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 the relay P2. As soon as the charging voltage exceeds 19 V, the transistor will close, the relay will release contacts K2.1 and the voltage supply to the charger will completely stop. As soon as the battery is connected, it will power the automation circuit, and the charger will immediately return to working condition.
The structure of the automatic charger
All parts of the charger are placed in the case of the B3-38 milliammeter, from which all its contents have been removed, except for the pointer device. Installation of elements, except for the automation circuit, is carried out by a hinged method.
The design of the milliammeter case consists of two rectangular frames connected by four corners. Holes are made in the corners with equal pitch, to which it is convenient to attach parts.
The TN61-220 power transformer is fixed with four M4 screws on an aluminum plate 2 mm thick, the plate, in turn, is attached with M3 screws to the lower corners of the case. The TN61-220 power transformer is fixed with four M4 screws on an aluminum plate 2 mm thick, the plate, in turn, is attached with M3 screws to the lower corners of the case. C1 is also installed on this plate. The photo below shows the charger.
A plate of fiberglass 2 mm thick is also fixed to the upper corners of the case, and capacitors C4-C9 and relays P1 and P2 are screwed to it. A printed circuit board is also screwed to these corners, on which an automatic battery charging control circuit is soldered. In reality, the number of capacitors is not six, as according to the scheme, but 14, since in order to obtain a capacitor of the required rating, it was necessary to connect them in parallel. Capacitors and relays are connected to the rest of the charger circuit through a connector (blue in the photo above), which made it easier to access other elements during installation.
A ribbed aluminum radiator is installed on the outer side of the rear wall to cool the power diodes VD2-VD5. There is also a 1 A fuse Pr1 and a plug (taken from the computer power supply) for supplying power.
The power diodes of the charger are fixed with two clamping bars to the heatsink inside the case. For this, a rectangular hole is made in the rear wall of the case. 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 on the right side. The installation of the electrical circuit is made with colored wires, alternating voltage - brown, positive - red, negative - blue wires. The cross section of the wires 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.
Due to the larger scale and calibration of the device in the measurement area, the voltage reading accuracy was 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. A distinctive feature of this LED is 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. Of the measuring instruments, you will need any voltmeter, pointer tester or multimeter designed to measure DC 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 voltage regulator chip DA1 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 output 2 from the board, and if 9 V appears on it, then the microcircuit is working, and it is necessary to find and eliminate the short circuit.
Checking the surge protection system
I decided to start describing the principle of operation of the circuit with a simpler part of the circuit, to which strict standards for the response voltage are not imposed.
The function of disconnecting the AZU from the mains in the event of a battery disconnection is performed by a part of the circuit assembled on an operational differential amplifier A1.2 (hereinafter referred to as OU).
Operating principle of an operational differential amplifier
Without knowing the principle of operation of the op-amp, it is difficult to understand the operation of the circuit, so I will give a brief 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 low current charging mode through the capacitor C4. When the voltage level drops below 12.54 V, the relay should turn on and switch the AZU to the charging mode with a current of a given value.
The turn-on threshold voltage of 12.54 V can be adjusted by changing the value of the resistor R9, but this is not necessary.
Using switch S2, it is possible to disable automatic operation by turning on relay P1 directly.
Capacitor charger circuit
without automatic shutdown
For those who do not have sufficient experience in assembling electronic circuits or do not need to automatically turn off the charger at the end of battery charging, I offer a simplified version of the device for charging acid car batteries. A distinctive feature of the circuit is its simplicity for repetition, reliability, high efficiency and stable charge current, protection against incorrect battery connection, 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.
The proposed simple circuit for charging batteries is 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 terminal of the battery must be connected to the positive terminal of the charger) to its terminals. If the switch S3 is in the lower position, then the arrow of the device on the charger will immediately show the voltage that the battery produces. It remains to insert the power cord into the socket and the battery charging process will begin. The voltmeter will already begin to show the charging voltage.
Long-term operation of the car leads to the fact that the alternator stops charging the battery. As a result, the car will no longer start. To revive the car you need a charger. In addition, lead-acid batteries are highly sensitive to temperatures. Therefore, problems may arise with their work if the temperature is below zero outside the window.
The charger for the car is not particularly technically complex. To assemble it, you do not need to have any highly specialized knowledge, enough perseverance and ingenuity. Of course, certain parts will be needed, but they can be easily purchased on the radio market for next to nothing.
Varieties of chargers for cars
Science does not stand still. Technology is developing at an incredible speed, it is not surprising that transformer chargers are gradually disappearing from the market, and they are being replaced by pulse and automatic chargers.
The pulse charger for the car has the compact sizes. His easy to use, and unlike the transformer type, devices of this class provide a full battery charge. The charging process takes place in two stages: first at a constant voltage, then at a current. The design consists of the same type of schemes.
The automatic charger for the car differs in extreme simplicity in operation. In fact, this is a multifunctional diagnostic center, which is extremely difficult to assemble on your own.
The most advanced devices of this class will notify you with a signal when the poles are connected incorrectly. Moreover, the power supply will not even start. It is impossible to ignore the diagnostic functions of the device. It is able to measure the battery capacity and even the charge level.
There is a timer in the electrical circuits. Therefore, an automatic charger for cars allows you to charge various types:
- complete,
- fast,
- restorative.
As soon as the automatic car charger finishes charging, a beep will sound and the power supply will automatically stop.
Three ways to make a DIY car charger
How to make charging from a computer unit
Old computers are not uncommon. Someone leaves them out of a sense of nostalgia, while others expect to use serviceable components somewhere. If you don’t have an old desktop computer at home, it’s okay. Second-hand the power supply can be purchased for 200-300 rubles.
Power supplies from desktop computers are ideal for creating any chargers. As a controller, the TL494 chip or the KA7500 similar to it is used here.
The power supply for the charger must be 150 W or more. All wires from -5, -12, +5, +12 V sources are soldered. The same is done with the resistor R1. It needs to be replaced with a tuning resistor. In this case, the value of the latter should be 27 ohms.
The operation of a charger for a car from a power supply is extremely simple. The voltage from the bus labeled +12 V is transmitted to the top output. At the same time, conclusions 14 and 15 are simply cut because of their uselessness.
Important! The only conclusion to be left is the sixteenth. It is adjacent to the main wire. However, it must be turned off.
A potentiometer-regulator R10 should be installed on the rear wall of the power supply. It is also necessary to skip two cords: one for connecting the terminals, the other for the network. Additionally, you need to prepare a block of resistors. It will allow you to make adjustments.
To make the above block, you will need two current-measuring resistors. It is best to use 5W8R2J. A power of 5 watts is enough. The block resistance will be 0.1 ohm, and the total power will be 10 watts.
To adjust, you need a tuning resistor. It is attached to the same board. Part of the printed track is preliminarily removed. This will eliminate the possibility of communication between the case and the main circuit, and will also greatly increase the safety of the car charger.
Before as solder conclusions 1, 14-16, they must first be tinned. Stranded thin wires are soldered. The full charge is determined by the open circuit voltage. The standard interval is 13.8-14.2 V.
The full charge is set by a variable resistor. It is important that the potentiometer R10 is at the same time in the middle position. To connect the output to the terminals, special clamps are installed on the ends. It is best to use the "crocodile" type.
The insulating tubes of the clamps must be made in different colors. Traditionally, red is a plus, blue is a minus. But you can choose any colors you like. It's not essential.
Important! If you mix up the wires, this will damage the device.
To save time and money when assembling a charger for a car, you can exclude a volt and ammeter from the design. The initial current can be set using the potentiometer R10. Recommended value 5.5 and 6.5 A.
Charger from adapter
The best option for making a car charger would be a 12 volt adapter. But when choosing a voltage, you must first consider the parameters of the battery.
The adapter wire must be cut at the end and exposed. Approximately 5-7 centimeters for comfortable work will be enough. Wires with opposite charges must be laid at a distance of 40 centimeters from each other. A "crocodile" is put on the end of each.
The clamps are connected in series to the battery. Plus to plus, minus to minus. After that, all you need to do is turn on the adapter. This is one of the easiest ways to create a car charger with your own hands.
Important! During the charging process, you need to make sure that the battery does not overheat. If this happens, the process must be immediately interrupted in order to avoid damage to the battery.
Everything ingenious is simple or a charger for a car from a light bulb and a diode
Everything you need to create this charger can be found at home. The main element of the design will be an ordinary light bulb. At the same time, its power should not exceed 200 watts.
Important! The more power, the faster the battery will charge.
Some care must be taken when charging. Do not charge a low-capacity battery with a 200-watt light bulb. Most likely this will lead to the fact that he just boils. There is a simple calculation formula that will help you choose the optimal light bulb wattage for your battery.
You will also need a semiconductor diode that will only conduct electricity in one direction. It can be made from a regular laptop charger. The final element of the design will be a wire with terminals and a plug.
It is very important to follow safety rules when creating a charger for a car. First, always turn off the circuit from the network before touching one of the elements with your hand. Secondly, all contacts must be carefully insulated. There should be no exposed wires.
When assembling the circuit, all elements are connected in series: lamp, diode, battery. It is important to know the polarity of the diode in order to connect everything correctly. For added safety, use rubber gloves.
When assembling the circuit, pay special attention to the diode. It usually has an arrow that looks at the plus. Since it passes electricity in only one direction, this is extremely important. You can use a tester to check the polarity of the terminals.
If everything is set up and connected correctly, the light will burn in half a channel. If there is no light, then you did something wrong or the battery is completely discharged.
The charging process itself takes about 6-8 hours. After this time period, the car charger must be disconnected from the mains to avoid overheating the battery.
If you urgently need to recharge the battery, the process can be accelerated. The main thing is that the diode is powerful enough. You will also need a heater. All elements are connected in one chain. The efficiency of this charging method is only 1%, but the speed is many times higher.
Results
The simplest charger for a car can be assembled with your own hands in a few hours. At the same time, a set of necessary materials can be found in every home. More complex devices require more time to create, but they have increased reliability and a good level of security.
Car owners often face the problem battery discharge. If this happens far from service stations, car dealerships and gas stations, you can make a device for charging the battery yourself from the available parts. Consider how to make a charger for a car battery with your own hands, with minimal knowledge of electrical work.
Such a device is best used only in critical situations. However, if you are familiar with electrical engineering, electrical and fire safety rules, have the skills of electrical measurements and installation work, a home-made charger may well replace the factory unit.
Causes and signs of battery discharge
During the operation of the battery, when the engine is running, the battery is constantly recharged from the car's generator. You can check the charging process by connecting a multimeter to the battery terminals with the engine running, measuring the charging voltage of the car battery. The charge is considered normal if the voltage at the terminals is between 13.5 and 14.5 volts.
For a full charge, you need to drive a car for at least 30 kilometers, or about half an hour in the urban rhythm of traffic.
The voltage of a normally charged battery during parking should be at least 12.5 volts. In the event that the voltage is less than 11.5 Volts, the car engine may not start during the start. Causes of battery discharge:
- The battery has significant wear ( more than 5 years of operation);
- improper use of the battery, leading to sulfation of the plates;
- long-term parking of the vehicle, especially in the cold season;
- urban rhythm of car movement with frequent stops when the battery does not have enough time to charge;
- non-switched off electrical appliances of the car during parking;
- damage to electrical wiring and vehicle equipment;
- electrical leakage.
Many car owners in the on-board tool kit do not have the means to measure battery voltage ( voltmeter, multimeter, probe, scanner). In this case, you can be guided by indirect signs of a battery discharge:
- dim glow of the lights on the dashboard when the ignition is turned on;
- lack of rotation of the starter when starting the engine;
- loud clicks in the starter area, the lights on the dashboard go out at startup;
- complete lack of reaction of the car to the ignition.
If these signs appear, first of all, it is necessary to check the battery terminals, if necessary, clean and tighten them. In the cold season, you can try to bring the battery into a warm room for a while and warm it up.
You can try to “light up” a car from another car. If these methods do not help or are impossible, you have to use a charger.
Universal charger with your own hands. Video:
Operating principle
Most devices charge batteries with constant or pulsed currents. How many amps does it take to charge a car battery? The charge current is chosen equal to one tenth of the battery capacity. With a capacity of 100 A * h, the charging current of a car battery will be 10 Amperes. The battery will take about 10 hours to fully charge.
Charging a car battery with high currents can lead to the process of sulfation. To avoid this, it is better to charge the battery with low currents, but for a longer time.
Pulse devices significantly reduce the effect of sulfation. Some pulse chargers have a desulfation mode that allows you to restore battery performance. It consists in a sequential charge-discharge with pulsed currents according to a special algorithm.
When charging the battery, do not allow overcharging. It can lead to boiling of the electrolyte, sulfation of the plates. It is necessary that the device has its own system of control, measurement of parameters and emergency shutdown.
Since the 2000s, special types of batteries have been installed on cars: AGM and gel. Charging these types of car batteries is different than normal.
As a rule, it is three-stage. Up to a certain level, the charge goes with a large current. Then the current decreases. The final charge occurs with even smaller pulsed currents.
Charging a car battery at home
Often in driving practice, a situation arises when, having parked the car near the house in the evening, in the morning it turns out that the battery is discharged. What can be done in such a situation when there is no soldering iron at hand, no details, but you need to get started?
Usually, a small capacity remains on the battery, it just needs to be “pulled up” a little so that there is enough charge to start the engine. In this case, a power supply from some household or office equipment, such as a laptop, can help.
Charging from a laptop power supply
The voltage that the laptop power supply produces is usually 19 volts, the current is up to 10 amperes. This is enough to charge the battery. But it is IMPOSSIBLE to directly connect the power supply to the battery. It is necessary to include a limiting resistor in series in the charge circuit. As it can take a car light bulb, better for interior lighting. It can be purchased at the nearest gas station.
Usually the middle pin of the connector is positive. A light bulb is connected to it. The + battery is connected to the second output of the light bulb.
The negative terminal is connected to the negative terminal of the power supply. The power supply usually has a label showing the polarity of the connector. A couple of hours of charging in this way is enough to start the engine.
Diagram of a simple charger for a car battery.
Charging from a household network
A more extreme charging method is directly from a household outlet. It is used only in a critical situation, using the maximum electrical safety measures. To do this, you need a lighting lamp ( not energy saving).
You can use an electric stove instead. You also need to purchase a rectifier diode. Such a diode can be "borrowed" from a faulty energy-saving lamp. At this time, the voltage supplied to the apartment, it is better to de-energize. The scheme is shown in the figure.
The charge current with a lamp power of 100 watts will be approximately 0.5 A. Overnight, the battery will be recharged by only a few ampere-hours, but this may be enough to start. If you connect three lamps in parallel, then the battery will be charged three times more. If you connect an electric stove instead of a light bulb ( at the lowest power), then the charge time will be significantly reduced, but this is very dangerous. In addition, a diode can break through, then a battery short circuit is possible. Charging methods from 220V are dangerous.
Charging for car batteries with your own hands. Video:
Homemade car battery charger
Before you make a charger for a car battery, you should evaluate your experience in electrical work, knowledge of electrical engineering, based on this, proceed to the choice of a charger circuit for a car battery.
You can look in the garage, there may be old devices or blocks. The power supply from an old computer is suitable for the device. It has almost everything:
- socket 220 V;
- power switch;
- wiring diagram;
- cooling Fan;
- connection leads.
The voltages on it are standard: +5 V, -12 V and +12 Volts. To charge the battery, it is better to use a +12 Volt, 2 Ampere wire. The output voltage must be raised to the level of +14.5 - +15.0 Volts. This can usually be done by changing the value of the resistance in the feedback circuit ( about 1 kiloohm).
Limiting resistance can not be set, the electronic circuit will independently adjust the charge current within 2 Amperes. It is easy to calculate that it will take about a day to fully charge a 50 Ah battery. Appearance of the device.
You can pick up or buy at the flea market a network transformer with a secondary winding voltage of 15 to 30 volts. These were used in old TVs.
Transformer devices
The simplest diagram of a device with a transformer.
Its disadvantage is the need to limit the current in the output circuit and the associated large power losses and heating of the resistors. Therefore, capacitors are used to regulate the current.
Theoretically, by calculating the value of the capacitor, you can not use a power transformer, as shown in the diagram.
When buying capacitors, you should choose the appropriate rating with a voltage of 400 V or more.
In practice, devices with current regulation have received greater use.
You can choose schemes for impulse home-made chargers for a car battery. They are more complex circuitry, require certain skills during installation. Therefore, if you do not have special skills, it is better to buy a factory block.
Pulse chargers
Pulse chargers have a number of advantages:
The principle of operation of pulse devices is based on the conversion of the alternating voltage of a household electrical network into a constant one using a VD8 diode assembly. The DC voltage is then converted into pulses of high frequency and amplitude. The pulse transformer T1 again converts the signal into a constant voltage, which charges the battery.
Since the reverse conversion is carried out at a high frequency, the dimensions of the transformer are much smaller. The feedback necessary to control the charge parameters is provided by optocoupler U1.
Despite the apparent complexity of the device, with proper assembly, the unit starts working without additional adjustment. Such a device provides a charge current of up to 10 amperes.
When charging a battery using a homemade device, you must:
- place the device and the battery on a non-conductive surface;
- comply with electrical safety requirements use gloves, rubber mat, electrically insulated tool);
- do not leave the charger turned on for a long time without control, monitor the voltage and temperature of the battery, and the charging current.
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 charger for a car battery 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 multiplied by 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 regulated charger is simple to repeat, and is easily assembled by surface mounting without the need for PCB etching. However, keep in mind that field-effect transistors are placed on a radiator, the heating of which will be noticeable. It is more convenient to use an old computer cooler by connecting its fan to the charger outlets. 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 looking 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 raise the 12 V voltage to the desired value in them, since other output voltages are also controlled, and they will inevitably “float away” with this setting, and the power supply protection will work. You can use laptop chargers that produce a single output voltage, they are much more convenient for rework.
Transformer - converts the mains supply voltage of 220 volts into 12 volts, which is necessary for us, or in some devices up to 14.4 volts (the latter corresponds to the supply voltage of the car's electrical network when the generator is running)
A diode bridge is four interconnected diodes that convert alternating electricity into direct electricity.
Charge control unit - one of the most important elements that controls charge currents. Allows you to charge the battery completely and at the same time not overcharge it (does not allow the electrolyte inside the battery to boil)
Regulators, connectors, indicators and other controls.
Wires and terminals to connect to the battery.
So consider one of the cheapest charger samples - the market value is about $ 40.
Charger Specifications:
Charges batteries from 10 to 75 amp hours.
It is possible to charge 6v or 12v batteries for a car, motorcycle, scooter, moped, etc.
(On the front panel, we can visually find a special switch between voltages of 6 or 12 volts of the battery).
The current supplied to the battery at the end of the charge is automatically reduced.
(On the front panel, we can also see an ammeter to indicate the charge current)
Having examined the charger from the inside, we can find such basic elements
- transformer
- diode bridge
- fuse
- output voltage switch
- wires to the terminals connected to the battery.
In our version, there is no charge control unit.
In principle, this scheme also has the right to life and it works as follows.
How the charger works:
The transformer is designed for a certain charge current - say no more than 7.5 amperes.
When connecting a discharged battery with a maximum allowable capacity of 75 Amperes, the transformer delivers a maximum allowable current of 7.5 Amperes, which is 1/10 of the battery capacity.
As the battery charges, the voltage at its terminals increases and the charge current decreases (which is why, due to the laws of physics, the current supplied to the battery at the end of charging will decrease).
Unfortunately, such a charger is unlikely to finish the charging process sometime, and if your battery is faulty and does not gain the required capacity, the charge current will not decrease.
In the modern world, more and more people are leaning towards buying a maintenance-free battery. If something happens to it and it does not charge, it must be replaced.
A charger without a control unit will not help you restore the properties of the battery in any way, but again, in our time, rarely anyone does this. More complex devices are able to create a pulsed charging mode, when each charging pulse is followed by a charging pulse. This allows you to renew the properties of the battery.
Often, more advanced chargers also have a discharge function, as the battery must always be in full charge and discharge mode - this allows you to save its capacity.
If you use unattended batteries and you just need to urgently charge the battery after a long car inactivity or after a cold night - you can make such a charger yourself.
1. Transformer.
The first thing you need is a 12 volt to 14 volt transformer with a thick secondary winding that can provide 1/10th of your battery's capacity.
Do not use a transformer for a calculator or player, they are very low-power. You may be able to find a more powerful transformer, say from an old TV (such as TS-180-2). If your transformer does not produce the desired voltage, you can wind the desired secondary yourself - with a thick copper wire, several turns until the desired voltage is reached.
Remember when you work with a transformer that it is connected to a 220 volt network - be very careful (this is life threatening)!
If you managed to find or make such a transformer, then you will need to buy a diode bridge.
2. Diode bridge
Factory made diode bridge. Designed for high charger currents
This is a fairly common product - all you need to know is just the current for which it must be rated. In our case, it is still 7.5 amperes.
If the diode bridge could not be found, you can find 4 diodes all according to the same indicator and assemble the diode bridge from them.
Next, at the output of the diode bridge, you need to put the car fuse on the same calculated current of 7.5 Amperes. If you accidentally short the terminals or mix them up on the battery, you will burn the fuse, not the transformer.
3. Ammeter
To complete the picture, you can also install an ammeter in series with the fuse to keep track of how much current is flowing from your charger. At the same time, you will be able to understand the state of the battery at the moment.
4. Wires and terminals.
The following are wires and terminals that can be connected to the battery. Here you have complete freedom of action. It is best to take copper wires with a thickness of at least 1 mm. Terminals can be taken either ordinary automobile or crocodiles as in the factory version.
It is also worth putting a fuse in front of the transformer, say, 220 Volts 0.5 Amperes, which would double secure your transformer on both sides, in terms of input and output current.
Thus, you will get a device that, in several small parameters, will be even better and more reliable than the factory counterpart.
If you have a desire to make the device even more functional, you can search the Internet for charge control units.
The main advantages of the battery charge control unit:
- regulates the charge current - reduces it to minimum values until the battery is fully charged
- turns off the charging unit when the battery is fully charged
- discharges the battery completely for a complete clean charge cycle
- charges the battery with pulsed currents, alternating charge and discharge to restore capacity.
In today's hectic world of maintenance-free batteries with a lifespan of five years, you're unlikely to be in the business of refurbishing batteries.
In any case, good luck in your endeavors!
