DIY repair of the charger for the bosch al1814cv screwdriver

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chaos is an unknown order

You can also try replacing C3.

ps. I advise you to install the transistor V5 with a deliberately new one. If it has a low gain, but the unit starts up, then further destruction will be an order of magnitude greater.

Yes, I dropped them, one shows about a megaohm, the second about 300k, can they be replaced with one 1.2M? Why are there 2 of them?

There is no normal oscilloscope, there is an oscil usb oscilloscope, but what should it measure and what should it show there?

Now I'm not at the computer, I'll try to do it in the evening. Link to the diagram in 1 post

These resistors provide bias to the mosfet. Without this, the mosfet will not open, and the voltage across the transformer will be zero.
But the mosfet opens in a very narrow gap - approximately 5 to 6 volts. Therefore, it will definitely not work to hit with one resistor. So the story was something like this: they put a megohm - less than the required one, which will obviously open the mosfet, and then a little more was added to it - selection for the optimal mode.

If you have zero on the primary winding of the transformer, and the mosfet is working properly, then it does not open. We must look for why.
You can try to measure the voltage at its gate, preferably with a digital device with a high input impedance.
Check capacitor C6 for broken. If it is OK, and you also changed V5, and if there are 4 - 5 volts at the gate, begin to carefully reduce R3R4. The voltage at the gate should increase from this, and at some point the mosfet must begin to open.
I would put a variable instead of 300k, and they would determine the desired value.
Be careful with an excessive decrease in these resistances: if the mosfet is opened so much that it cannot close, then this is a short circuit, and the fuse will burn out, and maybe something else.

It would also be good to check the rectifier diode on the secondary winding. If this diode is broken, then this can effectively suppress the generation, and experiments with increasing the voltage at the gate will then result in overload and combustion of the mosfet.

Help with the subject.
Symptoms: You plug it into an outlet - the indicator lights up constantly.
Connect the battery - the indicator will blink and light up constantly. (When I was working, it blinked until the end of charging, then it was constantly on.)
Accordingly, the battery is not charged.

The transformer is working, the diode bridge is normal.
There is no voltage at the terminals (without a connected battery). (Should it be? If the third terminal hangs in the air, should there be voltage?)
The battery was temporarily taken away, I can not check the voltage under load.
Does it make sense to check the TYN208 thyristor (V5 on the radiator) or is it most likely in the control?

Microcircuit 6HKB 07501758.
Visual inspection did not reveal a problem. There was a suspicion of poor soldering at the V5, if it was soldered - the result is the same.

Charging is a bit similar to BOSCH AL1419DV, here the diagram was given: ">
This diagram is:

Available tool: multimeter, soldering iron. No oscilloscope.

Greetings, dear colleagues. Today we will repair and upgrade the charger at the same time. Bosch AL 1115 CV... Extend its life by improving heat dissipation from vulnerable parts of the device and good ventilation. This charging is widely known for its frequent breakdowns due to overheating and combustion of the power transistor.

I came in a sad state and loaded with a complaint from the owner: “Something cracked there, got cold and stopped working! Didn't do anything special! That I now buy a new one or have a chance to fix it! : - / ". Of course, I calmed him down and praised him for his pragmatism.

I opened the charger with him, saw a burnt board under a burnt resistor, some cracked low-power transistor, a blown fuse. Immediately I was struck by the "radiator" of the power transistor, or rather its absence, because instead of it there was a small iron plate on which the power key was actually fixed. I drew the owner's attention to this deliberate factory jamb (perhaps for the sake of profit) and suggested installing a real radiator instead, as well as drilling more ventilation holes in the device case, since I did not have a small fan and the owner did not want to take out a large radiator outside the case. After agreeing on the price, they hit it on the hands.

After soldering one leg out of the board, it was finally determined to be faulty: the power field-effect transistor V5, an almost cut-off low-resistance resistor R5 (about 2.5 MΩ, at a rate of 3.3 Ohm) in the field source circuit, a punctured low-voltage diode V8 in the binding of the PC817 optocoupler, a burned-out resistor R6 in the circuit of the transistor V6 and the actual transistor of the oscillator V6 itself.

Resistor crack due to overheating

Soldered-out PCB

The problem dug in in the high-voltage power part of the circuit. To make it understandable and easier for you and yourself to repair, "what goes where", etc. decided to draw the faulty part of the circuit from the board.

Using my old technique. Let me explain briefly, it is simple. I draw elements from the side of the board tracks with a gel pen, so as not to get confused and not to return to the beginning every time. After that, I draw a draft on paper, and then the final final version.

Method for drawing a circuit from the board side

Draft version of the schematic drawing

High-voltage part of the circuit Bosch AL 1115 CV

Polevika V5 STP5N80ZF not found, found an analog K3565 (900V, 15A in pulse mode). By and large, any such field worker will do, the main thing is not to be weaker in impulse current and voltage. Low-power transistor V6 2N3904 autogenerator, replaced with a domestic KT3102A, in a metal case and with gilded legs! Anyway, it's expensive to remember and reapply cool Soviet transistors! 🙂 V8 diode 1N4148 (the Soviet analogue of KD522) was found immediately, as it is widespread. I had to tinker with the resistors R6 and R5, but the Internet helped to understand the native resistance values ​​(the color stripes either turned black or even burned out!) And the number according to the R6 scheme (the place of the board with the number burned out!).

I soldered new parts, washed the board from the helium pen and flux with alcohol, connected it to the network through a 220V × 65W safety light and turned it on. The charger started working, the green LED lit up, with a constant glow. Plugged in the battery - the charging process started, the LED blinked green. After 5 minutes I turned off the charge, my own "radiator" was slightly warm.

I installed a relatively normal radiator, having previously sanded, thoroughly sanded and degreased the surfaces of the radiator and transistor, and lubricated the transistor with thermal grease for normal heat dissipation. For clarity, I drew you a picture of the principle and importance of grinding, see.

Brushed and degreased heatsink and field-effect transistor

The importance of surface sanding

Cooling radiator before and after

A suitable (at a glance, according to approximate calculations) radiator for our field worker did not fit into such a small case, as an alternative to fence the fan to a small radiator or drill more ventilation holes and try not to overheat the device. Or install the radiator outward towards the body. As you know, we stopped with the owner on a cooler-free version, but with new holes.

Since the radiator took up a lot of space, it was necessary to transfer the nearby filtering and power-supplying capacitor C2 to the charger to the side, having previously increased its legs with wiring. Drilled from the heart holes in the bottom and top covers! 🙂

Upgrading the bottom of the charger case

Upgrading the top of the charger case

I collected it, turned it on, after 15 minutes of working with the battery, I measured the temperature under the casing and on the radiator of the field worker. In the case of the board, the temperature turned out to be within the normal range, on the radiator of the field worker is also within the normal range (the approximate critical temperature according to the datasheet of this transistor is 150C °).

Transistor heatsink temperature

After half an hour, the fully discharged battery was charged, and no overheating was observed.

The result of my struggle to save the drowning charger. As a result, we got a pumped-up charging, creative and stylish modding of the case, the owner's hope for a long work of the device. Satisfaction with the creative work done and a monetary allowance in the amount ... known only to me. 🙂
Good luck with your repairs!
And all the best!

Without a doubt, the power tool greatly facilitates our work, and also reduces the time of routine operations. All kinds of self-powered screwdrivers are now in use.

Consider the device, the schematic diagram and the repair of the battery charger from the Interskol screwdriver.

First, let's take a look at the schematic diagram. It is copied from a real charger PCB.

Charger PCB (CDQ-F06K1).

The power section of the charger consists of a GS-1415 power transformer. Its power is about 25-26 watts. I counted according to the simplified formula, which I have already spoken about here.

The reduced alternating voltage 18V from the secondary winding of the transformer is fed to the diode bridge through the fuse FU1. The diode bridge consists of 4 diodes VD1-VD4 type 1N5408. Each of the 1N5408 diodes withstands a forward current of 3 amperes. The electrolytic capacitor C1 smooths out the voltage ripple downstream of the diode bridge.

The basis of the control circuit is a microcircuit HCF4060BE, which is a 14-bit counter with elements for the master oscillator. It drives the pnp bipolar transistor S9012. The transistor is loaded on the S3-12A electromagnetic relay. A kind of timer is implemented on the U1 microcircuit, which turns on the relay for a given charge time - about 60 minutes.

When the charger is connected to the network and the battery is connected, the contacts of the JDQK1 relay are open.

The HCF4060BE microcircuit is powered by the VD6 zener diode - 1N4742A (12V). The zener diode limits the voltage from the mains rectifier to 12 volts, since its output is about 24 volts.

If you look at the diagram, it is not difficult to notice that before pressing the “Start” button, the U1 HCF4060BE microcircuit is de-energized - disconnected from the power source. When the “Start” button is pressed, the supply voltage from the rectifier goes to the 1N4742A zener diode through the resistor R6.

Further, the reduced and stabilized voltage is supplied to the 16th pin of the U1 microcircuit. The microcircuit starts to work, and the transistor also opens S9012that she runs.

The supply voltage through the open transistor S9012 is supplied to the winding of the electromagnetic relay JDQK1. The relay contacts close and supply voltage to the battery. The battery starts charging. Diode VD8 (1N4007) bypasses the relay and protects the S9012 transistor from a reverse voltage surge that occurs when the relay coil is de-energized.

The VD5 diode (1N5408) protects the battery from discharge if the mains supply is suddenly turned off.

What happens after the contacts of the "Start" button open? The diagram shows that when the contacts of the electromagnetic relay are closed, the positive voltage through the diode VD7 (1N4007) goes to the Zener diode VD6 through a damping resistor R6. As a result, the U1 microcircuit remains connected to the power source even after the button contacts are open.

Replaceable battery GB1 is a block in which 12 nickel-cadmium (Ni-Cd) cells, each 1.2 volts, are connected in series.

In the schematic diagram, the elements of the replaceable battery are circled with a dotted line.

The total voltage of such a composite battery is 14.4 volts.

A temperature sensor is also built into the battery pack. In the diagram, it is designated as SA1.In principle, it is similar to the thermal switches of the KSD series. Thermoswitch marking JJD-45 2A... Structurally, it is fixed on one of the Ni-Cd cells and fits tightly to it.

One of the terminals of the temperature sensor is connected to the negative terminal of the storage battery. The second pin is connected to a separate, third connector.

When connected to a 220V network, the charger does not show its work in any way. Indicators (green and red LEDs) are off. When a removable battery is connected, a green LED lights up, which indicates that the charger is ready for use.

When the “Start” button is pressed, the electromagnetic relay closes its contacts, and the battery is connected to the output of the mains rectifier, and the battery charging process begins. The red LED lights up and the green one goes out. After 50-60 minutes, the relay opens the battery charging circuit. The green LED lights up and the red one goes out. Charging is complete.

After charging, the voltage at the battery terminals can reach 16.8 volts.

This algorithm of work is primitive and eventually leads to the so-called "memory effect" of the battery. That is, the capacity of the battery decreases.

If you follow the correct algorithm for charging the battery, for a start, each of its elements must be discharged to 1 volt. Those. a block of 12 batteries must be discharged to 12 volts. In the charger for the screwdriver, this mode not implemented.

Here is the charging characteristic of one 1.2V Ni-Cd battery cell.

The graph shows how the cell temperature changes during charging (temperature), the voltage across its terminals (voltage) and relative pressure (relative pressure).

Specialized charge controllers for Ni-Cd and Ni-MH batteries, as a rule, operate according to the so-called delta -ΔV method... The figure shows that at the end of the cell charging, the voltage decreases by a small amount - about 10mV (for Ni-Cd) and 4mV (for Ni-MH). From this change in voltage, the controller determines whether the element is charged.

Also, during charging, the temperature of the element is monitored using a temperature sensor. Immediately on the graph you can see that the temperature of the charged element is about 45 0 WITH.

Let's go back to the charger circuit from the screwdriver. It is now clear that the JDD-45 thermal switch monitors the temperature of the battery pack and breaks the charge circuit when the temperature reaches somewhere 45 0 C. Sometimes this happens before the timer on the HCF4060BE chip goes off. This happens when the battery capacity has decreased due to the “memory effect”. At the same time, a full charge of such a battery occurs a little faster than in 60 minutes.

As you can see from the circuitry, the charging algorithm is not the most optimal and, over time, leads to a loss of the battery's electrical capacity. Therefore, a universal charger such as the Turnigy Accucell 6 can be used to charge the battery.

Over time, due to wear and tear and moisture, the SK1 "Start" button begins to work poorly, and sometimes even fails. It is clear that if the SK1 button fails, we will not be able to supply power to the U1 microcircuit and start the timer.

There may also be a failure of the VD6 Zener diode (1N4742A) and the U1 microcircuit (HCF4060BE). In this case, when the button is pressed, charging does not turn on, there is no indication.

In my practice, there was a case when the zener diode struck, with a multimeter it “rang” like a piece of wire. After replacing it, the charging began to work properly. Any zener diode for a stabilization voltage of 12V and a power of 1 W is suitable for replacement. You can check the Zener diode for “breakdown” in the same way as a conventional diode. I already talked about checking diodes.

After repair, you need to check the operation of the device. Press the button to start charging the battery. After about an hour, the charger should turn off (the “Network” indicator (green) will light up. We take out the battery and make a “control” measurement of the voltage at its terminals. The battery must be charged.

If the elements of the printed circuit board are in good order and do not arouse suspicion, and the charging mode does not turn on, then the thermal switch SA1 (JDD-45 2A) in the battery pack should be checked.

The scheme is quite primitive and does not cause problems when diagnosing a malfunction and repairing, even for novice radio amateurs.

The need for a home workshop of hand-held power tools is obvious - this is help with repairs, construction and many other matters that arise in everyday life. Intensive development of technologies such as: the creation and implementation of brushless motors, various current controllers and load optimization, the constant development of technology in the production of rechargeable batteries, make this tool economical and reliable.

The technologies of innovations of autonomous power supply units also do not stand aside. Already released batteries and chargers with a voltage of 36V at 25 A / h. bringing the work of the tool closer to a source from a stationary power supply. One of the leading developers in this industry is Bosch, a manufacturer of tools and chargers for a Bosch screwdriver.

Consider some types of power supplies for a working tool

An autonomous power supply unit for hand tools consists of separate cells that can accumulate charged electrons in their active component - this can be Ca-Ni (cadmium - nickel), Ni-MH (nickel - metal hydride), Li - ion (lithium - ion ). Currently, these active ingredients are one of the most popular in the production of battery assemblies.

The principle inherent in batteries is based on the retention of charged electrons in the active layer. With an external power source applied to the plus - anode and minus - cathode, charged electrons are actively incorporated into the active component and kept there in a charged state. When a load is connected, the polarity is reversed and the electrons begin to move in the opposite direction, creating an electric current in the load circuit. The capacity of the battery or, in other words, its power depends on how much the active layer of charged electrons can hold.

Power, or as it is also called the capacity of the battery, is the main criterion when choosing a tool in operation for work and which ultimately depends on the amount of work being done. If, for example, work is needed during construction in a round-the-clock mode, then several powerful batteries will be needed, but if the tool is used as an assistant in current affairs in the mode: unscrew - twist - put down, there will be no need for special power.

The concept of power is a physical quantity that is calculated by multiplying the voltage U, measured in volts (V), by the capacitance I, in amperes / hours (A / h_). And it is defined as the product of these values. For example, battery voltage 10V, capacity 1.5 A / hour, Power P = U * I (W). P = 10 * 1.5 = 15W, and the 18V, 10 A / h battery will already have a power of P = 18 * 10 = 180W. That is, the last battery can work at the same load 10 times more.

One of the simplest charger solutions for batteries with a li-ion active component is a device made on a TL431 microcircuit, which acts as a zener diode for current.

An alternating voltage of 220 volts is lowered on a transformer, followed by rectification on diodes D2 and D1 and smoothing of pulses on a capacitor C1 with a capacitance of 470 Mf. Resistor R4 is required to open the base of the reverse conduction transistor, its value is selected from 5 to 4 ohms. As the charge accumulates in the battery, the voltage at the terminals will increase and an increased voltage will flow to the base of the transistor, which will close the emitter-collector junction, thereby reducing the charging current. Output transistors can be used such as KT819, KT 817, KT815, it is desirable to use heat sinks for them. The charge current is adjusted by selecting R1.

Due to the specifics of production, especially in Asian countries, each li-ion battery has different current characteristics. those.one of the entire assembly can charge faster than the rest - this will lead to an increase in the voltage at the contacts of the battery, its overheating, which can lead to the failure of the entire set.

For successful charging of cells with li-ion components, chargers for Bosch screwdriver batteries are used for each cell separately. Those. if the set consists of three elementary batteries, then three batteries are charged separately. Such a charger is called a balancer.

A balancer is an apparatus in which each individual cell in an assembly is charged. In principle, the balancer device is no different from the above-described circuit with a current stabilizer on the TL 130, only with several identical devices for each individual battery. Naturally, the terminal contacts must be on the battery assemblies as well.

The features of the balancer are also the fact that the circuit design is made in such a way as to regulate the charging process of each individual cell and the entire battery as a whole. For this charger, a load compensator is provided, as well as several fuses that burn out in the event of an overload or short circuit. Some manufacturers additionally complete with protection against overheating of the transformer winding. The overheating protection is located under the cover paper insulation of the step-down transformer. The fuse is triggered when it reaches 120 -130 ° C, unfortunately, it is not restored later.

Advice! To get out of this situation, you can advise simply to exclude it from the circuit by connecting the lead ends together. When upgrading the transformer in this way, it is sufficient to have a conventional fuse in the device.

An approximate schematic solution of the balancer is shown in the figure.

Another signature feature of the chargers for Bosch screwdriver batteries is their versatility.

It is no secret that any company that produces hand tools makes separate charges for it, as a result, if the tool is used for intensive work, then it fails in two or three years, and the charger remains, often several of them accumulate.

Bosch offers universal chargers with voltage regulation for several standard ranges, for example 12V, 14V, 16V, 18V. Or 16V, 18V, 24V, 36V. Such a circuit solution is achieved by using a burst switch to adjust the resistance of the output current.

Below are the approximate values ​​of the resistors R1 and R2 for adjusting the voltage at the terminals of the elementary batteries - R1 Ohm + R2 Ohm = UB:

• 22kΩ + 33kΩ = 4.16V
• 15kΩ + 22kΩ = 4.20V
• 47kΩ + 68kΩ = 4.22V

The difference between Ca-Ni and Li-ion (lithium-ion) is that they are less demanding on charging modes. And the fact is that overvoltage and full discharge are very dangerous for lithium-ion, after which these batteries may lose the ability to charge or otherwise be fraught with an internal short circuit.

Ca - Ni - must be discharged at least 70% before charging. If this condition is not met, then the cells will lose capacity with each charge - this phenomenon is called "Memory Effect". To reduce this phenomenon, Bosch offers a charger with a load controller, in which the recovery process begins with automatic discharge to the desired value.

Advice. If there is no such device, then for an approximate control of the discharge, you can use an ordinary incandescent lamp with a lamp filament voltage equal to the battery. A dim glow indicates that the battery is discharged to the desired level.

One of the most common devices for charging 12 V batteries is a charger made according to the scheme below. The memory is assembled from a step-down transformer for 12-18 V and a current of at least 8 A. The alternating voltage of the secondary winding is fed to the diode bridge or assembly for rectification. The necessary smoothing of the ripple is performed by a capacitor with a capacity of at least 100 Mf.

The diagram provides for indication of the network connection, the charging process and the end of the process. For this, a classical adjustment scheme is used along the base of the transistor in the emitter-collector circuit of which the LED is turned on. The circuit opens the voltage at the base coming through the resistance R2. The required charging voltage is provided by the VD1 Zener diode, which can be from 12 to 16V. This circuit will charge the battery in 4-5 hours.

For faster charging of hand tool batteries, an impulse current supply circuit is used. Pulse charging provides a more intensive introduction of charged electrons into the active layer without exceeding the permissible current density values. The classical scheme of such a device operates on bipolar transistors, which are controlled by a pulse-width modulated signal (PWM) converter based on integrated circuits at the output with a pulse transformer. The circuit is assembled on the basis of a classic pulse frequency converter with voltage and current load. Such a charger for a Bosch screwdriver is more expensive than usual, but a 3-4 times reduction in the recovery time of batteries compensates for this disadvantage.

Attention! Some firms position their charger with accelerated charging by increasing the nominal allowed current. This can take the battery out of service well ahead of time. Accelerated charging is only possible with impulse current.

Mains power through the diode bridge VD1 - VD4 is supplied to the smoothing electrolytic capacitor C1 with a capacity of 100 mF. To start the integrated circuit, power is supplied through the resistor R1, after which the generator generates pulses.

The pulses generated in the initial stage open the gate of the field-effect transistor. The transistor opens and control pulses go to the primary winding of the transformer, generating pulses on the secondary winding. For the stable operation of the microcircuit, the incoming voltage from the resistance R1 is not enough, therefore, to stabilize the power supply, part of the pulses are removed from the legs 7-11 of the transformer and fed to the microcircuit to ensure stable operation of the device.

Recently, Bosch has acquired a relatively compact charger for a professional tool "blue" at 10.8V, a distinctive feature from the rest of it may be a step-down transformer in a separate power supply, which is connected directly to the mains socket. The numbers of the abbreviation designation AL1115 (30) indicate the first two digits for a voltage of 10, 8 V, the second 1.5 (3, 0) A - for current loads.

This unit can only charge lithium-ion batteries. The circuit used in this device is impulse, the time from the beginning to the end of full recovery is 30 minutes. Made in an original compact body with natural cooling. Made in China, 2 year warranty. Size (length x width x height) - 21 x 13 x 9 cm. Weight with packaging 420g. Indication of the network, the beginning of the process and the end.

The original circuit is shown below

The operation of the unit can be understood from the above described operation of the circuit for a pulsed memory.

Another innovative idea from Bosch is the GAL 1830 CV induction charger.
It must be said right away that an induction base requires a special battery pack with a built-in device for receiving induction energy and converting it.

The kit includes the actual induction base, frames for hanging on the wall, if desired, you can purchase battery assemblies separately. In order to start the process, it is enough to put the battery on the base. The beginning of the process is indicated by LED illumination of 5 LED indicators. Power supply of the base is 220V. To get started, simply place the battery on the base surface without removing it from the working tool.

It is possible to mount the base on the wall, for this it is placed in a special metal frame that is suspended on a vertical plane. The design itself, despite the 30 V accessory, can charge batteries from 10 to 30 Volts.

• if you make a full cycle of a 2 A / h battery, the base heats up to about 40 - 50 ° C. in the lower part;
• induction batteries are about 10% larger in size and weight than those with a wired base.

Despite the novelty, it is clear that the system is well thought out and has great prospects.

You can buy a charger for a Bosch screwdriver or another company on our website by registering and going through a simple navigation. Here you can also see a large number of hand tools of any power, price and purpose.
Ask and get answers to all your questions from the manager on duty.

Learn more about wireless products in the video.

Often, the native charger that comes with the screwdriver works slowly, taking a long time to charge the battery. For those who use a screwdriver intensively, this is very interfering with their work. Despite the fact that the kit usually includes two batteries (one is installed in the handle of the tool and in operation, and the other is connected to a charger and is in the process of charging), often the owners cannot adapt to the duty cycle of the batteries. Then it makes sense to make a charger with your own hands and charging will become more convenient.

Batteries are not of the same type and may have different charge modes. Nickel-cadmium (Ni-Cd) batteries are a very good source of energy, capable of delivering a lot of power. However, for environmental reasons, their production has been discontinued and they will be encountered less and less. Now they have been superseded by lithium-ion batteries everywhere.

Sulfuric acid (Pb) lead gel batteries have good characteristics, but they make the instrument heavier and therefore are not very popular, despite the relative cheapness. Since they are gelatinous (a solution of sulfuric acid is thickened with sodium silicate), there are no plugs in them, the electrolyte does not flow out of them and they can be used in any position. (By the way, nickel-cadmium batteries for screwdrivers also belong to the gel class.)

Lithium-ion batteries (Li-ion) are now the most promising and advanced in technology and on the market. Their feature is the complete tightness of the cell. They have a very high power density, are safe to use (thanks to the built-in charge controller!), Are beneficially disposed of, are the most environmentally friendly, and have low weight. In screwdrivers, they are currently used very often.

The nominal voltage of the Ni-Cd cell is 1.2 V. The nickel-cadmium battery is charged with a current from 0.1 to 1.0 of the nominal capacity. This means that a 5 amp-hour battery can be charged with a current of 0.5 to 5 A.

The charge of sulfuric acid batteries is well known to all people holding a screwdriver in their hands, because almost every one of them is also a car enthusiast. The nominal voltage of the Pb-PbO2 cell is 2.0 V, and the charging current of the lead sulfuric acid battery is always 0.1 C (current fraction of the nominal capacity, see above).

The lithium-ion cell has a nominal voltage of 3.3 V. The charging current of the lithium-ion battery is 0.1 C. At room temperature, this current can be gradually increased to 1.0 C - this is a fast charge. However, this is only suitable for those batteries that have not been over-discharged. When charging lithium-ion batteries, be sure to observe the voltage exactly. The charge is made up to 4.2 V for sure. Exceeding dramatically reduces service life, decreasing - decreases capacity. Watch the temperature when charging. A warm battery should either be limited to a current of 0.1 C, or turned off before it cools down.

ATTENTION! If the lithium-ion battery overheats when charged over 60 degrees Celsius, it may explode and catch fire! Do not rely too much on the built-in safety electronics (charge controller).

When charging a lithium battery, the control voltage (end-of-charge voltage) forms an approximate series (the exact voltages depend on the specific technology and are indicated in the passport for the battery and on its case):

The charge voltage should be monitored with a multimeter or a circuit with a voltage comparator tuned exactly to the battery being used.But for “entry-level electronics engineers”, you can really only offer a simple and reliable scheme, described in the next section.

The charger below will provide the correct charging current for any of the listed batteries. Screwdrivers are powered by batteries with different voltages of 12 volts or 18 volts. It doesn't matter, the main parameter of a battery charger is the charge current. The voltage of the charger when the load is disconnected is always higher than the rated voltage, it drops to normal when the battery is connected while charging. During the charging process, it corresponds to the current state of the battery and is usually slightly higher than the nominal at the end of charging.

The charger is a current generator based on a powerful composite transistor VT2, which is powered by a rectifier bridge connected to a step-down transformer with sufficient output voltage (see the table in the previous section).

This transformer must also have sufficient power to provide the required current for continuous operation without overheating the windings. Otherwise, it may burn out. The charge current is set by adjusting the resistor R1 with the battery connected. It remains constant during charging (the more constant, the higher the voltage from the transformer. Note: the voltage from the transformer should not exceed 27 V).

Resistor R3 (at least 2 W 1 Ohm) limits the maximum current, and the VD6 LED is on while the charge is in progress. By the end of the charge, the LED light decreases and it goes out. However, do not forget to accurately monitor the voltage and temperature of lithium-ion batteries!

All details in the described scheme are mounted on a printed circuit board made of foil-coated PCB. Instead of the diodes indicated in the diagram, you can take the Russian diodes KD202 or D242, they are quite available in the old electronic scrap. It is necessary to arrange the parts so that there are as few intersections as possible on the board, ideally not a single one. You should not get carried away with the high density of installation, because you are not assembling a smartphone. It will be much easier for you to solder the parts if 3-5 mm remain between them.

The transistor must be installed on a heat sink of sufficient area (20-50 cm2). It is best to mount all parts of the charger in a convenient homemade case. This will be the most practical solution, nothing will interfere with your work. But here great difficulties can arise with the terminals and connection to the battery. Therefore, it is better to do this: take an old or faulty charger from friends, suitable for your battery model, and rework it.

• Open the case of the old charger.
• Remove all the former filling from it.
• Pick up the following radioelements: