Do-it-yourself automatic charger for a car. We make our own chargers for car batteries. Device requirements

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 to prevent overcharging 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:

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.
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.
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.
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.
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.
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.
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.
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:

All devices, including the battery, must be on a fire-resistant surface.
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, since you will have to deal with an open voltage of 220 volts.

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

General information

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

Charging a battery, the circuit and principles of operation of this device are discussed even in a school physics course. But, alas, by the time they graduate, much of this knowledge is forgotten. Therefore, we hasten to remind you that the operation of a battery is based on the principle of a voltage difference (potential) between two plates, which are specially immersed in an electrolyte solution.

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

How does a battery work?

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

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

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

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

Principle of operation

We'll look at lead-acid batteries as an example.

When there is a load on the terminal, a chemical reaction begins to occur, which is accompanied by the release of electricity. Over time, the battery will drain. How is it restored? Is there a simple diagram?

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

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

What electrical circuits for charging batteries exist?

The classic device is made of a rectifier and transformer. If we consider the same car batteries with a voltage of 12 V, then the chargers for them have a constant current of approximately 14 V.

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

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

Recovery process

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

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

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

Charger

The described device can be purchased or assembled with your own hands. For the second option, we will need electrical circuits for charging batteries. The choice of technology by which it will be made should depend on which batteries are the target. You will need the following components:

(designed on ballast capacitors and a transformer). The higher the indicator can be achieved, the greater the current will be. In general, this should be enough for charging to work. But the reliability of this device is very low. So, if the contacts are broken or something is mixed up, then both the transformer and the capacitors will fail.
Protection in case of connecting the “wrong” poles. To do this, you can construct a relay. So, the conditional connection is based on a diode. If you confuse plus and minus, it will not pass current. And since there is a relay connected to it, it will be de-energized. Moreover, this circuit can be used with a device based on both thyristors and transistors. It must be connected to the break in the wires with which the charging itself is connected to the battery.
Automation that battery charging should have. The circuit in this case must ensure that the device will work only when it is really needed. To do this, resistors change the response threshold of the control diode. 12 V batteries are considered to be fully rated when their voltage is within 12.8 V. Therefore, this indicator is desirable for this circuit.

Conclusion

So we looked at what battery charging is. The circuit of this device can be made on a single board, but it should be noted that this is quite complicated. That's why they are made multi-layered.

As part of the article, various circuit diagrams were presented to your attention, which make it clear how, in fact, batteries are charged. But you need to understand that these are only general images, and more detailed ones, with indications of the chemical reactions taking place, are special for each type of battery.

An automatic car battery charger consists of a power supply and protection circuits.

You can assemble it yourself if you have electrical installation skills. During assembly, both complex electrical circuits and simpler versions of the device are designed.

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Requirements for homemade chargers

In order for the charger to automatically restore the car battery, strict requirements are imposed on it:
Any simple modern memory device must be autonomous. Thanks to this, the operation of the equipment does not have to be monitored, in particular if it operates at night. The device will independently control the operating parameters of voltage and charge current. This mode is called automatic.
The charging equipment must independently provide a stable voltage level of 14.4 volts. This parameter is necessary to restore any batteries operating in a 12-volt network.
The charging equipment must ensure irreversible disconnection of the battery from the device under two conditions. In particular, if the charge current or voltage increases by more than 15.6 volts. The equipment must have a self-locking function. To reset the operating parameters, the user will have to turn off and activate the device.
The equipment must be protected from overvoltage, otherwise the battery may fail. If the consumer confuses the polarity and incorrectly connects the negative and positive contacts, a short circuit will occur. It is important that charging equipment provides protection. The circuit is supplemented with a safety device.

To connect the charger to the battery, you will need two wires, each of which must have a cross-section of 1 mm2. An alligator clip must be installed on one end of each conductor. On the other side, split tips are installed. The positive contact must be made in a red sheath, and the negative contact in a blue sheath. For a household network, a universal cable equipped with a plug is used.

Vladimir Kalchenko spoke in detail about the modification of the charger and the use of wires suitable for this purpose.

Automatic charger design

The simplest example of a charger structurally includes the main part - a step-down transformer device. This element reduces the voltage parameter from 220 to 13.8 volts, which is required to restore the battery charge. But the transformer device can only reduce this value. And the conversion of alternating current to direct current is carried out by a special element - a diode bridge.

Each charger must be equipped with a diode bridge, since this part rectifies the current value and allows it to be divided into positive and negative poles.

In any circuit, an ammeter is usually installed behind this part. The component is designed to demonstrate current strength.

The simplest designs of chargers are equipped with pointer sensors. More advanced and expensive versions use digital ammeters, and in addition to them, the electronics can be supplemented with voltmeters.

Some device models allow the consumer to change the voltage level. That is, it becomes possible to charge not only 12-volt batteries, but also batteries designed to operate in 6- and 24-volt networks.

Wires with positive and negative terminals extend from the diode bridge. They are used to connect equipment to the battery. The entire structure is enclosed in a plastic or metal case, from which comes a cable with a plug for connecting to the electrical network. Also, two wires with a negative and positive terminal clamp are output from the device. To ensure safer operation of the charging equipment, the circuit is supplemented with a fusible safety device.

User Artem Kvantov clearly disassembled the proprietary charging device and talked about its design features.

Automatic charger circuits

If you have skills in working with electrical equipment, you can assemble the device yourself.

Simple circuits

These types of devices are divided into:

devices with one diode element;
equipment with a diode bridge;
devices equipped with smoothing capacitors.

Circuit with one diode

There are two options here:

You can assemble a circuit with a transformer device and install a diode element after it. At the output of the charging equipment, the current will be pulsating. Its beats will be serious, since one half-wave is actually cut off.
You can assemble the circuit using a laptop power supply. It uses a powerful rectifying diode element with a reverse voltage of more than 1000 volts. Its current must be at least 3 amperes. The outer terminal of the power plug will be negative and the inner terminal will be positive. Such a circuit must be supplemented with a limiting resistance, which can be used as a light bulb to illuminate the interior.

It is permissible to use a more powerful lighting device from a turn signal, side lights or brake lights. When using a laptop power supply, this may cause it to overload. If a diode is used, then an incandescent lamp of 220 volts and 100 watts must be installed as a limiter.

When using a diode element, a simple circuit is assembled:

First comes the terminal from a 220-volt household outlet.
Then - the negative contact of the diode element.
The next one will be the positive terminal of the diode.
Then a limiting load is connected - a lighting source.
Next will be the negative terminal of the battery.
Then the positive terminal of the battery.
And the second terminal for connecting to a 220-volt network.

When using a 100-watt light source, the charging current will be approximately 0.5 amperes. So in one night the device will be able to transfer 5 A/h to the battery. This is enough to turn the vehicle's starter mechanism.

To increase the indicator, you can connect three 100-watt lighting sources in parallel; this will replenish half the battery capacity overnight. Some users use electric stoves instead of lamps, but this cannot be done, since not only the diode element will fail, but also the battery.

The simplest circuit with one diode Electrical diagram for connecting the battery to the network

Circuit with diode bridge

This component is designed to “wrap” the negative wave upward. The current itself will also pulsate, but its beats are much less. This version of the scheme is used more often than others, but is not the most effective.

You can make a diode bridge yourself using a rectifying element, or purchase a ready-made part.

Electrical circuit of a charger with a diode bridge

Circuit with smoothing capacitor

This part should be rated for 4000-5000 uF and 25 volts. A direct current is generated at the output of the resulting electrical circuit. The device must be supplemented with 1 ampere safety elements, as well as measuring equipment. These parts allow you to control the battery recovery process. You don’t have to use them, but then you will need to connect a multimeter periodically.

While monitoring voltage is convenient (by connecting terminals to probes), monitoring current will be more difficult. In this operating mode, the measuring device will have to be connected to an electrical circuit. The user will need to turn off the power from the network each time and put the tester in current measurement mode. Then turn on the power and disassemble the electrical circuit. Therefore, it is recommended to add at least one 10 amp ammeter to the circuit.

The main disadvantage of simple electrical circuits is the lack of ability to adjust the charging parameters.

When selecting the element base, you should select operating parameters so that the output current is 10% of the total battery capacity. A slight decrease in this value is possible.

If the resulting current parameter is greater than required, the circuit can be supplemented with a resistor element. It is installed on the positive output of the diode bridge, immediately before the ammeter. The resistance level is selected in accordance with the bridge used, taking into account the current indicator, and the power of the resistor should be higher.

Electrical circuit with a smoothing capacitor device

Circuit with the ability to manually adjust the charge current for 12 V

To make it possible to change the current parameter, it is necessary to change the resistance. A simple way to solve this problem is to install a variable trimmer resistor. But this method cannot be called the most reliable. To ensure higher reliability, it is necessary to implement manual adjustment with two transistor elements and a trimming resistor.

Using a variable resistor component, the charging current will vary. This part is installed after the composite transistor VT1-VT2. Therefore, the current through this element will be low. Accordingly, the power will also be small, it will be about 0.5-1 W. The operating rating depends on the transistor elements used and is selected experimentally; the parts are designed for 1-4.7 kOhm.

The circuit uses a 250-500 W transformer device, as well as a secondary winding of 15-17 volts. The diode bridge is assembled on parts whose operating current is 5 amperes or more. Transistor elements are selected from two options. These can be germanium parts P13-P17 or silicon devices KT814 and KT816. To ensure high-quality heat removal, the circuit must be placed on a radiator device (at least 300 cm3) or a steel plate.

At the output of the equipment, a safety device PR2 is installed, rated at 5 amperes, and at the input - PR1 at 1 A. The circuit is equipped with signal light indicators. One of them is used to determine the voltage in a 220 volt network, the second is used to determine the charging current. It is allowed to use any lighting sources rated for 24 volts, including diodes.

Electrical circuit for a charger with manual adjustment function

Over-reversal protection circuit

There are two options for implementing such a memory:

using relay P3;
by assembling a charger with integral protection, but not only from overvoltage, but also from overvoltage and overcharging.

With relay P3

This version of the circuit can be used with any charging equipment, both thyristor and transistor. It must be included in the cable break through which the battery is connected to the charger.

Scheme for protecting equipment from reverse polarity on relay P3

If the battery is not connected to the network correctly, the VD13 diode element will not pass current. The electrical circuit relay is de-energized and its contacts are open. Accordingly, current will not be able to flow to the battery terminals. If the connection is made correctly, the relay is activated and its contact elements are closed, so the battery is charged.

With integrated overvoltage, overcharge and overvoltage protection

This version of the electrical circuit can be built into an already used homemade power source. It uses the slow response of the battery to a voltage surge, as well as relay hysteresis. The voltage with the release current will be 304 times less than this parameter when triggered.

An AC relay is used with an activation voltage of 24 volts, and a current of 6 amperes flows through the contacts. When the charger is activated, the relay turns on, the contact elements close and charging begins.

The voltage parameter at the output of the transformer device drops below 24 volts, but at the output of the charger there will be 14.4 V. The relay must maintain this value, but when an extra current appears, the primary voltage will drop even more. This will turn off the relay and break the charging circuit.

The use of Schottky diodes in this case is impractical, since this type of circuit will have serious disadvantages:

There is no protection against voltage surges across the contact if the battery is completely discharged.
There is no self-locking of the equipment. As a result of exposure to extra current, the relay will turn off until the contact elements fail.
Unclear operation of equipment.

Because of this, adding a device to this circuit to adjust the operating current does not make sense. The relay and transformer device are precisely matched to each other so that the repeatability of the elements is close to zero. The charging current passes through the closed contacts of relay K1, as a result of which the likelihood of their failure due to burning is reduced.

Winding K1 must be connected according to a logical electrical circuit:

to the overcurrent protection module, these are VD1, VT1 and R1;
to the surge protection device, these are elements VD2, VT2, R2-R4;
as well as to the self-locking circuit K1.2 and VD3.

Circuit with integrated protection against overvoltage, overcharge and overvoltage

The main disadvantage is the need to set up a circuit using a ballast load, as well as a multimeter:

Elements K1, VD2 and VD3 are desoldered. Or you don’t have to solder them during assembly.
The multimeter is activated, which must be configured in advance to measure a voltage of 20 volts. It must be connected instead of winding K1.
The battery is not connected yet; a resistor device is installed instead. It should have a resistance of 2.4 ohms for a charge current of 6 A or 1.6 ohms for 9 amperes. For 12 A, the resistor should be rated at 1.2 ohms and no less than 25 W. The resistor element can be wound from a similar wire that was used for R1.
A voltage of 15.6 volts is supplied to the input from the charging equipment.
The current protection should operate. The multimeter will show voltage since the resistance element R1 is selected with a slight excess.
The voltage parameter is reduced until the tester shows 0. The output voltage value must be recorded.
Then part VT1 is desoldered, and VD2 and K1 are installed in place. R3 must be placed in the lowest position in accordance with the electrical diagram.
The voltage of the charging equipment increases until the load reaches 15.6 volts.
Element R3 rotates smoothly until K1 is triggered.
The charger voltage is reduced to the value that was previously recorded.
Elements VT1 and VD3 are installed and soldered back. After this, the electrical circuit can be checked for functionality.
A working but dead or undercharged battery is connected through an ammeter. A tester must be connected to the battery, which is pre-configured to measure voltage.
The test charge must be carried out with continuous monitoring. At the moment when the tester shows 14.4 volts on the battery, it is necessary to detect the content current. This parameter should be normal or close to the lower limit.
If the content current is high, the charger voltage should be reduced.

Automatic shutdown circuit when the battery is fully charged

The automation must be an electrical circuit equipped with a power supply system for an operational amplifier and a reference voltage. For this, a DA1 class 142EN8G stabilizer board for 9 volts is used. This circuit must be designed so that the output voltage level remains virtually unchanged when measuring the board temperature by 10 degrees. The change will be no more than hundredths of a volt.

In accordance with the description of the circuit, the automatic deactivation system when the voltage increases by 15.6 volts is done on half of the A1.1 board. Its fourth pin is connected to the voltage divider R7 and R8, from which a reference value of 4.5V is supplied. The operating parameter of the resistor device sets the activation threshold of the charger to 12.54 V. As a result of using the diode element VD7 and part R9, it is possible to provide the desired hysteresis between the activation and shutdown voltages of the battery charge.

Electrical circuit of the charger with automatic deactivation when the battery is charged

The description of the action of the scheme is as follows:

When a battery is connected, the voltage level at the terminals of which is less than 16.5 volts, a parameter is set at the second terminal of circuit A1.1. This value is enough for the transistor element VT1 to open.
This detail is being discovered.
Relay P1 is activated. As a result, the primary winding of the transformer device is connected to the network through a block of capacitor mechanisms via contact elements.
The process of replenishing the battery charge begins.
When the voltage level increases to 16.5 volts, this value at output A1.1 will decrease. The decrease occurs to a value that is not enough to maintain the transistor device VT1 in the open state.
The relay is switched off and contact elements K1.1 are connected to the transformer unit through the capacitor device C4. With it, the charge current will be 0.5 A. In this state, the equipment circuit will operate until the voltage on the battery drops to 12.54 volts.
After this happens, the relay is activated. The battery continues to charge at the user-specified current. This circuit implements the ability to disable the automatic adjustment system. For this purpose, switching device S2 is used.

This operating procedure for an automatic charger for a car battery helps prevent its discharge. The user can leave the equipment turned on for at least a week, this will not harm the battery. If the voltage in the household network goes out, when it returns, the charger will continue to charge the battery.

If we talk about the principle of operation of the circuit assembled on the second half of the A1.2 board, then it is identical. But the level of complete deactivation of charging equipment from the power supply will be 19 volts. If the voltage is less, at the eighth output of board A1.2 it will be sufficient to hold the transistor device VT2 in the open position. With it, current will be supplied to relay P2. But if the voltage is more than 19 volts, then the transistor device will close and the contact elements K2.1 will open.

Required materials and tools

Description of parts and elements that will be required for assembly:

Power transformer device T1 class TN61-220. Its secondary windings must be connected in series. You can use any transformer whose power is no more than 150 watts, since the charging current is usually no more than 6A. The secondary winding of the device, when exposed to an electric current of up to 8 amperes, should provide a voltage in the range of 18-20 volts. If a ready-made transformer is not available, parts of similar power can be used, but the secondary winding will need to be rewinded.
Capacitor elements C4-C9 must comply with the MGBC class and have a voltage of at least 350 volts. Any type of device can be used. The main thing is that they are intended to operate in alternating current circuits.
Any diode elements VD2-VD5 can be used, but they must be rated for a current of 10 amperes.
Parts VD7 and VD11 are flint impulse.
Diode elements VD6, VD8, VD10, VD5, VD12, VD13 must withstand a current of 1 ampere.
LED element VD1 - any.
As a VD9 part, it is allowed to use a device of class KIPD29. The main feature of this light source is the ability to change color if the polarity of the connection is changed. To switch the light bulb, contact elements K1.2 of relay P1 are used. If the battery is being charged with the main current, the LED lights up yellow, and if the recharging mode is turned on, it turns green. It is possible to use two devices of the same color, but they must be connected correctly.
Operational amplifier KR1005UD1. You can take the device from an old video player. The main feature is that this part does not require two polar power supplies; it can operate at a voltage of 5-12 volts. Any similar spare parts can be used. But due to different numbering of pins, it will be necessary to change the design of the printed circuit.
Relays P1 and P2 must be designed for voltages of 9-12 volts. And their contacts are designed to operate with a current of 1 ampere. If devices are equipped with several contact groups, it is recommended to solder them in parallel.
Relay P3 is 9-12 volts, but the switching current will be 10 amperes.
Switching device S1 must be designed to operate at 250 volts. It is important that this element has enough switching contact components. If the adjustment step of 1 ampere is not important, then you can install several switches and set the charge current to 5-8 A.
Switch S2 is designed to deactivate the charge level control system.
You will also need an electromagnetic head for a current and voltage meter. Any type of device can be used, as long as the total deviation current is 100 µA. If not voltage is measured, but only current, then a ready-made ammeter can be installed in the circuit. It must be rated to operate with a maximum continuous current of 10 amps.

User Artem Kvantov spoke in theory about the circuit of the charging equipment, as well as the preparation of materials and parts for its assembly.

Procedure for connecting the battery to chargers

The instructions for turning on the charger consist of several steps:

Cleaning the battery surface.
Removing plugs for filling liquid and monitoring the electrolyte level in jars.
Setting the current value on the charging equipment.
Connecting the terminals to the battery with correct polarity.

Surface cleaning

Guidelines for completing the task:

The car's ignition is turned off.
The hood of the car opens. Using appropriately sized wrenches, disconnect the clamps from the battery terminals. To do this, you do not need to unscrew the nuts; they can be loosened.
The fixing plate that secures the battery is dismantled. This may require a socket or sprocket wrench.
The battery is dismantled.
Its body is cleaned with a clean rag. Subsequently, the lids of the cans to fill the electrolyte will be unscrewed, so the weight must not be allowed to get inside.
A visual diagnosis of the integrity of the battery case is performed. If there are cracks through which electrolyte leaks, it is not advisable to charge the battery.

User Battery Technician talked about cleaning and flushing the battery case before servicing it.

Removing Acid Fill Plugs

If the battery is serviceable, you need to unscrew the caps on the plugs. They can be hidden under a special protective plate; it must be removed. To unscrew the plugs, you can use a screwdriver or any metal plate of the appropriate size. After dismantling, it is necessary to evaluate the electrolyte level; the liquid should completely cover all the cans inside the structure. If it is not enough, then you need to add distilled water.

Setting the charge current value on the charger

The current parameter for recharging the battery is set. If this value is 2-3 times greater than the nominal value, then the charging procedure will occur faster. But this method will lead to a decrease in battery life. Therefore, you can set this current if the battery needs to be recharged quickly.

Connecting the battery with correct polarity

The procedure is performed like this:

Clamps from the charger are connected to the battery terminals. First the connection is made to the positive terminal, this is the red wire.
The negative cable does not need to be connected if the battery remains in the car and has not been removed. This contact can be connected to the vehicle body or to the cylinder block.
The plug from the charging equipment is inserted into the socket. The battery begins to charge. The charging time depends on the degree of discharge of the device and its condition. The use of extension cords is not recommended when performing this task. Such a wire must be grounded. Its value will be sufficient to withstand the current load.

The VseInstrumenti channel talked about the features of connecting a battery to a charger and observing polarity when performing this task.

How to determine the degree of battery discharge

To complete the task you will need a multimeter:

The voltage value is measured on a car with the engine turned off. The vehicle's electrical network in this mode will consume part of the energy. The voltage value during measurement should correspond to 12.5-13 volts. The tester leads are connected with correct polarity to the battery contacts.
The power unit is started, all electrical equipment must be turned off. The measurement procedure is repeated. The working value should be in the range of 13.5-14 volts. If the resulting value is greater or less, this indicates a low battery and the generator device is not operating normally. An increase in this parameter at low negative air temperatures cannot indicate battery discharge. Perhaps at first the resulting indicator will be higher, but if over time it returns to normal, this indicates efficiency.
The main energy consumers are turned on - the heater, radio, optics, rear window heating system. In this mode, the voltage level will be in the range from 12.8 to 13 volts.

The discharge value can be determined in accordance with the data given in the table.

How to calculate the approximate battery charging time

To determine the approximate recharging time, the consumer needs to know the difference between the maximum charge value (12.8 V) and the current voltage. This value is multiplied by 10, resulting in the charging time in hours. If the voltage level before recharging is 11.9 volts, then 12.8-11.9 = 0.8. By multiplying this value by 10, you can determine that the recharging time will be approximately 8 hours. But this is provided that a current of 10% of the battery capacity is supplied.

When parked for a long time, the car battery discharges over time. On-board electrical equipment constantly consumes a small current, and the battery undergoes a self-discharge process. But even regular use of the machine does not always provide sufficient charge.

This is especially noticeable in winter on short trips. In such conditions, the generator does not have time to restore the charge spent on the starter. Only a car battery charger will help here. which you can do yourself.

Why do you need to charge the battery?

Modern cars use lead-acid batteries. Their peculiarity is that with a constant weak charge, plate sulfation process. As a result, the battery loses capacity and cannot cope with starting the engine. You can avoid this by regularly charging the battery from the network. With its help, you can recharge the battery and prevent, and in some cases even reverse, the sulfation process.

A homemade battery charger (UZ) is indispensable in cases where you leave the car in the garage for the winter. Due to self-discharge, the battery loses 15-30% capacity per month. Therefore, it will not be possible to start the car at the beginning of the season without first charging it.

Charger requirements for car batteries

Availability of automation. The battery is charged mainly at night. Therefore, the charger should not require control of current and voltage by the car owner.
Sufficient tension. The power supply (PS) must provide 14.5 V. If the voltage drops across the charger, you need to choose a higher voltage power supply.
Protective system. If the charging current is exceeded, the automation must irreversibly disconnect the battery. Otherwise, the device may fail and even catch fire. The system should be reset to its original state only after human intervention.
Reverse polarity protection. If the battery terminals are incorrectly connected to the charger, the circuit should immediately turn off. The system described above copes with this task.

Common mistakes in the design of homemade memory devices

Connecting the battery to the home electrical network through a diode bridge and ballast in the form of a capacitor with resistance. The large-capacity paper-oil capacitor required in this case will cost more than a purchased “charger”. This connection scheme creates a large reactive load, which can "to confuse" modern protection devices and electricity meters.
Creation of a charger based on a powerful transformer with a primary winding on 220V and secondary on 15V. There will be no problems with the operation of such equipment, and its reliability will be the envy of space technology. But making such a battery charger with your own hands will serve as a clear illustration of the expression "shoot sparrows from a cannon". And the heavy, bulky design is not ergonomic and easy to use.

Protection circuit

The probability that a short circuit will sooner or later occur at the output of the battery charger 100% . The cause may be a polarity reversal, a loose terminal, or another operator error. Therefore, you need to start with the design of the protection device (PD). It should respond quickly and clearly when overloaded and break the output circuit.

There are two designs of ultrasound:

External, designed as a separate module. They can be connected to any 14 volt DC voltage source.
Internal, integrated into the body of a specific “charger”.

The classic Schottky diode circuit only helps if the battery is connected incorrectly. But the diodes will simply burn out from overload when connected to a discharged battery or a short circuit at the charger output

It is better to use the universal scheme presented in the figure. It uses relay hysteresis and the slow response of the acid battery to voltage surges.

When there is a load surge in the circuit, the voltage on the relay coil drops and it turns off, preventing overload. The problem is that this circuit does not protect against polarity reversal. Also, the system does not permanently shut down when the current is exceeded, rather than due to a short circuit. When overloaded, the contacts will begin to continuously “clap” and this process will not stop until they burn out. Therefore, another circuit based on a pair of transistors and a relay is considered better.

The relay winding here is connected by diodes in an “or” logical circuit to the self-locking circuit and control modules. Before operating the charger, you need to configure it by connecting a ballast load to it.

What current source to use

A DIY charger requires a power source. Parameters required for battery 14.5-15 V/ 2-5 A (amp hours). Switching power supplies (UPS) and transformer-based units have such characteristics.

The advantage of a UPS is that it may well already be available. But the labor intensity of creating a charger for a battery based on it is much higher. Therefore, it is not worth buying a switching power supply for use in a car charger. It is better then to make a simpler and cheaper power source from a transformer and a rectifier.

Battery charger diagram:

Power supply for “charging” from the UPS

The advantage of a power supply from a computer is that it already has a built-in protective circuit. However, you will have to work hard to redo the design a little. To do this you need to do the following:

remove all output wires except yellow ones (+12V), black (ground) and green (PC turn-on wire).
short-circuit the green and black wires;
install a power switch (if there is no standard one);
find the feedback resistor in the circuit +12V;
replace with a variable resistor 10 kOhm;
turn on the power supply;
by rotating the variable resistor, set it at the output 14.4 V;
measure the current resistance of the variable resistor;
replace the variable resistor with a constant one of the same value (2% tolerance);
connect a voltmeter to the output of the power supply to monitor the charging process (optional);
connect the yellow and black wires into two bundles;
connect wires with clamps to them for connection to the terminals.

Tip: You can use a universal multimeter instead of a voltmeter. To power it, you should leave one red wire (+5 V).

The DIY battery charger is ready. All that remains is to connect the device to the mains and charge the battery.

Charger on transformer

The advantage of a transformer power source is that its electrical inertia is higher than that of a battery. This improves the security and reliability of the circuit.

Unlike a UPS, there is no built-in protection. Therefore, you need to take care to prevent overloading the charger you made yourself. This is also extremely important for car batteries. Otherwise, with overcurrent and voltage overloads, any troubles are possible: from burnout of the windings to splashing of acid and even explosion of the battery.

Charger from an electronic transformer (Video)

This video talks about an adjustable power supply, which is based on a converted 12V electronic transformer with a power of 105 W. In combination with a pulse stabilizer module, a reliable and compact charger is obtained for all types of batteries. 1.4-26V 0-3A.

A homemade power supply consists of two blocks: a transformer and a rectifier.

You can find a ready-made part with suitable windings or wind it yourself. The second option is more preferable, since you can find a transformer with an output 14.3-14.5 volts you are unlikely to succeed. You will have to use ready-made solutions that provide 12.6 V. You can increase the voltage by about 0.6 V by assembling a rectifier with a midpoint using Schottky diodes.

The power of the windings must be at least 120 watt, diode parameters - 30 amps/ 35 volts. This is enough to charge the battery normally.

You can use a thyristor rectifier. To obtain 14 V at the output, the input AC voltage to the rectifier should be about 24 volts. It will not be difficult to find a transformer with such parameters.

The easiest way- buy an adjustable rectifier for 18 or 24 volts and adjust it so that it produces 14.4 V

I know that I’ve already gotten all sorts of different chargers, but I couldn’t help but repeat an improved copy of the thyristor charger for car batteries. Refinement of this circuit makes it possible to no longer monitor the state of charge of the battery, also provides protection against polarity reversal, and also saves the old parameters

On the left in the pink frame is a well-known circuit of a phase-pulse current regulator; you can read more about the advantages of this circuit

The right side of the diagram shows a car battery voltage limiter. The point of this modification is that when the voltage on the battery reaches 14.4V, the voltage from this part of the circuit blocks the supply of pulses to the left side of the circuit through transistor Q3 and charging is completed.

I laid out the circuit as I found it, and on the printed circuit board I slightly changed the values of the divider with the trimmer

This is the printed circuit board I got in the SprintLayout project

The divider with trimmer on the board has changed, as mentioned above, and also added another resistor to switch the voltage between 14.4V-15.2V. This voltage of 15.2V is necessary for charging calcium car batteries

There are three LED indicators on the board: Power, Battery connected, Polarity reversal. I recommend putting the first two green, the third LED red. The variable resistor of the current regulator is installed on the printed circuit board, the thyristor and diode bridge are placed on the radiator.

I'll post a couple of photos of the assembled boards, but not in the case yet. There are also no tests of a charger for car batteries yet. I'll post the rest of the photos once I'm in the garage.

I also started drawing the front panel in the same application, but while I’m waiting for a parcel from China, I haven’t started working on the panel yet

I also found on the Internet a table of battery voltages at different states of charge, maybe it will be useful to someone

An article about another simple charger would be interesting.

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