Power supply for a drill-driver from an “electronic transformer. Homemade power supply for a cordless screwdriver Bp from an electronic transformer for a screwdriver
A cordless screwdriver is undoubtedly a useful tool, the main advantage of which is mobility. But when native batteries die completely or partially, buying new ones results in a tidy sum, comparable to half the cost of a new tool. Many people simply buy a new screwdriver, but I suggest, due to the loss of mobility, to make a reliable power source for it, which will forever remove the problem of constantly charging half-dead batteries.
Let's take a look at the pros and cons of such an upgrade.
Let's start with the cons. The biggest and only problem is tying the screwdriver to the socket with wires, which is more than covered by the following pluses:
- The screwdriver is always ready to work, the problem of uncharged batteries (or discharged at the wrong time) disappears.
- Feels great in an environment of low and negative temperatures, unlike the battery.
- If native batteries are dead, and a toad is strangling buying new ones, then the power supply completely replaces the batteries.
If you are satisfied with these conditions, then let's start!
The power supply can be made pulse or transformer. Why I settled on the transformer version, it will be clear as you read the article. If your screwdriver works on 12 or 14 volts, then I advise you to stop on a switching power supply from a computer. This option requires a minimum of alteration and costs.
Patient #1
Reason for upgrade: Batteries drain quickly, even when when they were new.
Purpose of modernization: Get a battery-powered, mains-powered hybrid.
For power, a current is needed, about 10A. This raises the question of using a computer power supply, but that's bad luck - the screwdriver works from 18v. When applying 12v to it, it turns very sluggishly and you can slow it down by hand with almost no effort. Although some argue that a screwdriver turns normally from 12 volts, but now, so to speak, the myth has been verified and destroyed.
There are 2 options left - to redo the PWM control of the pulse unit so that it gives the desired voltage, or use a transformer with the desired voltage.
Another disadvantage of a switching power supply is that it is designed to operate at room temperature, and it is not known how it will behave at a lower one. In principle, the transformer practically does not care in what conditions it is operated. Although these are all assumptions, not tested in practice.
A powerful 18 volt transformer is quite difficult to find, but for me it became impossible. At this point, I wanted to return to the option with a computer power supply, but suddenly, as the masters of the 7th category say, a toroidal transformer with a wound primary winding accidentally fell into my hands. It remains only to wind the secondary, I got about 90 turns with 1.5 wire.
If you decide rewind the transformer to another voltage, then the program will help you power trans.
The power supply is made in a case from the AT block. The role of the rectifier is played by 10 ampere Schottky diodes connected in a bridge circuit. 220 goes to the native connector of the block, 18v comes out from the connector designed to connect the monitor. The toggle switch is a power switch, and the LED indicates the presence of 18v.
For convenience in work and carrying the unit is equipped with a folding handle:
Since I need a hybrid, I had to bring out a separate power line to connect the unit:
In this case, do not forget to disconnect the batteries when working from the unit.
Taking the opportunity, when disassembling the screwdriver, I added the illumination of the working area:
The result is this mutant:
Patient #2
Reason for upgrade: The native battery died, the restoration is not justified.
Purpose of modernization: Replace battery with power supply.
Here I came across a 12 volt unit, and I connected it to a computer power supply. But it was not chickpeas - the block began to go into defense. I connected it to a more powerful PSU, the picture did not change. The reason for this was a short-circuited motor winding. The motor brushes turned out to be quite large, and I decided to make a transformer power supply, there is no protection in it. In any case, the engine will work for some time, and then it can be replaced (perfectly suitable for other screwdrivers and car pumps).
This is where the UPS transformer came in handy, which had successfully lain under my desk for half a decade, waiting for its finest hour. Just under the desired 12c.
Everything is assembled according to the same principle, only instead of Schottky diodes I used 3 Schottky diode assemblies, extracted from computer PSUs.
In the previous block, I used a whole cord to connect the monitor, but you should not do this. The cross section of the native cord is small, and causes heat and losses. It is better to use only the connector. I soldered a two-core PVA 2.5 square to it:
It is better not to use a very long low-voltage cord, there will be losses. It is better to make the power cord longer.
He took out the cans from the battery case and connected the power:
The machine is ready
Finally, I started to implement my old idea, namely to provide power for a screwdriver from a 220 volt network. Undoubtedly, some of you also have a screwdriver, with a worn out, unusable battery that no longer takes a charge. There were two copies in my location.
The first (black) has an operating voltage of 18 volts. It was him that I originally wanted to power from the network, because. fits comfortably in the hand and quite powerful. But the button is missing. Perhaps in the future I will cut off the handle and make it look like a drill. The second copy is designed for 12 volts. Served for quite a long time. Of course, you can purchase a new battery or, in extreme cases, replace the banks. But still, I want to have a ready-made tool at hand, especially since it is not always convenient to use an electric drill. she is heavy. A power transformer will help us to realize this idea.
A step-down transformer TS-250-36 was used. "250" is its rated power, and the number 36 means that the output will be 36 V. It has an O-shaped magnetic circuit. Its windings are arranged in such a way that half of the primary is wound on the left, the second half on the right side. The secondary winding, which is located on top of the primary, is wound in a similar way.
It is not difficult to distinguish the windings from each other in a step-down transformer, because the secondary is made of a thicker wire, and the one to which the mains voltage is supplied from a thinner wire. This is due to the fact that a smaller current flows through it.
The windings have a symmetrical arrangement and two halves of 18 volts are connected by a wire (the connection point is clearly visible in the bottom photo). I will use one half.
But before you rewind the transformer, you need to take measurements. I urge you to be careful when working with current, do not touch live parts, and always check whether the measurement limit on the multimeter is set correctly.
On the right, the voltage on half of the secondary winding is measured. As you can see, the voltage is slightly higher than the passport values, because. no load is connected here.
So I separated one half and now proceed to disassemble the transformer. Between the layers of paper 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, almost half of the turns had to be removed.
When determining the required voltage, it must be taken into account that after the transformer there will be a diode bridge, which will reduce the voltage by about a couple of volts. But adding a smoothing capacitor will cause the voltage to rise by about 1.4 times. Those. in the absence of load, the rectified voltage across the capacitor will be equal to the amplitude value.
As we unwind the secondary, we take measurements. Soon, I settled on a value of 11.2 Volts, because. I was afraid of drawdown when connecting the load.
Now that the transformer is ready (although some may use a ready-made one with the right parameters), now it's time to get acquainted with the circuit.
A diode bridge (VDS) must be soldered to the output of the transformer in order to convert the alternating current into a pulsating direct current.
The diode bridge can be assembled from separate diodes or used ready-made. When choosing it, you should take into account how many amperes your screwdriver consumes (select a bridge with a margin).
We solder the wires from the secondary winding to the terminals of the diode bridge, where the letters are AC (alternating current).
Well, after the bridge, you need to solder a capacitor to smooth out the ripples. Its voltage must exceed the supply voltage of the screwdriver at least twice. And the capacitance is from 470 uF to 2200 uF.
If desired, a switch and a fuse can be added in front of the transformer in the circuit.
So, after connecting the circuit, I took measurements. The idle voltage at the output of the power supply (when the load is not connected) is 15 volts. When you start the screwdriver, it sags to 11.5 volts, which is the norm, so it's okay. A fully charged new battery put out 13 volts.
This is what the instrument looks like from the inside. Here you can find the limiting parameters of the button, and you can also notice that the engine is controlled by a powerful field-effect transistor.
In order to make it convenient to connect to the power supply, I disassembled the battery. We need contacts from him.
This detail needs to be tinned. I managed to solder using rosin, but in some cases a flux may be required for soldering aluminum.
Of course, when soldering wires from the power supply, do not forget about the polarity, usually it is indicated on the battery case.
The compartment became very light. The wire was sealed with hot glue.
Tests have shown that the screwdriver, when working from the power supply, coped with the tasks.
There is a video for this article that shows in detail the process of creating a power supply, rewinding a transformer, connecting and testing.
List of radio elements
| Designation | Type | Denomination | Quantity | Note | Shop | My notepad |
|---|---|---|---|---|---|---|
| T | A step-down transformer | Select by voltage | 1 | To notepad | ||
| VDS | Diode Rectifier Assembly | PBL405 | 1 | Better more powerful | To notepad | |
| WITH | electrolytic capacitor | 470...2200 uF | 1 | Not less than 50V |
Pulse converters have high efficiency, small size and weight.
These products are not expensive, about 1 ruble per watt. After completion, it is quite possible to use them to power amateur radio structures. There are many articles on the web on this topic. I want to share my experience of reworking the Taschibra 105W electronic transformer.
Consider the circuit diagram of the electronic converter.
The mains voltage through the fuse is supplied to the diode bridge D1-D4. The rectified voltage feeds the half-bridge converter on transistors Q1 and Q2. The diagonal of the bridge formed by these transistors and capacitors C1, C2 includes the winding I of the pulse transformer T2. The start of the converter is provided by a circuit consisting of resistors R1, R2, capacitor C3, diode D5 and diac D6. The feedback transformer T1 has three windings - a current feedback winding, which is connected in series with the primary winding of the power transformer, and two windings of 3 turns, feeding the base circuits of the transistors.
The output voltage of the electronic transformer is a rectangular pulse with a frequency of 30 kHz, modulated with a frequency of 100 Hz.
In order to use an electronic transformer as a power source, it must be modified.
We connect a capacitor at the output of the rectifier bridge to smooth out the ripple of the rectified voltage. The capacitance is selected at the rate of 1uF per 1W. The operating voltage of the capacitor must be at least 400V.
When a rectifier bridge with a capacitor is connected to the network, a surge of current occurs, so you need to include an NTC thermistor or a 4.7 Ohm 5W resistor in the break of one of the network wires. This will limit the starting current.
If a different output voltage is needed, we rewind the secondary winding of the power transformer. The diameter of the wire (wire harness) is selected based on the load current.
Electronic transformers have a current feedback, so the output voltage will vary depending on the load. If no load is connected, the transformer will not start. In order to prevent this from happening, you need to change the current feedback circuit to the voltage feedback.
We remove the current feedback winding and put a jumper on the board instead. Then we pass a flexible stranded wire through a power transformer and make 2 turns, then we pass the wire through a feedback transformer and make one turn. The ends of the wire passed through the power transformer and the feedback transformer are connected through two 6.8 Ohm 5 W resistors connected in parallel. This current-limiting resistor sets the conversion frequency (approximately 30kHz). As the load current increases, the frequency becomes larger.
If the converter does not start, it is necessary to change the winding direction.
In Taschibra transformers, transistors are pressed against the case through cardboard, which is unsafe to use. In addition, paper is a very poor conductor of heat. Therefore, it is better to install transistors through a heat-conducting pad.
To rectify an alternating voltage with a frequency of 30 kHz, we install a diode bridge at the output of an electronic transformer.
The best results were shown, of all the tested diodes, by domestic KD213B (200V; 10A; 100kHz; 0.17µs). At high load currents, they heat up, so they must be installed on the radiator through heat-conducting gaskets.
Electronic transformers do not work well with capacitive loads or do not start at all. For normal operation, a smooth start of the device is required. The L1 choke contributes to a smooth start. Together with the 100uF capacitor, it also performs the function of filtering the rectified voltage.
Choke L1 50µG is wound on a T106-26 core from Micrometals and contains 24 turns of 1.2mm wire. Such cores (yellow, with one white edge) are used in computer power supplies. Outer diameter 27mm, inner 14mm, and height 12mm. By the way, other parts can be found in the dead power supplies, including a thermistor. 
If you have a screwdriver or other tool whose battery has expired, then you can place a power supply from an electronic transformer in the battery case. As a result, you will get a tool that works from the network.
For stable operation, it is advisable to put a resistor of approximately 500 Ohm 2W at the output of the power supply.
In the process of setting up the transformer, you need to be extremely careful and accurate. High voltage is present on the elements of the device. Do not touch the flanges of the transistors to check whether they are heated or not. It must also be remembered that after switching off, the capacitors remain charged for some time.
A lot of tinkering enthusiasts now use cordless drills-drivers. The tool is really very useful, as it speeds up and simplifies the work of screwing screws, bolts and does not connect you to the mains. At the same time, the capacity
a standard battery is clearly not enough. It is a pity that there are no mains power supplies for screwdrivers on sale (I mean power supplies capable of turning the motor, not a charger). I realized this when I decided to replace the old wooden floor in the apartment with a new one. Having read the Internet, I decided to fasten the boards not with nails, but with screws, as. judging by the material read, this should have a positive effect on reducing floor creaking, plus you can always creak a board"twist". I got to work, and then it turned out that one 12-volt battery of a screwdriver is barely enough to screw 4-5 boards (boards 4 meters long, logs every 30-40 cm, thus for 40-50 screws). Then comes a long pause for charging. Even having a spare
the battery does not help, because the discharge occurs in 15-20 minutes of such work, and it takes several hours to charge. The screwdriver cannot work from its charger due to insufficient current at its output. Then I found a way out by powering the screwdriver from a huge old laboratory power source. But this is not the case, since the laboratory source is too heavy and bulky, and therefore there was a desire to make a compact power supply for a screwdriver.
I began to examine the contents of my closet in order to find a suitable basis for the power supply. First, I looked at the MP-1 and MP-3 blocks from old TVs, the power supply from a faulty printer HP, and then caught my eye« electronic transformer» for low voltage halogen lamps. The measured current consumption of the screwdriver at maximum load (coupling on"14" and hold the cartridge with your hands so that the clutch snaps in) turned out to be equal to 7-8A.
Thus, the power of the source should be somewhere around 100 W. " Electronic transformer» was just such a power (bad that without a significant margin)
I want to remind you that« electronic transformer» for halogen lamps is a simple switching power supply, the output of which is an alternating voltage with a frequency of several tens of kHz. modulated by mains voltage with a frequency of 50 Hz. This is possible and suitable for powering lamps, but not for powering a DC electric motor with a power regulator, which in fact is a screwdriver from an electrical point of view.
Figure 1 shows a diagram drawn from the board.« electronic transformer» Tachiba brand ( appears to be a Chinese counterfeit Toshiba). The disadvantages of the scheme lie on the surface. - there is no smoothing capacitor after the mains rectifier (therefore modulation with a frequency of 50 Hz) and there is no output rectifier with a large storage capacitor.
Figure 2 shows the revised circuit. Lamp H1 is needed as a load during operation
block at idle, necessary to start it. But there was also a practical application for it. The lamp is placed in a metal tube and taped to the body of a screwdriver with electrical tape, so that a very useful flashlight is obtained. Unlike the built-in LED backlight, which is in the screwdriver, it is more convenient because it shines brighter and the light spot is wider and, most importantly, it shines all the time, and not just when the electric motor is running.
Structurally, everything is done quite compactly.
But I had to sacrifice one of the battery packs (there are two of them in the screwdriver kit). All batteries were removed from the block, an empty case with contacts was left.
Then, in this case with glue" liquid Nails " an electronic transformer board, an output diode bridge and additional capacitors are fixed. The board is very compact (55 x35 mm), and small-sized imported capacitors, so everything fit without problems. It remains to drill a hole in the case for the power cord with a plug. Now, I usually work with the network unit, but if I need autonomous work, I remove it and fasten the battery.
Karimov, A M
A cordless screwdriver is a great helper in the household. The tool, together with the master, works in the house and in the garden, works in the garage or in the field. Until the battery runs out. The number of charge-discharge cycles of the battery is limited, the battery also deteriorates from idleness: self-discharge destroys the elements. On average, the battery lasts 3 years, after which it has to be replaced. You can save the tool by converting it to a network one. The conversion is done in different ways.
Is it really worth redoing?
Without batteries, a screwdriver turns into a piece of iron. When the batteries stop holding a charge, you have to look for new batteries. Firstly, it is expensive - the price of batteries is up to 80% of the cost of a screwdriver, it is more efficient to buy a new tool. Secondly, batteries are not always on sale, for example, if the model is discontinued. Thirdly, a prudent owner seeks to use all opportunities to save money.
Converting a cordless screwdriver to work from the mains is a good way out. What does it give:
- The tool gets a new life.
- No more batteries needing to be charged.
- Tool torque is independent of battery power.
The disadvantage of the converted design is the dependence on the outlet and the length of the network cable.
Attention! Work at a height exceeding two meters with a converted screwdriver is not allowed.
How to convert a cordless screwdriver to work from a 220 volt network
The craftsmen came up with several ways to convert a screwdriver to work from the mains. All of them are to provide the motor with the required supply voltage using an intermediate source or converter.
Table: power supply options for corded screwdriver
| Power supply | Advantages | Flaws |
| Complete screwdriver charger. |
| The charger takes up space on the table. |
| A ready-made power supply placed in the case of an old battery. |
|
|
| A homemade power supply placed in the case of an old battery. |
|
|
| External power supply | An easy makeover. |
|
| Power supply from the computer |
|
|
Connecting the screwdriver to the charger
Attention! At low voltage, there are high losses in the wire, so the cable between the charger and the tool should be no longer than 1 meter, with a cross section of at least 2.5 square meters. mm.
Sequencing:
- Disassemble the old battery and remove the dead cells from it.
- Drill a hole for the cable in the battery case, thread the cable through the hole. It is advisable to seal the connection with electrical tape or heat shrink tubing so that the wire does not break out of the housing.
- The elements removed from the battery will violate the weight distribution of the screwdriver - the hand will get tired. To restore balance, a weight should be placed in the body - it can be a dense tree or a piece of rubber.
- Solder the cable to the terminals of the former battery connected to the screwdriver.
- Assemble the battery case.
- It remains to test the updated tool in operation.
Solder or attach two wires to the charger terminals with crocodile clips.
Installation of a ready-made power supply in the case of an old battery
Attention! In a closed case, the power supply does not cool well. It is recommended to make holes in the walls of the case. Do not operate the tool without interruption for more than 15 minutes.
Procedure:
- Disassemble the old battery and remove the non-working elements from it.
- Install the power supply into the battery case. Connect high voltage contacts and low voltage terminals.
- Assemble and close the battery case.
- Install the battery in the screwdriver.
- Connect the power supply plug to the socket and check the updated network tool in operation.
Homemade power supply
Attention! Follow the rules of electrical safety. Soldering and connection should be carried out with the device de-energized.
Step-by-step instruction:
- Disassemble the case of the old battery, remove the dead batteries from it.
- Install the elements of the electrical circuit of the power supply on the circuit board, solder the contacts.
- Install the assembled board into the case. Check the tester for the presence of voltage at the output.
Power supply in the case
- Connect the low voltage wires to the terminals of the old battery. Assemble the body.
It remains only to assemble the battery case
Connect the screwdriver to the mains and check its operation.
Video: homemade lithium battery for a screwdriver
Connecting to an external power supply
Attention! In the process of refinement, you will need to disassemble the body of the screwdriver and intervene in the electrical circuit. Remember the disassembly sequence to assemble all parts in reverse order.
What to do:
Connecting to a power supply from a computer
Instruction:
- Find or buy a power supply from a computer with a power of at least 300 watts.
- Disassemble the screwdriver body. Find the motor power wires inside. Solder the connectors for the computer power supply to the wires.
- Remove the connectors for connecting the computer power supply from the case.
- Connect the screwdriver to the new power supply.
- Connect the power supply to the network and check the operation of the device.
Video: power supply for a screwdriver from a computer PSU
How to power a screwdriver while maintaining its autonomy
If the master works in a building that is not connected to electricity, and the batteries have already deteriorated, there are ways to power the screwdriver:
- replace old battery banks with new ones;
- connect the screwdriver to the car battery;
- connect the tool to another battery, for example, taken from an uninterruptible power supply.
Replacing old elements
Attention! When replacing batteries, pay attention to the correct polarity of the cells.
Procedure:
Attention! Charge the converted battery only with a specially selected charger.
Connecting to an external battery
Sequencing:
- Buy or find an external battery, for example, take it from an unnecessary uninterruptible power supply.
- Take a wire with a cross section of at least 2.5 square meters. mm. Remove the insulation and install clamp terminals suitable for fastening to the battery on the copper ends.
- Place the other end of the cable into the case of the old battery and solder to the terminals inserted into the screwdriver.
- Insert the battery case into the screwdriver, connect the cable with terminals to the battery.
- Test the restored tool in operation.
An electric cordless tool lasts several times longer than the batteries that power it. Throwing a screwdriver with unusable elements into the trash is unreasonable. The real owner will be able to repair the device by transferring it to another power source, thereby giving it a new life.
