The cordless tool is more mobile and easier to use than its networked counterparts. But do not forget about the significant drawback of a cordless tool, this is how you yourself understand the fragility of batteries. Buying new batteries separately is comparable in price to purchasing a new tool.

After four years of service, my first screwdriver, or rather batteries, began to lose capacity. To begin with, I assembled one of two batteries by choosing working "banks", but this upgrade did not last long. I reworked my screwdriver on a network - it turned out to be very inconvenient. I had to buy the same, but new 12 volt "Interskol DA-12ER". The batteries in the new screwdriver lasted even less. As a result, two serviceable screwdrivers and more than one working battery.

On the Internet, they write a lot on how to solve this problem... It is proposed to convert old Ni-Cd batteries to Li-ion 18650 batteries. At first glance, there is nothing complicated about that. You remove old Ni-Cd batteries from the case and install new Li-ion batteries. But it turned out to be not so simple. What you need to pay attention to when upgrading your cordless tool is described below.

For alteration you will need:

I'll start with 18650 lithium-ion batteries.

The rated voltage of the 18650 cells is 3.7 V. According to the seller, the capacity is 2600 mAh, the marking is ICR18650 26F, the dimensions are 18 by 65 mm.

The advantages of Li-ion batteries over Ni-Cd are smaller dimensions and weight, with a higher capacity, as well as the absence of the so-called "memory effect". But lithium-ion batteries have serious drawbacks, namely:

1. Subzero temperatures drastically reduce capacity, which cannot be said about nickel-cadmium batteries. Hence the conclusion - if the tool is often used at low temperatures, then replacing it with Li-ion will not solve the problem.

2. A discharge below 2.9 - 2.5V and an overcharge above 4.2V can be critical, a complete failure is possible. Therefore, a BMS board is needed to control the charge and discharge, if it is not installed, then the new batteries will quickly fail.

The internet mostly describes how to remake a 14 volt screwdriver - perfect for retrofitting. With a series connection of four 18650 cells and a nominal voltage of 3.7V. we get 14.8V. - just what you need, even with a full charge plus another 2V it is not scary for the electric motor. And what about a 12V instrument. There are two options, install 3 or 4 18650 cells, if three is not enough, especially with a partial discharge, and if four is too much. I chose four and, in my opinion, made the right choice.

And now about the BMS board, it is also from AliExpress.

This is the so-called charge control board, battery discharge, specifically in my case CF-4S30A-A. As you can see from the marking, it is calculated for a battery of four 18650 cells and a discharge current of up to 30A. It also has a built-in so-called "balancer", which controls the charge of each element separately and eliminates uneven charging. For the correct operation of the board, the batteries for assembly are taken of the same capacity and preferably from the same batch.

In general, there are a great many BMS boards on sale with different characteristics. I do not advise taking for currents below 30A - the board will constantly go into protection and to restore operation, you need to briefly apply a charging current to some boards, and for this you need to remove the battery and connect it to the charger. There is no such drawback on the board that we are considering, you just release the trigger of the screwdriver and in the absence of short-circuit currents, the board will turn on by itself.

For charging the converted battery, the native universal charger was perfect. In recent years, Interskol has begun to equip its tools with universal chargers.

The photo shows to what voltage the BMS board charges my battery together with a standard charger. The voltage on the battery after charging 14.95V is slightly higher than that required for a 12-volt screwdriver, but it is rather even better. My old screwdriver became faster and more powerful, and fears that it would burn out, after four months of use, gradually disappeared. That seems to be all the main nuances, you can start reworking.

We disassemble the old battery.

We solder the old cans and leave the terminals together with the temperature sensor. If you also remove the sensor, then when using the standard charger, it will not turn on.

According to the diagram in the photo, we solder 18650 cells into one battery. Jumpers between the "banks" must be made with a thick wire of at least 2.5 kV. mm, since the currents during the operation of the screwdriver are large, and with a small cross-section, the power of the tool will sharply drop. The network writes that it is impossible to solder Li-ion batteries because they are afraid of overheating, and they recommend connecting using spot welding. You can only solder you need a soldering iron of at least 60 watts more powerful. The most important thing is to solder quickly so as not to overheat the element itself.

It should look something like this to fit into the battery case.

Cordless tools use battery power to operate. Naturally, from time to time it is necessary to replenish the used stock. This process is called charging. In the process of charging and discharging, reversible chemical reactions occur in the battery, which determine the principle of its operation.

Varieties of devices for charging

Carrying out the same function, chargers have a variety of options for the internal structure. By the type of voltage conversion of the household electrical network, the structures for charging screwdrivers differ as follows:

• Transformer;
• Inverter (pulse).

Transformer devices initially appeared in the first place, since they required the simplest electronic base. The classic design of the device includes:

• Transformer;
• Rectifier bridge;
• Filtering capacity;
• Current stabilizer;
• Control circuit.

Regardless of the type of stabilizer and additional options, transformer chargers are united by such a disadvantage as large dimensions and weight. This is due to the fact that the weight and dimensions of the transformer increase in proportion to the power of the product. Accordingly, those chargers that have acceptable weight and dimensions are capable of delivering small values ​​of the charging current, and the charging process takes a long time.

Devices of the inverter type, which use the conversion of the input voltage into high-frequency current, are free from this drawback. This approach allows the use of small-sized transformers operating with high power values. With dimensions much smaller than those of transformer structures, inverter ones are capable of generating a significant charging current. In this case, the battery charging time is reduced to one hour or less.

Additional functions

The simplest charger (charger) does not monitor the condition of the battery. All this rests with the user. As a result, regular undercharging, prolonged charging, suboptimal charging process, all this leads to a sharp reduction in battery life. This type of circuitry is used only in the cheapest models of screwdrivers and cannot be recommended for purchase.

More expensive models have a built-in charge controller or sleep timer. The battery is charged until the required capacity is reached or after a certain time. In the latter case, undercharging is possible, but prolonged voltage supply is excluded. The charge level is monitored by the battery voltage level. Most types of tools in the middle price range use just such memory models.

The most advanced models have a charge controller circuit based on the use of a microcontroller. In this case, in addition to the actual charge, a preliminary discharge of not fully depleted elements is applied and up to a strictly defined value. This procedure eliminates the appearance of the "memory" effect inherent in alkaline batteries and helps to equalize the capacity individual elements battery. The battery is charged according to a specific algorithm according to the manufacturer's requirements.

The charge level is monitored by the battery voltage. The delta method is used. It is based on the peculiarity of Ni-Cd and Ni-MH batteries to a certain decrease in voltage when fully charged. The controller circuitry reacts to a voltage drop at the end of the time period and cuts off the charging current.

Charger for a screwdriver on microcontrollers will have a high cost, but at the same time will significantly extend the service life of an expensive battery and shorten the full charge time. This type of charge controller comes with expensive professional screwdriver models.

Charge voltage and form factor

Manufacturers do not have uniform standard by supply voltage of the instrument. On the one hand, the low voltage of the battery reduces its cost by reducing the number of cells, on the other hand, higher-voltage batteries provide a number of advantages:

• Higher power of the device;
• At the same power, the current consumption is reduced;
• The service life between charges is increased.

The increased number of elements increases the cost of the tool, so this approach is typical of manufacturers of high-quality and expensive equipment.

Note! If the weight of the tool is important, then preference should be given to low-voltage products. 18-volt screwdrivers have the most significant weight. The exception is lithium-ion batteries, but they can only be found in the most expensive models tool.

Since the EMF of Ni-Cd and Ni-MH batteries has a strictly defined value, namely 1.2V, then the voltage of the battery cells is reduced to a number of several values:

• 10 batteries - 12.0V;
• 11 batteries - 13.2V;
• 12 batteries - 14.4V;
• 13 batteries - 16.6V;
• 14 batteries - 17.8V.

You can find other values, both downward and upward, but infrequently.

For simplicity, many manufacturers report the battery voltage as rounded. For instance, accumulator battery with 14 elements is often labeled 18 volts, and with 10 – 12 volts.

Screwdriver batteries differ not only in voltage, but also in the shape of the fasteners and the location of the terminals. An important conclusion follows from this.

Important! Various rechargeable batteries and devices for charging them are not compatible with each other. The only exceptions are products from one manufacturer, which were created with compatibility in mind.

Modernization of chargers

Do-it-yourself alteration of standard chargers for a screwdriver is usually done in order to improve their characteristics. The most easily amenable to alteration are transformer-type designs, in which only the monitoring and control circuit changes. Inverter converters are much more difficult to change. In most cases, revision requires a complete replacement of the internal "filling" of the device.

As a rule, charging blocks of the lower price category are subject to alterations. The main options that are introduced into the converted structure are – this is the control of the charge level and automatic shutdown... Alterations of this type, made using analog circuitry, are not particularly difficult and are available to a beginner and average radio amateur.

The manufacture of more complex structures, controlled by a microcontroller, is only possible for experienced craftsmen, and besides, they do not make much sense. As already mentioned, the simplest devices are produced for cheap models of the tool, respectively, and the quality of the batteries in them is not up to par. The gain in the reliability of storage batteries, the extension of their life will turn out to be disproportionate to the costs of such a modification of the charger.

Repair

Just like a rework, repairing a screwdriver charger requires certain knowledge in the field of radio engineering. Without experience, power cords and fuses can be replaced. It should be noted that such faults occupy one of the main places in frequency. Lack of charge and power indication is usually associated with a broken wire or blown fuse. Both faults are detected by dialing with an ohmmeter.

A more serious repair of the screwdriver charging, especially in expensive designs, is complicated by the lack of a schematic diagram.

Important! Independent or improper repair of chargers for lithium-ion batteries can lead to fire and even explosion of the battery, since batteries of this type are extremely sensitive to the charging mode.

Video

When using a screwdriver, users often encounter damage to the charger (charger). First of all, this is due to the instability of the parameters of the electrical network to which the charger is connected, and secondly, with the failure of the battery. This problem is solved in two ways: buying a new charger for a screwdriver or repairing it yourself.

Types of chargers

The popularity of the screwdriver is due to the fact that it simplifies the process of screwing or unscrewing various fasteners but. Characterized by mobility and small size, it is indispensable for assembling furniture structures, disassembling equipment, roofing and others. construction works... The tool owes its mobility to the rechargeable batteries included in its design.

The advantage of using batteries is the possibility of their repeated use. Batteries, giving the accumulated energy to the device, periodically need to be recharged themselves. To restore the value of their capacity, chargers are used.

The screwdriver battery is charged in two ways: with a built-in or external charger. The built-in charger allows you to charge the battery without removing it from the screwdriver. The capacity recovery circuit is located directly with the battery. While the remote means their extraction and installation in a separate charging device. Distinguish chargers by the type of recoverable batteries. The batteries used are:

• nickel-cadmium (NiCd);
• nickel metal hydride (NiMH);
• lithium-ion (LiIon).

The final cost of a screwdriver depends not least on the type of batteries used and the capabilities of the charger. Chargers are available in 12 volts, 14.4 volts and 18 volts. In addition, storage devices are divided according to their capabilities and can have:

• indication;
• fast charging;
• different type of protection.

The most used chargers use a slow charge due to a low current. They do not contain an indication of operation in their design and do not turn off automatically. This is more true for built-in capacity recovery devices. Chargers built on pulsed circuits provide the possibility of accelerated charging. They automatically turn off when the required voltage is reached or in the event of an emergency.

Types of batteries used

Nickel-cadmium batteries do not have problems when charging at an accelerated rate. Such batteries have a high load capacity, a low price and easily tolerate work at sub-zero temperatures. The disadvantages include: memory effect, toxicity, high self-discharge rate. Therefore, before charging this type of battery, it must be completely discharged. The battery has a high self-discharge rate and discharges quickly even when not in use. Currently, they are practically not produced due to their toxicity. Of all types, they have the smallest capacity.

Nickel metal hydride is superior to NiCd in all respects. They have less self-discharge, less pronounced memory effect. With the same dimensions, they have a large capacity. They contain no toxic material, cadmium. In the price category, this type occupies an average position, therefore, it is the most common type of capacitive elements in a screwdriver.

Lithium-ion is characterized by high capacity and low self-discharge. These batteries do not tolerate overheating and deep discharge. In the first case, they are capable of exploding, and in the second, they will no longer be able to restore their capacity. They are also capable of working at subzero temperatures and have no memory effect. The use of a charger with a microcontroller made it possible to protect the battery from overcharging, thereby making this type the most attractive for use. For the price they are more expensive than the first two types.

In addition, the main characteristic of rechargeable batteries is their capacity. The higher this indicator, the longer the screwdriver works. The unit of measure for capacity is milliamperes per hour (mAh). The design of the battery consists in connecting the batteries in series and placing them in a common housing. For Li-Ion, the voltage on one cell is 3.3 volts, for NiCd and NiMH - 1.2 volts.

The principle of operation of the memory

If the charger fails, it makes sense to first try to restore it. For repairs, it is advisable to have a charging device circuit and a multimeter. The circuitry of many charging devices is based on the HCF4060BE microcircuit. Its switching circuit forms the delay of the charging time interval. It includes a crystal oscillator circuit and a 14-bit binary counter, making it easy to implement a timer.

The principle of operation of the charger circuit is easier to disassemble into real example... This is how it looks in the Interskol screwdriver:

This circuit is designed to charge 14.4 volt batteries. It has an LED indication showing the connection to the network, LED2 is on, and the charging process is on, LED1 is on. The U1 HCF4060BE microcircuit or its analogs: TC4060, CD4060 is used as a counter. The rectifier is assembled on VD1-VD4 power diodes of the 1N5408 type. The Q1 PNP transistor operates in the key mode, the control contacts of the S3-12A relay are connected to its terminals. The key operation is controlled by the U1 controller.

When you turn on the charger AC voltage 220 volt network through a fuse goes to a step-down transformer, at the output of which its value is 18 volts. Further, passing through, it straightens and falls on the smoothing capacitor C1 with a capacity of 330 μF. The voltage across it is 24 volts. When the battery is connected, the contact block of the relay is in the open position. Microcircuit U1 is powered through a Zener diode VD6 with a constant signal equal to 12 volts.

When the "Start" SK1 button is pressed, the 16th output of the U1 controller receives a stabilized signal through the resistor R6. Key Q1 opens and current flows through it to the relay outputs. The contacts of the S3-12A device are closed and the charging process begins. The VD8 diode, connected in parallel with the transistor, protects it from a voltage surge caused by a relay disconnection.

The used SK1 button works non-latching. When it is released, all power is supplied through the VD7, VD6 chain and the limiting resistance R6. And also power is supplied to LED1 through resistor R1. The LED lights up, signaling that the charging process has started. The operating time of the U1 microcircuit is set for one hour of operation, after which the power is removed from the transistor Q1 and, accordingly, from the relay. Its contact group breaks and the charge current disappears. LED1 goes out.

This charger is equipped with an overheating protection circuit. Such protection is realized using a temperature sensor - thermocouple SA1. If during the process the temperature reaches more than 45 degrees Celsius, then the thermocouple will work, the microcircuit will receive a signal and the charge circuit will break. After the end of the process, the voltage at the battery terminals reaches 16.8 volts.

This charging method is not considered smart, The charger cannot determine the state of the battery... Because of this, the battery life of the screwdriver will decrease due to the development of the memory effect. That is, the capacity of the battery decreases every time it is charged.

Homemade charging devices

It is quite simple to make your own charging for a 12 volt screwdriver with your own hands, by analogy with the one used in the Interskol memory. To do this, you need to take advantage of the ability of the thermal relay to break the contact when a certain temperature is reached.

In the circuit, R1 and VD2 are a charge current flow sensor, R1 is designed to protect the VD2 diode. When voltage is applied, the transistor VT1 opens, a current passes through it and the LH1 LED starts to glow. The voltage value drops on the R1, D1 chain and is applied to the battery. The charge current flows through the thermal relay. As soon as the temperature of the battery to which the thermal relay is connected exceeds permissible value, it works. The relay contacts switch, and the charge current begins to flow through the resistance R4, the LH2 LED lights up, indicating the end of the charge.

Two-transistor circuit

Another simple device can be performed on the available elements. This circuit operates on two transistors KT829 and KT361.

The magnitude of the charge current is controlled by the KT361 transistor to the collector, to which the LED is connected. This transistor also controls the state of the KT829 composite element. As soon as the capacity of the battery begins to increase, the charge current decreases and the LED, accordingly, smoothly goes out. Resistance R1 sets the maximum current.

The moment the battery is fully charged is determined by the required voltage on it. The required value is set by a variable resistor of 10 kOhm. To check it, you need to put a voltmeter on the battery connection terminals without connecting it itself. Any rectifier unit designed for a current of at least one ampere is used as a constant voltage source.

Using a specialized microcircuit

Manufacturers of screwdrivers are trying to reduce the prices of their products, often this is achieved by simplifying the memory scheme. But such actions lead to the rapid failure of the battery itself. Using a universal microcircuit designed specifically for the MAXIM MAX713 charger, you can achieve good performance in the charging process. This is what the charger circuit for an 18 volt screwdriver looks like:

The MAX713 microcircuit allows you to charge nickel-cadmium and nickel-metal hydride batteries in a fast charge mode, with a current of up to 4 C. It can monitor the battery parameters and, if necessary, reduce the current automatically. At the end of charging, the microcircuit-based circuit consumes practically no energy from the battery. It can interrupt its work on time or when a temperature sensor is triggered.

HL1 is for power indication and HL2 is for fast charge display. The setup of the scheme is as follows. To begin with, the charging current is selected, usually its value is equal to 0.5 C, where C is the capacity of the battery in ampere-hours. The PGM1 pin is connected to the positive supply voltage (+ U). The power of the output transistor is calculated by the formula P = (Uin - Ubat) * Isar, where:

• Uin - the highest voltage at the input;
• Ubat - battery voltage;
• Isar - charging current.

The resistance of R1 and R6 is calculated by the formulas: R1 = (Uin-5) / 5, R6 = 0.25 / Isar. The choice of time after which the charging current will turn off is determined by connecting the PGM2 and PGM3 pins to different pins. So, for 22 minutes, PGM2 is left unconnected, and PGM3 is connected to + U, for 90 minutes, PGM3 is connected to the 16th leg of the REF chip. When it is necessary to increase the charging time to 180 minutes, the PGM3 is shorted to the 12 leg of the MAX713. The longest time of 264 minutes is achieved by connecting PGM2 with the second leg, and PGM3 with the 12th leg of the microcircuit.

Charging the screwdriver without charger

It is not difficult to restore a battery without the help of a charger, but many do not know how. You can charge the screwdriver battery without a charger using any constant voltage power supply. Its value should be equal to or slightly greater than the voltage value of the battery being charged. For example, for a 12V battery, you can take a rectifier to charge a car. Using terminal clamps and wires, connect them, observing the polarity, to each other for thirty minutes, while controlling the temperature of the battery.

And you can also refine the power supply with high voltage using a simple integrated stabilizer. The LM317 microcircuit allows you to control the input signal up to 40 volts. You will need two stabilizers: one turns on according to the voltage stabilization circuit, and the second - current. Such a scheme can also be used when reworking a charger that does not have nodes for monitoring the charging process.

The scheme works quite simply. During operation, a voltage drop is formed across the resistor R1, it is enough for the LED to light up. As the charge progresses, the current in the circuit drops. After a while, the voltage on the stabilizer will be low and the LED will turn off. Resistor Rx sets the highest current. Its power is chosen at least 0.25 watts. With this scheme, the battery will not be able to overheat as the device will automatically shut down when the battery is fully charged.

You can often find harmful advice that you can charge the battery using a diode bridge and a 100 W incandescent lamp. It is absolutely impossible to do this, because there is no galvanic isolation and, in addition to fatal defeat electric shock, the battery may explode.

Almost all screwdrivers operate on batteries. The average battery capacity is 12 mAh. And in order for it to always be in working order, a constant recharge is needed. This requires a charger specific to each type of battery. However, they differ greatly in their characteristics.

Currently producing 12-18 V models... It is also worth noting that manufacturers use different components for chargers. different models... To figure this out, you should familiarize yourself with the standard schematic of these chargers.

Standard wiring diagram for charger

The basis standard scheme is an three-channel type microcircuit... In this version, four transistors are attached to the microcircuit, very different in capacitance and high-frequency capacitors (pulse or transient). Open-type thyristors or tetrodes are used to stabilize the current. The current conductivity is regulated by dipole filters. This electrical circuit easily copes with network congestion.

Schematic diagram

The purpose of power tools is primarily to make our daily work less tedious and chore. In the home, a screwdriver is an indispensable assistant in the repair or disassembly (assembly) of furniture and other household items. Autonomous power supply screwdriver makes it more mobile and convenient to use. The charger is a power source for any cordless power tool, including a screwdriver. For example, let's get acquainted with the device and the schematic diagram.

For circuit diagrams of chargers of 18 V screwdrivers are used transistors several capacitors and a diode bridge tetrode. Frequency stabilization is carried out by the grid trigger. The conductivity of the charging current for 18V is typically 5.4 μA. Sometimes, chromatic resistors are used to improve conductivity. The capacitance of the capacitors, in this case, should not be higher than 15 pF.

The design of the cordless device for the screwdriver

The "banks" of the battery are enclosed in a housing that has four contacts, including two power plus and minus for discharge / charge. Upper control contact switched on via thermistor(thermal sensor) that protects the battery from overheating while charging. When it gets too hot, it limits or cuts off the charge current. The service contact is connected through a 9 kΩ resistor, which equalizes the charge of all elements of complex charging stations, but they are usually used for industrial devices.

Standard and individual characteristics of the Interskol charger

Power supply elements

The battery is the most expensive part of a screwdriver and is approximately 70% of the total cost tool. If it fails, you will have to spend money on purchasing a practically new screwdriver. But if you have certain skills and knowledge, you can fix the breakdown yourself. This requires certain knowledge about the features and structure of a battery or charger.

All elements of a screwdriver, as a rule, have standard characteristics and dimensions. Their main difference is the value of energy consumption, which is measured in A / h (ampere / hour). The capacity is indicated on each element of the power supply (they are called "banks").

"Banks" are: lithium - ionic, nickel - cadmium and nickel - metal - hydride. The voltage of the first type is 3.6 V, others have a voltage of 1.2 V.

Battery malfunction determined by a multimeter. He will determine which of the "cans" is out of order.

DIY battery repair

To repair a screwdriver battery, you need to know its design and accurately determine the location of the breakdown and the malfunction itself. If even one element fails, the entire circuit will lose its functionality. The presence of a "donor" in which all the elements are in order or new "banks" will help solve this problem.

A multimeter or a 12V lamp will tell you which item is faulty. To do this, you need to put the battery to charge until it is fully charged. Then disassemble the case and measure voltage all elements of the chain. If the voltage of the "cans" is lower than the nominal, then you need to mark them with a marker. Then collect the battery and let it run until its power drops noticeably. After that, disassemble again and measure the voltage of the marked "cans". The voltage sag on them should be most noticeable. If the difference is 0.5 V or more, and the element is working, then this indicates its imminent failure. Such elements must be replaced.

Using a 12V lamp, you can also identify faulty circuit elements. To do this, connect a fully charged and disassembled battery to the plus and minus contacts on a 12V lamp. The load created by the lamp will be discharge the battery... Then measure the sections of the chain and identify the faulty links. Repair (refurbishment or replacement) can be done in two ways.

1. The defective element is cut off and a new one is soldered with a soldering iron. This applies to lithium ion batteries. Since it is not possible to restore their work.
2. Nickel - cadmium and nickel - metal - hydride cells can be recovered if an electrolyte is present that has lost volume. To do this, they are stitched with voltage, as well as enhanced current, which helps to eliminate the memory effect and increases the capacity of the element. Although it will not be possible to completely eliminate the defect. Perhaps, after a while, the malfunction will return. Much the best option there will be replacement of the failed elements.

Replacing the required chain elements

To repair a battery for a screwdriver, you will need spare battery, from which, you can borrow the necessary parts or purchase new chain elements. New "banks" must meet the required parameters. To replace them, you will need a soldering iron, tin, rosin or flux.

DIY universal charger

To charge the battery device, you can make a homemade charger, USB powered... Required components for this: socket, USB charger, 10 amp fuse, required connectors, paint, electrical tape and tape. For this you need:

As you can see, this the process will not take long and won't be too ruinous for your family budget.

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 the 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 high power. However, for environmental reasons, their production has been discontinued and they will be encountered less and less frequently. 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 gel-like (the sulfuric acid solution 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.

Charge modes

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 charging 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 “electronics engineers entry level”You can really only offer a simple and reliable scheme, described in the next section.

Charger + (Video)

The charger below provides 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 during charging. During charging, 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 when the battery is 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 about precise voltage control. lithium ion batteries and their temperature!

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 KD202 or D242 diodes, 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:

• Choose the right size for printed circuit board, which fits into the body along with the details from the above diagram, draw with nitro paint its paths along schematic diagram, pickle in copper sulphate and unsolder all the details. The radiator for the transistor must be installed on an aluminum plate so that it does not touch any part of the circuit. The transistor itself is tightly screwed to it with a screw and an M3 nut.
• Assemble the board in the case and solder the terminals according to the scheme, strictly observing the polarity. Lead out the wire for the transformer.
• Install the transformer with a 0.5 A fuse in a small suitable housing and provide a separate connector for connecting the converted charging unit. It is best to take connectors from computer power supplies, install dad in a case with a transformer, and connect mom to the bridge diodes in the charger.

The assembled device will work reliably if you have carefully and carefully performed