Do-it-yourself adjustable car battery charger. Homemade chargers for car batteries: a simple diagram. General information about the battery charging process

Car owners often face the problem battery discharge. If this happens far from service stations, car dealerships and gas stations, you can make a device for charging the battery yourself from the available parts. Consider how to make a charger for a car battery with your own hands, with minimal knowledge of electrical work.

Such a device is best used only in critical situations. However, if you are familiar with electrical engineering, electrical and fire safety rules, have the skills of electrical measurements and installation work, a home-made charger may well replace the factory unit.

Causes and signs of battery discharge

During the operation of the battery, when the engine is running, the battery is constantly recharged from the car's generator. You can check the charging process by connecting a multimeter to the battery terminals with the engine running, measuring the charging voltage of the car battery. The charge is considered normal if the voltage at the terminals is between 13.5 and 14.5 volts.

For a full charge, you need to drive a car for at least 30 kilometers, or about half an hour in the urban rhythm of traffic.

The voltage of a normally charged battery during parking should be at least 12.5 volts. In the event that the voltage is less than 11.5 Volts, the car engine may not start during the start. Causes of battery discharge:

• The battery has significant wear ( more than 5 years of operation);
• improper use of the battery, leading to sulfation of the plates;
• long parking vehicle, especially in the cold season;
• urban rhythm of car movement with frequent stops when the battery does not have enough time to charge;
• non-switched off electrical appliances of the car during parking;
• damage to electrical wiring and vehicle equipment;
• electrical leakage.

Many car owners in the on-board tool kit do not have the means to measure battery voltage ( voltmeter, multimeter, probe, scanner). In this case, you can be guided by indirect signs of a battery discharge:

• dim glow of the lights on the dashboard when the ignition is turned on;
• lack of rotation of the starter when starting the engine;
• loud clicks in the starter area, the lights on the dashboard go out at startup;
• complete lack of reaction of the car to the ignition.

If these signs appear, first of all, it is necessary to check the battery terminals, if necessary, clean and tighten them. In the cold season, you can try to bring the battery into a warm room for a while and warm it up.

You can try to “light up” a car from another car. If these methods do not help or are impossible, you have to use a charger.

Universal charger with your own hands. Video:

Operating principle

Most devices charge batteries permanently or impulse currents. How many amps does it take to charge a car battery? The charge current is chosen equal to one tenth of the battery capacity. With a capacity of 100 A * h, the charging current of a car battery will be 10 Amperes. The battery will take about 10 hours to fully charge.

Charging a car battery with high currents can lead to the process of sulfation. To avoid this, it is better to charge the battery with low currents, but for a longer time.

Pulse devices significantly reduce the effect of sulfation. Some pulse chargers have a desulfation mode that allows you to restore battery performance. It consists in a sequential charge-discharge with pulsed currents according to a special algorithm.

When charging the battery, do not allow overcharging. It can lead to boiling of the electrolyte, sulfation of the plates. It is necessary that the device has its own system of control, measurement of parameters and emergency shutdown.

Since the 2000s, special types of batteries have been installed on cars: AGM and gel. Charging these types of car batteries is different than normal.

As a rule, it is three-stage. Up to a certain level, the charge goes with a large current. Then the current decreases. The final charge occurs with even smaller pulsed currents.

Charging a car battery at home

Often in driving practice, a situation arises when, having parked the car near the house in the evening, in the morning it turns out that the battery is discharged. What can be done in such a situation when there is no soldering iron at hand, no details, but you need to get started?

Usually, a small capacity remains on the battery, it just needs to be “pulled up” a little so that there is enough charge to start the engine. In this case, a power supply from some household or office equipment, such as a laptop, can help.

Charging from a laptop power supply

The voltage that the laptop power supply produces is usually 19 volts, the current is up to 10 amperes. This is enough to charge the battery. But it is IMPOSSIBLE to directly connect the power supply to the battery. It is necessary to include a limiting resistor in series in the charge circuit. As it can take a car light bulb, better for interior lighting. It can be purchased at the nearest gas station.

Usually the middle pin of the connector is positive. A light bulb is connected to it. The + battery is connected to the second output of the light bulb.

The negative terminal is connected to the negative terminal of the power supply. The power supply usually has a label showing the polarity of the connector. A couple of hours of charging in this way is enough to start the engine.

Diagram of a simple charger for a car battery.

Charging from a household network

A more extreme charging method is directly from a household outlet. It is used only in critical situation using maximum electrical safety measures. To do this, you need a lighting lamp ( not energy saving).

You can use an electric stove instead. You also need to purchase a rectifier diode. Such a diode can be "borrowed" from a faulty energy saving lamp. At this time, the voltage supplied to the apartment, it is better to de-energize. The scheme is shown in the figure.

The charge current with a lamp power of 100 watts will be approximately 0.5 A. Overnight, the battery will be recharged by only a few ampere-hours, but this may be enough to start. If you connect three lamps in parallel, then the battery will be charged three times more. If you connect an electric stove instead of a light bulb ( at the lowest power), then the charge time will be significantly reduced, but this is very dangerous. In addition, a diode can break through, then a battery short circuit is possible. Charging methods from 220V are dangerous.

Charging for car batteries with your own hands. Video:

Homemade car battery charger

Before you make a charger for a car battery, you should evaluate your experience in electrical work, knowledge of electrical engineering, based on this, proceed to the choice of a charger circuit for a car battery.

You can look in the garage, there may be old devices or blocks. The power supply from an old computer is suitable for the device. It has almost everything:

• socket 220 V;
• power switch;
• wiring diagram;
• cooling Fan;
• connection leads.

The voltages on it are standard: +5 V, -12 V and +12 Volts. To charge the battery, it is better to use a +12 Volt, 2 Ampere wire. The output voltage must be raised to the level of +14.5 - +15.0 Volts. This can usually be done by changing the value of the resistance in the circuit feedback (about 1 kiloohm).

Limiting resistance can not be set, the electronic circuit will independently adjust the charge current within 2 Amperes. It is easy to calculate that it will take about a day to fully charge a 50 Ah battery. Appearance of the device.

You can pick up or buy at the flea market a network transformer with a secondary winding voltage of 15 to 30 volts. These were used in old TVs.

Transformer devices

The simplest diagram of a device with a transformer.

Its disadvantage is the need to limit the current in the output circuit and the associated large power losses and heating of the resistors. Therefore, capacitors are used to regulate the current.

Theoretically, by calculating the value of the capacitor, you can not use a power transformer, as shown in the diagram.

When buying capacitors, you should choose the appropriate rating with a voltage of 400 V or more.

In practice, devices with current regulation have received greater use.

You can choose schemes of impulse home-made chargers for car battery. They are more complex circuitry, require certain skills during installation. Therefore, if you do not have special skills, it is better to buy a factory block.

Pulse chargers

Pulse chargers have a number of advantages:

The principle of operation of pulse devices is based on the conversion AC voltage household power supply into a constant with the help of a VD8 diode assembly. The DC voltage is then converted into pulses of high frequency and amplitude. The pulse transformer T1 again converts the signal into a constant voltage, which charges the battery.

Since the reverse conversion is carried out at a high frequency, the dimensions of the transformer are much smaller. The feedback necessary to control the charge parameters is provided by optocoupler U1.

Despite the apparent complexity of the device, with proper assembly, the unit starts working without additional adjustment. Such a device provides a charge current of up to 10 amperes.

When charging the battery with homemade device necessary:

• place the device and the battery on a non-conductive surface;
• comply with electrical safety requirements use gloves, rubber mat, electrically insulated tool);
• do not leave the charger turned on for a long time without control, monitor the voltage and temperature of the battery, and the charging current.

Who has no time to "bother" with all the nuances of charging a car battery, monitor the charging current, turn it off in time so as not to overcharge, etc., we can recommend a simple car battery charging scheme with automatic shutdown when the battery is fully charged. This scheme uses one powerful transistor to determine the battery voltage.

Diagram of a simple automatic car battery charger

List of required parts:

• R1 \u003d 4.7 kOhm;
• P1 = 10K trim;
• T1 = BC547B, KT815, KT817;
• Relay \u003d 12V, 400 Ohm, (automobile, for example: 90.3747);
• TR1 = voltage of the secondary winding 13.5-14.5 V, current 1/10 of the battery capacity (for example: battery 60A / h - current 6A);
• Diode bridge D1-D4 \u003d for a current equal to the rated current of the transformer \u003d not less than 6A (for example, D242, KD213, KD2997, KD2999 ...), mounted on a radiator;
• Diodes D1 (in parallel with the relay), D5,6 = 1N4007, KD105, KD522…;
• C1 = 100uF/25V.
• R2, R3 - 3 kOhm
• HL1 - AL307G
• HL2 - AL307B

The circuit lacks an indicator of charging, current control (ammeter) and limitation charging current. If desired, you can put an ammeter on the output in the gap of any of the wires. LEDs (HL1 and HL2) with limiting resistances (R2 and R3 - 1 kOhm) or bulbs in parallel with C1 "network", and to the free contact RL1 "end of charge".

Changed scheme

A current equal to 1/10 of the battery capacity is selected by the number of turns of the secondary winding of the transformer. When winding the secondary of the transformer, it is necessary to make several layers for selection the best option charging current.

The charge of a car (12-volt) battery is considered complete when the voltage at its terminals reaches 14.4 volts.

The shutdown threshold (14.4 volts) is set by the trimming resistor P1 when the battery is connected and fully charged.

When charging a discharged battery, the voltage on it will be about 13V, during the charging process, the current will drop, and the voltage will increase. When the voltage on the battery reaches 14.4 volts, the transistor T1 will turn off the relay RL1, the charge circuit will be broken and the battery will be disconnected from charging voltage with diodes D1-4.

When the voltage drops to 11.4 volts, charging resumes again, such a hysteresis is provided by diodes D5-6 in the emitter of the transistor. The circuit threshold becomes 10 + 1.4 = 11.4 volts, which can be considered as an automatic restart of the charging process.

Such a homemade simple automatic car charger will help you control the charging process, do not track the end of charging and do not recharge your battery!

Site materials used: homemade-circuits.com

Another version of the charger circuit for a 12-volt car battery with automatic shutdown after charging

The circuit is a little more complicated than the previous one, but with a clearer response.

Table of voltages and the percentage of discharge of batteries that are not connected to the charger

P O P U L I R N O E:

Good and necessary in the household of the master will be a device that receives high temperature flame (about 2000 ° C) from several liters water!

You can verify this by reading the description of the device of the electrolyzer developed by me.

Offered very simple design, in which there are no cylinders, gearboxes, valves and a complex burner.



A simple economical do-it-yourself metal detector on a single chip

If you have lost a ring, a key, a screwdriver... and you know the approximate place of loss, then do not despair! You can assemble a metal detector with your own hands or ask a friend of a radio amateur to assemble simple do-it-yourself metal detector. Below is a diagram of a metal detector that is easy to manufacture and proven over the years, which (with certain skills) can be made in one day. The simplicity of the described metal detector is that it is assembled on just one very common microcircuit K561LA7 (CD4011BE). The setup is also easy and does not require expensive measuring instruments. An oscilloscope or frequency meter is enough to tune the generators. If everything is done without errors and from serviceable elements, then these devices will not be needed.

The simplest DIY 3G / 4G antenna

In my country house there are connection problems due to low level signal.

In the article below, I will tell you how I solved the problem with connecting my 3G modem for free, in just 5 minutes of work.

Sometimes it happens that the battery in the car sits down and it is no longer possible to start it, because the starter does not have enough voltage and, accordingly, current to turn the engine shaft. In this case, you can “light it up” from another car owner so that the engine starts and the battery starts charging from the generator, but this requires special wires and a person who wants to help you. You can also charge the battery yourself using a specialized charger, but they are quite expensive and you don’t have to use them very often. Therefore, in this article we will take a closer look at a homemade device, as well as instructions on how to make a charger for a car battery with your own hands.

Homemade device

Normal voltage on a battery disconnected from the vehicle is between 12.5V and 15V. Therefore, the charger must provide the same voltage. The charge current should be approximately 0.1 of the capacity, it may be less, but this will increase the charging time. For a standard battery with a capacity of 70-80 Ah, the current should be 5-10 amps, depending on the specific battery. Our homemade battery charger must meet these parameters. To assemble a charger for a car battery, we need the following items:

Transformer. We can use any of the old electrical appliances or those bought on the market with an overall power of about 150 watts, more, but not less, otherwise it will get very hot and may fail. Well, if the voltage of its output windings is 12.5-15 V, and the current is about 5-10 amperes. You can see these parameters in the documentation for your part. If there is no required secondary winding, then it will be necessary to rewind the transformer for another output voltage. For this:

Thus, we have found or assembled the perfect transformer to make a DIY battery charger.

We will also need:

Having prepared all the materials, you can proceed to the very process of assembling a car memory.

Assembly technology

To make a charger for a car battery with your own hands, you must follow the step-by-step instructions:

1. We create a homemade charging scheme for the battery. In our case, it will look like this:
   
2. We use the transformer TS-180-2. It has several primary and secondary windings. To work with it, you need to connect two primary and two secondary windings in series to get the desired voltage and current at the output.
   
   
3. With the help of a copper wire, we connect pins 9 and 9 'to each other.
   
4. On a fiberglass plate we assemble a diode bridge from diodes and radiators (as shown in the photo).
   
5. Conclusions 10 and 10 'we connect to the diode bridge.
6. Install a jumper between pins 1 and 1'.
   
7. Using a soldering iron, we attach a power cord with a plug to terminals 2 and 2 '.
8. We connect a 0.5 A fuse to the primary circuit, a 10-amp fuse, respectively, to the secondary circuit.
9. In the gap between the diode bridge and the battery, we connect an ammeter and a piece of nichrome wire. We fix one end of which, and the second should provide a movable contact, thus the resistance will change and the current supplied to the battery will be limited.
10. We isolate all connections with heat shrink or electrical tape and place the device in the case. This is necessary to avoid electric shock.
11. We install a moving contact at the end of the wire so that its length and, accordingly, the resistance are maximum. And connect the battery. By decreasing and increasing the length of the wire, you need to set the desired current value for your battery (0.1 of its capacity).
12. In the process of charging, the current supplied to the battery will decrease by itself and when it reaches 1 ampere, we can say that the battery is charged. It is also desirable to directly control the voltage on the battery, however, for this it must be disconnected from the charger, since when charging it will be slightly higher than the actual values.

The first start of the assembled circuit of any power source or memory is always carried out through an incandescent lamp, if it lights up at full heat - either there is an error somewhere, or the primary winding is closed! An incandescent lamp is installed in the break of the phase or neutral wire that feeds the primary winding.

This scheme for a home-made battery charger has one big drawback - it does not know how to independently disconnect the battery from charging after reaching the desired voltage. Therefore, you will have to constantly monitor the readings of the voltmeter and ammeter. There is a design that does not have this drawback, but its assembly will require additional parts and more effort.

A good example of a finished product

Operating rules

The disadvantage of a homemade charger for a 12V battery is that after the battery is fully charged, the device does not automatically turn off. That is why you will have to periodically glance at the scoreboard in order to turn it off in time. Another important nuance is that it is strictly forbidden to check the memory “for a spark”.

The article will tell you how to make your own homemade schemes you can use absolutely any, but most simple option manufacturing is a remake of a computer PSU. If you have such a block, it will be quite easy to find a use for it. For nutrition motherboards a voltage of 5, 3.3, 12 volts is used. As you understand, the voltage of 12 volts is of interest to you. The charger will allow you to charge batteries, the capacity of which lies in the range from 55 to 65 Ah. In other words, it will be enough to recharge the batteries of most cars.

General view of the scheme

To make an alteration, you need to use the scheme presented in the article. made from a personal computer power supply unit with your own hands, allows you to control the charging current and voltage at the output. It is necessary to pay attention to the fact that there is protection against short circuit - a 10 Amp fuse. But it is not necessary to install it, since most personal computer power supplies have protection that turns off the device in the event of a short circuit. Therefore, battery charger circuits from computer power supplies are able to protect themselves from short circuits.

SHI controller (designated DA1), as a rule, two types are used in the PSU - KA7500 or TL494. Now for some theory. Can a computer power supply properly charge the battery? The answer is yes, since lead batteries in most cars have a capacity of 55-65 ampere-hours. And for normal charging, it needs a current equal to 10% of the battery capacity - no more than 6.5 amperes. If the power supply has a power of more than 150 W, then its “+12 V” circuit is capable of delivering such a current.

The initial stage of rework

To repeat a simple homemade battery charger, you need to slightly improve the power supply:

1. Get rid of all unnecessary wires. Use a soldering iron to remove them so that they do not interfere.
2. According to the diagram given in the article, find the constant resistor R1, which must be unsoldered and a tuning resistor with a resistance of 27 kOhm should be installed in its place. Subsequently, a constant voltage of “+12 V” must be applied to the upper contact of this resistor. Without this, the device will not work.
3. The 16th output of the microcircuit is disconnected from the minus.
4. Next, you need to disconnect the 15th and 14th conclusions.

It turns out quite simple home-made. Any schemes can be used, but it is easier to make from a computer PSU - it is lighter, easier to operate, more affordable. When compared with transformer devices, the mass of devices differs significantly (as well as dimensions).

Charger settings

The back wall will now be the front, it is desirable to make it from a piece of material (textolite is ideal). On this wall, it is necessary to install a charging current regulator, indicated in the diagram R10. The current sense resistor is best used as high as possible - take two with 5 watts and 0.2 ohms. But it all depends on the choice of battery charger circuit. In some designs, you do not need to use powerful resistors.

When they are connected in parallel, the power is doubled, and the resistance becomes 0.1 ohm. On the front wall there are also indicators - a voltmeter and an ammeter, which allow you to control the corresponding parameters of the charger. To fine-tune the charger, a tuning resistor is used, with which voltage is applied to the 1st output of the SHI controller.

Device Requirements

final assembly

To pins 1, 14, 15 and 16, you need to solder stranded thin wires. Their insulation must be reliable so that heating does not occur under load, otherwise the home-made charger for the car will fail. After assembly, you need to set a voltage of about 14 volts (+/-0.2 V) with a trimmer resistor. It is this voltage that is considered normal for charging batteries. Moreover, this value should be in idle mode (without a connected load).

On the wires that connect to the battery, you need to install two crocodile clips. One is red, the other is black. You can buy these at any hardware or auto parts store. This is how a simple homemade charger for a car battery turns out. Connection diagrams: black is attached to the minus, and red to the plus. The charging process is fully automatic, no human intervention is required. But it is worth considering the main stages of this process.

Battery charging process

During the initial cycle, the voltmeter will show a voltage of approximately 12.4-12.5 V. If the battery has a capacity of 55 Ah, then you need to rotate the regulator until the ammeter shows a value of 5.5 Amperes. This means that the charging current is 5.5 A. As the battery charges, the current decreases and the voltage tends to a maximum. As a result, at the very end, the current will be 0, and the voltage will be 14 V.

Regardless of which selection of circuits and designs of chargers was used for manufacturing, the principle of operation is largely similar. When the battery is fully charged, the device starts to compensate for the self-discharge current. Therefore, you do not run the risk of overcharging the battery. Therefore, the charger can be connected to the battery for a day, a week, or even a month.

If you do not have measuring instruments that it would not be a pity to install in the device, you can refuse them. But for this it is necessary to make a scale for the potentiometer - to indicate the position for the charging current values ​​\u200b\u200bof 5.5 A and 6.5 A. Of course, the installed ammeter is much more convenient - you can visually observe the process of charging the battery. But the battery charger, made with your own hands without the use of devices, can be easily operated.

The photo shows a homemade automatic charger for charging car batteries at 12 V 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 with electric generator. To protect electrical equipment and appliances from overvoltage, which generates car generator, after it a relay-regulator is installed, which limits the voltage in the vehicle's on-board network 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.

Analysis of charger circuits

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

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 charge of the battery and fluctuations in the mains, it is not afraid of output short circuits. But it also has a drawback. If contact with the battery is lost during the charging process, 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 it with any acid batteries at 12 V. The device works flawlessly.

Schematic diagram of a car charger

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

If the repetition scheme seemed complicated to you, then you can assemble more that work 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, adjusting the value and stabilizing the current of the battery charge is ensured by connecting in series with the primary winding of the power transformer T1 ballast capacitors C4-C9. The larger the capacitance of the capacitor, the greater the current will charge the battery.

In practice, this is a finished 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 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 from the data in the table.

To adjust the current to reduce the number of capacitors, they can be connected in parallel in groups. I switch using two toggle switches, but you can put several toggle switches.

Protection scheme
from erroneous connection of battery poles

The protection circuit against polarity reversal of the charger when the battery is incorrectly connected to the terminals is made on the P3 relay. If the battery is connected incorrectly, the VD13 diode does not pass current, the relay is de-energized, the K3.1 relay contacts are open and no current flows to the battery terminals. When connected correctly, the relay is activated, contacts K3.1 are closed, and the battery is connected to the charging circuit. Such a reverse polarity protection circuit can be used with any charger, both transistor and thyristor. It is enough to include it in the wire break, with which the battery is connected to the charger.

The circuit for measuring the current and voltage of battery charging

Due to the presence of switch S3 in the diagram above, when charging the battery, it is possible to control not only the amount of charging current, but also voltage. When S3 is in the upper position, the current is measured, in the lower position, the voltage is measured. If the charger is not connected to the mains, the voltmeter will show the battery voltage, and when the battery is charging, the charging voltage. An M24 microammeter with an electromagnetic system was used as a head. R17 shunts the head in current measurement mode, and R18 serves as a divider when measuring voltage.

Scheme of automatic shutdown of the memory
when the battery is fully charged

To power the operational amplifier and create a reference voltage, a DA1 stabilizer chip of the 142EN8G type 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 for automatically shutting off charging when a voltage of 15.6 V is reached is made on the half of the A1.1 chip. Pin 4 of the microcircuit is connected to a 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 resistors R4-R6, resistor R5 is a trimmer for setting the threshold of the machine. The value of the resistor R9 sets the charger on threshold of 12.54 V. Due to the use of the VD7 diode and the resistor R9, the necessary hysteresis is provided between the on and off voltage of the battery charge.

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

As soon as the charge voltage reaches 16.5 V, the voltage at the output A1.1 will decrease to a value insufficient to keep the transistor VT1 in the open state. The relay will turn off and contacts K1.1 will connect the transformer through the standby capacitor C4, at which the charge current will be 0.5 A. The charger circuit will remain in this state until the voltage on the battery drops 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 proceed with the specified current. It is possible, if necessary, by switch S2 to disable the automatic control system.

Thus, the system of automatic tracking of battery charging will exclude the possibility of overcharging the battery. The battery can be left connected to the included charger for at least a whole 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 in the power grid will disappear voltage, when it appears, the charger will continue to charge the battery in normal mode

The principle of operation of the circuit for automatically shutting down the charger in case of overvoltage due to lack of load, assembled on the second half of the operational amplifier A1.2, is the same. Only the threshold for completely disconnecting the charger from the mains is selected to be 19 V. If the charging voltage is less than 19 V, the voltage at output 8 of the A1.2 chip is sufficient to keep the transistor VT2 open, at which voltage is applied to the relay P2. As soon as the charging voltage exceeds 19 V, the transistor will close, the relay will release contacts K2.1 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.

The structure of the automatic charger

All parts of the charger are placed in the case of the B3-38 milliammeter, from which all its contents have been removed, except for the pointer device. Installation of elements, except for the automation circuit, is carried out by a hinged method.

The design of the milliammeter case consists of two rectangular frames connected by four corners. Holes are made in the corners with equal pitch, to which it is convenient to attach parts.

The TN61-220 power transformer is fixed with four M4 screws on an aluminum plate 2 mm thick, the plate, in turn, is attached with M3 screws to the lower corners of the case. The TN61-220 power transformer is fixed with four M4 screws on an aluminum plate 2 mm thick, the plate, in turn, is attached with M3 screws to the lower corners of the case. C1 is also installed on this plate. The photo below shows the charger.

A plate of fiberglass 2 mm thick 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 an automatic battery charging control circuit is soldered. 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 required rating, it was necessary to connect them 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.

A ribbed aluminum radiator is installed on the outer side of the rear wall to cool the power diodes VD2-VD5. There is also a 1 A fuse Pr1 and a plug (taken from the computer power supply) for supplying power.

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

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

The ammeter shunt 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 burned-out switch tester. One end of the copper strips is soldered directly to the positive output terminal, a thick conductor is soldered to the second strip, coming from the P3 relay contacts. Yellow and red wires go to the pointer device from the shunt.

Charger automation circuit board

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 fiberglass.

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

The photo above is a view printed circuit board from the installation side of the parts with the part markings applied in red. Such a drawing is convenient when assembling a printed circuit board.

The PCB drawing above will come in handy when manufacturing it using laser printer technology.

And this drawing of a printed circuit board is useful when applying the current-carrying tracks of a printed circuit board manually.

The scale of the pointer instrument of the V3-38 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.

Thanks to larger size scale and calibration of the device in the measurement area, the accuracy of reading the voltage turned out to be 0.2 V.

Wires for connecting the AZU to the battery and network terminals

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

TO electrical network the charger is connected 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 used of the TN61-220 type, 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, any 150-watt transformer will do. The secondary winding of the transformer should 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 one and rewind the secondary winding. You can calculate the number of turns of the secondary winding of the transformer using a special calculator.

Capacitors C4-C9 of the MBGCH type for a voltage of at least 350 V. Capacitors of any type designed for operation in AC circuits can be used.

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

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

Relays P1 and P2 are any for a voltage of 9-12 V and contacts designed for a switched current of 1 A. R3 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 in the relay, then it is advisable to solder them in parallel.

Switch S1 of any type, designed 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 decision is fully justified. Switch S2 serves to disable the charge level control system. If the battery is charged with a high current, the system may operate 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 deviation 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 measurement current of 10 A, and control the voltage with an external dial gauge or multimeter by connecting them to the battery contacts.

Setting up the automatic adjustment and protection unit of the AZU

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

Adjustment can be made directly while charging the battery. But still, it’s better to make sure and check and adjust the automatic control and protection circuit of the AZU before installing it in the case. To do this, you need a DC power supply, which 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. Of the measuring instruments, you will need any voltmeter, pointer tester or multimeter designed to measure constant voltage, with a measurement limit from 0 to 20 V.

Checking the voltage regulator

After mounting all the parts on the printed circuit board, you need to supply a supply voltage of 12-15 V from the power supply to the common wire (minus) and pin 17 of the DA1 chip (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 output 2 of the voltage regulator chip DA1 is 9 V. If the voltage differs or changes, then DA1 is faulty.

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

Checking the surge protection system

I decided to start describing the principle of operation of the circuit with a simpler part of the circuit, to which strict standards for the response voltage are not imposed.

The function of disconnecting the AZU 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 OU).

Operating principle of an operational differential amplifier

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 OU has two inputs and one output. One of the inputs, which is indicated on the diagram with a “+” sign, is called non-inverting, and the second input, which is indicated with a “-” 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 scheme operational amplifier switched on without feedback, in the comparator mode - comparison of input voltages.

Thus, if the voltage at one of the inputs is unchanged, and at the second it changes, then at the moment of transition through the point of equality of the voltages at the inputs, the voltage at the output of the amplifier will change abruptly.

Checking the Surge Protection Circuit

Let's get back to the diagram. The non-inverting input of amplifier A1.2 (pin 6) is connected to a voltage divider collected on resistors R13 and R14. This divider is connected to a stabilized voltage of 9 V and therefore the voltage at the connection 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 the bus that carries the charging current, and the voltage on it changes depending on the amount of 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 more 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 contacts K2.1. The output voltage will also close the VD11 diode 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 AZU output), the voltage at pin 7 will become greater than at pin 6. In this case, the voltage at the output of the op-amp will drop abruptly to zero. The transistor will close, the relay will de-energize and contacts K2.1 will open. The supply voltage to the RAM will be cut off. 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 R14 of the divider. The voltage at pin 6 will instantly decrease, which will eliminate false positives at the moment of equality of voltages at the inputs of the op-amp due to ripples and noise. By changing the value of R15, you can change the hysteresis of the comparator, 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. When the voltage is less than 19 V, the voltmeter should show a voltage of 17-18 V (part of the voltage will drop across the transistor), and at a higher value - zero. It is still advisable to connect the relay winding 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 ​​​​of the corresponding dividers. If the divider resistors and the VD11 diode are working, then, therefore, the op-amp is faulty.

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

Checking the battery shutdown circuit when it is fully charged

The principle of operation of the 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 tuning resistor 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 contacts K1.1 switch the AZU to low current charging mode through the capacitor C4. When the voltage level drops below 12.54 V, the relay should turn on and switch the AZU to the charging mode with a current of a given 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.

Using switch S2, it is possible to disable automatic operation by turning on relay P1 directly.

Capacitor charger circuit
without automatic shutdown

For those who do not have enough assembly experience electronic circuits or does not need to automatically turn off the charger at the end of battery charging, 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 a stable charge current, the presence of protection against incorrect connection of the battery, automatic continuation of charging in the event of a power failure.

The principle of stabilization of the charging current remained unchanged and is ensured by the inclusion of 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 relay P1 is used.

When the battery is not connected, the relay contacts P1 K1.1 and K1.2 are open, and even if the charger is connected to the mains, current does not flow to the circuit. The same thing happens if you connect the battery by mistake in polarity. When the battery is connected correctly, the current from it flows through the VD8 diode to the relay winding P1, the relay is activated and its contacts K1.1 and K1.2 close. Through closed contacts K1.1 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 K1.2 relay are not needed, but if they are not there, then if the battery is connected by mistake, the current will flow from the positive terminal of the battery through the negative terminal of the charger, then through the diode bridge and then directly to the negative terminal of the battery and diodes the memory bridge will fail.

Suggested simple circuit for battery charging can be easily adapted to charge batteries at 6 V or 24 V. It is enough to replace relay P1 with the appropriate 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 device for indicating the charging current and voltage, turning it on as in the circuit of an automatic charger.

How to charge a car battery
automatic self-made memory

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

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

Next, you need to use switch S1 on the charger to set the value of the charge current 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 lower position, then the arrow of the device on the charger will immediately show the voltage that the battery produces. It remains to insert the power cord into the socket and the battery charging process will begin. The voltmeter will already begin to show the charging voltage.