DIY charger for 18 volt screwdriver. How to choose a charger for a screwdriver and can you make it yourself?

Often, drill buyers complain that the “native” charger for a screwdriver charges the battery too slowly. As a result, you have to repeatedly postpone work for 2-4 hours. There are 2 options to avoid this situation. In the first case, you will need to purchase a new charger, in the second, you will need to make it yourself.

Types of batteries

To figure out how to make a charger for a screwdriver, you first need to study the types of batteries and their charging modes. There are 3 types of batteries:

Nickel-cadmium

This type is referred to as Ni-Cd, it is considered a good voltage source that is capable of delivering high power. The only drawback is that such batteries are included in the list of prohibited products due to environmental considerations, so this variety will now be much less common on sale.

Nickel-cadmium batteries have an energy capacity of 1200 to 1500 mAh. The total power is provided and maintained by the number of cans inside

The maximum cell voltage is 1.2 V. The battery is charged with an electric current of 0.1-1 rated capacity. It turns out that a battery with a capacity of 5 A*h can be recharged with a current of 0.5-5 A.

VIDEO: 5 rules for charging nickel-cadmium batteries

Another name is Pb with acid gel filling. They have average characteristics and low cost. The downside is that the batteries have a large mass, which makes the device heavier. The main advantage is that it can be used in any position without the electrolyte leaking out of the container.

Their main feature is high voltage and resistance, due to which even at the end of the charge-discharge cycle there is no sharp drop in voltage

The maximum cell voltage level is 2 V, while the battery charging current always corresponds to 0.1 C.

Li-ion batteries for screwdriver

The most common type due to the complete sealing of the container. This option is characterized by increased power density, safety, environmental friendliness, low weight and ease of disposal.

Lithium-ion battery for screwdriver Li-ion 18650 Samsung 12.6V (Volt) 2400mAh

The lithium-ion cell has a maximum power of 3.3 Volts. The voltage can be gradually increased at room temperature from 0.1 to 1 C. This speeds up the charging process. But this method is only suitable for those batteries that have not been over-discharged.

It is important to remember here that the screwdriver is charged up to 4.2 Volts, exceeding it will affect the reduction in service life, and reducing it will reduce the capacity. It is very important to monitor the temperature when charging.

When developing a charger circuit for a screwdriver with your own hands, it is very important to consider which battery you plan to charge. You also need to additionally calculate its voltage - 12 Volts or 18 Volts. When operating a charger for a screwdriver, it is necessary to monitor the process using a multimeter or a system with a voltage comparator, which has been pre-configured for a specific type of battery.

VIDEO: Rules for choosing a battery for a screwdriver

How to assemble your own charger

Creating a homemade charger for a screwdriver requires compliance with safety precautions and carrying out work strictly according to a given scheme. You can use the drawing below, which is universal, since such charging equipment will be suitable for any type of battery. The only important parameter here is the charge current.

Homemade charger

When recharging, the current value fully corresponds to the existing state of the battery, and when the process is completed, the indicator becomes slightly higher.

Diagram of the simplest memory for a screwdriver

The charger for a screwdriver acts as an electric current generator using transistor VT2. It, in turn, receives power through a rectifier bridge in contact with a step-down transformer. The charge current level is adjusted by adjusting resistor R1 when the battery is turned on. It will always remain the same. R3 works as a rated current limiter. VD 6 is an LED, it acts as an indicator that determines whether charging is ongoing or has already completed.

All components from the charger circuit for a screwdriver are installed on a printed circuit board; domestic devices KD202 and D242 can be used as diodes. It is required to place the elements in such a way that there is a minimum number of intersections on the board; the ideal option would be if there are none. Leave at least 3 mm between parts.

The transistor is mounted on a heat sink 25-55 cm 2. The connection field for the charging components for screwdrivers must be covered with a housing. Here, difficulties may arise with the terminals and connection of the battery. Therefore, it is better to modify the screwdriver charger by upgrading the old one:

• open the case of the outdated recharger;
• remove all components and other filling from it;
• install a homemade circuit into the case.

The diagram must contain the following elements:

Stages of work:

1. Select the most optimal dimensions for the circuit, which easily fit into the case with all the listed components.
2. Draw a thread along all its paths according to the basic drawing, etch it in a copper frame and solder all the elements.
3. Install the heatsink on the aluminum plate so that it does not come into contact with any part of the board.
4. Securely fix the transistor with an M-3 nut.
5. Assemble the components strictly according to the diagram and solder the terminals to all necessary parts, observing polarity. Output the electrical wire for the transformer.
6. Install the transformer itself, together with a 0.5 A fuse, into the housing and equip it with an adapter to enable recharging.

VIDEO: How to charge a Li-ion battery using a screwdriver

Rating of chargers for screwdrivers

For those who do not plan to do their own assembly, we suggest choosing from a range of ready-made chargers from different manufacturers.

DEWALT DCB118

The FLEXVOLT DEWALT DCB118 universal device is used to restore batteries for DEWALT screwdrivers with a voltage of 54V; you can equally successfully charge any other devices with a nominal voltage of 18 volts.

FLEXVOLT DEWALT DCB118

For convenience, there is an indicator on the body, so you can monitor the process. Type of rechargeable batteries Li-ion. Weight 850 gr. Equipment price 3500 rub.

ONE+ Ryobi RC18120

It is declared as a highly specialized device intended only for charging Ryobi ONE+ series batteries. The advantage of having only one power supply - due to this, the weight of the device is even reduced (only 460 g), while the IntelliCell™ intelligent monitoring system has been introduced, when each cell is charged to maximum within 40-50 minutes, thereby increasing battery life .

ONE+ Ryobi RC18120

The voltage is 18 volts, the battery type is nickel-cadmium and lithium-ion. There are 4 positions of the level indicator - 25…50…75…100%. The case itself can be mounted on a wall. There is a light level indication. The cost of the device is 4850 rubles.

DC10WC (10.8 V) Makita

The device is used to restore lithium-ion batteries with a nominal voltage of 10.8 volts. There is a light indication, but no automatic stop. It is advisable to control the time to prevent overfilling the container.

DC10WC (10.8 V) Makita

Weight 1200 gr. with relatively small dimensions - only 20 cm in length. There is a 1-year manufacturer's warranty. Price 2200 rub.

VIDEO: How to properly charge Li-ion

Their capacity is on average 12 mAh. In order for the device to always remain in working condition, you need a charger. However, in terms of voltage they are quite different.

Nowadays, models are available for 12, 14 and 18 V. It is also important to note that manufacturers use various components for chargers. In order to understand this issue, you should look at the standard charger circuit.

Charging circuit

The standard electrical circuit of a screwdriver charger includes a three-channel type microcircuit. In this case, four transistors are required for the 12 V model. They can vary quite a bit in terms of capacity. In order for the device to cope with high clock frequencies, capacitors are attached to the chip. They are used for charging both pulse and transition type. In this case, it is important to take into account the characteristics of specific batteries.

Thyristors themselves are used in devices to stabilize current. Some models have open-type tetrodes. They differ in current conductivity. If we consider modifications for 18 V, then there are often dipole filters. These elements make it easy to cope with network congestion.

12V modifications

A 12 V screwdriver (circuit shown below) is a set of transistors with a capacity of up to 4.4 pF. In this case, the conductivity in the circuit is ensured at a level of 9 microns. To prevent the clock frequency from increasing sharply, capacitors are used. Resistors in models are mainly used as field resistors.

If we talk about charging on tetrodes, then there is an additional phase resistor. It copes well with electromagnetic vibrations. The negative resistance of 12 V chargers is maintained at 30 ohms. They are most often used for 10 mAh batteries. Today they are actively used in models of the Makita brand.

14V chargers

The charger circuit for a screwdriver with 14 V transistors includes five pieces. The microcircuit itself for converting current is only suitable for a four-channel type. Capacitors for 14 V models are pulsed. If we talk about batteries with a capacity of 12 mAh, then tetrodes are additionally installed there. In this case, there are two diodes on the microcircuit. If we talk about charging parameters, then the current conductivity in the circuit, as a rule, fluctuates around 5 microns. On average, the resistor capacitance in the circuit does not exceed 6.3 pF.

Direct charging current loads of 14 V can withstand 3.3 A. Triggers are installed in such models quite rarely. However, if we look at Bosch brand screwdrivers, they are often used there. In turn, in Makita models they are replaced by wave resistors. They are good for voltage stabilization. However, the charging frequency can vary greatly.

Circuit diagrams for 18 V models

At 18 V, the charger circuit for a screwdriver involves the use of only transition-type transistors. There are three capacitors on the microcircuit. The tetrode is directly installed with a grid trigger used to stabilize the limiting frequency in the device. If we talk about charging parameters at 18 V, then it should be mentioned that the current conductivity fluctuates around 5.4 microns.

If we consider chargers for Bosch screwdrivers, then this figure may be higher. In some cases, chromatic resistors are used to improve signal conductivity. In this case, the capacitance of the capacitors should not exceed 15 pF. If we consider chargers of the Interskol brand, then they use transceivers with increased conductivity. In this case, the maximum current load parameter can reach up to 6 A. Finally, mention should be made of Makita devices. Many of the battery models are equipped with high-quality dipole transistors. They cope well with increased negative resistance. However, problems in some cases arise with magnetic vibrations.

Chargers "Intrescol"

The standard charger for the Interskol screwdriver (the diagram is shown below) includes a two-channel microcircuit. All capacitors are selected for it with a capacity of 3 pF. In this case, transistors for 14 V models are used of the pulse type. If we consider modifications for 18 V, then you can find variable analogues there. The conductivity of these devices can reach up to 6 microns. In this case, the batteries are used on average 12 mAh.

Scheme for the Makita model

The charger circuit has a three-channel type microcircuit. There are three transistors in total in the circuit. If we talk about 18 V screwdrivers, then in this case the capacitors are installed with a capacity of 4.5 pF. Conductivity is ensured in the region of 6 microns.

All this allows you to remove the load from the transistors. The tetrodes themselves are of the open type. If we talk about 14 V modifications, then chargers are produced with special triggers. These elements allow you to cope perfectly with the increased frequency of the device. At the same time, they are not afraid of online surges.

Devices for charging Bosch screwdrivers

A standard Bosch screwdriver includes a three-channel chip. In this case, the transistors are of the pulse type. However, if we talk about 12 V screwdrivers, then adapter analogues are installed there. On average, they have a throughput of 4 microns. Capacitors in devices are used with good conductivity. The chargers of this brand have two diodes.

Triggers in devices are used only at 12 V. If we talk about the protection system, then transceivers are used only of the open type. On average, they can carry a current load of 6 A. In this case, the negative resistance in the circuit does not exceed 33 Ohms. If we talk separately about 14 V modifications, they are produced for 15 mAh batteries. Triggers are not used. In this case, there are three capacitors in the circuit.

Scheme for the "Skill" model

The charger circuit includes a three-channel microcircuit. In this case, models on the market are presented at 12 and 14 V. If we consider the first option, then the transistors in the circuit are used of the pulse type. Their current conductivity is no more than 5 microns. In this case, triggers are used in all configurations. In turn, thyristors are used only for 14 V charging.

Capacitors for 12 V models are installed with a varicap. In this case, they are not able to withstand large overloads. In this case, the transistors overheat quite quickly. There are three diodes directly in the 12 V charger.

Application of LM7805 regulator

The charger circuit for a screwdriver with an LM7805 regulator includes only two-channel microcircuits. Capacitors are used on it with a capacity of 3 to 10 pF. You can most often find regulators of this type in models of the Bosch brand. They are not suitable for 12V chargers directly. In this case, the negative resistance parameter in the circuit reaches 30 Ohms.

If we talk about transistors, then they are used in models of the pulse type. Triggers for regulators can be used. There are three diodes in the circuit. If we talk about 14 V modifications, then tetrodes are only suitable for them of the wave type.

Using BC847 transistors

The charger circuit for the BC847 transistorized screwdriver is quite simple. These elements are most often used by Makita. They are suitable for 12 mAh batteries. In this case, the microcircuits are of a three-channel type. Capacitors are used with dual diodes.

The triggers themselves are of the open type, and their current conductivity is at the level of 5.5 microns. A total of three transistors are required for charging at 12 V. One of them is installed near the capacitors. The rest in this case are located behind the reference diodes. If we talk about voltage, then 12 V charges with these transistors can handle overloads of 5 A.

Transistor device IRLML2230

Charging circuits with transistors of this type are found quite often. The Intreskol company uses them in 14 and 18 V versions. In this case, the microcircuits are used only of the three-channel type. The direct capacity of these transistors is 2 pF.

They tolerate current overloads from the network well. In this case, the conductivity indicator in the charges does not exceed 4 A. If we talk about other components, then the capacitors are installed of the pulse type. In this case, three of them will be required. If we talk about 14 V models, then they have thyristors for voltage stabilization.

A screwdriver is an indispensable tool, but the discovered flaw makes you think about making some modifications and improving the circuit of its charger. After leaving the screwdriver to charge overnight, the author of this video is a blogger AKA KASYAN The next morning I discovered heating of the battery of unknown origin. Moreover, the heating was quite serious. This is not normal and will dramatically reduce battery life. In addition, it is dangerous from a fire safety point of view.

Having disassembled the charger, it became clear that inside there was a simple circuit consisting of a transformer and a rectifier. Things were even worse at the docking station. An indicator LED and a small circuit on one transistor, which is only responsible for triggering the indicator when the battery is inserted into the docking station.
There are no charge control units or auto-shutdown, just a power supply that will charge indefinitely until the latter fails.

A search for information on the problem led to the conclusion that almost all budget screwdrivers have exactly the same charging system. And only expensive processor-controlled devices have smart charging and protection systems implemented both on the charger itself and in the battery. Agree, this is not normal. Perhaps, according to the author of the video, manufacturers specifically use such a system to ensure that batteries quickly fail. Market economy, conveyor belt of fools, marketing tactics and other clever and incomprehensible words.

Let's improve this device by adding a voltage stabilization system and charge current limitation. The battery is 18 volt, nickel-cadmium with a capacity of 1200 milliampere hours. The effective charge current for such a battery is no more than 120 milliamps. It will take a long time to charge, but it will be safe.

Let's first figure out what this modification will give us. Knowing the voltage of a charged battery, we will set exactly this voltage at the charger output. And when the battery is charged to the required level, the charging current will drop to 0. The process will stop, and current stabilization will allow the battery to be charged with a maximum current of no more than 120 milliamps, regardless of how discharged the latter is. In other words, we will automate the charging process and also add an indicator LED that will light up during the charging process and go off at the end of the process.

All the necessary radio components can be purchased cheaply in this Chinese store.
Node diagram. The design of such a unit is very simple and easy to implement. Costs only $1. Two lm317 microcircuits. The first is connected according to the current stabilizer circuit, the second stabilizes the output voltage.

So, we know that a current of about 120 milliamps will flow through the circuit. This is not a very large current, so there is no need to install a heat sink on the chip. This system works quite simply. During charging, a voltage drop is formed across resistor r1, which is enough for the LED to light up and as charging progresses, the current in the circuit will drop. After a certain amount of voltage drop across the transistor is insufficient, the LED will simply go out. Resistor r2 sets the maximum current. It is advisable to take it at 0.5 watt. Although it is possible at 0.25 watts. Using this link you can download a program for calculating the microcircuit.

This resistor has a resistance of about 10 ohms, which corresponds to a charging current of 120 milliamps. The second part is a threshold node. It stabilizes tension; the output voltage is set by selecting resistors r3, r4. For the most precise settings, the divider can be replaced with a 10 kilo-ohm multi-turn resistor.
The voltage at the output of the unconverted charger was about 26 volts, despite the fact that the test was carried out at a 3-watt load. The battery, as mentioned above, is 18 volts. Inside are 15 1.2 volt nickel-cadmium cans. The voltage of a fully charged battery is approximately 20.5 volts. That is, at the output of our node we need to set the voltage within 21 volts.

Now let's check the assembled block. As you can see, even with a short-circuited output, the current will not exceed 130 milliamps. And this is regardless of the input voltage, that is, the current limitation works as it should. We mount the assembled board into the docking station. We will use the original LED of the docking station as an indicator of the end of the charge, but with a transistor it is no longer needed.
The output voltage is also within the specified limits. Now you can connect the battery. The LED lights up, charging has begun, we will wait for the process to complete. As a result, we can say with confidence that we have definitely improved this charger. The battery does not heat up, and most importantly, it can be charged as much as you like, since the device automatically turns off when the battery is fully charged.

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.

Kinds

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 due to 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, which, as a rule, is set by their manufacturers, is to obtain the constant voltage and current load necessary 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 with an external unit, as the name suggests, consists of:

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 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 approximately the size of a matchbox. It will fit quite well in the factory box. There is no need to take the heatsink outside for the transistor. Enough air movement inside the housing

Pulse

Analogue devices take a long time to charge: on average 3-5 hours. Although for domestic purposes this is not terrible. Another thing is the professional sphere, where “time is money.” Such products cost accordingly; there are usually two batteries in the set.

Professionals often use pulse chargers. They have an intelligent process control circuit. Full charging time is impressive: about one hour. Of course, you can make the same fast analog charger, but then its weight and size will be impressive.

Pulse devices are compact and safe. High quality requires a thoughtful, complex design. However, you can repeat it too. The circuit below is suitable for use with nickel-cadmium batteries with a third signal pin.

The well-known MAX713 controller is used. Input voltage -25 V. Power supply - simple, so his diagram is not here.

The resulting screwdriver charger “is distinguished by its intelligence and intelligence.” It checks the voltage and turns on the accelerated charge mode. The battery is ready in about 1-1.5 hours. The scheme allows you to choose:

• charge voltage;
• Battery Type.

It shows the resistor value (R 19) for switching modes and the position of the jumpers. Using the proposed drawing, you can repair the damage. An additional incentive will be the financial issue. Savings are at least doubled.

Charging with a faulty battery

Sometimes it happens that the screwdriver itself works, but the battery is broken. There are several options to solve the problem:

Models with different voltages

It’s not enough to decide on the type of charger and the manufacturer’s brand; to purchase, you also need to know the voltage of your screwdriver. The most common options are 12, 14 and 18 V.

12 V chargers

The circuit can consist of transistors up to 4.4 pF. This can be seen in the diagram of the charger for a 12 volt screwdriver. Conductivity in the circuit is 9 microns. Capacitors are needed to control clock spikes. The resistors used are usually field resistors. Tetrode chargers have an additional phase resistor. It protects against electromagnetic vibrations.

12V chargers operate with a resistance of up to 30 ohms. They can often be found on 10 mAh batteries. Among well-known manufacturers, Makita is most often used.

14 V chargers

The diagram shows that for 14 V charging you need five transistors. Other chain features:

• The microcircuit is only suitable for four-channel;
• capacitors - pulse;
• To work with 12 mAh batteries, tetrodes are needed;
• two diodes;
• conductivity - about 5 microns;
• the average resistor capacitance is no more than 6.3 pF.

Devices created according to the circuit can withstand current up to 3.3 A. Triggers are rarely included in the circuit. The exception is Bosch products. In Makita products, triggers are successfully replaced with wave resistors.

18 V chargers

The charger for an 18-volt screwdriver uses only transition-type transistors in the circuit. Other product features include:

• three capacitors;
• tetrode and diode bridge;
• grid trigger;
• current conductivity is about 5.4 microns, sometimes chromatic resistors are used to increase it.

The use of high conductivity transceivers is a feature of the domestic company Interskol. The current load can reach up to 6 A. Makita often uses high quality dipole transistors in its models.

Whatever screwdriver manufacturer is chosen, the problem of replacing the charger can be easily solved. To do this, it is enough to at least know some of the features of your instrument.