Every car owner needs a battery charger, but it costs a lot, and regular preventive trips to a car service center are not an option. Battery service at a service station takes time and money. In addition, with a discharged battery, you still need to drive to the service station. Anyone who knows how to use a soldering iron can assemble a working charger for a car battery with their own hands.

A little theory about batteries

Any battery is a storage device for electrical energy. When voltage is applied to it, energy is stored due to chemical changes inside the battery. When a consumer is connected, the opposite process occurs: a reverse chemical change creates voltage at the terminals of the device, and current flows through the load. Thus, in order to get voltage from the battery, you first need to “put it down,” that is, charge the battery.

Almost any car has its own generator, which, when the engine is running, provides power to the on-board equipment and charges the battery, replenishing the energy spent on starting the engine. But in some cases (frequent or difficult engine starts, short trips, etc.) the battery energy does not have time to be restored, and the battery is gradually discharged. There is only one way out of this situation - charging with an external charger.

How to find out the battery status

To decide whether charging is necessary, you need to determine the state of the battery. The simplest option - “turns/does not turn” - is at the same time unsuccessful. If the battery “doesn’t turn”, for example, in the garage in the morning, then you won’t go anywhere at all. The “does not turn” condition is critical, and the consequences for the battery can be dire.

The optimal and reliable method for checking the condition of a battery is to measure the voltage on it with a conventional tester. At an air temperature of about 20 degrees dependence of the degree of charge on voltage on the terminals of the battery disconnected from the load (!) is as follows:

• 12.6…12.7 V - fully charged;
• 12.3…12.4 V - 75%;
• 12.0…12.1 V - 50%;
• 11.8…11.9 V - 25%;
• 11.6…11.7 V - discharged;
• below 11.6 V - deep discharge.

It should be noted that the voltage of 10.6 volts is critical. If it drops below, the “car battery” (especially a maintenance-free one) will fail.

Correct charging

There are two methods of charging a car battery - constant voltage and constant current. Everyone has their own features and disadvantages:

Homemade battery chargers

Assembling a charger for a car battery with your own hands is realistic and not particularly difficult. To do this, you need to have basic knowledge of electrical engineering and be able to hold a soldering iron in your hands.

Simple 6 and 12 V device

This scheme is the most basic and budget-friendly. Using this charger, you can efficiently charge any lead-acid battery with an operating voltage of 12 or 6 V and an electrical capacity of 10 to 120 A/h.

The device consists of a step-down transformer T1 and a powerful rectifier assembled using diodes VD2-VD5. The charging current is set by switches S2-S5, with the help of which quenching capacitors C1-C4 are connected to the power circuit of the primary winding of the transformer. Thanks to the multiple “weight” of each switch, various combinations allow you to stepwise adjust the charging current in the range of 1–15 A in 1 A increments. This is enough to select the optimal charging current.

For example, if a current of 5 A is required, then you will need to turn on the toggle switches S4 and S2. Closed S5, S3 and S2 will give a total of 11 A. To monitor the voltage on the battery, use a voltmeter PU1, the charging current is monitored using an ammeter PA1.

The design can use any power transformer with a power of about 300 W, including homemade ones. It should produce a voltage of 22–24 V on the secondary winding at a current of up to 10–15 A. In place of VD2-VD5, any rectifier diodes that can withstand a forward current of at least 10 A and a reverse voltage of at least 40 V are suitable. D214 or D242 are suitable. They should be installed through insulating gaskets on a radiator with a dissipation area of ​​at least 300 cm2.

Capacitors C2-C5 must be non-polar paper with an operating voltage of at least 300 V. Suitable, for example, are MBChG, KBG-MN, MBGO, MBGP, MBM, MBGCh. Similar cube-shaped capacitors were widely used as phase-shifting capacitors for electric motors in household appliances. A DC voltmeter of type M5−2 with a measurement limit of 30 V was used as PU1. PA1 is an ammeter of the same type with a measurement limit of 30 A.

The circuit is simple, if you assemble it from serviceable parts, then it does not need adjustment. This device is also suitable for charging six-volt batteries, but the “weight” of each of the switches S2-S5 will be different. Therefore, you will have to navigate the charging currents using an ammeter.

With continuously adjustable current

Using this scheme, it is more difficult to assemble a charger for a car battery with your own hands, but it can be repeated and also does not contain scarce parts. With its help, it is possible to charge 12-volt batteries with a capacity of up to 120 A/h, the charge current is smoothly regulated.

The battery is charged using a pulsed current; a thyristor is used as a regulating element. In addition to the knob for smoothly adjusting the current, this design also has a mode switch, when turned on, the charging current doubles.

The charging mode is controlled visually using the RA1 dial gauge. Resistor R1 is homemade, made of nichrome or copper wire with a diameter of at least 0.8 mm. It serves as a current limiter. Lamp EL1 is an indicator lamp. In its place, any small-sized indicator lamp with a voltage of 24–36 V will do.

A step-down transformer can be used ready-made with an output voltage on the secondary winding of 18–24 V at a current of up to 15 A. If you don’t have a suitable device at hand, you can make it yourself from any network transformer with a power of 250–300 W. To do this, wind all windings from the transformer except the mains winding, and wind one secondary winding with any insulated wire with a cross-section of 6 mm. sq. The number of turns in the winding is 42.

Thyristor VD2 can be any of the KU202 series with the letters V-N. It is installed on a radiator with a dispersion area of ​​at least 200 sq. cm. The power installation of the device is done with wires of minimal length and with a cross-section of at least 4 mm. sq. In place of VD1, any rectifier diode with a reverse voltage of at least 20 V and withstanding a current of at least 200 mA will work.

Setting up the device comes down to calibrating the RA1 ammeter. This can be done by connecting several 12-volt lamps with a total power of up to 250 W instead of a battery, monitoring the current using a known-good reference ammeter.

From a computer power supply

To assemble this simple charger with your own hands, you will need a regular power supply from an old ATX computer and knowledge of radio engineering. But the characteristics of the device will be decent. With its help, batteries are charged with a current of up to 10 A, adjusting the current and charge voltage. The only condition is that the power supply is desirable on the TL494 controller.

For creating DIY car charging from a computer power supply you will have to assemble the circuit shown in the figure.

Step by step steps required to finalize the operation will look like this:

1. Bite off all the power bus wires, with the exception of the yellow and black ones.
2. Connect the yellow and separately black wires together - these will be the “+” and “-” chargers, respectively (see diagram).
3. Cut all traces leading to pins 1, 14, 15 and 16 of the TL494 controller.
4. Install variable resistors with a nominal value of 10 and 4.4 kOhm on the power supply casing - these are the controls for regulating the voltage and charging current, respectively.
5. Using a suspended installation, assemble the circuit shown in the figure above.

If the installation is done correctly, then the modification is complete. All that remains is to equip the new charger with a voltmeter, an ammeter and wires with alligator clips for connecting to the battery.

In the design it is possible to use any variable and fixed resistors, except for the current resistor (the lower one in the circuit with a nominal value of 0.1 Ohm). Its power dissipation is at least 10 W. You can make such a resistor yourself from a nichrome or copper wire of the appropriate length, but you can actually find a ready-made one, for example, a 10 A shunt from a Chinese digital tester or a C5-16MV resistor. Another option is two 5WR2J resistors connected in parallel. Such resistors are found in switching power supplies for PCs or TVs.

What you need to know when charging a battery

When charging a car battery, it is important to follow a number of rules. This will help you Extend battery life and maintain your health:

The question of creating a simple battery charger with your own hands has been clarified. Everything is quite simple, all you have to do is stock up on the necessary tools and you can safely get to work.

When using acid batteries in a car or uninterruptible power supply systems, they need to be charged, preferably in automatic mode. Of course, charging must be provided by the device manufacturer. Fully provide the necessary modes for long-term operation and good condition of the battery installed in it. However, there are situations when there is a need for additional battery charging and maintenance:
1. Such situations arise in the cold season, when the car sits in the garage for a long time and the battery loses its charge. It happens that the driver did not turn off the consumers and the next day the car does not start.
2. In uninterruptible power supply systems, the situation is much better. The device constantly monitors the battery charge, charges it correctly and does not allow it to discharge more than necessary. Until an inquisitive mind gets into it to improve its characteristics.
For me, things went according to the second scenario.

One day, in winter, the energy supply situation deteriorated sharply. It soon became clear that this would take a long time, and I took out an uninterruptible power supply. It contained a 7 A/H battery, which was barely enough for a ten-watt LED lighting. The lights were turned off for 2-4 hours, sometimes there was no electricity for 6 hours. The electricity was turned on several times during the day for two hours, but it did not have time to charge. And I wanted to watch TV, because the 220 V output was idle.
Later I bought a used 75 A/H battery and took care of charging it. It had to be charged quickly and without human supervision. Moreover, the charger should be cheap and good.
The transformer was canceled immediately, since the mains voltage varied widely, at times dropping to 140 V. I had an inexpensive Chinese switching power supply 12 V, 60 W, called "S 60-12". However, it will not be difficult to purchase one in an online store or at a local lighting store.
The block has excellent basic characteristics:

After connecting to the battery, troubles began to arise:
1. voltage 13.2 V is not enough to charge
2. very high current when the battery voltage is low
3. battery discharge into the power supply

Let's look at the output circuits of our block and determine what can be done to solve the problems:
1. You can increase the output voltage by shunting a resistor from the control pin of TL431 to the common wire (R15, SVR1)
2. The current can be reduced by installing a powerful current-limiting resistor at the output, or by reducing the output voltage
3. We exclude battery discharge with a series diode

I had a weak 7 Ah battery, for which the discharge into the power supply (~50 mA) was significant, and I installed a bunch of diodes in series with the UPS output. Later, I gave up diodes when I switched to a larger battery.
First you need to increase the output voltage by installing a 12 kOhm resistor in parallel with R15 (see first figure). After this, the maximum voltage at the UPS output will become 16 V, without taking into account the drop on the diodes. The current limiting resistor was made of thick nichrome wire. If you don’t have one, you can buy a ready-made resistor. The voltage should be set at the output terminals after the diode loaded onto the lighting lamp to take into account the drop across the diode assembly. The table shows the nominal resistance (R) and maximum power dissipation (Pmax) of the resistor, for a charge voltage of 13.8 V. (Umax), a minimum battery voltage of 11 V. (Umin) and a maximum charge current of 20% of capacity (s) . This is a safe mode, since the current will drop linearly as it charges. You can independently calculate the resistance of the resistor:

R=(Umax-Umin)/0.2*c,

and the maximum power on it:

Pmax=(Umax-Umin) 2 /R

In general, the system turned out to be reliable, requiring no maintenance, but also with disadvantages. Of course, a resistor that heats up ungodly at high currents. Long charging time and inability to fully charge.
After purchasing a 75 A/H battery and operating it in constant TV watching mode (plus a 2*5W audio amplifier, T2 tuner, modem with router, charging a phone/tablet, lighting), the resistive circuit no longer had time to restore the wasted charge.

The switching power supply (UPS) stabilizes the output voltage using a controlled zener diode SHR1 TL431, part of the output circuit diagram is shown in the first figure. This zener diode opens when the voltage at the control pin exceeds 2.5V. We can say that in normal mode, the voltage at this point is always 2.5 V. Our circuit will act on this pin to change the output voltage. Please note that the output voltage range of this UPS is limited. It is not advisable to increase the output voltage more than 16 V, and if it decreases below 10 V, it turns off and attempts to start. It means that A battery discharged to less than 10 V cannot be charged by this charger. Just as this charger cannot be used as a laboratory power supply, due to the impossibility of adjusting the output voltage over a wide range and stabilizing the current during a short circuit.

A current stabilization circuit was quickly assembled and the diode was excluded. The design and diagram are presented below:

The presented scheme has several disadvantages.
1. Inability to quickly adjust current
2. Poor accuracy of current stabilization, depending on its level and output voltage
3. No indication of the end of the process, for quick charging of car batteries

The circuit worked for 4 months without malfunctions. The only maintenance is the constantly rotting wires on the battery terminals (not connected securely)

Now that the need for battery power has disappeared and I have free time, I decided to improve the device. Current regulation by an external variable resistor was introduced. Added error amplifier to improve accuracy. LED indication of operating mode has been introduced.

ATTENTION - soldering of a resistor that increases the output voltage of the UPS is not required in this version of the control circuit. Its function is performed by R10

As a result, the circuit diagram became slightly more complicated. The second op-amp IC1B operates in integrator/error amplifier mode, comparing the voltage at the output of IC1A, proportional to the output current, with the reference voltage at point RES.2 set by the regulator. At its output (pin 7 IC1B), the voltage can be in two states. Near zero, when the current cannot reach the value set by the resistor. And, about 3.5 V, when the output current is captured and stabilized, that is, charging occurs. The “Charge” LED connected to the LED point indicates the status of the device. The parallel zener diode regulator VR1 TL431 provides a reference voltage for the current regulator resistor. The voltage at its cathode should be 2.5 V. Two resistors R7, R8 instead of one are installed to reduce the power dissipation across them.
The value of the shunt resistance (Rsh), together with the gain IC1A (k) and the voltage at point RES.1 (Vref), determines the maximum value of the charging current (Imax) of the regulator:

Imax=Vref/(k*Rsh).

Where is the gain of the differential amplifier:

k=R5/R1, with R1=R2, R5=R3.

In our case:

Rsh=0.1 Ohm/3=0.0333 Ohm,
k=1500 Ohm/100 Ohm=15,
Imax=2.5 V/(15*0.0333 Ohm)=5 A.

After checking that the control board is installed correctly, you need to connect it correctly to the UPS. I tried to depict it clearly so that there would be no connection problems. The control wire should be connected to the disassembled unit, having first disconnected it from the 220 V network.!! Before turning it on, you need to install the power supply casing in its original place and adjust the resistor R10 to the maximum high resistance. Turn it on. we set the output voltage of the UPS to operate as part of an uninterruptible power supply device, with the contacts of the "Mode" button open, with resistor SVR1 (see the first figure) at 13-13.8 V. When you press the "Mode" button, you should set the output voltage to 14 ,4 V. resistor R10, for one-time charging of the battery. We check the voltage at the extreme terminals of the adjustment resistor, it should be 2.5 V. By connecting a working battery, we will check the regulation of the output current. The maximum current should not exceed 5 A for this UPS. If the current is not sufficient, you need to change the amplifier gain on IC1A. However, after this amplifier, you can put a trimming resistor on the common wire and connect the motor of this resistor to pin 5. IC1. to adjust the maximum. The minimum will be about zero amperes and does not need adjustment. To check the output current, you can use a powerful resistor or a coil from an electric stove, but current stabilization will only occur in a small voltage range from approximately 10 V to 13 or 14.4 V, depending on the switch settings.

The charger has features:
- When charging up to 14.4 V, it is necessary to monitor the state of the “Charge” LED. When charging is complete, it will go out and you should disconnect the charger from the battery.
- If the battery is faulty and its voltage is less than 10 V, the LED will flash and there will be no charge.
- If the output terminals are short-circuited, there will be no LED indication, but the internal protection in the UPS will operate.
- This charger does not have protection against polarity reversal of the battery terminals and it is advisable to install a 5 A fuse at the output.

The design of the control unit is made on a breadboard printed circuit board with output components. The circuit uses widely used elements. Instead of zener diode VR1, you can use an ordinary zener diode for a voltage of 3.3-5.1 V. (Vref), changing the coefficient. diff gain amplifier according to the above formula. The LED is ultra-bright red in a transparent casing, these shine well at low current. Variable regulator resistor of any convenient type with a rating of 1-10 kOhm.
I used 0.1 Ohm 1 W resistors as a current shunt; they are quite common and not in short supply. The connection to the shunt was made as shown in the figure and photograph. You can use a ready-made shunt or low-resistance resistors 0.03-0.01 Ohm with a power of 3 or more watts, for example MPR-5W, BPR56. As a last resort, you can use a coil of low-section copper wire, but the parameters will change as it warms up.

List of radioelements

Not bad Charger with good output characteristics can be made from old TVs with pulsed power supplies such as MP1, MP3-3, MP403, etc. Minor modification of the unit allows it to be used for charging battery with current up to 6-7A, repair of car radios and other equipment.

Battery charger from MP3-3

The whole point of remaking the block is to increase the load capacity of TPI and rectifier diodes, for this we connect windings with pins 12,18 and 10,20 in parallel, pin 20 is connected to the common pin of secondary sources (12), and pin 10 is connected to pin 18, rectifier diodes 12V and 15V turn it off and connect a diode with a current of 10-25A to pins 10, 18, which must be installed on a heat sink; for these purposes I used a heat sink from a standard 12 V stabilizer.

Details of which are unnecessary you can remove it from the board (except for the so-called outlet), you can put a new diode on it, connect a 470 pf capacitor in parallel to it and at the output electrolyte 470 uF x 40 V, parallel to it we put a load resistor MLT 2 with a nominal value of 510-680 ohms and a ceramic capacitor at 1 µF, these parts are installed to prevent the appearance of high-frequency voltage at the output of the power supply.

To adjust the output voltage You can use trimming resistor R2 according to the circuit, which is soldered off and instead of it we connect an external variable wire resistor of the PPZ type 1-1.5 kohm, adjusting the output voltage from 13V to 18V.

To put the block into mode To stabilize it, you need to load it; for this you can use a lamp from the refrigerator, connecting it to pins 6 and 18.

In your loading block I used the +28 V output, connecting to it a 28 V 5W lamp, which simultaneously serves as a backlight for the voltmeter scale with an extended scale from “five”. The unit heats up under load as in normal mode, but it will be better if you make forced airflow by installing a cooler from the computer.
When connecting the battery, it is necessary to observe the polarity and install a 10A fuse at the output.