Do-it-yourself automatic charger for a car battery. We make chargers for a car battery ourselves How to assemble a charger for a car battery
How to make a homemade automatic charger The photo shows a homemade automatic charger for charging
How to make a homemade automatic charger for a car battery
How to make a homemade automatic charger
for car battery
The photo shows a homemade automatic charger for charging 12 V car batteries with a current of up to 8 A, assembled in a housing from a B3-38 millivoltmeter.
Why do you need to charge your car battery?
The battery in the car is charged by an electric generator. To ensure a safe battery charging mode, a relay regulator is installed after the generator, providing a charging voltage of no more than 14.1 ± 0.2 V. To fully charge the battery, a voltage of 14.5 V is required. For this reason, the car generator cannot charge the battery 100%. Maybe. Therefore, it is necessary to periodically charge the battery with an external charger.
During warm periods, a battery charged only 20% can start the engine. At subzero temperatures, the battery capacity is halved, and starting currents increase due to thickened engine lubricant. Therefore, if you do not charge the battery in a timely manner, then with the onset of cold weather the engine may not start.
Analysis of charger circuits
Chargers are used to charge a car battery. You can buy it ready-made, but if you wish and have a little amateur radio experience, you can do it yourself, saving a lot of money.
There are many car battery charger circuits published on the Internet, but they all have drawbacks.
Chargers made with transistors generate a lot of heat and, as a rule, are afraid of short circuits and incorrect connection of the battery polarity. Circuits based on thyristors and triacs do not provide the required stability of the charging current and emit acoustic noise, do not allow battery connection errors and emit powerful radio interference, which can be reduced by placing a ferrite ring on the power cable.
The scheme for making a charger from a computer power supply looks attractive. The structural diagrams of computer power supplies are the same, but the electrical ones are different, and modification requires high radio engineering qualifications.
I was interested in the capacitor circuit of the charger, the efficiency is high, it does not generate heat, it provides a stable charging current regardless of the state of charge of the battery and fluctuations in the supply network, and is not afraid of output short circuits. But it also has a drawback. If during charging the contact with the battery is lost, the voltage on the capacitors increases several times (the capacitors and transformer form a resonant oscillatory circuit with the frequency of the mains), and they break through. It was necessary to eliminate only this one drawback, which I managed to do.
The result is a battery charger circuit that does not have the above listed disadvantages. For more than 15 years I have been charging any 12 V acid batteries with a homemade capacitor charger. The device works flawlessly.
Schematic diagram of an automatic charger
for car battery
Despite its apparent complexity, the circuit of a homemade charger is simple and consists of only a few complete functional units.
If the circuit to repeat seems complicated to you, then you can assemble a simpler one that works on the same principle, but without the automatic shutdown function when the battery is fully charged.
Current limiter circuit on ballast capacitors
In a capacitor car charger, regulation of the magnitude and stabilization of the battery charge current is ensured by connecting ballast capacitors C4-C9 in series with the primary winding of the power transformer T1. The larger the capacitor capacity, the greater the battery charging current.
In practice, this is a complete version of the charger; you can connect a battery after the diode bridge and charge it, but the reliability of such a circuit is low. If contact with the battery terminals is broken, the capacitors may fail.
The capacitance of the capacitors, which depends on the magnitude of the current and voltage on the secondary winding of the transformer, can be approximately determined by the formula, but it is easier to navigate using the data in the table.
To regulate the current in order to reduce the number of capacitors, they can be connected in parallel in groups. My switching is carried out using a two-bar switch, but you can install several toggle switches.
Protection circuit
from incorrect connection of battery poles
Circuit for measuring current and voltage of battery charging
Thanks to the presence of switch S3 in the diagram above, when charging the battery, it is possible to control not only the amount of charging current, but also the voltage. In the upper position of S3, the current is measured, in the lower position the voltage is measured. If the charger is not connected to the mains, the voltmeter will show the battery voltage, and when the battery is charging, the charging voltage. An M24 microammeter with an electromagnetic system is used as a head. R17 bypasses the head in current measurement mode, and R18 serves as a divider when measuring voltage.
Automatic charger shutdown circuit
when the battery is fully charged
To power the operational amplifier and create a reference voltage, a DA1 type 142EN8G 9V stabilizer chip is used. This microcircuit was not chosen by chance. When the temperature of the microcircuit body changes by 10º, the output voltage changes by no more than hundredths of a volt.
The system for automatically turning off charging when the voltage reaches 15.6 V is made on half of the A1.1 chip. Pin 4 of the microcircuit is connected to a voltage divider R7, R8 from which a reference voltage of 4.5 V is supplied to it. Pin 4 of the microcircuit is connected to another divider using resistors R4-R6, resistor R5 is a tuning resistor to set the operating threshold of the machine. The value of resistor R9 sets the threshold for switching on the charger to 12.54 V. Thanks to the use of diode VD7 and resistor R9, the necessary hysteresis is provided between the switch-on and switch-off voltages of the battery charge.
The scheme works as follows. When connecting a car battery to a charger, the voltage at the terminals of which is less than 16.5 V, a voltage sufficient to open transistor VT1 is established at pin 2 of microcircuit A1.1, the transistor opens and relay P1 is activated, connecting contacts K1.1 to the mains through a block of capacitors the primary winding of the transformer and battery charging begins. As soon as the charge voltage reaches 16.5 V, the voltage at output A1.1 will decrease to a value insufficient to maintain transistor VT1 in the open state. The relay will turn off and contacts K1.1 will connect the transformer through the standby capacitor C4, at which the charge current will be equal to 0.5 A. The charger circuit will be in this state until the voltage on the battery decreases to 12.54 V. As soon as the voltage will be set equal to 12.54 V, the relay will turn on again and charging will proceed at the specified current. It is possible, if necessary, to disable the automatic control system using switch S2.
Thus, the system of automatic monitoring of battery charging will eliminate the possibility of overcharging the battery. The battery can be left connected to the included charger for at least a whole year. This mode is relevant for motorists who drive only in the summer. After the end of the racing season, you can connect the battery to the charger and turn it off only in the spring. Even if there is a power outage, when it returns, the charger will continue to charge the battery as normal.
The principle of operation of the circuit for automatically turning off the charger in case of excess voltage due to the absence of a load collected on the second half of the operational amplifier A1.2 is the same. Only the threshold for completely disconnecting the charger from the supply network is set to 19 V. If the charging voltage is less than 19 V, the voltage at output 8 of microcircuit A1.2 is sufficient to hold transistor VT2 in the open state, in which voltage is applied to relay P2. As soon as the charging voltage exceeds 19 V, the transistor will close, the relay will release contacts K2.1 and the voltage supply to the charger will completely stop. As soon as the battery is connected, it will power the automation circuit, and the charger will immediately return to working condition.
Automatic charger design
All parts of the charger are placed in the housing of the V3-38 milliammeter, from which all its contents have been removed, except for the pointer device. The installation of elements, except for the automation circuit, is carried out using a hinged method.
The housing design of the milliammeter consists of two rectangular frames connected by four corners. There are holes made in the corners with equal spacing, to which it is convenient to attach parts.
The TN61-220 power transformer is secured with four M4 screws on an aluminum plate 2 mm thick, the plate, in turn, is attached with M3 screws to the lower corners of the case. The TN61-220 power transformer is secured with four M4 screws on an aluminum plate 2 mm thick, the plate, in turn, is attached with M3 screws to the lower corners of the case. C1 is also installed on this plate. The photo shows a view of the charger from below.
A 2 mm thick fiberglass plate is also attached to the upper corners of the case, and capacitors C4-C9 and relays P1 and P2 are screwed to it. A printed circuit board is also screwed to these corners, on which an automatic battery charging control circuit is soldered. In reality, the number of capacitors is not six, as in the diagram, but 14, since in order to obtain a capacitor of the required value it was necessary to connect them in parallel. The capacitors and relays are connected to the rest of the charger circuit via a connector (blue in the photo above), which made it easier to access other elements during installation.
A finned aluminum radiator is installed on the outer side of the rear wall to cool the power diodes VD2-VD5. There is also a 1 A Pr1 fuse and a plug (taken from the computer power supply) for supplying power.
The charger's power diodes are secured using two clamping bars to the radiator inside the case. For this purpose, a rectangular hole is made in the rear wall of the case. This technical solution allowed us to minimize the amount of heat generated inside the case and save space. The diode leads and supply wires are soldered onto a loose strip made of foil fiberglass.
The photo shows a view of a homemade charger on the right side. The installation of the electrical circuit is made with colored wires, alternating voltage - brown, positive - red, negative - blue wires. The cross-section of the wires coming from the secondary winding of the transformer to the terminals for connecting the battery must be at least 1 mm 2.
The ammeter shunt is a piece of high-resistance constantan wire about a centimeter long, the ends of which are sealed in copper strips. The length of the shunt wire is selected when calibrating the ammeter. I took the wire from the shunt of a burnt pointer tester. One end of the copper strips is soldered directly to the positive output terminal; a thick conductor coming from the contacts of relay P3 is soldered to the second strip. The yellow and red wires go to the pointer device from the shunt.
Printed circuit board of the charger automation unit
The circuit for automatic regulation and protection against incorrect connection of the battery to the charger is soldered on a printed circuit board made of foil fiberglass.
The photo shows the appearance of the assembled circuit. The printed circuit board design for the automatic control and protection circuit is simple, the holes are made with a pitch of 2.5 mm.
The photo above shows a view of the printed circuit board from the installation side with parts marked in red. This drawing is convenient when assembling a printed circuit board.
The printed circuit board drawing above will be useful when manufacturing it using laser printer technology.
And this drawing of a printed circuit board will be useful when applying current-carrying tracks of a printed circuit board manually.
Charger voltmeter and ammeter scale
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, print it on thick white paper and glue the moment on top of the standard scale with glue.
Thanks to the larger scale size and calibration of the device in the measurement area, the voltage reading accuracy was 0.2 V.
Wires for connecting the charger to the battery and network terminals
The wires for connecting the car battery to the charger are equipped with alligator clips on one side and split ends on the other side. The red wire is selected to connect the positive terminal of the battery, and the blue wire is selected to connect the negative terminal. The cross-section of the wires for connecting to the battery device must be at least 1 mm 2.
The charger is connected to the electrical network using a universal cord with a plug and socket, as is used to connect computers, office equipment and other electrical appliances.
About Charger Parts
Power transformer T1 is used type TN61-220, the secondary windings of which are connected in series, as shown in the diagram. Since the efficiency of the charger is at least 0.8 and the charging current usually does not exceed 6 A, any transformer with a power of 150 watts will do. The secondary winding of the transformer must provide a voltage of 18-20 V at a load current of up to 8 A. You can calculate the number of turns of the secondary winding of the transformer using a special calculator.
Capacitors C4-C9 type MBGCh for a voltage of at least 350 V. You can use capacitors of any type designed to operate in alternating current circuits.
Diodes VD2-VD5 are suitable for any type, rated for a current of 10 A. VD7, VD11 - any pulsed silicon ones. VD6, VD8, VD10, VD5, VD12 and VD13 are any that can withstand a current of 1 A. LED VD1 is any, VD9 I used type KIPD29. A distinctive feature of this LED is that it changes color when the connection polarity is changed. To switch it, contacts K1.2 of relay P1 are used. When charging with the main current, the LED lights up yellow, and when switching to the battery charging mode, it lights up green. Instead of a binary LED, you can install any two single-color LEDs by connecting them according to the diagram below.
The operational amplifier chosen is KR1005UD1, an analogue of the foreign AN6551. Such amplifiers were used in the sound and video unit of the VM-12 video recorder. The good thing about the amplifier is that it does not require two-polar power supply or correction circuits and remains operational at a supply voltage of 5 to 12 V. It can be replaced with almost any similar one. For example, LM358, LM258, LM158 are good for replacing microcircuits, but their pin numbering is different, and you will need to make changes to the printed circuit board design.
Relays P1 and P2 are any for a voltage of 9-12 V and contacts designed for a switching current of 1 A. P3 for a voltage of 9-12 V and a switching current of 10 A, for example RP-21-003. If there are several contact groups in the relay, then it is advisable to solder them in parallel.
Switch S1 of any type, designed to operate at a voltage of 250 V and having a sufficient number of switching contacts. If you don’t need a current regulation step of 1 A, then you can install several toggle switches and set the charging current, say, 5 A and 8 A. If you charge only car batteries, then this solution is completely justified. Switch S2 is used to disable the charge level control system. If the battery is charged with a high current, the system may operate before the battery is fully charged. In this case, you can turn off the system and continue charging manually.
Any electromagnetic head for a current and voltage meter is suitable, with a total deviation current of 100 μA, for example type M24. If there is no need to measure voltage, but only current, then you can install a ready-made ammeter designed for a maximum constant measuring current of 10 A, and monitor the voltage with an external dial tester or multimeter by connecting them to the battery contacts.
Setting up the automatic adjustment and protection unit of the automatic control unit
If the board is assembled correctly and all radio elements are in good working order, the circuit will work immediately. All that remains is to set the voltage threshold with resistor R5, upon reaching which the battery charging will be switched to low current charging mode.
The adjustment can be made directly while charging the battery. But still, it’s better to play it safe and check and adjust the automatic control and protection circuit of the automatic control unit before installing it in the case. To do this, you will need a DC power supply, which has the ability to regulate the output voltage in the range from 10 to 20 V, designed for an output current of 0.5-1 A. As for measuring instruments, you will need any voltmeter, pointer tester or multimeter designed to measure DC voltage, with a measurement limit from 0 to 20 V.
Checking the voltage stabilizer
After installing all the parts on the printed circuit board, you need to apply a supply voltage of 12-15 V from the power supply to the common wire (minus) and pin 17 of the DA1 chip (plus). By changing the voltage at the output of the power supply from 12 to 20 V, you need to use a voltmeter to make sure that the voltage at output 2 of the DA1 voltage stabilizer chip is 9 V. If the voltage is different or changes, then DA1 is faulty.
Microcircuits of the K142EN series and analogues have protection against short circuits at the output, and if you short-circuit its output to the common wire, the microcircuit will enter protection mode and will not fail. If the test shows that the voltage at the output of the microcircuit is 0, this does not always mean that it is faulty. It is quite possible that there is a short circuit between the tracks of the printed circuit board or one of the radio elements in the rest of the circuit is faulty. To check the microcircuit, it is enough to disconnect its pin 2 from the board and if 9 V appears on it, it means that the microcircuit is working, and it is necessary to find and eliminate the short circuit.
Checking the surge protection system
I decided to start describing the operating principle of the circuit with a simpler part of the circuit, which is not subject to strict operating voltage standards.
The function of disconnecting the charger from the mains in the event of a battery disconnection is performed by a part of the circuit assembled on an operational differential amplifier A1.2 (hereinafter referred to as the op-amp).
Operating principle of an operational differential amplifier
Without knowing the operating principle of the op-amp, it is difficult to understand the operation of the circuit, so I will give a brief description. The op-amp has two inputs and one output. One of the inputs, which is designated in the diagram by a “+” sign, is called non-inverting, and the second input, which is designated by a “–” sign or a circle, is called inverting. The word differential op-amp means that the voltage at the output of the amplifier depends on the difference in voltage at its inputs. In this circuit, the operational amplifier is switched on without feedback, in comparator mode – comparing input voltages.
Thus, if the voltage at one of the inputs remains unchanged, but changes at the second, then at the moment of transition through the point of equality of voltages at the inputs, the voltage at the output of the amplifier will change abruptly.
Testing the Surge Protection Circuit
Let's return to the diagram. The non-inverting input of amplifier A1.2 (pin 6) is connected to a voltage divider assembled across resistors R13 and R14. This divider is connected to a stabilized voltage of 9 V and therefore the voltage at the point of connection of the resistors never changes and is 6.75 V. The second input of the op-amp (pin 7) is connected to the second voltage divider, assembled on resistors R11 and R12. This voltage divider is connected to the bus through which the charging current flows, and the voltage on it changes depending on the amount of current and the state of charge of the battery. Therefore, the voltage value at pin 7 will also change accordingly. The divider resistances are selected in such a way that when the battery charging voltage changes from 9 to 19 V, the voltage at pin 7 will be less than at pin 6 and the voltage at the op-amp output (pin 8) will be more than 0.8 V and close to the op-amp supply voltage. The transistor will be open, voltage will be supplied to the winding of relay P2 and it will close contacts K2.1. The output voltage will also close diode VD11 and resistor R15 will not participate in the operation of the circuit.
As soon as the charging voltage exceeds 19 V (this can only happen if the battery is disconnected from the output of the charger), the voltage at pin 7 will become greater than at pin 6. In this case, the voltage at the op-amp output will abruptly decrease to zero. The transistor will close, the relay will de-energize and contacts K2.1 will open. The supply voltage to the RAM will be interrupted. At the moment when the voltage at the output of the op-amp becomes zero, diode VD11 opens and, thus, R15 is connected in parallel to R14 of the divider. The voltage at pin 6 will instantly decrease, which will eliminate false positives when the voltages at the op-amp inputs are equal due to ripple and interference. By changing the value of R15, you can change the hysteresis of the comparator, that is, the voltage at which the circuit will return to its original state.
When the battery is connected to the RAM, the voltage at pin 6 will again be set to 6.75 V, and at pin 7 it will be less and the circuit will begin to operate normally.
To check the operation of the circuit, it is enough to change the voltage on the power supply from 12 to 20 V and connect a voltmeter instead of relay P2 to observe its readings. When the voltage is less than 19 V, the voltmeter should show a voltage of 17-18 V (part of the voltage will drop across the transistor), and if it is higher, zero. It is still advisable to connect the relay winding to the circuit, then not only the operation of the circuit will be checked, but also its functionality, and by 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 op-amp output. If the voltages differ from those indicated above, you need to check the resistor values of the corresponding dividers. If the divider resistors and diode VD11 are working, then, therefore, the op-amp is faulty.
To check the circuit R15, D11, it is enough to disconnect one of the terminals of these elements; the circuit will work, only without hysteresis, that is, it turns on and off at the same voltage supplied from the power supply. Transistor VT12 can be easily checked by disconnecting one of the R16 pins and monitoring the voltage at the output of the op-amp. If the voltage at the output of the op-amp changes correctly, and the relay is always on, it means that there is a breakdown between the collector and emitter of the transistor.
Checking the battery shutdown circuit when it is fully charged
The operating principle of op amp A1.1 is no different from the operation of A1.2, with the exception of the ability to change the voltage cutoff threshold using trimming resistor R5.
The divider for the reference voltage is assembled on resistors R7, R8 and the voltage at pin 4 of the op-amp should be 4.5 V. This issue is discussed in more detail in the website article “How to charge a battery.”
To check the operation of A1.1, the supply voltage supplied from the power supply smoothly increases and decreases within 12-18 V. When the voltage reaches 15.6 V, relay P1 should turn off and contacts K1.1 switch the charger to low-current charging mode through a capacitor C4. When the voltage level drops below 12.54 V, the relay should turn on and switch the charger into charging mode with a current of a given value.
The switching threshold voltage of 12.54 V can be adjusted by changing the value of resistor R9, but this is not necessary.
Using switch S2, it is possible to disable the automatic operating mode by turning on relay P1 directly.
Capacitor charger circuit
without automatic shutdown
For those who do not have sufficient experience in assembling electronic circuits or do not need to automatically turn off the charger after charging the battery, I offer a simplified version of the device circuit for charging acid car batteries. A distinctive feature of the circuit is its simplicity for repetition, reliability, high efficiency and stable charging current, protection against incorrect battery connection, and automatic continuation of charging in the event of a loss of supply voltage.
The principle of stabilizing the charging current remains unchanged and is ensured by connecting a block of capacitors C1-C6 in series with the network transformer. To protect against overvoltage on the input winding and capacitors, one of the pairs of normally open contacts of relay P1 is used.
When the battery is not connected, the contacts of relays P1 K1.1 and K1.2 are open and even if the charger is connected to the power supply, no current flows to the circuit. The same thing happens if you connect the battery incorrectly according to polarity. When the battery is connected correctly, the current flows from it through the VD8 diode to the winding of relay P1, the relay is activated and its contacts K1.1 and K1.2 are closed. Through closed contacts K1.1, the mains voltage is supplied to the charger, and through K1.2 the charging current is supplied to the battery.
At first glance, it seems that relay contacts K1.2 are not needed, but if they are not there, then if the battery is connected incorrectly, current will flow from the positive terminal of the battery through the negative terminal of the charger, then through the diode bridge and then directly to the negative terminal of the battery and diodes the charger bridge will fail.
The proposed simple circuit for charging batteries can easily be adapted to charge batteries at a voltage of 6 V or 24 V. It is enough to replace relay P1 with the appropriate voltage. To charge 24-volt batteries, it is necessary to provide an output voltage from the secondary winding of transformer T1 of at least 36 V.
If desired, the circuit of a simple charger can be supplemented with a device for indicating charging current and voltage, turning it on as in the circuit of an automatic charger.
How to charge a car battery
automatic homemade memory
Before charging, the battery removed from the car must be cleaned of dirt and its surfaces wiped with an aqueous solution of soda to remove acid residues. If there is acid on the surface, then the aqueous soda solution foams.
If the battery has plugs for filling acid, then all the plugs must be unscrewed so that the gases formed in the battery during charging can escape freely. It is imperative to check the electrolyte level, and if it is less than required, add distilled water.
Next, you need to set the charge current using switch S1 on the charger and connect the battery, observing the polarity (the positive terminal of the battery must be connected to the positive terminal of the charger) to its terminals. If switch S3 is in the down position, the arrow on the charger will immediately show the voltage that the battery produces. All that remains is to insert the power cord plug into the socket and the battery charging process will begin. The voltmeter will already begin to show the charging voltage.
You can calculate the battery charging time using an online calculator, choose the optimal charging mode for the car battery and familiarize yourself with the rules of its operation by visiting the website article “How to charge the battery.”
Even with a fully functional car, sooner or later a situation may arise when you need an external source - a long parking period, side lights accidentally left on, and so on. Owners of old equipment are well aware of the need to regularly recharge the battery - this is due to the self-discharge of a “tired” battery and increased leakage currents in electrical circuits, primarily in the diode bridge of the generator.
You can purchase a ready-made charger: they Available in many variants and are easily accessible. But some may think that making a charger for a car battery with their own hands will be more interesting, while for others the ability to make a charger literally from scrap material will help them out.
Semiconductor diode + light bulb
It is not known who first came up with the idea of charging the battery in this way, but this is exactly the case when you can charge the battery literally with improvised means. In this circuit, the current source is a 220V electrical network, a diode is needed to convert alternating current into pulsating direct current, and the light bulb serves as a current-limiting resistor.
The calculation of this charger is as simple as its circuit:
- The current flowing through the lamp is determined based on its power as I=P/U, Where U– network voltage, P– lamp power. That is, for a 60 W lamp, the current in the circuit will be 0.27 A.
- Since the diode cuts off every second half-wave of the sinusoid, the real average load current, taking this into account, will be equal to 0.318*I.
As you can see, even when using a powerful lamp, the load current is small, which will allow the use of any common diode, for example 1N4004 (these usually come with alarm systems, are found in power supplies for low-power equipment, and so on). All you need to know to assemble such a device is that the stripe on the diode body indicates its cathode. Connect this contact to the positive terminal of the battery.
Do not connect this device to the battery unless it is removed from the vehicle to avoid high voltage damage to the on-board electronics!A similar manufacturing option is shown in the video
Rectifier
This memory is somewhat more complicated. This scheme is used in the cheapest factory devices:
To make a charger, you will need a mains transformer with an output voltage of at least 12.5 V, but not more than 14. Often a Soviet transformer of the TS-180 type is taken from tube TVs, which has two filament windings for a voltage of 6.3 V. When they are connected in series (the purpose of the terminals is indicated on the transformer body) we get exactly 12.6 V. A diode bridge (full-wave rectifier) is used to rectify the alternating current from the secondary winding. It can either be assembled from individual diodes (for example, D242A from the same TV), or you can buy a ready-made assembly (KBPC10005 or its analogues).
The rectifier diodes will heat up noticeably, and you will have to make a radiator for them from a suitable aluminum plate. In this regard, using a diode assembly is much more convenient - the plate is attached with a screw to its central hole using thermal paste.
Below is a diagram of the pin assignments of the TL494 microcircuit, the most common in switching power supplies:
We are interested in the circuit connected to pin 1. Looking through the traces connected to it on the board, find the resistor connecting this leg to the +12 V output. It is this that sets the output voltage of the 12-volt power supply circuit.
The topic of car chargers is of interest to many people. From this article you will learn how to convert a computer power supply into a full-fledged charger for car batteries. It will be a pulse charger for batteries with a capacity of up to 120 Ah, that is, charging will be quite powerful.
There is practically no need to assemble anything - you just need to remake the power supply. Only one component will be added to it.
A computer power supply has several output voltages. The main power buses have voltages of 3.3, 5 and 12 V. Thus, for the device to operate, you will need a 12-volt bus (yellow wire).
To charge car batteries, the output voltage should be around 14.5-15 V, therefore, 12 V from a computer power supply is clearly not enough. Therefore, the first step is to raise the voltage on the 12-volt bus to a level of 14.5-15 V.
Then, you need to assemble an adjustable current stabilizer or limiter so that you can set the required charge current.
The charger, one might say, will be automatic. The battery will be charged to the specified voltage with a stable current. As the charge progresses, the current will drop, and at the very end of the process it will be equal to zero.
When starting to manufacture a device, you need to find a suitable power supply. For these purposes, blocks containing the TL494 PWM controller or its full-fledged analog K7500 are suitable.
When the required power supply is found, you need to check it. To start the unit, you need to connect the green wire to any of the black wires.
If the unit starts up, you need to check the voltage on all buses. If everything is in order, then you need to remove the board from the tin case.
After removing the board, you need to remove all wires except two black, two green and go to start the unit. It is recommended to solder the remaining wires with a powerful soldering iron, for example, 100 W.
This step will require your full attention, as this is the most important point in the entire remodel. You need to find the first pin of the microcircuit (in the example there is a 7500 chip), and find the first resistor that is applied from this pin to the 12 V bus.
There are many resistors located on the first pin, but finding the right one will not be difficult if you test everything with a multimeter.
After finding the resistor (in the example it is 27 kOhm), you need to unsolder only one pin. To avoid confusion in the future, the resistor will be called Rx.
Now you need to find a variable resistor, say 10 kOhm. Its power is not important. You need to connect 2 wires about 10 cm long each in this way:
One of the wires must be connected to the soldered terminal of the Rx resistor, and the second must be soldered to the board in the place from which the terminal of the Rx resistor was soldered. Thanks to this adjustable resistor, it will be possible to set the required output voltage.
A charge current stabilizer or limiter is a very important addition that should be included in every charger. This unit is made on the basis of an operational amplifier. Almost any “ops” will do here. The example uses the budget LM358. There are two elements in the body of this microcircuit, but only one of them is needed.
A few words about the operation of the current limiter. In this circuit, an op-amp is used as a comparator that compares the voltage across a low-value resistor to a reference voltage. The latter is set using a zener diode. And the adjustable resistor now changes this voltage.
When the voltage value changes, the op amp will try to smooth out the voltage at the inputs and will do this by decreasing or increasing the output voltage. Thus, the “op-amp” will control the field-effect transistor. The latter regulates the output load.
A field-effect transistor needs a powerful one, since all the charging current will pass through it. The example uses IRFZ44, although any other appropriate parameter can be used.
The transistor must be installed on a heat sink, because at high currents it will heat up quite well. In this example, the transistor is simply attached to the power supply housing.
The printed circuit board was wired hastily
, but it turned out pretty good.Now all that remains is to connect everything according to the picture and begin installation.
The voltage is set to around 14.5 V. The voltage regulator does not need to be brought outside. For control on the front panel there is only a charge current regulator, and a voltmeter is also not needed, since the ammeter will show everything that needs to be seen when charging.
You can take a Soviet analog or digital ammeter.
Also on the front panel was a toggle switch for starting the device and output terminals. The project can now be considered complete.
The result is an easy-to-manufacture and inexpensive charger that you can safely replicate yourself.
Attached files
:In order for a car to start, it needs energy. This energy is taken from the battery. As a rule, it is recharged from the generator while the engine is running. When the car is not used for a long time or the battery is faulty, it discharges to such a state that that the car can no longer start. In this case, external charging is required. You can buy such a device or assemble it yourself, but for this you will need a charger circuit.
How a car battery works
A car battery supplies power to various devices in the car when the engine is turned off and is designed to start it. By type of execution, a lead-acid battery is used. Structurally, it is assembled from six batteries with a nominal voltage of 2.2 volts, connected in series. Each element is a set of lattice plates made of lead. The plates are coated with active material and immersed in an electrolyte.
The electrolyte solution contains distilled water and sulfuric acid. The frost resistance of the battery depends on the density of the electrolyte. Recently, technologies have emerged that allow the electrolyte to be adsorbed in glass fiber or thickened using silica gel to a gel-like state.
Each plate has a negative and positive pole, and they are isolated from each other using a plastic separator. The body of the product is made of propylene, which is not destroyed by acid and serves as a dielectric. The positive pole of the electrode is coated with lead dioxide, and the negative with sponge lead. Recently, rechargeable batteries with electrodes made of lead-calcium alloy have begun to be produced. These batteries are completely sealed and require no maintenance.
When a load is connected to the battery, the active material on the plates reacts chemically with the electrolyte solution and produces an electric current. The electrolyte depletes over time due to the deposition of lead sulfate on the plates. The battery begins to lose charge. During the charging process, a chemical reaction occurs in the reverse order, lead sulfate and water are converted, the density of the electrolyte increases and the charge is restored.
Batteries are characterized by their self-discharge value. It occurs in the battery when it is inactive. The main reason is contamination of the battery surface and poor quality of the distiller. The rate of self-discharge accelerates when the lead plates are destroyed.
Types of chargers
A large number of car charger circuits have been developed using different element bases and fundamental approaches. According to the principle of operation, charging devices are divided into two groups:
- Starting chargers, designed to start the engine when the battery is not working. By briefly supplying a large current to the battery terminals, the starter is turned on and the engine starts, and then the battery is charged from the car's generator. They are produced only for a certain current value or with the ability to set its value.
- Pre-start chargers, leads from the device are connected to the battery terminals and current is supplied for a long time. Its value does not exceed ten amperes, during which time the battery energy is restored. In turn, they are divided into: gradual (charging time from 14 to 24 hours), accelerated (up to three hours) and conditioning (about an hour).
Based on their circuit design, pulse and transformer devices are distinguished. The first type uses a high-frequency signal converter and is characterized by small size and weight. The second type uses a transformer with a rectifier unit as a basis; it is easy to manufacture, but have a lot of weight and low efficiency (efficiency).
Whether you made a charger for car batteries yourself or purchased it at a retail outlet, the requirements for it are the same, namely:
- output voltage stability;
- high efficiency value;
- short circuit protection;
- charge control indicator.
One of the main characteristics of the charger is the amount of current that charges the battery. Correctly charging the battery and extending its performance characteristics can only be achieved by selecting the desired value. The charging speed is also important. The higher the current, the higher the speed, but a high speed value leads to rapid degradation of the battery. It is believed that the correct current value will be a value equal to ten percent of the battery capacity. Capacity is defined as the amount of current supplied by the battery per unit of time; it is measured in ampere-hours.
Homemade charger
Every car enthusiast should have a charging device, so if there is no opportunity or desire to purchase a ready-made device, there is nothing left to do but charge the battery yourself. It is easy to make with your own hands both the simplest and multifunctional devices. For this you will need a diagram and a set of radioelements. It is also possible to convert an uninterruptible power supply (UPS) or computer unit (AT) into a device for recharging the battery.
Transformer charger
This device is the easiest to assemble and does not contain scarce parts. The circuit consists of three nodes:
- transformer;
- rectifier block;
- regulator
Voltage from the industrial network is supplied to the primary winding of the transformer. The transformer itself can be used of any type. It consists of two parts: the core and the windings. The core is assembled from steel or ferrite, the windings are made from conductor material.
The operating principle of the transformer is based on the appearance of an alternating magnetic field when current passes through the primary winding and transfers it to the secondary. To obtain the required voltage level at the output, the number of turns in the secondary winding is made smaller compared to the primary. The voltage level on the secondary winding of the transformer is selected to be 19 volts, and its power should provide a threefold reserve of charging current.
From the transformer, the reduced voltage passes through the rectifier bridge and goes to a rheostat connected in series to the battery. The rheostat is designed to regulate the voltage and current by changing the resistance. The rheostat resistance does not exceed 10 Ohms. The amount of current is controlled by an ammeter connected in series in front of the battery. With such a circuit it will not be possible to charge a battery with a capacity of more than 50 Ah, since the rheostat begins to overheat.
You can simplify the circuit by removing the rheostat, and install a set of capacitors at the input in front of the transformer, which are used as reactance to reduce the network voltage. The lower the nominal value of the capacitance, the less voltage is supplied to the primary winding in the network.
The peculiarity of such a circuit is that it is necessary to ensure a signal level on the secondary winding of the transformer that is one and a half times greater than the operating voltage of the load. This circuit can be used without a transformer, but it is very dangerous. Without galvanic isolation, you can get an electric shock.
Pulse charger
The advantage of pulsed devices is their high efficiency and compact size. The device is based on a pulse-width modulation (PWM) chip. You can assemble a powerful pulse charger with your own hands according to the following scheme.
The IR2153 driver is used as a PWM controller. After the rectifier diodes, a polar capacitor C1 with a capacity in the range of 47–470 μF and a voltage of at least 350 volts is placed in parallel with the battery. The capacitor removes mains voltage surges and line noise. The diode bridge is used with a rated current of more than four amperes and with a reverse voltage of at least 400 volts. The driver controls powerful N-channel field-effect transistors IRFI840GLC installed on radiators. The current of such charging will be up to 50 amperes, and the output power will be up to 600 watts.
You can make a pulse charger for a car with your own hands using a converted AT format computer power supply. They use the common TL494 microcircuit as a PWM controller. The modification itself consists of increasing the output signal to 14 volts. To do this, you will need to correctly install the trimmer resistor.
The resistor that connects the first leg of the TL494 to the stabilized + 5 V bus is removed, and instead of the second one, connected to the 12 volt bus, a variable resistor with a nominal value of 68 kOhm is soldered in. This resistor sets the required output voltage level. The power supply is turned on via a mechanical switch, according to the diagram indicated on the power supply housing.
Device on LM317 chip
A fairly simple but stable charging circuit is easily implemented on the LM317 integrated circuit. The microcircuit provides a signal level of 13.6 volts with a maximum current of 3 amperes. The LM317 stabilizer is equipped with built-in short circuit protection.
Voltage is supplied to the device circuit through the terminals from an independent DC power supply of 13-20 volts. The current, passing through the indicator LED HL1 and transistor VT1, is supplied to the stabilizer LM317. From its output directly to the battery via X3, X4. The divider assembled on R3 and R4 sets the required voltage value for opening VT1. Variable resistor R4 sets the charging current limit, and R5 sets the output signal level. The output voltage is adjustable from 13.6 to 14 volts.
The circuit can be simplified as much as possible, but its reliability will decrease.
In it, resistor R2 selects the current. A powerful nichrome wire element is used as a resistor. When the battery is discharged, the charging current is maximum, the VD2 LED lights up brightly; as the battery charges, the current begins to decrease and the LED dims.
Charger from an uninterruptible power supply
The rectifier is assembled using any powerful diodes, for example, domestic D-242 and a network capacitor of 2200 uF for 35-50 volts. The output will be a signal with a voltage of 18-19 volts. An LT1083 or LM317 microcircuit is used as a voltage stabilizer and must be installed on a radiator.
By connecting the battery, the voltage is set to 14.2 volts. It is convenient to control the signal level using a voltmeter and ammeter. The voltmeter is connected in parallel to the battery terminals, and the ammeter in series. As the battery charges, its resistance will increase and the current will decrease. It’s even easier to make the regulator using a triac connected to the primary winding of the transformer like a dimmer.
When making a device yourself, you should remember about electrical safety when working with a 220 V AC network. As a rule, a correctly made charging device made from serviceable parts starts working immediately, you just need to set the charging current.
I made this charger to charge car batteries, the output voltage is 14.5 volts, the maximum charge current is 6 A. But it can also charge other batteries, for example lithium-ion ones, since the output voltage and output current can be adjusted within a wide range. The main components of the charger were purchased on the AliExpress website.
These are the components:
You will also need an electrolytic capacitor 2200 uF at 50 V, a transformer for the TS-180-2 charger (see how to solder the TS-180-2 transformer), wires, a power plug, fuses, a radiator for the diode bridge, crocodiles. You can use another transformer with a power of at least 150 W (for a charging current of 6 A), the secondary winding must be designed for a current of 10 A and produce a voltage of 15 - 20 volts. The diode bridge can be assembled from individual diodes designed for a current of at least 10A, for example D242A.
The wires in the charger should be thick and short. The diode bridge must be mounted on a large radiator. It is necessary to increase the radiators of the DC-DC converter, or use a fan for cooling.
Charger assembly
Connect a cord with a power plug and a fuse to the primary winding of the TS-180-2 transformer, install the diode bridge on the radiator, connect the diode bridge and the secondary winding of the transformer. Solder the capacitor to the positive and negative terminals of the diode bridge.
Connect the transformer to a 220 volt network and measure the voltages with a multimeter. I got the following results:
- The alternating voltage at the terminals of the secondary winding is 14.3 volts (mains voltage 228 volts).
- The constant voltage after the diode bridge and capacitor is 18.4 volts (no load).
Using the diagram as a guide, connect a step-down converter and a voltammeter to the DC-DC diode bridge.
Setting the output voltage and charging current
There are two trimming resistors installed on the DC-DC converter board, one allows you to set the maximum output voltage, the other allows you to set the maximum charging current.
Plug in the charger (nothing is connected to the output wires), the indicator will show the voltage at the device output and the current is zero. Use the voltage potentiometer to set the output to 5 volts. Close the output wires together, use the current potentiometer to set the short circuit current to 6 A. Then eliminate the short circuit by disconnecting the output wires and use the voltage potentiometer to set the output to 14.5 volts.
This charger is not afraid of a short circuit at the output, but if the polarity is reversed, it may fail. To protect against polarity reversal, a powerful Schottky diode can be installed in the gap in the positive wire going to the battery. Such diodes have a low voltage drop when connected directly. With such protection, if the polarity is reversed when connecting the battery, no current will flow. True, this diode will need to be installed on a radiator, since a large current will flow through it during charging.
Suitable diode assemblies are used in computer power supplies. This assembly contains two Schottky diodes with a common cathode; they will need to be parallelized. For our charger, diodes with a current of at least 15 A are suitable.
It must be taken into account that in such assemblies the cathode is connected to the housing, so these diodes must be installed on the radiator through an insulating gasket.
It is necessary to adjust the upper voltage limit again, taking into account the voltage drop across the protection diodes. To do this, use the voltage potentiometer on the DC-DC converter board to set 14.5 volts measured with a multimeter directly at the output terminals of the charger.
How to charge the battery
Wipe the battery with a cloth soaked in soda solution, then dry. Remove the plugs and check the electrolyte level; if necessary, add distilled water. The plugs must be turned out during charging. No debris or dirt should get inside the battery. The room in which the battery is charged must be well ventilated.
Connect the battery to the charger and plug in the device. During charging, the voltage will gradually increase to 14.5 volts, the current will decrease over time. The battery can be conditionally considered charged when the charging current drops to 0.6 - 0.7 A.