Charger. We disassemble a charger from a Siemens mobile phone Forms of currents created by chargers

Summing up, we can say that pulse chargers fell in love with car owners not only by their compact dimensions, but also a high-quality charging process. The variety of choice of models requires special attention from the buyer. The tips above will help you make the right choice.

Below is a selection of good chargers recommended for ordering

Title and Description

How is the battery charged? Is the circuit of this device complicated or not, in order to make a device with your own hands? Is it fundamentally different from what is used for mobile phones? We will try to answer all the questions posed later in the article.

General information

The battery plays a very important role in the functioning of devices, units and mechanisms that require electricity to operate. So, in vehicles it helps start the car engine. And in mobile phones, batteries allow us to make calls.

Battery charging, circuit and principles of operation this device are considered even in the school physics course. But, alas, many of this knowledge have already been forgotten by the time they are released. Therefore, we hasten to remind you that the basis of the battery operation is based on the principle of the appearance of a voltage (potential) difference between two plates, which are specially immersed in an electrolyte solution.

The first batteries were copper-zinc. But since that time, they have significantly improved and modernized.

How the battery works

The only visible element of any device is the case. It ensures the generality and integrity of the design. It should be noted that the name "battery" can be fully applied to only one battery cell (they are also called banks), and there are only six of them in the same standard 12 V car battery.

We return to the body. Strict requirements are put forward to him. So, it should be:

• resistant to aggressive chemicals;
• able to withstand significant temperature fluctuations;
• with good vibration resistance.

All these requirements are met by a modern synthetic material - polypropylene. More detailed differences should be emphasized only when working with specific samples.

Principle of operation

We will consider lead acid batteries as an example.

When there is a load on the terminal, a chemical reaction begins, which is accompanied by the release of electricity. The battery will drain over time. How does it recover? Whether there is a simple circuit?

Charging the battery is not difficult. It is necessary to carry out the reverse process - electricity is supplied to the terminals, chemical reactions occur again (pure lead is restored), which will allow the battery to be used in the future.

Also, during charging, the density of the electrolyte increases. Thus, the battery restores its original properties. The better the technology and materials used in the manufacture, the more charge / discharge cycles the battery can withstand.

What electrical circuits for charging batteries exist

A classic device is made from a rectifier and a transformer. Considering all the same car batteries with a voltage of 12 V, then the charges for them have a constant current of about 14 V.

Why is it so? This voltage is necessary so that current can flow through a discharged car battery. If he himself has 12 V, then a device of the same power will not be able to help him, therefore they take higher values. But in everything you need to know when to stop: if you overestimate the voltage too much, it will have a detrimental effect on the service life of the device.

Therefore, if you want to make a device with your own hands, it is necessary for cars to look for suitable charging schemes for car batteries. The same applies to other techniques. If you need a charging circuit, then you need a 4 V device and no more.

Recovery process

Let's say you have a battery charging circuit from a generator, according to which the device was assembled. The battery is connected and the recovery process begins immediately. As it progresses, devices will grow. The charging current will drop along with it.

When the voltage approaches the maximum possible value, then this process practically does not occur at all. And this indicates that the device has been successfully charged and can be turned off.

Make sure that the battery current is only 10% of its capacity. Moreover, it is not recommended to either exceed this indicator or reduce it. So, if you follow the first path, the electrolyte will begin to evaporate, which will significantly affect the maximum capacity and battery life. On the second path, the necessary processes will not occur at the required intensity, which is why negative processes will continue, albeit to a somewhat lesser extent.

Charging

The described device can be bought or assembled by hand. For the second option, we need electrical circuits for charging batteries. The choice of the technology by which it will be done should depend on which batteries are targeted. You will need the following components:

1. (designed on ballast capacitors and transformer). The higher the indicator can be achieved, the more significant the current will be. In general, this should be enough for charging to work. But the reliability of this device is very low. So, if the contacts are broken or something is mixed up, then both the transformer and the capacitors will fail.
2. Protection in case of connection of "wrong" poles. A relay can be designed for this. So, the conditional tie is based on a diode. If you confuse plus and minus, then it will not pass current. And since a relay is tied to it, it will be de-energized. Moreover, this circuit can be used with a device based on both thyristors and transistors. It must be connected to the break of the wires, with the help of which the charging itself is connected to the battery.
3. Automation that battery charging should have. The circuit in this case must ensure that the device will only work when there is a real need for it. To do this, with the help of resistors, the response threshold of the monitoring diode is changed. It is believed that 12 V batteries are full when their voltage is within 12.8 V. Therefore, this figure is desirable for this circuit.

Conclusion

So we examined what a battery charging is. The circuit of this device can be performed on one board, but it should be noted that this is rather complicated. Therefore, they are made multi-layered.

Within the framework of the article, various schematic diagrams, which make it clear how, in fact, the batteries are charged. But it must be understood that these are only general images, and more detailed ones, having indications of the ongoing chemical reactions, are special for each type of battery.

Charger Is a special device designed to charge the battery with electricity from external sources. In most cases, they use power from the AC mains. Such devices can be used to recharge tablets, phones, laptops, toothbrushes, cars and other units where battery recharging is required.

Battery chargers are often included with purchased equipment, for example, a charger for a cell phone. But in some cases, such a device must be purchased independently. There are a large number of devices on sale today that allow you to recharge the battery. But for the right choice, you need to know how to correctly evaluate the selected product, which, first of all, you should pay attention to.

Views

The charger according to the method of its application can be:

• External.
• Built-in.

Devices can be classified according to the method of charging the battery, type of indication, performance, presence of the discharge function, and others. For example, in devices for cell phones, the indicator is the mobile screen, where the battery charge level is displayed.

Charges can also be:

• Rechargeable - the work is carried out according to the charge accumulation scheme and its further return to the battery device.

• Networked - power is supplied from the electrical network, after which the voltage is converted to the voltage required for a particular unit.

• Automotive - they operate from the cigarette lighter located in the car. The power source here is the on-board network.

• Universal Is a wire that has a connector for connecting a smartphone, as well as a USB connector for charging from a personal computer.

• Wireless - the phone does not interact directly with the current. The device represents a special platform. This accessory is based on the principle of an induction coil.

For different types of batteries, different charging devices are produced, for example, for NiCd, NiMH, Li-Ion or even combined batteries.

According to the method of charging, the devices can be charging with constant or pulse current. Devices can be professional or household depending on the required functions. Devices can be slow or fast in charging time.

Device

The charger in most cases includes the following items:

• Voltage transformer... It can be a switching power supply or a transformer.
• Voltage regulator... It maintains a constant voltage, regardless of its fluctuations occurring in the input circuit.
• Rectifier... This element converts electric current of alternating value into direct current, that is, the one that is required to charge the battery of a particular device. Each type of battery requires a certain amount of input voltage.
• A device that monitors the charging process or the strength of the electric current.
• Led indicator.

The charger may have other elements, for example, a battery in external units and other devices. Industrial devices additionally have blocks with electronic equipment that control the charging process. Such devices are used to simultaneously charge 3-5 rechargeable batteries. Certain models can charge simultaneously with pulsed currents and perform continuous charging.

Complex devices are equipped with microcontrollers that allow you to accurately track a number of parameters: temperature, battery voltage, charge and other indicators. More advanced devices even have a sensor outside temperature, because it significantly affects the charging process.

Operating principle

All devices that are used to recharge batteries almost always operate according to the same principle. When connected to an electrical network, a voltage of 220 V is supplied to the charger. The elements of the device adjust the strength and voltage of the current to those indicators that are necessary for charging a specific battery. In addition, each type of battery requires its own method and order of recharging.

For automotive lead acid batteries, it is recommended to recharge until they are completely discharged. Alkaline batteries should be fully discharged as they have a memory effect. But at the same time, both types of batteries should be recharged to the maximum value. Therefore, recently only automatic devices for machines that do not require human intervention. They only need to be connected to the mains and clamped to the battery terminals.

An automatic charger controls everything:

Monitors the charge level, cycle, as well as the procedure itself. After charging one hundred percent, the unit turns itself off. If the device is not disconnected, it will constantly monitor the battery status. When the charge drops, the sensors see this, as a result of which the battery begins to recharge. As a result, the charge level will be at 100 percent.

There are wireless charging systems that use the principle of electromagnetic induction. This means that charging occurs at a certain distance due to the appearance of an electric current in the closing circuit when the magnetic voltage that permeates this circuit changes. The system includes the first and second coils. The result is an inductively coupled system.
The alternating current flowing in the winding of the primary coil forms a magnetic field, forming an induction voltage in the second coil. It is this voltage that is used to charge the battery. But this principle works only at a certain short distance. When you remove the phone or other device, most of the magnetic field is dissipated, as a result, the secondary coil does not receive it.

There is also a manual charger, which is often used to charge a cell phone somewhere in the wilderness, where there is no electrical network, for example, in the taiga. However, the principle of their operation is completely different, they operate on the principle of wind turbines. The main element of such devices is the rotation handle. The function of this handle is comparable to that of a wind turbine propeller.

When the handle is twisted, the rotation is transferred to the rod. As a result, the kinetic energy, which is created by man, is directed to the generator of the charging device. It is the last element that produces an electric current with a low voltage of about 6 volts. This voltage is quite enough to charge a dead battery a little, make the necessary call or send a message.

Application

The charger is used to charge the batteries of devices and equipment:

• Cell phones and smartphones.
• Tablets.
• Laptops.
• Toothbrushes.
• Portable, and many other battery-powered electric tools.
• Electric cars.
• Portable vacuum cleaners, hair dryers.
• Cars, motorcycles and other equipment.

How to choose

A huge number of types of battery charging are sold. These are domestic and foreign models. Therefore, it is sometimes difficult to make a choice.

• If you need a device to charge your car from time to time, then take a look at a simple but reliable device without unnecessary functions. For example, such charging can be useful for charging the battery due to its idle time during cold weather or traveling to foreign countries on vacation.
• For beginners, it is best to choose automatic devices where no configuration is required. For experienced car owners, multifunctional or starter-chargers are recommended. The number of options is limited only by financial means.
• You only need to purchase a charger that is designed for your specific electrochemical system. You should be aware that most of the devices are used only for a specific type of equipment. For example, the phone connector may not fit or the device generates a current of a certain voltage. Whereas a certain device requires a completely different voltage. Do not charge the battery in case of voltage mismatch.
• Using a charger with a higher power rating will shorten the charging time, but the battery itself may have limitations. Rapid charging in the absence of such a function in the unit can reduce the battery life or even damage it.
• You should also pay attention to the shape, design, construction and dimensions of the charger. The choice here in this case depends on the buyer.
• When choosing a wireless device, you need to pay attention to the manufacturer of the equipment. Not every brand makes devices with batteries that are suitable for wireless charging. There are also "PMA" and "Qi" food standards. There may be limitations here as well. Not all technology can support these two standards.
• When choosing a wireless device, you should also pay attention to power, functionality, operating time and safety.

The photo shows a home-made automatic charger for charging 12 V car batteries with a current of up to 8 A, assembled in a case from a V3-38 millivoltmeter.

Why you need to charge your car battery
charger

The battery in the car is charged using electric generator... To protect electrical equipment and devices from overvoltage, which generates car generator, after it, a relay-regulator is installed, which limits the voltage in on-board network vehicle up to 14.1 ± 0.2 V. To fully charge the battery, a voltage of at least 14.5 V is required.

Thus, it is impossible to fully charge the battery from the generator, and before the onset of cold weather it is necessary to recharge the battery from the charger.

Charger circuit analysis

The scheme of making a charger from a computer power supply looks attractive. The structural diagrams of computer power supplies are the same, but the electrical ones are different, and a high radio technical qualification is required for revision.

I was interested in the capacitor circuit of the charger, the efficiency is high, it does not emit heat, it provides a stable charge current regardless of the degree of battery charge and fluctuations in the supply network, it is not afraid of output short circuits. But it also has a drawback. If during the charging process contact with the battery disappears, then the voltage on the capacitors increases several times, (the capacitors and the transformer form a resonant oscillatory circuit with the frequency of the mains), and they break through. It was necessary to eliminate only this single drawback, which I managed to do.

The result is a charger circuit without the above disadvantages. For more than 16 years I have been charging any 12 V acid batteries with it. The device works flawlessly.

Schematic diagram of a car charger

Despite the apparent complexity, the scheme of a homemade charger is simple and consists of only a few complete functional units.

If the scheme for repetition seemed complicated to you, then you can assemble more, working on the same principle, but without the automatic shutdown function when the battery is fully charged.

Current limiter circuit on ballast capacitors

In a capacitor car charger, the regulation of the magnitude and stabilization of the battery charge current is provided by connecting ballast capacitors C4-C9 in series with the primary winding of the power transformer T1. Than more capacity capacitor, the greater the battery charge current will be.

In practice, this is a complete version of the charger, you can connect the battery after the diode bridge and charge it, but the reliability of such a circuit is low. If contact with the battery terminals is broken, the capacitors may fail.

The capacitance of the capacitors, which depends on the magnitude of the current and voltage on the secondary winding of the transformer, can be approximately determined by the formula, but it is easier to navigate according to the table data.

For current regulation to reduce the number of capacitors, they can be connected in parallel in groups. My switching is carried out using two toggle switches, but you can put several toggle switches.

Protection circuit
from incorrect connection of the battery poles

The protection circuit against polarity reversal of the charger when the battery is incorrectly connected to the terminals is made on relay P3. If the battery is connected incorrectly, the VD13 diode does not pass current, the relay is de-energized, the contacts of the K3.1 relay are open and the current does not flow to the battery terminals. When connected correctly, the relay is triggered, the contacts K3.1 are closed, and the battery is connected to the charging circuit. This reverse polarity protection circuit can be used with any charger, both transistor and thyristor. It is enough to include it in the break of the wires, with the help of which the battery is connected to the charger.

Battery charging current and voltage measurement circuit

Due to the presence of the switch S3 in the diagram above, when charging the battery, it is possible to control not only the magnitude of the charging current, but also the voltage. At the top position S3, the current is measured, at the bottom - the voltage. If the charger is not connected to the mains, the voltmeter will show the battery voltage, and when charging in progress battery, then the charging voltage. The head is an M24 microammeter with an electromagnetic system. R17 shunts the head in current measurement mode, and R18 serves as a divider when measuring voltage.

Automatic charger shutdown circuit
when the battery is fully charged

To power the operational amplifier and create a reference voltage, a DA1 stabilizer chip of type 142EN8G for 9V was used. This microcircuit was not chosen by chance. When the temperature of the microcircuit case changes by 10º, the output voltage changes by no more than hundredths of a volt.

The system of automatic shutdown of charging when the voltage reaches 15.6 V is made on half of the A1.1 microcircuit. Pin 4 of the microcircuit is connected to the voltage divider R7, R8 from which a reference voltage of 4.5 V is supplied to it. Pin 4 of the microcircuit is connected to another divider on the resistors R4-R6, the resistor R5 is trimmer to set the operation threshold of the machine. The value of the resistor R9 sets the threshold for switching on the charger to 12.54 V. Thanks to the use of the VD7 diode and the resistor R9, the necessary hysteresis between the on and off voltage of the battery charge is provided.

The scheme works as follows. When connected to a car battery charger, the voltage at the terminals of which is less than 16.5 V, at pin 2 of the A1.1 chip, a voltage sufficient to open the VT1 transistor is set, the transistor opens and the P1 relay is triggered, connecting the K1.1 contacts to the mains through the capacitor bank primary winding of the transformer and battery charging begins.

As soon as the charge voltage reaches 16.5 V, the voltage at the A1.1 output will decrease to a value insufficient to maintain the VT1 transistor in the open state. The relay will turn off and the contacts K1.1 will connect the transformer through the standby capacitor C4, at which the charge current will be 0.5 A. In this state, the charger circuit will be in this state until the voltage on the battery decreases to 12.54 V. As soon as the voltage will be set equal to 12.54 V, the relay will turn on again and charging will go with the specified current. It is possible, if necessary, to turn off the automatic regulation system with switch S2.

Thus, the automatic tracking system of the battery charging will exclude the possibility of overcharging the battery. The battery can be left connected to the included charger for at least a year. This mode is relevant for motorists who drive only in summer time... After the end of the rally season, you can connect the battery to the charger and turn it off only in the spring. Even if the power supply fails, when it appears, the charger will continue to charge the battery normally

The principle of operation of the automatic shutdown circuit of the charger in case of overvoltage due to the absence of the load collected on the second half of the operational amplifier A1.2 is the same. Only the threshold complete shutdown 19 V is selected from the mains charger. If the charging voltage is less than 19 V, the voltage at the output 8 of the A1.2 chip is sufficient to keep the VT2 transistor open, in which the voltage is applied to relay P2. As soon as the charging voltage exceeds 19 V, the transistor will close, the relay will release the K2.1 contacts and the voltage supply to the charger will completely stop. As soon as the battery is connected, it will power the automation circuit, and the charger will immediately return to working condition.

Automatic charger design

All parts of the charger are located in the case of the V3-38 milliammeter, from which all its contents have been removed, except for the dial gauge. Installation of elements, except for the automation circuit, is carried out in a hinged way.

The milliammeter body design is two rectangular frames connected by four corners. In the corners with an equal pitch, holes are made to which it is convenient to attach parts.

The power transformer ТН61-220 is fixed on four M4 screws on an aluminum plate 2 mm thick, the plate, in turn, is fixed with M3 screws to the lower corners of the case. The power transformer ТН61-220 is fixed on four M4 screws on an aluminum plate 2 mm thick, the plate, in turn, is fixed with M3 screws to the lower corners of the case. C1 is also installed on this plate. The photo shows the bottom view of the charger.

A 2 mm thick fiberglass plate is also fixed to the upper corners of the case, and capacitors C4-C9 and relays P1 and P2 are screwed to it. A printed circuit board is also screwed to these corners, on which the circuit is soldered automatic control charging the battery. In reality, the number of capacitors is not six, as according to the scheme, but 14, since in order to obtain a capacitor of the desired rating, they had to be connected in parallel. Capacitors and relays are connected to the rest of the charger circuit through a connector (blue in the photo above), which made it easier to access other elements during installation.

On outside the rear wall is ribbed aluminum radiator for cooling power diodes VD2-VD5. There is also a 1 A fuse Pr1 and a plug (taken from the computer's power supply) for supplying the supply voltage.

The power diodes of the charger are fixed with two clamping bars to the radiator inside the case. For this, a rectangular hole is made in the rear wall of the case. This technical solution made it possible to minimize the amount of heat generated inside the case and save space. The leads of the diodes and the lead wires are soldered to a non-fixed strip made of foil-clad fiberglass.

The photo shows a view of a homemade charger on the right side. Mounting electrical circuit made with colored wires, alternating voltage - brown, positive - red, negative - wires of blue color... The cross-section of the wires leading from the secondary winding of the transformer to the terminals for connecting the battery must be at least 1 mm 2.

The shunt of the ammeter is a piece of high-resistance constantan wire about a centimeter long, the ends of which are soldered into copper strips. The length of the shunt wire is selected when calibrating the ammeter. I took the wire from the shunt of the burnt out arrow tester. One end of the copper strips is soldered directly to the positive output terminal, and a thick conductor is soldered to the second strip from the contacts of the P3 relay. A yellow and red wire goes to the dial gauge from the shunt.

Circuit board for the automatic charger unit

The circuit for automatic regulation and protection against incorrect connection of the battery to the charger is soldered on a printed circuit board made of foil-clad fiberglass.

The photo shows appearance the assembled circuit. The drawing of the printed circuit board of the automatic regulation and protection circuit is simple, the holes are made with a pitch of 2.5 mm.

The photo above is a view of the printed circuit board from the side of the installation of parts with the part marking in red. This drawing is useful for assembling a printed circuit board.

The drawing of the printed circuit board above will be useful when it is manufactured using technology using a laser printer.

And this drawing of the printed circuit board will come in handy when applying the conductive tracks of the printed circuit board by hand.

The scale of the dial gauge of the B3-38 millivoltmeter did not fit the required measurements, I had to draw my own version on the computer, printed it on thick white paper and glued the moment on top of the standard scale with glue.

Due to the larger scale size and the calibration of the device in the measurement area, the voltage reading accuracy is 0.2 V.

Wires for connecting the automatic control system to the terminals of the battery and the network

Alligator clips are installed on the wires for connecting the car battery to the charger on one side, and split lugs on the other side. To connect the positive terminal of the battery, the red wire is selected, to connect the negative terminal - blue. The cross-section of the wires for connecting the battery to the device must be at least 1 mm 2.

The charger is connected to the electrical network using a universal cord with a plug and socket, as is used to connect computers, office equipment and other electrical appliances.

About charger parts

The power transformer T1 is of the type TN61-220, the secondary windings of which are connected in series, as shown in the diagram. Since the efficiency of the charger is at least 0.8 and the charge current usually does not exceed 6 A, then any 150-watt transformer will do. The secondary winding of the transformer must provide a voltage of 18-20 V at a load current of up to 8 A. If there is no ready-made transformer, then you can take any suitable power and rewind the secondary winding. You can calculate the number of turns of the secondary winding of a transformer using a special calculator.

Capacitors C4-C9 of the MBGCH type for a voltage of at least 350 V. You can use capacitors of any type, designed to work in alternating current circuits.

Diodes VD2-VD5 are suitable for any type, designed for a current of 10 A. VD7, VD11 - any pulse silicon. VD6, VD8, VD10, VD5, VD12 and VD13 are any, withstanding a current of 1 A. LED VD1 - any, VD9 I used type KIPD29. Distinctive feature of this LED, that it changes the color of the glow when the polarity of the connection is changed. To switch it, contacts K1.2 of relay P1 are used. When charging with the main current, the LED shines yellow, and when switching to battery charging mode, it turns green. Instead of a binary LED, you can install any two one-color LEDs by connecting them according to the diagram below.

The KR1005UD1, an analogue of the foreign AN6551, was selected as the operational amplifier. Such amplifiers were used in the sound and video unit in the VM-12 video recorder. The amplifier is good in that it does not require two-pole power supply, correction circuits and remains operational at a supply voltage of 5 to 12 V. It can be replaced with almost any analogous one. Well suited for replacing microcircuits, for example, LM358, LM258, LM158, but their pin numbering is different, and you will need to make changes to the printed circuit board drawing.

Relays P1 and P2 are any for a voltage of 9-12 V and contacts designed for a switching current of 1 A. P3 for a voltage of 9-12 V and a switching current of 10 A, for example RP-21-003. If there are several contact groups, then it is desirable to solder them in parallel.

Switch S1 of any type, rated for operation at a voltage of 250 V and having a sufficient number of switching contacts. If you do not need a current regulation step of 1 A, then you can put several toggle switches and set the charge current, say, 5 A and 8 A. If you charge only car batteries, then this solution is quite justified. Switch S2 is used to disable the charging level monitoring system. If the battery is charged high current, the system may be triggered before the battery is fully charged. In this case, you can turn off the system and continue charging in manual mode.

Any electromagnetic head for a current and voltage meter is suitable, with a total deflection current of 100 μA, for example, type M24. If there is no need to measure voltage, but only current, then you can install a ready-made ammeter designed for a maximum constant current of measurement of 10 A, and monitor the voltage with an external dial tester or multimeter by connecting them to the battery contacts.

Setting up the automatic adjustment and protection unit

With an error-free assembly of the board and the health of all radio elements, the circuit will work immediately. It remains only to set the voltage threshold with the resistor R5, upon reaching which the battery charging will be transferred to the low current charging mode.

The adjustment can be done directly while charging the battery. But still, it is better to be on the safe side and check and adjust the automatic control and protection circuit of the automatic control system before installing it in the case. To do this, you will need a DC power supply that has the ability to regulate the output voltage in the range from 10 to 20 V, designed for an output current of 0.5-1 A. From measuring instruments you will need any voltmeter, dial tester or multimeter designed to measure constant voltage, with a measurement range from 0 to 20 V.

Checking the voltage regulator

After installing all the parts on the printed circuit board, you need to supply a 12-15 V supply voltage from the power supply to the common wire (minus) and pin 17 of the DA1 microcircuit (plus). By changing the voltage at the output of the power supply from 12 to 20 V, you need to use a voltmeter to make sure that the voltage at the output 2 of the DA1 voltage stabilizer chip is 9 V. If the voltage differs or changes, then DA1 is faulty.

Microcircuits of the K142EN series and analogs have protection against a short circuit at the output and if you short-circuit its output to a common wire, then the microcircuit will enter the protection mode and will not fail. If the check showed that the voltage at the output of the microcircuit is 0, then this does not always mean its malfunction. It is quite possible that there is a short circuit between the tracks of the printed circuit board, or one of the radio elements in the rest of the circuit is faulty. To check the microcircuit, it is enough to disconnect its pin 2 from the board, and if 9 V appears on it, it means that the microcircuit is working, and it is necessary to find and eliminate the short circuit.

Overvoltage protection system check

I decided to start the description of the principle of operation of the circuit with a simpler part of the circuit, which does not have strict standards for operating voltage.

The function of disconnecting the AMC from the mains in the event of a battery disconnection is performed by a part of the circuit assembled on an operational differential amplifier A1.2 (hereinafter referred to as the OA).

How an operational differential amplifier works

Without knowing the principle of operation of the op-amp, it is difficult to understand the operation of the circuit, so I will give short description... The op-amp has two inputs and one output. One of the inputs, which is indicated on the diagram by the "+" sign, is called non-inverting, and the second input, which is indicated by the "-" sign or a circle, is called inverting. The word differential op-amp means that the voltage at the output of the amplifier depends on the voltage difference at its inputs. In this circuit, the operational amplifier is switched on without feedback, in the comparator mode - comparison of input voltages.

Thus, if the voltage at one of the inputs will be unchanged, and at the second will change, then at the moment of crossing the point of equality of voltages at the inputs, the voltage at the amplifier output will change abruptly.

Overvoltage protection circuit check

Let's go back to the diagram. The non-inverting input of the amplifier A1.2 (pin 6) is connected to a voltage divider assembled on resistors R13 and R14. This divider is connected to a stabilized voltage of 9 V and therefore the voltage at the junction point of the resistors never changes and is 6.75 V. The second input of the op-amp (pin 7) is connected to the second voltage divider assembled on resistors R11 and R12. This voltage divider is connected to a bus carrying a charging current, and the voltage across it changes depending on the current and the state of charge of the battery. Therefore, the voltage value at pin 7 will also change accordingly. The divider resistances are selected in such a way that when the battery charging voltage changes from 9 to 19 V, the voltage at pin 7 will be less than at pin 6 and the voltage at the op-amp output (pin 8) will be greater than 0.8 V and close to the op-amp supply voltage. The transistor will be open, voltage will be supplied to the relay winding P2 and it will close the contacts K2.1. The output voltage will also close the diode VD11 and the resistor R15 will not participate in the operation of the circuit.

As soon as the charging voltage exceeds 19 V (this can only happen if the battery is disconnected from the AMU output), the voltage at pin 7 will be greater than at pin 6. In this case, the voltage at the op-amp output will abruptly decrease to zero. The transistor will close, the relay will de-energize and the contacts K2.1 will open. The supply voltage to the RAM will be stopped. At the moment when the voltage at the output of the op-amp becomes zero, the VD11 diode will open and, thus, R15 will be connected in parallel to the R14 of the divider. The voltage at pin 6 will instantly decrease, which will exclude false alarms at the moment when the voltages at the inputs of the op-amp are equal due to ripple and noise. By changing the value of R15, you can change the comparator hysteresis, that is, the voltage at which the circuit will return to its original state.

When the battery is connected to the RAM, the voltage at pin 6 will again be set to 6.75 V, and at pin 7 it will be less and the circuit will start working normally.

To check the operation of the circuit, it is enough to change the voltage on the power supply from 12 to 20 V and by connecting a voltmeter instead of relay P2, observe its readings. At a voltage less than 19 V, the voltmeter should show a voltage of 17-18 V (part of the voltage will drop on the transistor), and if it is higher, it should be zero. It is still advisable to connect the relay coil to the circuit, then not only the operation of the circuit will be checked, but also its performance, and by clicking the relay it will be possible to control the operation of the automation without a voltmeter.

If the circuit does not work, then you need to check the voltages at inputs 6 and 7, the output of the op-amp. If the voltages differ from those indicated above, you need to check the resistor values \u200b\u200bof the corresponding dividers. If the divider resistors and the VD11 diode are serviceable, then the op-amp is faulty.

To test the R15, D11 circuit, it is enough to disconnect one of the terminals of these elements, the circuit will work only without hysteresis, that is, it turns on and off at the same voltage supplied from the power supply. The VT12 transistor can be easily checked by disconnecting one of the R16 pins and monitoring the voltage at the op-amp output. If the voltage at the op-amp output changes correctly, and the relay is on all the time, then there is a breakdown between the collector and the emitter of the transistor.

Checking the battery disconnect circuit when it is fully charged

The principle of operation of op-amp A1.1 is no different from the operation of A1.2, with the exception of the ability to change the voltage cut-off threshold using the trimmer R5.

To check the operation of A1.1, the supply voltage supplied from the power supply gradually increases and decreases within 12-18 V. When the voltage reaches 15.6 V, relay P1 should turn off and, using the contacts K1.1, switch the ACC to low-current charging through a capacitor C4. When the voltage level drops below 12.54 V, the relay should turn on and switch the AMC to the charging mode with a given current value.

The turn-on threshold voltage of 12.54 V can be adjusted by changing the value of the resistor R9, but this is not necessary.

By means of switch S2 it is possible to disable automatic operation by switching on relay P1 directly.

Capacitor charger circuit
without automatic shutdown

For those who do not have sufficient assembly experience electronic circuits or does not need to automatically turn off the charger at the end of charging the battery, I propose a simplified version of the device circuit for charging acid car batteries. A distinctive feature of the circuit is its simplicity for repetition, reliability, high efficiency and stable charging current, protection against incorrect battery connection, automatic continuation of charging in the event of a power failure.

Stabilization principle charging current remained unchanged and is provided by connecting a block of capacitors C1-C6 in series with the network transformer. To protect against overvoltage on the input winding and capacitors, one of the pairs of normally open contacts of the P1 relay is used.

When the battery is not connected, the contacts of the P1 relay K1.1 and K1.2 are open, and even if the charger is connected to the mains, no current flows to the circuit. The same happens if you connect the battery by mistake in polarity. With the correct connection of the battery, the current from it flows through the VD8 diode to the winding of the P1 relay, the relay is triggered and its contacts K1.1 and K1.2 are closed. Through the closed contacts K1.1, the mains voltage is supplied to the charger, and through K1.2, the charging current is supplied to the battery.

At first glance, it seems that the contacts of the relay K1.2 are not needed, but if they are not there, then with wrong connection battery, current will flow from the positive terminal of the battery through the negative terminal of the charger, then through diode bridge and then directly to the negative terminal of the battery and the diodes of the charger bridge will fail.

The proposed simple circuit for charging batteries is easily adapted to charge batteries for a voltage of 6 V or 24 V. It is enough to replace relay P1 with the corresponding voltage. To charge 24 volt batteries, it is necessary to provide an output voltage from the secondary winding of the transformer T1 of at least 36 V.

If desired, the circuit of a simple charger can be supplemented with a charging current and voltage indication device, turning it on as in an automatic charger circuit.

How to charge a car battery
automatic homemade charger

Before charging, the battery removed from the car must be cleaned of dirt and wipe its surfaces, to remove acid residues, with an aqueous solution of soda. If there is acid on the surface, then the aqueous solution of soda foams.

If the battery has plugs for filling acid, then all plugs must be unscrewed so that the gases formed during charging in the battery can freely escape. It is imperative to check the electrolyte level, and if it is less than required, add distilled water.

Next, you need to set the charge current with the switch S1 on the charger and connect the battery observing the polarity (the positive terminal of the battery must be connected to the positive terminal of the charger) to its terminals. If the switch S3 is in the down position, the arrow of the device on the charger will immediately show the voltage supplied by the battery. It remains to insert the plug of the power cord into the outlet and the battery charging process will begin. The voltmeter will already begin to show the charging voltage.