A simple battery charging circuit. Car battery charger circuit - from simple to complex

There are cases, especially in winter, when car owners need to recharge the car battery from an external power source. Of course, people who do not have good skills in working with electrical engineering, it is advisable to buy a factory battery charger, it’s even better to buy a start-up Charger to start the engine with a discharged battery without loss of time for external recharging.

But if you have a little knowledge in the field of electronics, you can assemble a simple charger do it yourself.

general characteristics

For proper maintenance of the battery and prolonging its service life, recharging is required when the voltage at the terminals drops below 11.2 V. At this voltage, the engine is likely to start, but if it is parked for a long time in winter, this will lead to sulfation of the plates and, as a result, to a decrease in capacity batteries. When parking 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 bring it to a warm place, remembering to monitor charge level.

The battery is charged with direct 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 life of the battery, methods of desulfation of battery plates are used. The battery is discharged to less than five volts by repeatedly drawing a large current of short duration. An example of such consumption is starting a starter. After that, a slow full charge is made with a small current within one ampere. Repeat the process 8-9 times. The desulfation method is long in time, but according to all studies it gives a good result.

It must be remembered that when charging it is important not to overcharge the battery. The charge is made up 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 consequence, the destruction of the plates. Factory charging devices have charge control and subsequent shutdown systems. Build your own systems, without having sufficient knowledge in electronics, it is quite difficult.

Do-it-yourself assembly schemes

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

Charging scheme for emergency cases

There are times when a car that has stood overnight near the house cannot be started in the morning due to a dead battery. There can be many reasons for this unfortunate circumstance.

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

Great as a power source laptop charger. It has an output voltage of 19 volts and a current of 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 salon light bulb. Can be used more powerful lamps, for example, on the dimensions, but this will create an extra load on the power supply, which is very undesirable.

An elementary circuit is being assembled: the minus of the power supply is connected to the light bulb, the light bulb to the minus 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 the 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 system unit of the computer. The output voltages of such blocks are +5 and +12 volts with an output current of about two amperes. These parameters allow you to assemble a weak charger, which, when properly assembled, will serve the owner for a long time and reliably. Fully charging the battery will take a long time and will depend on the capacity of the battery, but there will be no plate desulfation effect. So, step by step assembly device:

1. Disassemble the power supply and unsolder all wires except green. Remember or mark the input points of black (GND) and yellow +12 V.
2. Solder the green wire to the place where the black one was (this is necessary to start the unit without a PC motherboard). In place of the black wire, solder a tap, which will be negative for charging the battery. In place of the yellow wire, solder the positive battery charging lead.
3. You need to find a TL 494 chip or its equivalent. The list of analogues 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, you can use 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 a voltage of 220 volts goes to the primary winding of the transformer, so safety measures must be observed when starting the unit without a case.
5. Solder the found resistor, measure its resistance with a tester. Choose a variable resistor that is close in value. Set it to the value of the required resistance and solder it in place of the removed circuit element with flexible wires.
6. 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 protection and, as a result, shutdown.
7. Solder a variable resistor without knocking down its setting, and measure the resulting resistance. Select the required or as close as possible resistance value or dial from several resistors and solder it into the circuit.
8. Check the unit, the output should be the desired voltage. If desired, a voltmeter can be connected to the outputs on the plus and minus circuit by placing it on the case for clarity. Subsequent assembly occurs in the reverse order. The device is ready for use.

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

Charger circuit from an old transformer

If you don’t have an old power supply from a computer at hand, and radio engineering experience allows you to mount simple circuits yourself, then you can use the following fairly interesting scheme battery charging 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 set of voltages on the secondary windings of about 25 volts is suitable.

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 by any imported analogues. There are many analogues, and they are 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 applied to replace the control transistor KT 827A (VT 1) and the zener diode D 814 A (VD 3). The transistor is mounted on a radiator.

Adjustment of the supplied voltage is carried out by a variable resistor R2. The scheme is simple and obviously working. It can be collected by a person with minimal knowledge of electronics.

Pulse charging for batteries

The circuit is difficult to assemble, but this is the only drawback. Finding a simple circuit for a pulsed charging unit is unlikely to succeed. This is offset by the pluses: such blocks almost do not heat up, while they have serious power and high efficiency, they are distinguished by their compact size. The proposed circuit, mounted on a board, fits into a container with a size of 160 * 50 * 40 mm. To assemble the device, it is necessary to understand the principle of operation of the PWM (Pulse Width Modulation) generator. In the proposed version, it is implemented using a common and inexpensive controller IR 2153.

With the applied capacitors, 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 capacitors of 470 microfarads, the power will double. It will be possible to charge a battery with a capacity of up to two hundred ampere / hours.

When using devices without automatic battery charge control, you can use the simplest network, daily Chinese-made relay. This eliminates 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 power supply is interrupted 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 battery failure. A new battery will cost much more.

Precautionary measures

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

1. All appliances, including batteries, must be placed on a fireproof 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 batteries, do not allow the electrolyte to boil. The voltage and current parameters are controlled by the tester. Primary control will help determine the time to fully charge the battery, which will come in handy in the future.

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

Often, car owners have to deal with such a phenomenon as the inability to start the engine due to battery discharge. To solve the problem, you will need to use a battery charger, which costs a lot of money. In order not to spend money on buying a new charger for a car battery, you can make it yourself. It is only important to find a transformer with the necessary characteristics. To make a homemade device, you do not have to be an electrician, and the whole process as a whole will take no more than a few hours.

Features of the functioning of batteries

Not all drivers are aware that lead-acid batteries are used in cars. Such batteries are distinguished by their endurance, therefore they are able to serve up to 5 years.

To charge lead batteries, a current is used that is equal to 10% of the total battery capacity. This means that to charge a battery with a capacity of 55 Ah, a charging current of 5.5 A is required. devices. A small charging current does not extend the life of the battery, but it is not capable of negatively affecting the integrity of the device.

This is interesting! When a current of 25 A is applied, the battery is quickly recharged, so after 5-10 minutes after connecting a charger with this rating, you can start the engine. Such a large current is given out by modern inverter chargers, only it negatively affects the battery life.

When the battery is charging, the charging current flows back to the working one. The voltage for each bank should not be higher than 2.7 V. There are 6 cans installed in the 12 V battery, which are not connected to each other. Depending on the voltage of the battery, the number of cans differs, as well as the required voltage for each can. If the voltage is higher, then this will lead to the process of decomposition of the electrolyte and plates, which contributes to the failure of the battery. To exclude the occurrence of the electrolyte boiling process, the voltage is limited to 0.1 V.

The battery is considered discharged if, when connecting a voltmeter or multimeter, the devices show a voltage of 11.9-12.1 V. Such a battery should be recharged immediately. A charged battery has a voltage at the terminals of 12.5-12.7 V.

An example of the voltage at the terminals of a charged battery

The charging process is the restoration of the spent capacity. Batteries can be charged in two ways:

1. D.C. In this case, the charging current is regulated, the value of which is 10% of the device's capacity. Charging time is 10 hours. The charge voltage in this case changes from 13.8 V to 12.8 V for the entire duration of the charge. The disadvantage of this method is that it is necessary to control the charging process and turn off the charger in time before the electrolyte boils. This method is gentle for the battery and has a neutral effect on their service life. To implement this method, transformer chargers are used.
2. Constant pressure. In this case, a voltage of 14.4 V is applied to the battery terminals, and the current changes from large values ​​to smaller ones automatically. Moreover, this change in current depends on such a parameter as time. The longer the battery is charged, the lower the current becomes. Recharging the battery will not be able to get, unless you forget to turn off the device and leave it for several days. The advantage of this method is that after 5-7 hours the battery will be charged by 90-95%. The battery can also be left unattended, so this method is popular. However, few car owners are aware that this charging method is an “emergency”. Using it significantly reduces battery life. In addition, the more often you charge in this way, the faster the device will discharge.

Now even an inexperienced driver can understand that if there is no need to rush to charge the battery, then it is better to give preference to the first option (by current). At accelerated recovery charge reduces the life of the device, so it is highly likely that in the near future you will need to buy a new battery. Based on the foregoing, the material will consider options for the manufacture of chargers for current and voltage. For manufacturing, you can use any improvised devices, which we will talk about later.

Battery charging requirements

Before carrying out the procedure for manufacturing a homemade battery charger, you must pay attention to the following requirements:

1. Providing a stable voltage of 14.4 V.
2. Device autonomy. This means that a homemade device should not require supervision, as the battery is often charged at night.
3. Ensuring that the charger turns off when the charging current or voltage increases.
4. Reverse polarity protection. If the device is connected to the battery incorrectly, then protection should work. For implementation, a fuse is included in the circuit.

Polarity reversal is a dangerous process, as a result of which the battery can explode or boil. If the battery is in good condition and only slightly discharged, then if the charger is connected incorrectly, the charge current will increase above the nominal value. If the battery is discharged, then when the polarity is reversed, an increase in voltage above the set value is observed and, as a result, the electrolyte boils.

Options for homemade battery chargers

Before proceeding with the development of a battery charger, it is important to understand that such a device is homemade and can negatively affect battery life. However, sometimes such devices are simply necessary, as they can significantly save money on the purchase of factory devices. Consider what you can make do-it-yourself chargers for batteries from and how to do it.

Charging from a light bulb and a semiconductor diode

This charging method is relevant for such options when you need to start a car on a dead battery at home. In order to do this, you will need the constituent elements for assembling the device and a source of alternating voltage 220 V (socket). The scheme of a homemade charger for a car battery contains the following elements:

1. Incandescent lamp. An ordinary light bulb, which is also popularly referred to as "Ilyich's lamp". The lamp power affects the battery charge rate, so the higher this indicator, the faster the engine can be started. The best option is a lamp with a power of 100-150 watts.
2. semiconductor diode. An electronic element whose main purpose is to conduct current in one direction only. The need for this element in the charging design is to convert AC voltage to DC. Moreover, for such purposes, you will need a powerful diode that can withstand a large load. You can use a diode, both domestically produced and imported. In order not to buy such a diode, it can be found in old receivers or power supplies.
3. Plug for connection to a socket.
4. Wires with terminals (crocodiles) for connection to the battery.

It is important! Before assembling such a circuit, you need to understand that there is always a risk to life, so you should be extremely careful and careful.

Scheme for connecting a charger from a light bulb and a diode to a battery

Connect the plug to the outlet only after the entire circuit has been assembled and the contacts have been insulated. To avoid the occurrence of a short circuit current, a 10 A circuit breaker is included in the circuit. When assembling the circuit, it is important to consider the polarity. A light bulb and a semiconductor diode must be connected to the positive battery terminal circuit. When using a 100 W light bulb, a charging current of 0.17 A will flow to the battery. To charge a 2A battery, you need to charge it for 10 hours. The greater the power of the incandescent lamp, the higher the value of the charging current.

It makes no sense to charge a completely dead battery with such a device, but recharging it in the absence of a factory charger is quite realistic.

Rectifier battery charger

This option also belongs to the category of the simplest homemade chargers. The basis of such a memory includes two main elements - a voltage converter and a rectifier. There are three types of rectifiers that charge the device in the following ways:

• D.C;
• alternating current;
• asymmetrical current.

Rectifiers of the first option charge the battery exclusively with direct current, which is cleared of alternating voltage ripples. AC rectifiers supply a pulsating AC voltage to the battery terminals. Asymmetric rectifiers have a positive component, and half-wave rectifiers are used as the main structural elements. Such a scheme has best result compared to AC and DC rectifiers. It is its design that will be discussed further.

In order to assemble a high-quality battery charger, you will need a rectifier and a current amplifier. The rectifier consists of the following elements:

• fuse;
• powerful diode;
• Zener diode 1N754A or D814A;
• switch;
• variable resistor.

Circuit diagram of asymmetric rectifier

In order to assemble the circuit, you will need to use a fuse rated for a maximum current of 1 A. The transformer can be taken from an old TV, the power of which should not exceed 150 W, and the output voltage should be 21 V. As a resistor, you need to take a powerful element of the brand MLT- 2. The rectifier diode must be rated for a current of at least 5 A, therefore best option- these are models of the type D305 or D243. The amplifier is based on a regulator based on two transistors of the KT825 and 818 series. During installation, transistors are installed on radiators to improve cooling.

The assembly of such a circuit is carried out in a hinged way, that is, all the elements are located on the old board cleared of tracks and are connected to each other using wires. Its advantage is the ability to adjust the output current for battery charging. The disadvantage of the scheme is the need to find necessary elements and position them correctly.

The simplest analogue of the scheme presented above is a more simplified version, shown in the photo below.

Simplified diagram of a rectifier with a transformer

It is proposed to use a simplified circuit using a transformer and a rectifier. In addition, you will need a 12 V and 40 W light bulb (car). It will not be difficult even for a beginner to assemble the circuit, but it is important to pay attention to the fact that the rectifier diode and the light bulb must be located in the circuit that is fed to the negative terminal of the battery. The disadvantage of such a scheme is to obtain a pulsating current. To smooth out ripples, as well as reduce strong beats, it is recommended to use the diagram below.

Diode bridge circuit with smoothing capacitor reduces ripple and reduces runout

Charger from a computer power supply: step by step instructions

Recently, such an option for car charging has become popular, which you can make yourself using a computer power supply.

Initially, you will need a working power supply. For such purposes, even a unit with a power of 200 watts is suitable. It produces a voltage of 12 V. It will not be enough to charge the battery, so it is important to increase this value to 14.4 V. Step-by-step instruction manufacturing a memory for a battery from a power supply from a computer is as follows:

1. Initially, all extra wires that come out of the power supply are soldered. Leave only the green wire. Its end must be soldered to the negative contacts, from where the black wires came out. This manipulation is done so that when the unit is connected to the network, the device starts immediately.

   

   The end of the green wire must be soldered to the negative contacts where the black wires were located.

2. The wires that will be connected to the battery terminals must be soldered to the output contacts of the minus and plus of the power supply. The plus is soldered to the exit point of the yellow wires, and the minus to the exit point of the black ones.
3. At the next stage, it is necessary to reconstruct the operating mode of pulse-width modulation (PWM). The TL494 or TA7500 microcontroller is responsible for this. For reconstruction, you will need the lower leftmost leg of the microcontroller. To get to it, you need to flip the board.

   

   The TL494 microcontroller is responsible for the PWM operation mode

4. Three resistors are connected to the bottom pin of the microcontroller. We are interested in the resistor, which is connected to the output of the 12 V block. It is marked in the photo below with a dot. This element should be unsoldered, and then measure the resistance value.

   

   The resistor marked with a purple dot must be soldered

5. The resistor has a resistance of about 40 kOhm. It must be replaced with a resistor with a different resistance value. To clarify the value of the required resistance, it is required to initially solder the regulator (variable resistor) to the contacts of the remote resistor.

   

   Solder the regulator in place of the removed resistor.

6. Now the device should be connected to the network, having previously connected a multimeter to the output terminals. The output voltage is changed with a regulator. You need to get a voltage value of 14.4 V.

   

   The output voltage is regulated by a variable resistor

7. As soon as the voltage value is reached, you should unsolder the variable resistor, and then measure the resulting resistance. For the example described above, its value is 120.8 kΩ.

   

   The resulting resistance should be 120.8 kOhm

8. Based on the obtained resistance value, you should select a similar resistor, and then solder it in place of the old one. If you cannot find a resistor of this resistance value, then you can choose it from two elements.

   

   Soldering resistors in series adds up their resistance

9. After that, the operability of the device is checked. Optionally, a voltmeter can be installed to the power supply (you can also use an ammeter), which will allow you to control the voltage and charging current.

General view of the charger from the computer power supply

This is interesting! The assembled charger has the function of protection against short circuit current, as well as against overload, however, it does not protect against polarity reversal, so you should solder the output wires of the appropriate color (red and black) so as not to be confused.

When the charger is connected to the battery terminals, a current of about 5-6 A will be supplied, which is the optimal value for devices with a capacity of 55-60A / h. The video below shows how to make a battery charger from a computer power supply with voltage and current regulators.

What other storage options are available for the battery

Consider a few more options for independent battery chargers.

Using laptop charger for battery

One of the simplest and quick ways reviving a dead battery. To implement a battery revitalization scheme using a laptop charger, you will need:

1. Charger from any laptop. The parameters of the chargers are 19 V and the current is about 5 A.
2. Lamp halogen power 90 W.
3. Connecting wires with clips.

We turn to the implementation of the scheme. The light bulb is used to limit the current to the optimum value. Instead of a light bulb, you can use a resistor.

A laptop charger can also be used to "revitalize" a car battery.

It is not difficult to assemble such a scheme. If charging from a laptop is not planned to be used for its intended purpose, then the plug can be cut off, and then connected to the wires with clamps. First, use a multimeter to determine the polarity. The bulb is connected to a circuit that goes to the positive terminal of the battery. The negative terminal from the battery is connected directly. Only after connecting the device to the battery, you can supply voltage to the power supply.

Do-it-yourself memory from a microwave oven or similar devices

Using the transformer block that is inside the microwave, you can make a charger for the battery.

A step-by-step instruction for making a home-made charger from a microwave transformer block is presented below.

Scheme for connecting a transformer unit, a diode bridge and a capacitor to a car battery

The assembly of the device can be carried out on any basis. At the same time, it is important that all structural elements were well protected. If necessary, the circuit can be supplemented with a switch, as well as a voltmeter.

Transformerless charger

If the search for a transformer has led to a dead end, then you can use the simplest circuit without step-down devices. Below is a diagram that allows you to implement a charger for a battery without using voltage transformers.

Electrical diagram of the charger without the use of a voltage transformer

The role of transformers is performed by capacitors, which are designed for a voltage of 250V. At least 4 capacitors should be included in the circuit, placing them in parallel. In parallel with the capacitors, a resistor and an LED are connected to the circuit. The role of the resistor is to dampen the residual voltage after the device is disconnected from the network.

The circuit also includes a diode bridge, designed to work with currents up to 6A. The bridge is connected to the circuit after the capacitors, and the wires going to the battery for charging are connected to its terminals.

How to charge a battery from a homemade device

Separately, you should understand the question of how to properly charge the battery with a homemade charger. To do this, it is recommended to adhere to the following recommendations:

1. Polarity respect. It is better to once again check the polarity of a home-made device with a multimeter than to “bite your elbows”, because the reason for the failure of the battery was an error with the wires.
2. Do not test the battery by closing the contacts. This method only "kills" the device, and does not revive it, as indicated in many sources.
3. The device should be connected to the 220 V network only after the output terminals are connected to the battery. The device is turned off in the same way.
4. Compliance with safety precautions, since work is carried out not only with electricity, but also with battery acid.
5. The charging process of the battery must be controlled. The slightest malfunction can lead to serious consequences.

Based on the above recommendations, it can be concluded that homemade devices although they are acceptable, they are still not able to replace the factory ones. Making homemade chargers is not safe, especially if you are not sure that you can do it right. The material presents the simplest schemes for the implementation of chargers for car batteries, which will always be useful on the farm.

Now it makes no sense to assemble a charger for car batteries on your own: there is a huge selection of ready-made devices in stores, their prices are reasonable. However, let's not forget that it's nice to do something useful with your own hands, especially since a simple car battery charger can be assembled from improvised parts, and its price will be a penny.

The only thing to immediately warn about is that circuits without precise adjustment of the current and output voltage, which do not have a current cutoff at the end of the charge, are suitable for charging only lead-acid batteries. For AGM and the use of such chargers damages the battery!

How to make a simple transformer device

The circuit of this charger from a transformer is primitive, but workable and is assembled from available parts - factory chargers of the simplest type are designed in the same way.

At its core, this is a full-wave rectifier, hence the requirements for the transformer: since the voltage at the output of such rectifiers is equal to the nominal AC voltage times the root of two, then at 10V on the transformer winding we will get 14.1 V at the charger output. Any diode bridge is taken with a direct current of more than 5 amperes or it can be assembled from four separate diodes, and a measuring ammeter is selected with the same current requirements. The main thing is to place it on a radiator, which in the simplest case is an aluminum plate with an area of ​​at least 25 cm2.

The primitiveness of such a device is not only a minus: due to the fact that it has neither adjustment nor automatic shutdown, it can be used to “resuscitate” sulfated batteries. But we must not forget about the lack of protection against polarity reversal in this circuit.

The main problem is where to find a transformer of suitable power (at least 60 W) and with a given voltage. Can be used if a Soviet incandescent transformer turns up. However, its output windings have a voltage of 6.3V, so you will have to connect two in series, unwinding one of them so that you get a total of 10V at the output. An inexpensive transformer TP207-3 is suitable, in which the secondary windings are connected as follows:

At the same time, we unwind the winding between terminals 7-8.

Simple electronic charger

However, you can do without rewinding by supplementing the circuit with an electronic output voltage regulator. In addition, such a scheme will be more convenient in garage applications, as it will allow you to adjust the charge current during supply voltage drops, it is also used for small-capacity car batteries if necessary.

The role of the regulator here is performed by the composite transistor KT837-KT814, the variable resistor regulates the current at the output of the device. When assembling the charge, the 1N754A zener diode can be replaced with the Soviet D814A.

The circuit of the adjustable charger is simple to repeat, and is easily assembled by surface mounting without the need for etching. printed circuit board. However, keep in mind that field-effect transistors are placed on a radiator, the heating of which will be noticeable. It's better to use the old computer cooler by connecting its fan to the outlets of the charger. Resistor R1 must have a power of at least 5 W, it is easier to wind it from nichrome or fechral on your own or connect 10 one-watt resistors of 10 ohms in parallel. You can not put it, but we must not forget that it protects the transistors in the event of a short circuit.

When choosing a transformer, focus on the output voltage of 12.6-16V, take either an incandescent transformer by connecting two windings in series, or select a ready-made model with the desired voltage.

Video: The simplest battery charger

Alteration of the charger from the laptop

However, you can do without searching for a transformer if you have an unnecessary laptop charger at hand - with a simple alteration, we will get a compact and lightweight switching power supply that can charge car batteries. Since we need to get a voltage at the output of 14.1-14.3 V, no ready-made power supply will work, but the conversion is simple.
Let's look at a section of a typical scheme, according to which devices of this kind are assembled:

In them, maintaining a stabilized voltage is carried out by a circuit from a TL431 microcircuit that controls an optocoupler (not shown in the diagram): as soon as the output voltage exceeds the value set by resistors R13 and R12, the microcircuit lights up the optocoupler LED, informs the PWM controller of the converter a signal to reduce the duty cycle of the supplied to the pulse transformer. Difficult? In fact, everything is easy to make with your own hands.

Having opened the charger, we find not far from the TL431 output connector and two resistors connected to the Ref leg. It is more convenient to adjust the upper arm of the divider (in the diagram - resistor R13): by reducing the resistance, we reduce the voltage at the output of the charger, increasing it - we raise it. If we have a 12 V charger, we need a resistor with a large resistance, if the charger is 19 V, then with a smaller one.

Video: Charging for car batteries. Protection against short circuit and polarity reversal. DIY

We solder the resistor and instead install a trimmer, pre-configured by the multimeter for the same resistance. Then, having connected a load (a light bulb from a headlight) to the output of the charger, we turn it on and smoothly rotate the trimmer engine, while simultaneously controlling the voltage. As soon as we get a voltage in the range of 14.1-14.3 V, we turn off the memory from the network, fix the trimming resistor engine with varnish (at least for nails) and assemble the case back. It will take no more time than you spent reading this article.

There are also more complex stabilization schemes, and they can already be found in Chinese blocks. For example, here the optocoupler is controlled by the TEA1761 chip:

However, the setting principle is the same: the resistance of the resistor soldered between the positive output of the power supply and the 6th leg of the microcircuit changes. In the above diagram, two parallel resistors are used for this (thus, a resistance that is out of the standard series is obtained). We also need to solder a trimmer instead of them and adjust the output to the desired voltage. Here is an example of one of these boards:

By dialing, you can understand that we are interested in a single resistor R32 on this board (circled in red) - we need to solder it.

Similar recommendations are often found on the Internet on how to make a homemade charger from a computer power supply. But keep in mind that all of them are essentially reprints of old articles from the beginning of the 2000s, and such recommendations are not applicable to more or less modern power supplies. It is no longer possible to simply increase the voltage of 12 V to the desired value in them, since other output voltages are also controlled, and they will inevitably “float away” with this setting, and the protection of the power supply will work. You can use laptop chargers that produce a single output voltage, they are much more convenient for rework.

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

Why you need to charge your car battery
charger

The battery in the car is charged by an electric generator. To protect electrical equipment and appliances from 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 IN.

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 any 12 V acid batteries with it. 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 the summer. After the end of the rally season, you can connect the battery to the charger and turn it off only in the spring. Even if the mains voltage fails, when it appears, the charger will continue to charge the battery in the 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 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.

Power transformer TH61-220 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 the circuit is soldered. automatic control battery charging. 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.

On the outer side of the rear wall there is a ribbed aluminum radiator for cooling 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 in back wall the body has a rectangular hole. This 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 with right side. Mounting 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 the appearance of the assembled circuit. 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.

In the photo above, a view of the printed circuit board from the installation side of the parts with the parts marked 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.

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

About charger parts

The power transformer T1 is 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 power supplies, correction circuits and remains operational with a supply voltage of 5 to 12 V. You can replace it 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. From measuring instruments you will need any voltmeter, pointer tester or multimeter designed to measure direct voltage, with a measurement limit of 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 DA1 voltage regulator chip is 9 V. If the voltage differs or changes, then DA1 is faulty.

Chips of the K142EN series and analogues have output short circuit protection, and if you short-circuit its output to a common wire, 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 pin 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 circuit, the operational amplifier is turned on without feedback, in the comparator mode - comparing the 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 charging mode with a small current 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 the closed contacts K1.1, the mains voltage is supplied to the charger, and through K1.2, the charging current is supplied to the battery.

At first glance, it seems that the contacts of the 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 the aqueous solution of 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 battery terminal 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.