding 12-8, 29V from a winding 12- 10 and 125V with windings 12-6. Thus, you can get a power source for powering any electronic device, such as ULF with a preliminary cascade.

However, this is limited to this, because the rewind transformer TPI-8-1. rather thankless job. Its core is tightly glued and when you try to separate it breaks completely not where you expect. So in general, any voltage from this unit cannot be obtained, except with the help of a secondary lowering stabilizer.

The IRF840 transistor can be replaced with an IRFBC40 (which is basically the same thing), or with a BUZ90, KP707V2.

The KD202 diode can be replaced with any more modern rectifier diode for a direct current of at least 10A.

As a radiator for VT1 transistor, you can use the radiator of the key transistor available on the MP-403 module board, having slightly altered it.

Video: How to replace the battery for a 14v screwdriver

How to make power supplies for a screwdriver from energy-saving light bulbs?

Modern power tools are popular in that they allow you not to get attached to the mains during operation, which expands the possibilities of their operation, even in the field. The presence of a battery pack significantly limits the duration of active work, so screwdrivers and drills require constant access to a power source. Unfortunately, for modern tools (most often made in China), the power battery has little reliability and often quickly fails, so folk craftsmen have to do with materials at hand to not only assemble a switching power supply, but also save money on this. An example of such a handmade is a switching power supply (UPS) for an 18 V cordless screwdriver, assembled from elements of an inoperative energy-saving lamp, which can be useful even after one’s “death”.

The structure and principle of operation of an energy-saving lamp

The structure of the energy-saving lamp

To understand how an energy-saving lamp can be useful, consider its structure. The design of the lamp consists of the following components:

  1. A sealed glass tube (flask) inside coated with a phosphor composition. The flask is filled with an inert gas (argon) and mercury vapor.
  2. Plastic housing made of non-combustible material.
  3. A small electronic circuit board (electronic ballast) with ballasts (PRA), which is responsible for starting up and eliminates flicker of the device. Ballasts of modern devices are equipped with a filter that protects the lamp from network interference.
  4. A fuse that protects the components of the board from power surges that can cause the device to ignite.
  5. Cases. ballasts, fuses and connecting wires are “packed” in it. A marking is placed on the case, which contains information on voltage, power and color temperature.
  6. A socle that provides contact between the lamp and the power supply (the most common socles are E14, E27, GU10, G5.3).

Two spirals (electrodes) are connected to the lamp bulb, which, under the influence of current, heat up and emit electrons from their surface. As a result of the interaction of electrons with mercury vapors, a smoldering charge arises in the flask, which gives rise to UV radiation. By acting on the phosphor, ultraviolet “makes” the lamp glow. The color temperature of the "housekeeper" is determined by the chemical composition of the phosphor.

Types of breakdowns of energy-saving lamps

An energy-saving lamp can fail in two cases:

  • the bulb of the lamp broke;
  • the electronic ballast (EB) (high-frequency voltage converter), which is responsible for converting alternating current to a constant, gradual heating of the electrodes and preventing the device from flickering during power-up, has failed.

If the bulb is destroyed, the lamp can simply be thrown away, and if the electronic ballast breaks down, it can be repaired or used for its own purposes, for example, used to make UPSs, adding an isolation transformer and a rectifier to the circuit.

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

Electronic ballast is “equipped” with the following electrical elements:

  • a bipolar transistor operating at voltages up to 700 V and currents up to 4A;
  • protective diodes (in the main, these are elements of the D4126L type or similar);
  • pulse transformer;
  • throttle;
  • bi-directional dinistor, similar to the dual KN102;
  • 10 / 50V capacitor
  • some electronic circuits are equipped with field-effect transistors.

The figure below shows the composition of the electronic ballast of the lamp with a functional description of each element.

Some electronic circuits of energy-saving lamps allow almost completely replacing the circuit of a home-made pulsed source, supplementing it with several elements and making small changes.

Separate converter circuits operate on electrolytic capacitors or contain a specialized microcircuit. Such electronic circuits are better not to use, because they are often the sources of failures of many electronic devices.

What is common between the electric circuits of the “housekeeper” and the UPS?

Below is one of the common electrical circuits of the lamp, supplemented by a jumper AA, replacing the missing parts and the lamp, a pulse transformer and a rectifier. Circuit elements highlighted in red can be deleted.

The electric circuit of the "housekeeper" at 25 W

As a result of some changes and necessary additions, as can be seen from the diagram below, it is possible to assemble a switching power supply, where the added elements are highlighted in red.

Final UPS circuitry

What PSU power parameters can be achieved from an energy-saving lamp?

The "second" life of the "housekeeper" is often used by modern radio amateurs. Indeed, for their hand-made products, a power transformer is often required, with the presence of which certain difficulties arise, starting with its purchase and ending with the consumption of a large amount of wire for winding and the overall dimensions of the final product. Therefore, craftsmen got used to replace the transformer with a switching power supply. over, if for these purposes using the electronic ballast of a faulty lighting device, this will significantly save money, especially for a transformer with a power of more than 100 watts.

A low-power switching power supply can be built by secondary winding the frame of an existing inductor. To obtain a higher power supply unit, an additional transformer is required. A switching power supply unit of 100 W m more can be made on the basis of EB lamps with a power of 20-30 W, the circuit of which will have to be slightly changed, supplementing it with a rectifying diode bridge VD1-VD4 and changing the cross section of the inductor winding L0 upwards.

Homemade transformer power supply

If it is not possible to increase the gain of the transistors, it will be necessary to increase the current of their base by changing the values ​​of the resistors R5-R6 to smaller ones. In addition, you will have to increase the power parameters of the resistors of the base and emitter circuits. At a low generation frequency, it is necessary to replace the capacitors C4, C6 with elements with a larger capacity.

Homemade power supply

A low-power switching power supply with power parameters of 3.7-20 W does not require the use of a pulse transformer. To do this, it will be enough to increase the number of turns of the magnetic circuit on an existing inductor. A new winding can be wound on top of the old. To do this, it is recommended to use MGTF wire with fluoroplastic insulation, which will fill the lumen of the magnetic circuit, which will not require a large amount of material and provide the necessary power of the device.

To increase the power of the UPS, you will have to use a transformer, which can also be built on the basis of an existing EB choke. Only for this it is recommended to use a varnished winding copper wire, after having prewound a protective film on the native throttle winding in order to avoid breakdown. The optimal number of turns of the secondary winding is usually selected empirically.

How to connect a new UPS to a screwdriver?

To connect a switching power supply assembled on the basis of electronic ballast, it is necessary to disassemble the screwdriver by removing all the fasteners. Using soldering or heat-shrink tubing, we connect the device’s motor wires to the UPS output. The connection of the wires by twisting is not a desirable contact, so we forget about it as an unreliable one. First, in the tool body, drill a hole through which we empty the wires. To prevent accidental tearing, the wire must be crimped with an aluminum clip at the very opening of the inner surface of the power tool housing. Clips that exceed the diameter of the hole will not allow the wire to be mechanically damaged and fall out of the case.

As you can see, even after working out, the energy-saving lamp can last a long time, bringing benefits. On its basis, you can assemble a low-power supply pulse block up to 20 W, which perfectly replaces the battery of an electric tool with 18 V or any other charger. To do this, you can use the elements of the electronic ballast of an energy-saving lamp and the technology described above, which is used by craftsmen, most often, to repair a dead battery or save on buying a new power source.

The power supply unit for a HAMMER screwdriver model ACD121B

The SCHEME is taken from our site and in Google it is on each site.

Well, in general, I tailored it to my needs and got such a scarf.

First gutted the battery pack.

Installed a scarf in the battery pack.

I glued the cooler first with my favorite superglue and then with Chinese snot from a thermo gun.