DIY battery charging rectifier. DIY car battery chargers

There are times, especially in winter, when car owners need to recharge their car battery from an external power source. Of course, people who do not have good electrical skills will It is advisable to buy a factory battery charger, it’s even better to purchase a starting-charger to start the engine with a discharged battery without wasting time on external recharging.

But if you have a little knowledge in the field of electronics, you can assemble a simple charger with your own hands.

general characteristics

To properly maintain the battery and extend its service life, recharging is required when the voltage at the terminals drops below 11.2 V. At this voltage, the engine will most likely start, but if parked for a long time in winter, this will lead to sulfation of the plates and, as a result, a decrease in capacity batteries. When parked for a long time in winter, it is necessary to regularly monitor the voltage at the battery terminals. It should be 12 V. It is best to remove the battery and take it to a warm place, not forgetting monitor the charge level.

The battery is charged using constant or pulsed current. When using a constant voltage power supply, the current for proper charging should be one tenth of the battery capacity. If the battery capacity is 50 Ah, then a current of 5 amperes is required for charging.

To extend the battery life, battery plate desulfation techniques are used. The battery is discharged to a voltage of less than five volts by repeated consumption of a large current of short duration. An example of such consumption is starting the starter. After this, a slow full charge is carried out with a small current within one ampere. Repeat the process 8-9 times. The desulfation method takes a long time, but according to all studies it gives good results.

It must be remembered that when charging, it is important not to overcharge the battery. The charge is carried out to a voltage of 12.7-13.3 volts and depends on the battery model. Maximum charge indicated in the documentation for the battery, which can always be found on the Internet.

Overcharging causes boiling, increases the density of the electrolyte and, as a result, the destruction of the plates. Factory charging devices have charge monitoring and subsequent shutdown systems. Assemble such systems yourself, without having sufficient knowledge in electronics, it is quite difficult.

DIY assembly diagrams

It is worth talking about simple charging devices that can be assembled with minimal knowledge in electronics, and the charge capacity can be monitored by connecting a voltmeter or an ordinary tester.

Charging circuit for emergencies

There are times when a car that has been parked overnight near the house cannot be started in the morning due to a discharged battery. There can be many reasons for this unpleasant circumstance.

If the battery was in good condition and slightly discharged, the following will help solve the problem:

Ideal as a power source laptop charger. It has an output voltage of 19 volts and a current of within two amperes, which is quite enough to complete the task. On the output connector, as a rule, the internal input is positive, the external circuit of the plug is negative.

As a limiting resistance, which is mandatory, you can use a cabin light bulb. More can be used powerful lamps, for example, from the dimensions, but this will create an extra load on the power supply, which is very undesirable.

An elementary circuit is assembled: the negative of the power supply is connected to the light bulb, the light bulb to the negative of the battery. Plus goes directly from the battery to the power supply. Within two hours the battery will receive a charge to start the engine.

From a power supply from a desktop computer

Such a device is more difficult to manufacture, but it can be assembled with minimal knowledge of electronics. The basis will be an unnecessary block from the computer system unit. The output voltages of such units are +5 and +12 volts with an output current of about two amperes. These parameters allow you to assemble a low-power charger, which, if assembled correctly will serve the owner for a long time and reliably. Fully charging the battery will take a long time and will depend on the battery capacity, but will not create the effect of desulfation of the plates. So, step-by-step assembly of the device:

1. Disassemble the power supply and unsolder all wires except the green one. Remember or mark the input locations of black (GND) and yellow +12 V.
2. Solder the green wire to the place where the black one was located (this is necessary to start the unit without a PC motherboard). In place of the black wire, solder a lead, which will be negative for charging the battery. In place of the yellow wire, solder the positive lead for charging the battery.
3. You need to find a TL 494 chip or its equivalent. A list of analogs is easy to find on the Internet; one of them will definitely be found in the circuit. With all the variety of blocks, they are not produced without these microcircuits.
4. From the first leg of this microcircuit - it is the lower left one, find the resistor that goes to the +12 volt output (yellow wire). This can be done visually along the tracks in the diagram, or using a tester by connecting the power and measuring the voltage at the input of the resistors going to the first leg. Do not forget that the primary winding of the transformer carries a voltage of 220 volts, so you need to take safety precautions when starting the unit without a housing.
5. Unsolder the found resistor and measure its resistance with a tester. Select a variable resistor that is close in value. Set it to the desired resistance value and solder it in place of the removed circuit element with flexible wires.
6. By starting the power supply by adjusting the variable resistor, get a voltage of 14 V, ideally 14.3 V. The main thing is not to overdo it, remembering that 15 V is usually the limit for working out the protection and, as a result, shutting down.
7. Unsolder the variable resistor without changing its setting, and measure the resulting resistance. Select the required or closest resistance value from several resistors and solder it into the circuit.
8. Check the unit, the output should have the required voltage. If desired, you can connect a voltmeter to the outputs on the plus and minus circuit, placing it on the case for clarity. Subsequent assembly occurs in reverse order. The device is ready for use.

The unit will perfectly replace an inexpensive factory charger and is quite reliable. But you MUST remember that the device has overload protection, but this will not save you from polarity errors. Simply put, if you confuse the plus and minus when connecting to the battery, The charger will instantly fail.

Charger circuit from an old transformer

If you don’t have an old computer power supply at hand, and your radio engineering experience allows you to install simple circuits yourself, then you can use the following rather interesting battery charging circuit with control and regulation of the supplied voltage.

To assemble the device, you can use transformers from old uninterruptible power supplies or Soviet-made TVs. Any powerful step-down transformer with a total voltage set on the secondary windings of approximately 25 volts will do.

The diode rectifier is assembled on two KD 213A diodes (VD 1, VD 2), which must be installed on the radiator and can be replaced with any imported analogues. There are many analogues, and they can be easily selected from reference books on the Internet. Surely the necessary diodes can be found at home in old unnecessary equipment.

The same method can be used to replace the control transistor KT 827A (VT 1) and zener diode D 814 A (VD 3). The transistor is installed on the radiator.

The supply voltage is adjusted by variable resistor R2. The scheme is simple and obviously working. It can be assembled by a person with minimal knowledge of electronics.

Pulse charging for batteries

The circuit is difficult to assemble, but this is the only drawback. It is unlikely that you will be able to find a simple circuit for a pulse charging unit. This is compensated by the advantages: such blocks hardly heat up, at the same time they have serious power and high efficiency, and are compact in size. The proposed circuit, mounted on a board, fits into a container measuring 160*50*40 mm. To assemble the device, you need to understand the operating principle of the PWM (Pulse Width Modulation) generator. In the proposed version, it is implemented using the common and inexpensive IR 2153 controller.

With capacitors used, the power of the device is 190 watts. This is enough to charge any light car battery with a capacity of up to 100 Ah. By installing 470 µF capacitors, the power will double. It will be possible to charge batteries with a capacity of up to two hundred amperes/hours.

When using devices without automatic battery charge control, you can use the simplest network, daily relay made in China. This will eliminate the need to monitor the time the unit is disconnected from the network.

The cost of such a device is about 200 rubles. Knowing the approximate charging time of your battery, you can set the desired shutdown time. This ensures that the electricity supply is cut off in a timely manner. You can get distracted by business and forget about the battery, which can lead to boiling, destruction of the plates and failure of the battery. A new battery will cost much more

Precautionary measures

When using self-assembled devices, the following safety precautions should be observed:

1. All devices, including the battery, must be on a fire-resistant surface.
2. When using the manufactured device for the first time, it is necessary to ensure full control of all charging parameters. It is imperative to control the heating temperature of all charging elements and the battery; the electrolyte should not be allowed to boil. The voltage and current parameters are controlled by a tester. Primary monitoring will help determine the time it takes to fully charge the battery, which will be useful in the future.

Assembling a battery charger is easy even for a beginner. The main thing is to do everything carefully and follow safety measures, because you will have to deal with an open voltage of 220 volts.

Almost every modern motorist has encountered battery problems. In order to resume its normal operation, you must have a mobile charger. It allows you to revive the device in a matter of seconds.

The main component of any charging is the transformer. Thanks to it, you can make a simple charger with your own hands at home.

Here you will find out what parts you will need when assembling the structure. Advice from experienced experts will help you avoid common mistakes.

How should the battery be charged?

It is necessary to charge the battery according to certain rules that will help extend the service life of this device. Violation of one of the points may cause premature failure of parts.

Charging parameters must be selected in accordance with the characteristics of the car battery. This process allows adjustment of a specialized device that is sold in specialized departments. As a rule, it has a fairly high cost, which makes it not accessible to every consumer.

That is why most people prefer to make the charger power supply with their own hands. Before you begin the work process, you need to familiarize yourself with the types of chargers for the car.

Types of charging for batteries

The process of charging batteries is the restoration of lost power. To do this, use special terminals that produce constant current and constant voltage.

It is important to observe polarity during the connection process. Incorrect installation will result in a short circuit, which will cause parts inside the vehicle to catch fire.

To quickly reanimate the battery, it is recommended to use constant voltage. It can restore the car's functionality in 5 hours.

Simple charger circuit

What can a charger be made from? All parts and consumables can be used from old household appliances.

For this you will need:

A step-down transformer. It is found in old tube TVs. It helps to reduce 220 V to the required 15 V. The output of the transformer will produce an alternating voltage. In the future, it is recommended to straighten it. To do this you will need a rectifying diode. The diagrams on how to make a charger with your own hands show a drawing of the connections of all elements.

Diode bridge. Thanks to it, negative resistance is obtained. The current is pulsating, but controlled. In some cases, a diode bridge with a smoothing capacitor is used. It provides constant current.

Consumables. There are fuses and meters here. They help control the entire charging process.

Multimeter. It will indicate power fluctuations during the charging process of the car battery.

This device will become very hot during operation. A special cooler will help prevent the installation from overheating. It will control power surges. It is used instead of a diode bridge. The photo of the do-it-yourself charger shows ready-made equipment for recharging a car battery.

The process can be regulated by changing the resistance. To do this, use a tuning resistor. This method is used in most cases.

You can manually adjust the supply current using two transistors and a trimming resistor. These parts ensure a uniform supply of constant voltage and ensure the correct level of voltage at the output. There are many ideas and instructions on the Internet on how to make a charger.

DIY charger photo

Automatic devices are simple in design, but very reliable in operation. Their design was created using a simple design without unnecessary electronic additions. They are designed for simple charging of batteries of any vehicles.

Pros:

1. The charger will last for many years with proper use and proper maintenance.

Minuses:

1. Lack of any protection.
2. Eliminating discharge mode and the possibility of reconditioning the battery.
3. Heavy weight.
4. Quite a high cost.

The classic charger consists of the following key elements:

1. Transformer.
2. Rectifier.
3. Adjustment block.

Such a device produces direct current at a voltage of 14.4V, not 12V. Therefore, according to the laws of physics, it is impossible to charge one device with another if they have the same voltage. Based on the above, the optimal value for such a device is 14.4 Volts.

The key components of any charger are:

• transformer;
• mains plug;
• fuse (provides short circuit protection);
• wire rheostat (adjusts the charging current);
• ammeter (shows the strength of electric current);
• rectifier (converts alternating current to direct current);
• rheostat (regulates current and voltage in the electrical circuit);
• bulb;
• switch;
• frame;

Wires for connection

To connect any charger, as a rule, red and black wires are used, red is positive, black is negative.

When choosing cables to connect a charger or starting device, you must select a cross-section of at least 1 mm2.

Attention. Further information is provided for informational purposes only. Whatever you want to bring to life, you do at your own discretion. Incorrect or inept handling of certain spare parts and devices will cause them to malfunction.

Having looked at the available types of chargers, let’s move on directly to making them ourselves.

Charging the battery from the computer power supply

To charge any battery, 5-6 ampere hours is enough, this is about 10% of the capacity of the entire battery. Any power supply with a capacity of 150 W or more can produce it.

So, let's look at 2 ways to make your own charger from a computer power supply.

Method one

For manufacturing you need the following parts:

• power supply, power from 150 W;
• resistor 27 kOhm;
• current regulator R10 or resistor block;
• wires with a length of 1 meter;

Work progress:

1. To start we will need to disassemble the power supply.
2. We extract wires we do not use, namely -5v, +5v, -12v and +12v.
3. We replace the resistor R1 to a pre-prepared 27 kOhm resistor.
4. Removing the wires 14 and 15, and 16 we simply turn off.
5. From the block We bring out the power cord and wires to the battery.
6. Install the current regulator R10. In the absence of such a regulator, you can make a homemade resistor block. It will consist of two 5 W resistors, which will be connected in parallel.
7. To set up the charger, We install a variable resistor in the board.
8. To exits 1,14,15,16 We solder the wires and use a resistor to set the voltage to 13.8-14.5V.
9. At the end of the wires connect the terminals.
10. We delete the remaining unnecessary tracks.

Important: adhere to the complete instructions, the slightest deviation can lead to burnout of the device.

Method two

To manufacture our device using this method, you will need a slightly more powerful power supply, namely 350 W. Since it can output 12-14 amps which will satisfy our needs.

Work progress:

1. In computer power supplies The pulse transformer has several windings, one of them is 12V, and the second is 5V. To make our device, you only need a 12V winding.
2. To start our block you will need to find the green wire and connect it to the black wire. If you use a cheap Chinese unit, there may be a gray wire instead of a green one.
3. If you have an old power supply and with a power button, the above procedure is not needed.
4. Further, we make 2 thick busbars from the yellow and black wires, and cut off the unnecessary wires. A black tire will be a minus, a yellow one will be a plus.
5. To improve reliability Our device can be swapped. The fact is that the 5V bus has a more powerful diode than the 12V.
6. Since the power supply has a built-in fan, then he is not afraid of overheating.

Method three

For manufacturing we will need the following parts:

• power supply, power 230 W;
• board with TL 431 chip;
• resistor 2.7 kOhm;
• resistor 200 Ohm power 2 W;
• 68 Ohm resistor with a power of 0.5 W;
• resistor 0.47 Ohm power 1 W;
• 4-pin relay;
• 2 diodes 1N4007 or similar diodes;
• resistor 1kOhm;
• bright LED;
• wire length of at least 1 meter and cross-section of at least 2.5 mm 2, with terminals;

Work progress:

1. Desoldering all wires except 4 black and 2 yellow wires, since they carry power.
2. Close the contacts with a jumper, responsible for overvoltage protection so that our power supply does not turn off due to overvoltage.
3. We replace it on a board with a TL 431 chip built-in resistor for a 2.7 kOhm resistor, to set the output voltage to 14.4 V.
4. Add a 200 Ohm resistor with a power of 2 W per output from the 12V channel, to stabilize the voltage.
5. Add a 68 Ohm resistor with a power of 0.5 W per output from the 5V channel, to stabilize the voltage.
6. Solder the transistor on the board with the TL 431 chip, to eliminate obstacles when setting the voltage.
7. Replace the standard resistor, in the primary circuit of the transformer winding, to a 0.47 Ohm resistor with a power of 1 W.
8. Assembling a protection scheme from incorrect connection to the battery.
9. Unsolder from the power supply unnecessary parts.
10. We output necessary wires from the power supply.
11. Solder the terminals to the wires.

For ease of use of the charger, connect an ammeter.

The advantage of such a homemade device is the inability to recharge the battery.

The simplest device using an adapter

cigarette lighter adapter

Now consider the case when there is no unnecessary power supply, our battery is dead and needs to be charged.

Every good owner or fan of all kinds of electronic devices has an adapter for recharging autonomous equipment. Any 12V adapter can be used to charge a car battery.

The main condition for such charging is that the voltage supplied by the source is no less than that of the battery.

Work progress:

1. Necessary cut off the connector from the end of the adapter wire and peel off the insulation at least 5 cm.
2. Since the wire goes double, it is necessary to divide it. The distance between the ends of the 2 wires must be at least 50 cm.
3. Solder or tape to the ends of the terminal wire for secure fixation on the battery.
4. If the terminals are the same, then you need to take care of putting insignia on them.
5. The biggest disadvantage of this method consists of constant monitoring of the temperature of the adapter. Since if the adapter burns out, it can render the battery unusable.

Before connecting the adapter to the network, you must first connect it to the battery.

Charger made from a diode and a household light bulb

Diode is a semiconductor electronic device that is capable of conducting current in one direction and has a resistance equal to zero.

The charging adapter for the laptop will be used as a diode.

To manufacture this type of device, we will need:

• charging adapter for laptop;
• bulb;
• wires with a length of 1 m;

Each car charger produces about 20V voltage. Since the diode replaces the adapter and passes voltage only in one direction, it is protected from short circuits that can occur if connected incorrectly.

The higher the power of the light bulb, the faster the battery charges.

Work progress:

1. To the positive wire of the laptop adapter We connect our light bulb.
2. From a light bulb we throw the wire to the positive.
3. Disadvantage from the adapter directly connect to the battery.

If connected correctly, our light bulb will glow because the current at the terminals is low and the voltage is high.

Also, you need to remember that proper charging requires an average current of 2-3 amperes. Connecting a high-power light bulb leads to an increase in current strength, and this, in turn, has a detrimental effect on the battery.

Based on this, you can connect a high-power light bulb only in special cases.

This method involves constantly monitoring and measuring the voltage at the terminals. Overcharging the battery will produce excessive amounts of hydrogen and may damage it.

When charging the battery in this way, try to stay near the device, since leaving it temporarily unattended can lead to failure of the device and the battery.

Checking and setting

To test our device, you must have a working car light bulb. First, using a wire, we connect our light bulb to the charger, remembering to observe the polarity. We plug in the charger and the light comes on. Everything is working.

Each time, before using a homemade charging device, check its functionality. This check will eliminate all possibilities of damaging your battery.

How to charge a car battery

Quite a large number of car owners consider charging the battery a very simple matter.

But in this process there are a number of nuances on which the long-term operation of the battery depends:

Before you put the battery on charge, you need to carry out a number of necessary actions:

1. Use chemical resistant gloves and goggles.
2. After removing the battery carefully inspect it for signs of mechanical damage and traces of liquid leakage.
3. Unscrew the protective caps, to release the generated hydrogen, to avoid boiling the battery.
4. Take a close look at the liquid. It should be transparent, without flakes. If the liquid is dark in color and there are signs of sediment, seek professional help immediately.
5. Check fluid level. Based on current standards, there are marks on the side of the battery, “minimum and maximum,” and if the fluid level is below the required level, it must be refilled.
6. Flood Only distilled water is needed.
7. Don't turn it on charger into the network until the crocodiles are connected to the terminals.
8. Observe polarity when connecting alligator clips to the terminals.
9. If during charging If you hear boiling sounds, then unplug the device, let the battery cool down, check the fluid level and then you can reconnect the charger to the network.
10. Make sure that the battery is not overcharged, since the condition of its plates depends on this.
11. Charge the battery only in well-ventilated areas, as toxic substances are released during the charging process.
12. Electrical network must have installed circuit breakers that turn off the network in the event of a short circuit.

After you charge the battery, over time the current will drop and the voltage at the terminals will increase. When the voltage reaches 14.5V, charging should be stopped by disconnecting from the network. When the voltage reaches more than 14.5 V, the battery will begin to boil and the plates will become free of liquid.

The photo shows a homemade automatic charger for charging 12 V car batteries with a current of up to 8 A, assembled in a housing from a B3-38 millivoltmeter.

Why do you need to charge your car battery?
charger

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

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

Analysis of charger circuits

The scheme for 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 modification requires high radio engineering qualifications.

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

The result was a charger circuit without the above-mentioned 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 its apparent complexity, the circuit of a homemade charger is simple and consists of only a few complete functional units.

If the circuit to repeat seems complicated to you, then you can assemble a more one that works 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, regulation of the magnitude and stabilization of the battery charge current is ensured by connecting ballast capacitors C4-C9 in series with the primary winding of the power transformer T1. The larger the capacitor capacity, the greater the battery charging current.

In practice, this is a complete version of the charger; you can connect a 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 using the data in the table.

To regulate the current in order to reduce the number of capacitors, they can be connected in parallel in groups. My switching is carried out using a two-bar switch, but you can install several toggle switches.

Protection circuit
from incorrect connection of battery poles

The protection circuit against polarity reversal of the charger in case of incorrect connection of the battery to the terminals is made using relay P3. 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. This reverse polarity protection circuit can be used with any charger, both transistor and thyristor. It is enough to connect it to the break in the wires with which the battery is connected to the charger.

Circuit for measuring current and voltage of battery charging

Thanks 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 the voltage. In the upper position of S3, 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 is used as a head. R17 bypasses 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 type 142EN8G 9V stabilizer chip is used. This microcircuit was not chosen by chance. When the temperature of the microcircuit body changes by 10º, the output voltage changes by no more than hundredths of a volt.

The system for automatically turning off charging when the voltage reaches 15.6 V is made on 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 using resistors R4-R6, resistor R5 is a tuning resistor to set the operating threshold of the machine. The value of resistor R9 sets the threshold for switching on the charger to 12.54 V. Thanks to the use of diode VD7 and resistor R9, the necessary hysteresis is provided between the switch-on and switch-off voltages of the battery charge.

The scheme works as follows. When connecting a car battery to a charger, the voltage at the terminals of which is less than 16.5 V, a voltage sufficient to open transistor VT1 is established at pin 2 of microcircuit A1.1, 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 output A1.1 will decrease to a value insufficient to maintain 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 equal to 0.5 A. 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 proceed at the specified current. It is possible, if necessary, to disable the automatic control system using switch S2.

Thus, the system of automatic monitoring of battery charging will eliminate 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 the summer. After the end of the racing season, you can connect the battery to the charger and turn it off only in the spring. Even if there is a power outage, when it returns, the charger will continue to charge the battery as normal.

The principle of operation of the circuit for automatically turning off the charger in case of excess voltage due to the lack of load collected on the second half of the operational amplifier A1.2 is the same. Only the threshold for completely disconnecting the charger from the supply network is set to 19 V. If the charging voltage is less than 19 V, the voltage at output 8 of the A1.2 chip is sufficient to hold the transistor VT2 in the open state, in 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.

Automatic charger design

All parts of the charger are placed in the housing of the V3-38 milliammeter, from which all its contents have been removed, except for the pointer device. The installation of elements, except for the automation circuit, is carried out using a hinged method.

The housing design of the milliammeter consists of two rectangular frames connected by four corners. There are holes made in the corners with equal spacing, to which it is convenient to attach parts.

The TN61-220 power transformer is secured 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 secured 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 shows a view of the charger from below.

A 2 mm thick fiberglass plate is also attached 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 in the diagram, but 14, since in order to obtain a capacitor of the required value it was necessary to connect them in parallel. The capacitors and relays are connected to the rest of the charger circuit via a connector (blue in the photo above), which made it easier to access other elements during installation.

A finned 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 Pr1 fuse and a plug (taken from the computer power supply) for supplying power.

The charger's power diodes are secured using two clamping bars to the radiator inside the case. For this purpose, a rectangular hole is made in the rear wall of the case. This technical solution allowed us to minimize the amount of heat generated inside the case and save space. The diode leads and supply wires are soldered onto a loose strip made of foil fiberglass.

The photo shows a view of a homemade charger on the right side. The installation of the electrical circuit is made with colored wires, alternating voltage - brown, positive - red, negative - blue wires. The cross-section of the wires coming 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 sealed in copper strips. The length of the shunt wire is selected when calibrating the ammeter. I took the wire from the shunt of a burnt pointer tester. One end of the copper strips is soldered directly to the positive output terminal; a thick conductor coming from the contacts of relay P3 is soldered to the second strip. The yellow and red wires go to the pointer device from the shunt.

Printed circuit board of the charger automation 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 fiberglass.

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

The photo above shows a view of the printed circuit board from the installation side with parts marked in red. This drawing is convenient when assembling a printed circuit board.

The printed circuit board drawing above will be useful when manufacturing it using laser printer technology.

And this drawing of a printed circuit board will be useful when applying 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, so I had to draw my own version on the computer, print it on thick white paper and glue the moment on top of the standard scale with glue.

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

Wires for connecting the charger to the battery and network terminals

The wires for connecting the car battery to the charger are equipped with alligator clips on one side and split ends on the other side. The red wire is selected to connect the positive terminal of the battery, and the blue wire is selected to connect the negative terminal. The cross-section of the wires for connecting to the battery 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

Power transformer T1 is used 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 charging current usually does not exceed 6 A, any transformer with a power of 150 watts 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 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 type MBGCh for a voltage of at least 350 V. You can use capacitors of any type designed to operate in alternating current circuits.

Diodes VD2-VD5 are suitable for any type, rated for a current of 10 A. VD7, VD11 - any pulsed silicon ones. VD6, VD8, VD10, VD5, VD12 and VD13 are any that can withstand a current of 1 A. LED VD1 is any, VD9 I used type KIPD29. A distinctive feature of this LED is that it changes color when the connection polarity is changed. To switch it, contacts K1.2 of relay P1 are used. When charging with the main current, 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.

The operational amplifier chosen is KR1005UD1, an analogue of the foreign AN6551. Such amplifiers were used in the sound and video unit of the VM-12 video recorder. The good thing about the amplifier is that it does not require bipolar power supply or correction circuits and remains operational at a supply voltage of 5 to 12 V. It can be replaced with almost any similar one. For example, LM358, LM258, LM158 are good for replacing microcircuits, but their pin numbering is different, 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 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 in the relay, then it is advisable to solder them in parallel.

Switch S1 of any type, designed to operate at a voltage of 250 V and having a sufficient number of switching contacts. If you don’t need a current regulation step of 1 A, then you can install several toggle switches and set the charging current, say, 5 A and 8 A. If you charge only car batteries, then this solution is completely justified. Switch S2 is used 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 manually.

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 measuring current 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 of the automatic control unit

If the board is assembled correctly and all radio elements are in good working order, the circuit will work immediately. All that remains is to set the voltage threshold with resistor R5, upon reaching which the battery charging will be switched to low current charging mode.

The adjustment can be made directly while charging the battery. But still, it’s better to play it safe and check and configure the automatic control and protection circuit of the automatic control unit before installing it in the housing. To do this, you will 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. As for measuring instruments, you will need any voltmeter, pointer tester or multimeter designed to measure DC voltage, with a measurement limit from 0 to 20 V.

Checking the voltage stabilizer

After installing all the parts on the printed circuit board, you need to apply 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 DA1 voltage stabilizer chip is 9 V. If the voltage is different or changes, then DA1 is faulty.

Microcircuits of the K142EN series and analogues have protection against short circuits at the output, and if you short-circuit its output to the common wire, the microcircuit will enter protection mode and will not fail. If the test shows that the voltage at the output of the microcircuit is 0, this does not always mean that it is faulty. 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.

Checking the surge protection system

I decided to start describing the operating principle of the circuit with a simpler part of the circuit, which is not subject to strict operating voltage standards.

The function of disconnecting the charger 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 op-amp).

Operating principle of an operational differential amplifier

Without knowing the operating principle of the op-amp, it is difficult to understand the operation of the circuit, so I will give a brief description. The op-amp has two inputs and one output. One of the inputs, which is designated in the diagram by a “+” sign, is called non-inverting, and the second input, which is designated by 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 difference in voltage at its inputs. In this circuit, the operational amplifier is switched on without feedback, in comparator mode – comparing input voltages.

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

Testing the Surge Protection Circuit

Let's return to the diagram. The non-inverting input of amplifier A1.2 (pin 6) is connected to a voltage divider assembled across resistors R13 and R14. This divider is connected to a stabilized voltage of 9 V and therefore the voltage at the point of connection 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 through which the charging current flows, 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 winding of relay P2 and it will close contacts K2.1. The output voltage will also close diode VD11 and 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 output of the charger), the voltage at pin 7 will become 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 contacts K2.1 will open. The supply voltage to the RAM will be interrupted. At the moment when the voltage at the output of the op-amp becomes zero, diode VD11 opens and, thus, R15 is connected in parallel to R14 of the divider. The voltage at pin 6 will instantly decrease, which will eliminate false positives when the voltages at the op-amp inputs are equal due to ripple and interference. 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 begin to operate 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 connect a voltmeter instead of relay P2 to 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 if it is higher, 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 functionality, and by the clicks of 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 op-amp output. If the voltages differ from those indicated above, you need to check the resistor values ​​of the corresponding dividers. If the divider resistors and diode VD11 are working, then, therefore, the op-amp is faulty.

To check the circuit R15, D11, 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. Transistor VT12 can be easily checked by disconnecting one of the R16 pins 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 always on, it means that there is a breakdown between the collector and emitter of the transistor.

Checking the battery shutdown circuit when it is fully charged

The operating principle of op amp A1.1 is no different from the operation of A1.2, with the exception of the ability to change the voltage cutoff threshold using trimming resistor R5.

To check the operation of A1.1, the supply voltage supplied from the power supply smoothly 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 charger to low current charging mode through a capacitor C4. When the voltage level drops below 12.54 V, the relay should turn on and switch the charger into charging mode with a current of a given value.

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

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

Capacitor charger circuit
without automatic shutdown

For those who do not have sufficient experience in assembling electronic circuits or do not need to automatically turn off the charger after charging the battery, I offer a simplified version of the circuit diagram for charging acid-acid car batteries. A distinctive feature of the circuit is its ease of repetition, reliability, high efficiency and stable charging current, protection against incorrect battery connection, and automatic continuation of charging in the event of a loss of supply voltage.

The principle of stabilizing the charging current remains unchanged and is ensured 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 relay P1 is used.

When the battery is not connected, the contacts of relays P1 K1.1 and K1.2 are open and even if the charger is connected to the power supply, no current flows to the circuit. The same thing happens if you connect the battery incorrectly according to polarity. When the battery is connected correctly, the current from it flows through the VD8 diode to the winding of relay P1, the relay is activated and its contacts K1.1 and K1.2 are closed. Through 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 relay contacts K1.2 are not needed, but if they are not there, then if the battery is connected incorrectly, 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 charger bridge will fail.

The proposed simple circuit for charging batteries can be easily adapted to charge batteries at a voltage of 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 transformer T1 of at least 36 V.

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

How to charge a car battery
automatic homemade memory

Before charging, the battery removed from the car must be cleaned of dirt and its surfaces wiped with an aqueous solution of soda to remove acid residues. If there is acid on the surface, then the aqueous soda solution 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. 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 using 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 switch S3 is in the down position, the arrow on the charger will immediately show the voltage the battery is producing. All you have to do is plug the power cord into the socket and the battery charging process will begin. The voltmeter will already begin to show the charging voltage.