Charger (charging) for a screwdriver: types and assembly diagrams

What it is?

A screwdriver battery charger is a device that allows you to replenish battery energy lost due to the use of the tool. Due to the ability to charge the battery many times, the battery itself can have a relatively small size and capacity, as long as the number of recharge cycles is large and the charger provides a high rate of restoration of the original charge.

All chargers can be globally divided into 2 classes: built-in and remote. In the first case, there is no need to specifically remove the battery for charging - the cable with an electrical plug is attached directly to the body of the instrument (or even permanently attached to it), which is quite convenient. Remote chargers are a separate mechanism that involves removing the battery from the screwdriver body, inserting it into a special clamp, and the latter has the same cable with a plug and is plugged into a socket. Each of the solutions has its own advantages and disadvantages, but more on that later.

If the above division into classes does not fundamentally affect the operation of the mechanism, then matching the type of charger to the type of battery is critically important. The fact is that even today batteries for power tools are available in several types, each of which has its own operating characteristics. If the charger does not meet the required parameters, this can lead to very rapid battery damage. To understand what criteria a charger should have, let’s briefly consider the features of all the main types of batteries.

1. Nickel-cadmium batteries are quite rare today - their popularity is falling due to many factors, including the toxicity of the contents, the ability to quickly self-discharge, high weight with a relatively low charge, and the “memory effect”. The last criterion means that the battery must always be first completely discharged and then fully charged; if this rule is not followed, its capacity, already low, will begin to decrease literally before our eyes. Perhaps the only huge advantage of this type of battery is its ability to operate normally at any low temperature. At the same time, they are also capable of withstanding high loads, which is why chargers for them are often made with the ability to charge as quickly as possible - this is very important, since you always need to charge from 0% to 100%.
2. Nickel-metal hydride batteries are considered an improved version of nickel-cadmium batteries - the disadvantages are generally the same, but they are all expressed to a noticeably lesser extent. In addition, the contents of such batteries do not contain toxic components. The advantages are also very similar to those of the previous type of battery, which is why these batteries are already much more common, and the chargers for both types are very similar. The only indicator in which metal hydride power supplies are worse than cadmium ones is cost.
3. Lithium-ion batteries are rightly considered the most modern and technically the best. They are devoid of most of the disadvantages of the batteries described above, for example, they weigh little with a significant amount of charge, self-discharge by a few percent per month of inactivity, and are completely devoid of the “memory effect”. For a long time they were criticized for a somewhat accelerated discharge when working in frosty conditions, but in recent years this problem has been gradually solved. True, there are still disadvantages, and the highest cost is far from the only one. So, it is extremely undesirable to completely discharge such a battery - after this it may not restore its original capacity, although the advantage is that it can be recharged at any time due to the absence of a “memory effect”. Another problem is the possibility of a battery exploding when overheated from overcharging, so the charger for such a battery must be equipped with a microcontroller.

Among other things, chargers can differ in voltage - 12, 14.4 or 18 volts (this indicator must correspond to that recommended in the instructions for the screwdriver). Additional options include a special option for accelerated charging, as well as an indication of the charge level and automatic shutdown in case of a full charge or some unforeseen situation. The presence of additional functions negatively affects the cost of the charger.

Principle of operation

The charger should not be perceived as a simple cable that allows you to power the battery from an electrical outlet - this device is always somewhat more complicated. Depending on the exact set of functions of a particular instance, it may be structured differently, however, in general, the methods for achieving the goal are always approximately the same. Since it is impossible to charge a screwdriver battery directly from a 220 V outlet, the key part of any charger is a step-down transformer, which provides a significant reduction in voltage. He himself, as a rule, does not lower the voltage to the required value - the current acquires the necessary characteristics only later, passing through diode bridges and microcircuits.

To prevent the entire contents of the charger, not to mention the battery or the screwdriver as a whole, from burning out due to too high voltage in the power supply network, a fuse is installed at the very beginning of the circuit. Charge limitation is usually achieved in one of the two most common ways - either the microcontroller measures the current in the battery, or the charging time is limited by a timer.

The first option is good in the case of lithium-ion batteries, since they can be charged at any time, which means that the exact charging time cannot be determined. In this case, overcharging threatens to explode, so it is very important that the microcontroller is able to determine the charge level and turn off the power supply in time. The timer is good for recharging different types of nickel batteries - they are not afraid of overcharging, and they must be completely discharged before the procedure, so the charging time is always approximately the same.

For increased ease of use, some expensive charger models are also equipped with indicators, which are usually ordinary LEDs. Often they perform different functions - one can demonstrate the fact that the device is connected to the network, another shows that the current is not lost anywhere in the microcircuits and flows into the battery, others can even indicate the approximate charge level, highlighting only a certain part of the line in which they are lined up.

How does a screwdriver charger work?

The operating principle of the charger for different screwdriver batteries is as follows:

1. When the device is connected to the network, a voltage of 220V passes through the fuse.
2. The alternating voltage goes to a step-down transformer. The voltage value is converted to 18.
3. The charge enters the diode bridge.
4. There is a rectification and transition to capacitor C1, its capacitance is 330 μF. The voltage is converted to 24V.

The relay closes after switching on by pressing the button. The battery begins to charge at the output of the mains rectifier. The average time to fully charge the battery in a screwdriver is 50-60 minutes. These are average figures that apply to 12, 14 or 18 volt batteries.

Block diagram of a screwdriver

Screwdrivers from different manufacturers are built on different element bases, but the structural electrical circuit for all is approximately the same. The power tool consists of:

• removable battery;
• control boards;
• trigger switch combined with speed controller;
• frequency control range switch (may be missing);
• electric motor (commutator or brushless).

When making your own power source for a screwdriver, you need to pay attention to two parameters:

• voltage;
• rated output current.

With voltage, everything is simple - the new power source must have an output voltage equal to the rated supply voltage of the power tool. A decrease leads to a loss of torque, an increase leads to a decrease in resource. Operation of the control board at low voltage is not guaranteed; at high voltage, it is likely to fail.

The required operating current is more difficult to determine. Manufacturers of power tools rarely indicate current consumption. A little more often they indicate power in watts. But on the nameplates of screwdrivers you can find the following data:

• operating voltage (in volts);
• rotation speed (in revolutions per minute);
• torque (in newtons per meter).

These data seem sufficient to calculate the operating current.

Label with electrical characteristics of the DEKO DKCD20FU screwdriver.

In fact, not everything is so rosy. If you use data from a real screwdriver and try to calculate the rated current, you will get an absurd result.

First, the output power is calculated using the formula:

P=T*RPM/9550, where:

• P – power, kW;
• T – torque, N/m;
• RPM – rotation speed, rpm;
• 9550 is a coefficient that combines the conversion from one unit to another.

For the given data it turns out:

P=42*1350/9550=5.9 kW.

This developed power must be divided by the efficiency (approximately equal to 0.8), resulting in a power consumption of about 7 kW. At a voltage of 20 volts, the batteries must deliver a current of 350 A!!! With a capacity of 2 Ah, the battery will be discharged in 20 seconds (even if theoretically the battery provides such a current). This is the promised absurdity. The reason for this may be crafty declarations of revolutions or torque. Perhaps the greatest torque is produced only at a certain speed, but even if you know it, there will be little practical sense. After all, a screwdriver operates at different frequencies.

Therefore, you need to focus on the following figures obtained experimentally:

• idle speed – 1..2 amperes;
• average load – 4..6 A;
• maximum load – 8..11 A;
• current surges during full braking – up to 30 A.

You can clarify these figures for a specific screwdriver by measuring the actual current consumption in different modes, putting together a simple circuit for this, and driving the power tool under different loads.

Circuit for measuring current consumption.

Or you can not specify, but focus on the numbers indicated above. A power supply will be needed for a maximum current of 10 A (but not less than 5..6), preferably with overcurrent protection.

Types of batteries

A charger for a screwdriver is created taking into account the features of an autonomous power source. The following sections discuss popular rechargeable batteries

When studying the compatibility of functional components of a screwdriver, it is recommended to pay special attention to charge recovery modes

Nickel-cadmium

These batteries are different:

• reasonable cost;
• good energy indicators;
• long service life.

Unfortunately, big problems arise at the disposal stage. Harmful chemical compounds in Ni-Cd batteries cause great harm to the environment. For this reason, the use of such products is gradually being phased out in many countries.

If other data is not indicated by the manufacturer, select the operating mode along with a suitable electrical circuit diagram for the screwdriver according to the following data:

• to extend service life, it is recommended to “train” with 2-6 full work cycles before starting operation and subsequently every 6-8 months;
• long-term storage in a discharged state is permissible;
• pre-discharge voltage – from 0.9 to 1 V;
• the nominal capacity is maintained only at positive temperatures;
• overheating is unacceptable during the recovery process (not higher than +40°C);
• the completion of the cycle is indicated by a slight decrease in voltage;
• The charge current is calculated using the formula:

2*C.

Important! The letter “C” denotes the capacity indicated in the battery passport. If C=2.5 A*h, you can use a charge with a current of 5A = 2*2.5

Sulfuric acid batteries for screwdrivers

Products in this category are created on the basis of lead cells with an acid-type gel electrolyte. Advantages:

• simplicity;
• reasonable price;
• Possibility of use in any position.

The main disadvantages of sulfuric acid batteries are their significant dimensions and heavy weight. The cells are charged with a voltage of 1.8-2 V while maintaining a current of 0.1-0.15 * C.

Li-ion batteries for screwdriver

This is the most common modern solution. Batteries of a similar design are used in smartphones and laptops, and other household and professional equipment. Pros:

• better performance compared to the analogues discussed above in terms of energy storage per unit volume (weight);
• wide operating temperature range;
• long-term preservation of good operating parameters;
• no excessive recycling requirements.

One standard cell is charged with a voltage of 3.6V to a level of 4.2V. Exceeding the threshold set by the manufacturer will shorten the service life. A low level limits savings capabilities. The energy potential of batteries is restored with careful temperature control.

What is needed for remodeling

To remake a screwdriver, you need to briefly familiarize yourself with the electrical diagram of the tool. The tool is driven by an electric motor. Depending on the power and class of the tool, the voltage can be 12, 14, 18 volts. The electric motor receives power from a battery of batteries of the appropriate voltage.

The engine transmits torque to the cartridge through a mechanical gearbox. Engine speed is changed both by the gear reduction system and by a reversible electronic speed controller combined with a power button.

Screwdriver device:

1. Accumulator battery.
2. Speed ​​regulator.
3. Power button.
4. Electric motor.
5. Gearbox.
6. Cartridge.

The main difficulty in converting a screwdriver to operate on a 220-volt network is that it requires more power. Nickel-cadmium or lithium batteries provide it without problems. But not every power supply can produce the required power.

How much power does the power supply need and how much does the screwdriver consume from the power supply?

Calculating the required power of the power supply is not difficult - you need to multiply the current consumed by the electric motor of the tool by the voltage. For example, the tool is powered by a battery with a voltage of 12 volts. The current that the electric motor needs to operate is 10 amperes. We get 120 watts. But this is the minimum value.

To ensure normal operation under loads, for example, when driving a screw into hard wood, the power supply must be selected with a margin of 30-40%. Otherwise, the screwdriver will not be able to work normally under load or the power supply will fail.

The current strength, depending on the model, can be 7-10 A for household screwdrivers and 30-40 A for professional models. The battery voltage can be 12 V, 14 V, 18 V depending on the specific model.

Important! The current required by a screwdriver to operate depends on the load. At idle, the current is minimal and increases significantly during startup or when tightening a screw.

The required voltage, power and battery capacity parameters are usually indicated on the label of the tool itself or in the technical documentation for it.

If the operating voltage of the instrument is 12 V, the number of options for choosing a power source increases, for example, you can connect it to a computer power supply. It is quite possible to purchase an old one with a power of 300 W for a low price. In addition, the output power is sufficient with reserve. The advantages of this option include: ease of modification, as well as the fact that a computer power supply with a power of 300 W or more is relatively easy to find.

The block parameters are indicated on a sticker located on the wall. For example, it states that a voltage of 220 v is supplied to the input, a current of 25 A is supplied to the output of 12 v. We get a power of 300 W.

If desired, you can use the following as a 12 V power source from the mains:

• LED driver;
• electronic transformer for powering low voltage halogen lamps;
• car battery charger.

If the instrument is designed to be powered at a different voltage, say 14 V or 18 V, there are few options for choosing a power supply. For a tool operating on a voltage of 14 V and having a maximum current of up to 25A, a universal power supply unit AIDA BSh 14 PRO is available for sale. There is also an 18 V power supply, designed for current up to 20 A, AIDA BSh-18 PRO.

It is not recommended to consider using the original included charger or power supplies for laptops. Such power supplies are not able to supply the current required for normal operation of the tool.

You can make your own power supply for the required voltage. But this requires certain knowledge of electronics. A diagram of such a power supply can be viewed here. There are power supply circuits that can be mounted instead of batteries.

When connecting power from the charger to the screwdriver, you must use a wire with a cross-section larger than 2.5 mm². Otherwise, the wire will become very hot, which can lead to melting of the insulation and a short circuit.

The level of voltage loss also depends on the length of the wire. The longer the wire, the correspondingly greater the losses. If you choose the wrong wire length, it may turn out that the screwdriver “does not pull”, it cannot be used to tighten a screw into hard wood, etc.

The quality of the wire connection also affects the voltage loss. Wires connected by twisting will have a high transition resistance, which will significantly affect voltage losses.

Important! Do not connect the screwdriver to the power source with a wire having a small cross-sectional area. This threatens failure of the tool itself and a fire.

Transformer block for powering a screwdriver

Transformer power supplies are devices that contain a transformer that reduces the input voltage. In addition to it, such blocks contain a diode rectifier and a filter capacitor. The capacitor smoothes out the output voltage ripple. In fact, the transformer produces the same type of voltage as in a 220-volt network, or rather, sinusoidal. When operating from uninterrupted sources, its shape may be completely non-sinusoidal. The shape of the rectified voltage is not constant over time, so it is necessary to install an element that maintains a constant output voltage, which is done on a smoothing capacitor.

Advantages of transformer blocks:

• Simplicity and reliability. • The components are easy to find commercially. • No parts that create radio wave interference.

DIY screwdriver charger

The problem of making a charger yourself does not arise very often, due to the large number of options suitable for almost all models of screwdrivers. It’s just that sometimes situations arise when the charger is missing, or it suddenly fails, and there is no way to purchase a new one. In this case, you can try to make a charger yourself.

You should first stock up on all the necessary materials. You will need a non-working battery, a battery cup, a soldering iron, a hot-melt gun, a regular Phillips screwdriver, a drill and a sharp knife with replaceable blades. After this, you can begin making the charger. First of all, the charging cup is opened, after which all conductors are unsoldered from the terminals. Next, the internal electronics are removed. When performing this operation, the polarity of the terminals must be observed to avoid confusion and errors in the future.

The case of a non-working battery must be opened and the wires carefully unsoldered from the terminals. For further work you will need a connector and a top cover. Plus and minus on the terminals are marked with a pencil or marker. At the base of the charging cup, holes are marked through which the prepared lid and the terminals of the supply wires will be attached. The conductors are carefully passed through the holes, observing polarity, after which they are connected to the terminals and connectors by soldering.

Next, the body needs to be fastened with special hot-melt adhesive; the bottom cover is attached to the base of the glass using self-tapping screws. The resulting structure must be inserted into the battery and the charging process begins. A flashing indicator will indicate that the device is assembled correctly. Only a few chargers are equipped with so-called smart systems that significantly extend the battery life. An 18-volt screwdriver charger can solve this problem.

A voltage stabilization system and charging current limitation are added to the design of conventional charging. The result is a nickel-cadmium battery design with a capacity of 1200 mAh. Charging will be performed in a safe mode, with a maximum current of no higher than 120 mA, but it will take more time than usual.

A screwdriver is a tool that almost every home craftsman has. Like other electrical devices, it requires connection to the network or accumulates charge. The last option is the most common. To recharge the removable battery, you need a charger. Usually it is included in the set. However, like any other device, a screwdriver charger is not immune to damage. To restore the functionality of the tool, you will have to purchase a replacement or make it yourself.

There are many chargers available to suit specific brands and models of tools. All of them can be divided into main types.

Analog with built-in power supply

Analog ones with a built-in power supply are quite in demand. This is due to its low cost. Usually they do not belong to professional equipment, they quickly break down and “do not grab stars from the sky.” The minimum task that their manufacturers usually set is to obtain the constant voltage and current load required for operation.

The devices operate on the principle of a stabilizer. You can do it yourself using the diagram provided. To work you need to remember:

1. The voltage at the output of the charging unit is greater than the battery rating.
2. Any type of battery is suitable.
3. You can use a regular circuit board.
4. Such stabilizers use a compensation principle: unnecessary energy is removed and heat is removed. To dissipate it, you can take, for example, a copper radiator. Area - 20 cm².
5. The input transformer (Tr1) changes the voltage from 220 to 20 V. Its power is determined by the current and voltage at the output.
6. The current is rectified by a diode bridge (VD1).
7. You can borrow the manufacturers' solution: an assembly of Schottky diodes.
8. After rectification, the current is pulsating, which is harmful. For smoothing, an electrolytic capacitor (C1) is needed.
9. KR142EN is used as a stabilizer. For 12 V its index is 8B.
10. Control is based on a transistor (VT2) and resistors (tuning).
11. Automatic shutdown after charging is usually not provided. You will have to determine the required time yourself. Alternatively, you can use a circuit that includes a diode (VD2) and a transistor (VT1). After charging, the LED (HL1) goes out. There are also more serious options with a switch and an electronic key that turn off automatically.

If the tool is a budget one, the circuit of its “native” charger may be simpler. It is not surprising that such products quickly fail. Sometimes a relatively new screwdriver is left without charging. Using the scheme discussed above, you can approach the issue responsibly and the device will most likely last longer than the purchased one. A suitable transformer and stabilizer are determined individually for a specific screwdriver.

Analog chargers with external power supply

Analog with an external unit, as the name suggests, consists of:

• from the network block;
• charger

The block is normal, includes:

• transformer;
• diode bridge;
• rectifier;
• capacitor filter.

Factory assemblies usually do not have a heat sink. Its role can be played by a high-power resistor. One of the typical causes of breakdowns is due to thermal conditions.

To correct the situation, you first need to find out whether the power source is working. If it functions, it is supplemented with a control circuit; if not, another one is sought. It is quite suitable, for example, from a laptop. It has 18 V output, which is quite enough. The remaining parts are usually not difficult to find. They cost very little and can be borrowed from other equipment.

The control unit diagram is shown below. The transistor KT817 is used, for amplification - KT818. Need a radiator. Approximate area: 30−40 cm². Up to 10 W will be dissipated here

Many Chinese manufacturers are trying to save on literally every little thing. This should be avoided if you need more or less decent quality. The homemade circuit has a 1 kOhm trimmer. It is needed to accurately set the current. At the output there is a 4.7 Ohm resistor. It dissipates heat. The LED will notify you when charging is complete

The resulting control board is about the size of a matchbox. It will fit quite well in the factory box. There is no need to take the radiator outside for the transistor. Enough air movement inside the housing

Charging a screwdriver without a charger

Restoring a battery without the help of a charger is not difficult, but many people have no idea 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 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 to each other for about thirty minutes, observing the polarity, while monitoring the temperature of the battery.

You can also modify power devices with higher voltages using a simple integrated stabilizer. The LM317 chip allows you to control an input signal up to 40 volts. You will need two stabilizers: one is switched on according to the voltage stabilization circuit, and the second - on the current. This scheme can also be used when converting a charger that does not have charging process control units.

The scheme works quite simply. During operation, a voltage drop is formed across resistor R1; it is enough for the LED to light up. As it charges, the current in the circuit drops. After some time, the voltage on the stabilizer will be low and the LED will go out. Resistor Rx sets the highest current. Its power is selected to be at least 0.25 watts. When using this scheme, the battery will not be able to overheat, since the device automatically turns off when the battery is fully charged.

Originally posted 2018-04-06 09:06:40.

Features of proper storage to increase service life

Knowing how corded and cordless screwdrivers work, it remains to figure out how to care for them in order to extend their service life. Everything is as simple as the principle of operation of a screwdriver. When storing, the following recommendations are taken into account:

1. Prevent water from entering the instrument
2. Do not miss or drop the device, as in addition to damaging the housing, internal devices may fail.
3. Ensure that the chuck is regularly lubricated to increase its service life
4. If various contaminants get inside, then before using the device again, you should disassemble and clean it.
5. Do not store the tool with completely discharged batteries.
6. The device should be stored and operated in a temperature range not lower than -5 and not higher than +30 degrees
7. Cool the bit when drilling

Only by following all of the above recommendations can you ensure long-term use of the tool without breakdowns. The service life of the device also depends on the quality, since a cheap Chinese screwdriver cannot serve for a long time a priori, because only low-quality components are used in its production.

To summarize, it is worth noting that not only the master whose work is related to the operation of the device, but also beginners who use the tool for the first time should know how a screwdriver works. This will extend the life of the screwdriver, and will also eliminate the need to take the device to a service center if malfunctions occur.

How to connect a screwdriver directly to a laptop charger

This method requires minimal technical knowledge from you. If there is a need to convert a screwdriver into a network one, an unnecessary laptop charger can help you, since it has similar characteristics and can easily be found in any home. First you need to look at the output voltage of the charger. 12-19V chargers are suitable.

It is important to check the voltage and current of the charger

The battery pack will need to be modified; to do this, you need to disassemble it and remove the failed batteries.

1. Take a laptop charger.
2. Cut off the connector and strip the wires of insulation.
3. Take the bare wires and solder them. If this is not possible, tape them with electrical tape.
4. Make a hole in the body for the wire and assemble the structure.

Types of batteries used for chargers

Batteries for chargers are divided into nickel-cadmium, lead-acid and lithium-ion.

Ni-Cad type batteries have the following characteristics:

• great resource;
• good energy capacity;
• extremely low environmental friendliness.

Lead-acid batteries have the following parameters:

• large dimensions and corresponding weight;
• ease of use in any position;
• lowest price.

Lithium-ion batteries have the following characteristics:

• good reliability;
• great resource;
• high capacity;
• undemanding to recycling.

The most popular and universal are li-ion batteries. They are used everywhere, not only in screwdrivers, but also in gadgets and cars.

Homemade charging devices

It’s quite simple to make a charger for a 12-volt screwdriver yourself, by analogy with the one used in the Interskol charger. To do this, you will 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 represent a sensor for the flow of charge current, R1 is designed to protect the diode VD2. When voltage is applied, transistor VT1 opens, current passes through it and LED LH1 begins to glow. The voltage drops across the chain R1, D1 and is applied to the battery. The charging current passes through the thermal relay. As soon as the temperature of the battery to which the thermal relay is connected exceeds the permissible value, it is triggered. The relay contacts switch and the charging current begins to flow through resistance R4, the LED LH2 lights up, indicating the end of the charge.

Circuit with two transistors

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

The amount of 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 component. As soon as the battery capacity begins to increase, the charging current decreases and the LED gradually goes out accordingly. 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 with a 10 kOhm variable resistor. To check it, you will need to place a voltmeter on the battery connection terminals, without connecting the battery itself. Any rectifier unit designed for a current of at least one ampere is used as a constant voltage source.

Using a custom chip

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

The MAX713 chip allows you to charge nickel-cadmium and nickel-metal hydride batteries in fast charge mode, with a current of up to 4 C. It can monitor battery parameters and, if necessary, reduce the current automatically. Once charging is complete, the IC-based circuit draws virtually no power from the battery. It can interrupt its operation due to time or when the temperature sensor is triggered.

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

• Uin – highest voltage at the input;
• Ubat – battery voltage;
• Icharge – charging current.

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

Types of batteries

Batteries are of different types and their charging modes may be different. Nickel-cadmium (Ni-Cd) batteries are a very good source of energy and are capable of delivering high power. However, for environmental reasons their production has ceased and they will become less and less common. Now they have been replaced everywhere by lithium-ion batteries.

Sulfuric acid (Pb) lead gel batteries have good characteristics, but they make the tool heavier and therefore are not very popular, despite their relative cheapness. Since they are gel (the sulfuric acid solution is thickened with sodium silicate), there are no plugs in them, the electrolyte does not leak 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 promoted in technology and on the market. Their feature is the complete sealing of the cell. They have a very high power density, are safe to use (thanks to the built-in charge controller!), can be disposed of favorably, are the most environmentally friendly, and are lightweight. They are currently used very often in screwdrivers.

Homemade power supply

It is necessary to start making a homemade power supply if you have knowledge in the field of radio engineering. It is necessary to prepare parts and tools in advance and fully concentrate on the work, during which the radio element may fail or suffer electric shock (supply voltage 220 V).

The simplest scheme

During manufacturing, it is necessary to prepare a housing for mounting radio components, a tool, a piece of getinax, wire and radio components. Then proceed with assembly according to diagram 1.

Scheme 1 – Simple 12 or 18 volt power supply.

Almost any transformer with the following parameters is suitable: power 250..300 W, secondary voltage 24..30 V, and current rated from 15 A and above. The diode bridge is assembled from powerful diodes (selected from a reference book). After assembly, it is necessary to check the supply voltage: if it is higher than the required value, then you need to reduce the voltage of winding II (reducing the number of turns). At low voltage, wind the secondary with a wire of the same cross-section. After assembly, install it in the housing.

Provided that the screwdriver is not powerful enough, you can install it directly in the battery compartment. If the power supply is assembled separately, it is recommended to provide cooling, because during engine startup the rated current increases by 7 times. As a result of this increase, a load is placed on the power supply unit, and it begins to heat up. Heating occurs due to insufficient power from the power supply. After the power supply is ready, you need to check the screwdriver: run it several times and make sure that the radio elements do not heat up. When using a converted screwdriver, you must adhere to the basic requirements:

1. It is necessary to give the tool time to cool down after every 20..30 minutes of operation.
2. Do not work at high heights or do it carefully (the BP may fall and, as a result, loss of balance and injury).
3. Monitor the condition of the power cable; it should not be pinched (this can lead to a short circuit, which is fraught with negative consequences for the tool and people).

Thus, if the screwdriver battery outputs 18 V or 12 V, it is not at all necessary to buy a new battery or screwdriver. It all depends on the scope of use of the tool: if you need to move the tool, you should replace the battery or purchase a new screwdriver. In the case where mobility does not play a special role, you need to convert it to power from the network. By following simple recommendations and observing safety regulations, you can not only increase the likelihood of extending the service life, but also reduce the risk of injury.

Easy tool restoration

The main advantage of a cordless screwdriver is its mobility. These tools use a lithium-ion battery, which is protected from overload and complete discharge. In addition, there is protection against overcharging in the form of a separate circuit built into the element itself. The main power source (primary) is 220 V, and the battery is also recharged.

Depending on the model of the screwdriver, the battery receives a charging voltage from 14 V to 21 V. The battery output produces a supply voltage from 12 to 18 V. This type of battery lasts a long time, but if the tool is not used for a long time, the built-in discharge protection will not help battery cells: discharge occurs constantly.

To increase service life, it is necessary to constantly discharge and charge the battery. If for some reason it was not possible to “keep track” of the tool, a specific battery element often fails. There are basic ways to solve this problem:

1. Replace the battery with a new one.
2. Buy a new tool.
3. Convert a mains-powered screwdriver.

When replacing the battery, please note that a new one is quite difficult to find. The tools are made in such a way that it is difficult to find spare parts for them. It is not profitable for a company to produce its product with high repairability, since it needs income from the purchase of products. You can only find a new battery at dealers. In addition, another option is possible: disassemble the battery and replace the faulty battery.

When purchasing a new tool, the user tends to buy a model of a higher quality, forgetting about the rules for using lithium-ion batteries. Basic rules that will help preserve the service life of the tool for a long time:

1. When purchasing in winter, it is strictly forbidden to “launch” the tool immediately. You need to wait about an hour until it “warms up” to room temperature.
2. Place the battery on charge.
3. Perform the battery charging and discharging cycle about 3 times.

If none of the options for solving the problem are suitable, you need to start converting the screwdriver to a network one with your own hands. It's easy to do. There are many simple and complex ways. Changing the tool model has several positive aspects:

1. There is no need to recharge the battery.
2. The load on the mechanical part is reduced.
3. Lots of power supply options.
4. Increasing the quality characteristics of the product.

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Types of battery cells

These devices use elements of different types and voltages, each of which has its own advantages and disadvantages.
The most common are nickel-cadmium (Ni – Cd) with a voltage of 1.2V.

Advantages:

• low price;
• stored in a discharged state.

Flaws:

• have a memory effect;
• high self-discharge;
• small capacity;
• small number of charge/discharge cycles.

More advanced nickel-metal hydride (Ni-MH) voltages are 1.2V.

Advantages:

• less memory effect and self-discharge;
• large capacity and number of charge/discharge cycles.

Flaws:

• higher price;
• do not tolerate low temperatures and storage in a discharged state.

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

Advantages:

• no memory effect;
• very low self-discharge current;
• high specific capacity, allowing to reduce the weight and dimensions of the device;
• the number of charge/discharge cycles is many times higher than other types of batteries.

Flaws:

• high price;
• loss of capacity three years after manufacture.