Car battery charger with adjustment circuit. Circuit diagram of a charger for a car battery - from simple to complex. Adjustable circuits
Now there is no point in collecting it yourself Charger for car batteries: stores have a huge selection of ready-made devices, 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 car battery It is quite possible to assemble it from scrap parts, and its price will be a pittance.
The only thing you should immediately warn about is that circuits without precise regulation of the current and voltage at the output, which do not have a current cutoff at the end of charging, are suitable for charging only lead-acid batteries. For AGM and the use of such charges leads to damage to the battery!
How to make a simple transformer device
The circuit of this transformer charger is primitive, but functional and 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 rated AC voltage multiplied by the root of two, then with 10V on the transformer winding we get 14.1V at the output of the charger. You can take any diode bridge with a direct current of more than 5 amperes or assemble it from four separate diodes; a measuring ammeter is also 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 disadvantage: due to the fact that it has neither adjustment nor automatic shutdown, it can be used to “reanimate” 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 filament transformer turns up. However, its output windings have a voltage of 6.3V, so you will have to connect two in series, winding 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 electronically regulated charger
However, you can do without rewinding by adding an electronic output voltage stabilizer to the circuit. In addition, such a circuit will be more convenient for garage use, since it will allow you to adjust the charge current during power supply voltage drops; it is also used for small-capacity car batteries, if necessary.
The role of the regulator here is played by the composite transistor KT837-KT814, the variable resistor regulates the current at the output of the device. When assembling the charger, the 1N754A zener diode can be replaced with the Soviet D814A.
The variable charger circuit is easy to replicate and can be easily assembled without the need to etch the printed circuit board. However, keep in mind that field-effect transistors are placed on a radiator, the heating of which will be noticeable. It's more convenient to use the old one computer cooler by connecting its fan to the charger outputs. Resistor R1 must have a power of at least 5 W; it is easier to wind it from nichrome or fechral yourself or connect 10 one-watt 10 ohm resistors in parallel. You don’t have to install it, but we must not forget that it protects the transistors in the event of a short circuit.
When choosing a transformer, focus on an output voltage of 12.6-16V; take either a filament transformer by connecting two windings in series, or select a ready-made model with the desired voltage.
Video: The simplest battery charger
Remaking a laptop charger
However, you can do without searching for a transformer if you have an unnecessary laptop charger at hand - with a simple modification we will get a compact and lightweight pulse block power supply capable of charging car batteries. Since we need to get an output voltage of 14.1-14.3 V, no ready-made power supply will work, but the conversion is simple.
Let's look at the site standard scheme, according to which devices of this kind are assembled:
In them, maintaining a stabilized voltage is carried out by a circuit from the TL431 microcircuit that controls the 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, tells 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 do with your own hands.
Having opened the charger, we find not far from the output connector TL431 and two resistors connected to the Ref. It is more convenient to adjust the upper arm of the divider (resistor R13 in the diagram): by decreasing the resistance, we reduce the voltage at the output of the charger; by increasing it, we raise it. If we have a 12 V charger, we will need a resistor with a higher resistance, if the charger is 19 V, then with a smaller one.
Video: Charging for car batteries. Protection against short circuit and reverse polarity. With your own hands
We unsolder the resistor and instead install a trimmer, pre-set on the multimeter to the same resistance. Then, having connected a load (a light bulb from a headlight) to the output of the charger, we turn it on to the network and smoothly rotate the trimmer motor, while simultaneously controlling the voltage. As soon as we get the voltage within 14.1-14.3 V, we disconnect the charger from the network, fix the trimmer resistor slide with nail polish (at least for nails) and put the case back together. 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 diagram shown, two parallel resistors are used for this (thus obtaining a resistance that is outside the standard series). We also need to solder a trimmer instead and adjust the output to the desired voltage. Here is an example of one of these boards:
By checking, we can understand that we are interested in the single resistor R32 on this board (circled in red) - we need to solder it.
There are often similar recommendations on the Internet on how to make a homemade charger from computer unit nutrition. But keep in mind that all of them are essentially reprints of old articles from the early 2000s, and such recommendations are not applicable to more or less modern power supplies. In them it is no longer possible to simply raise the 12 V voltage to the required value, since other output voltages are also controlled, and they will inevitably “float away” with such a 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 conversion.
How does the battery charge? Is the circuit of this device complicated or not, in order to make the device with your own hands? Is it fundamentally different from what is used for mobile phones? We will try to answer all the questions posed further in the article.
General information
The battery plays very well important role in the functioning of devices, units and mechanisms that require electricity to operate. So, in vehicles it helps to start the car engine. And in mobile phones batteries allow us to make calls.
Charging a battery, the circuit and principles of operation of this device are discussed even in a school physics course. But, alas, by the time they graduate, much of this knowledge is forgotten. Therefore, we hasten to remind you that the operation of a battery is based on the principle of a voltage difference (potential) between two plates, which are specially immersed in an electrolyte solution.
The first batteries were copper-zinc. But since then they have improved and modernized significantly.
How does a battery work?
The only visible element of any device is the case. It provides commonality and integrity to the design. It should be noted that the name “battery” can be fully applied to only one battery cell (they are also called banks), and for the same standard 12 V car battery there are only six of them.
Let's return to the body. Strict demands are placed on him. So, it should be:
- resistant to aggressive chemicals;
- able to withstand significant temperature fluctuations;
- with good vibration resistance.
All these requirements are met by modern synthetic material - polypropylene. More detailed differences should only be highlighted when working with specific samples.
Principle of operation
We'll look at lead-acid batteries as an example.
When there is a load on the terminal, a chemical reaction begins to occur, which is accompanied by the release of electricity. Over time, the battery will drain. How is it restored? Is there a simple diagram?
Charging a battery is not difficult. It is necessary to carry out the reverse process - electricity is supplied to the terminals, chemical reactions occur again (pure lead is restored), which in the future will allow the use of the battery.
Also, during charging, the density of the electrolyte increases. Thus, the battery restores its original properties. The better the technology and materials used in manufacturing, the more charge/discharge cycles the battery can withstand.
What electrical circuits for charging batteries exist?
The classic device is made of a rectifier and transformer. If we consider the same car batteries with a voltage of 12 V, then the chargers for them have a constant current of approximately 14 V.
Why is this so? This voltage is necessary so that current can flow through a discharged car battery. If he himself has 12 V, then a device of the same power will not be able to help him, so they take more high values. But in everything you need to know when to stop: if you increase the voltage too much, it will have a detrimental effect on the service life of the device.
Therefore, if you want to make a device with your own hands, you need to look for suitable charging schemes for car batteries for cars. The same applies to other technology. If a charging circuit is needed, then a 4 V device is needed and no more.
Recovery process
Let's say you have a circuit for charging a battery from a generator, according to which the device was assembled. The battery is connected and the recovery process begins immediately. As it progresses, the devices will grow. The charging current will drop along with it.
When the voltage approaches the maximum possible value, this process practically does not occur at all. This indicates that the device has successfully charged and can be turned off.
It is necessary to ensure that the battery current is only 10% of its capacity. Moreover, it is not recommended to either exceed this figure or reduce it. So, if you follow the first path, the electrolyte will begin to evaporate, which will significantly affect the maximum capacity and operating time of the battery. On the second path, the necessary processes will not occur at the required intensity, which is why the negative processes will continue, although to a somewhat lesser extent.
Charger
The described device can be purchased or assembled with your own hands. For the second option we will need electrical circuits charging batteries. The choice of technology by which it will be made should depend on which batteries are the target. You will need the following components:
- (designed on ballast capacitors and a transformer). The higher the indicator can be achieved, the greater the current will be. In general, this should be enough for charging to work. But the reliability of this device is very low. So, if the contacts are broken or something is mixed up, then both the transformer and the capacitors will fail.
- Protection in case of connecting the “wrong” poles. To do this, you can construct a relay. So, the conditional connection is based on a diode. If you confuse plus and minus, it will not pass current. And since there is a relay connected to it, it will be de-energized. Moreover, this circuit can be used with a device based on both thyristors and transistors. It must be connected to the break in the wires with which the charging itself is connected to the battery.
- Automation that battery charging should have. The circuit in this case must ensure that the device will work only when it is really needed. To do this, resistors change the response threshold of the control diode. 12 V batteries are considered to be fully rated when their voltage is within 12.8 V. Therefore, this indicator is desirable for this circuit.
Conclusion
So we looked at what battery charging is. The circuit of this device can be made on a single board, but it should be noted that this is quite complicated. That's why they are made multi-layered.
Within the framework of the article, various circuit diagrams, which make it clear how batteries are actually charged. But it is necessary to understand that these are only general images, and more detailed ones, with indications of ongoing chemical reactions, are specific to each type of battery.
The battery receives a charge in the car from the generator while driving vehicle. However, as a safety element, the electrical circuit includes a monitoring relay, which ensures the output voltage from the generator at a level of 14 ±0.3V.
Since it is known that the sufficient level to fully and quickly charge the battery should be 14.5 V, it is obvious that the battery will need help to fill the entire capacity. In this case, you will either need a store-bought device, or you will need to make a charger for a car battery yourself at home.
In the warm season, even a half-discharged car battery will allow you to start the engine. During frosts, the situation is worse, because at negative temperatures the capacity decreases, and at the same time the inrush currents increase. Due to the increase in viscosity of cold oil, more force is required to spin the crankshaft. This means that in the cold season the battery needs maximum charge.
A large number of different options for homemade chargers allows you to choose a circuit for different levels of knowledge and skill of the manufacturer. There is even an option in which the car is manufactured using a powerful diode and an electric heater. A two-kilowatt heater connected to a 220 V household network, in a series circuit with a diode and battery, will give the latter a little more than 4 A of current. Overnight the circuit will “crank up” 15 kW, but the battery will receive a full charge. Although the overall efficiency of the system is unlikely to exceed 1%.
Those who are planning to make a simple do-it-yourself battery charger with transistors should be aware that such devices can overheat significantly. They also have problems with incorrect polarity and accidental short circuits.
For thyristor and triac circuits, the main problems are charge stability and noise. The downside is also radio interference, which can be eliminated with a ferrite filter, and polarity problems.
You can find many proposals for converting a computer power supply into a homemade battery charger. But you need to know that although block diagrams These devices are similar, but the electrical ones have significant differences. For proper rework, you will need sufficient experience in working with circuits. Blind copying during such alterations does not always lead to the desired result.
Schematic diagram of capacitors
The most interesting may be the capacitor circuit of a homemade charger for a car battery. It has high efficiency, does not overheat, produces a stable current, regardless of the charge level of the battery and possible problems with network fluctuations, and also withstands short-term short circuits.
Visually the picture seems too bulky, but detailed analysis all areas become clear. It is even equipped with a shutdown algorithm when the battery is fully charged.
Current limiter
For capacitor charging, regulation of current strength and its stability is ensured by sequential connection of the transformer winding with ballast capacitors. In this case, a direct relationship is observed between the battery charging current and the capacitor capacity. Increasing the latter, we get a larger amperage.
Theoretically, this circuit can already work as a battery charger, but the problem will be its reliability. Weak contact with the battery electrodes will destroy unprotected transformers and capacitors.
Any student studying physics will be able to calculate the required capacitance for capacitors C=1/(2πvU). However, it will be faster to do this using a pre-prepared table:
You can reduce the number of capacitors in the circuit. To do this, they are connected in groups or using switches (toggle switches).
Reverse polarity protection in charger
To avoid problems when reversing the polarity of the contacts, the circuit contains relay P3. Incorrectly connected wires will be protected by the VD13 diode. It will not allow current to flow in the wrong direction and will not allow contact K3.1 to close; accordingly, the wrong charge will not flow to the battery.
If the polarity is correct, the relay will close and charging will begin. This circuit can be used on any type of homemade charging devices, even with thyristors or transistors.
Switch S3 controls the voltage in the circuit. The lower circuit gives the voltage value (V), and with the upper connection of the contacts we get the current level (A). If the device is connected only to the battery without being connected to a household network, then you can find out the battery voltage in the corresponding switch position. The head is an M24 microammeter.
Automation for homemade charging
We select a nine-volt circuit 142EN8G as the power supply for the amplifier. This choice is justified by its characteristics. Indeed, with temperature fluctuations of the board case even by ten degrees, the voltage fluctuations at the device output are reduced to an error of hundredths of a volt.
Self-shutdown is triggered at a voltage parameter of 15.5 V. This part of the circuit is marked A1.1. The fourth pin of the microcircuit (4) is connected to the divider R8, R7 where a voltage of 4.5 V is output to it. The other divider is connected to resistors R4-R5-R6. As a setting for this circuit, the adjustment of resistor R5 is used to indicate the level of excess. Using R9 in the microcircuit, the lower level of switching on the device is controlled, which is carried out at 12.5 V. Resistor R9 and diode VD7 provide a voltage range for uninterrupted charging operation.
The operating algorithm of the circuit is quite simple. By connecting to the charger, the voltage level is monitored. If it is below 16.5 V, then the circuit sends a command to open transistor VT1, which, in turn, starts the connection of relay P1. After this, the primary winding of the installed transformer is connected, and the battery charging process is started.
After dialing full capacity and obtaining the output voltage parameter at a level of 16.5 V, then the voltage in the circuit is reduced in order to keep transistor VT1 open. The relay switches off. The current supply to the terminals is reduced to half an amp. The charging cycle starts again only after the voltage at the battery terminals drops to 12.5 V, then the charging supply is resumed.
This is how the machine controls the possibility of not recharging the battery. The circuit can be left in working condition even for several months. This option will be especially relevant for those who use the car seasonally.
Charger layout
The body of such a device can be a VZ-38 milliammeter. We remove unnecessary insides, leaving only the dial indicator. We install everything except the machine using a hinged method.
The electrical appliance consists of a pair of panels (front and back), which are fixed using perforated carbon horizontal beams. Through such holes it is convenient to attach any structural elements. A two-millimeter aluminum plate is used to position the power transformer. It is attached with self-tapping screws to the bottom of the device.
A fiberglass plate with relays and capacitors is mounted on the upper plane. A circuit board with automation is also attached to the perforated ribs. Relays and capacitors of this element are connected using a standard connector.
A radiator on the rear wall will help reduce the heating of the diodes. It would be appropriate to place fuses and a powerful plug in this area. It can be taken from the computer's power supply. To clamp the power diodes we use two clamping bars. Their use will allow rational use of space and reduce heat generation inside the unit.
It is advisable to carry out installation using intuitive wire colors. We take red as positive, blue for negative, and highlight the alternating voltage using, for example, brown. The cross-section in all cases should be more than 1 mm.
The ammeter readings are calibrated using a shunt. One of its ends is soldered to the contact of relay P3, and the second is soldered to the positive output terminal.
Components
Let's look at the insides of the device, which form the basis of the charger.
Printed circuit board
Fiberglass is the basis for the printed circuit board, which acts as protection against voltage surges and connection problems. The image is formed with a step of 2.5 mm. Without any problems, this circuit can be made at home.
Location of elements in reality 
Soldering layout 
Board for manual soldering
There is even a schematic plan with highlighted elements on it. A clean image is applied to a substrate using powder printing on laser printers. For the manual method of applying tracks, another image is suitable.
Graduation scale
The indication of the installed VZ-38 milliammeter does not correspond to the actual readings given by the device. To make adjustments and correct graduation, it is necessary to glue a new scale to the base of the indicator behind the arrow.
The updated information will correspond to reality with an accuracy of 0.2 V.
Connecting cables
The contacts that will connect to the battery must have a spring clip with teeth (“crocodile”) at the ends. To distinguish between the poles, it is advisable to immediately select the positive part in red, and take the negative cable with a clamp in blue or black.
The cable cross-section must be more than 1 mm. To connect to a household network, a standard non-separable cable with a plug from any old office equipment is used.
Electrical components for homemade battery charging
TN 61-220 is suitable as a power transformer, because the output current will be at the level of 6 A. For capacitors, the voltage must be more than 350 V. For the circuit for C4 to C9 we take the MBGC type. Diodes from 2 to 5 are needed to withstand a ten-amp current. The 11th and 7th can be taken with any impulse ones. VD1 is an LED, and the 9th one can be an analogue of KIPD29.
For the rest, you need to focus on the input parameter that allows a current of 1A. In relay P1, you can use two LEDs with different color characteristics, or you can use a binary LED.
AN6551 operational amplifier can be replaced domestic analogue KR1005UD1. They can be found in old audio amplifiers. The first and second relays are selected from the range of 9-12 V and a current of 1 A. For several contact groups in the relay device, we use paralleling.
Setup and launch
If everything is done without errors, the circuit will work immediately. We adjust the threshold voltage using resistor R5. It will help transfer the charge to correct mode low currents.
Car owners often face a problem battery discharge. If this happens far from service stations, auto shops and gas stations, you can independently make a device for charging the battery from available parts. Let's look at how to make a charger for a car battery with your own hands, having minimal knowledge of electrical installation work.
This device is best used only in critical situations. However, if you are familiar with electrical engineering, electrical and fire safety rules, and have skills in electrical measurements and installation work, a homemade charger can easily 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 vehicle'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 from 13.5 to 14.5 Volts.
To fully charge, you need to drive the car for at least 30 kilometers, or about half an hour in city traffic.
The voltage of a normally charged battery during parking should be at least 12.5 Volts. If the voltage is less than 11.5 Volts, the car engine may not start during the start. Reasons for battery discharge:
- The battery has significant wear ( more than 5 years of operation);
- improper operation of the battery, leading to sulfation of the plates;
- long-term parking of the vehicle, especially in the cold season;
- urban rhythm of car driving with frequent stops when the battery does not have time to charge sufficiently;
- leaving the car's electrical appliances on while parked;
- damage to the electrical wiring and equipment of the vehicle;
- leaks in electrical circuits.
Many car owners do not have the means to measure battery voltage in their on-board tool kit ( voltmeter, multimeter, probe, scanner). In this case, you can be guided by indirect signs of battery discharge:
- dim glow of light bulbs dashboard when the ignition is turned on;
- lack of starter rotation when starting the engine;
- loud clicks in the starter area, lights on the dashboard going out when starting;
- complete lack of reaction from the car when the ignition is turned on.
If the listed symptoms appear, first of all you need 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” the car from another car. If these methods do not help or are not possible, you have to use a charger.
DIY universal charger. 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 Ah, the charging current of a car battery will be 10 Amperes. The battery will have to be charged for about 10 hours until it is fully charged.
Charging a car battery with high currents can lead to the sulfation process. 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, which allows you to restore battery functionality. It consists of sequential charge-discharge with pulsed currents according to a special algorithm.
When charging the battery, do not allow it to overcharge. It can lead to boiling of the electrolyte and sulfation of the plates. It is necessary that the device has its own control system, parameter measurement and emergency shutdown.
Since the 2000s, special types began to be installed on cars batteries: AGM and gel. Charging a car battery of these types differs from the normal mode.
As a rule, it is three-stage. Up to a certain level, the charge occurs with a large current. Then the current decreases. The final charge occurs with even smaller pulse 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 is discovered that the battery is discharged. What can be done in such a situation when there is no soldering iron at hand, no parts, but you need to start it?
Usually the battery has a small capacity left; it just needs to be “tightened 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, for example, a laptop, can help.
Charging from a laptop power supply
The voltage produced by the laptop power supply is usually 19 Volts, the current is up to 10 Amps. This is enough to charge the battery. But you CANNOT connect the power supply directly to the battery. It is necessary to include a limiting resistance in series in the charging circuit. You can use a car light bulb as it, better for interior lighting. It can be purchased at your nearest gas station.
Typically the middle pin of the connector is positive. A light bulb is connected to it. The + battery is connected to the second terminal of the light bulb.
The negative terminal is connected to the negative terminal of the power supply. The power supply usually has a label indicating the polarity of the connector. A couple of hours of charging using this method is enough to start the engine.
Circuit diagram of a simple charger for a car battery.
Charge from a household network
A more extreme charging method is directly from a household outlet. It is used only in a critical situation, using maximum electrical safety measures. To do this you will 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. During this time, it is better to turn off the voltage supplied to the apartment. The diagram is shown in the figure.
The charging current with a lamp power of 100 Watts will be approximately 0.5 A. Overnight the battery will be recharged for only a few ampere-hours, but this may be enough to start. If you connect three lamps in parallel, the battery will charge three times more. If you connect an electric stove instead of a light bulb ( at the lowest power), then the charging time will be significantly reduced, but this is very dangerous. In addition, the diode may break through, then the battery may short out. Charging methods from 220 V are dangerous.
DIY car battery charger. Video:
Homemade car battery charger
Before making a charger for a car battery, you should evaluate your experience in electrical installation work and knowledge of electrical engineering, and based on this, proceed to choosing a charger circuit for a car battery.
You can look in the garage to see if there are old devices or units. A power supply from an old computer is suitable for the device. It has almost everything:
- 220 V connector;
- power switch;
- electrical circuit;
- cooling Fan;
- connection terminals.
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 resistance value in the feedback circuit ( about 1 kiloohm).
There is no need to install a limiting resistance; the electronic circuit will independently regulate the charge current within 2 Amperes. It is easy to calculate that it will take about a day to fully charge a 50 A*h battery. Appearance devices.
You can pick up or buy at a flea market a network transformer with a secondary winding voltage from 15 to 30 Volts. These were used in old TVs.
Transformer devices
The simplest circuit diagram of a device with a transformer.
Its disadvantage is the need to limit the current in the output circuit and the associated big losses power and resistor heating. Therefore, capacitors are used to regulate the current.
Theoretically, having calculated the value of the capacitor, you can not use a power transformer, as shown in the diagram.
When purchasing capacitors, you should choose the appropriate rating with a voltage of 400 V or more.
In practice, devices with current regulation have become more widely used.
You can choose pulse homemade charger circuits for a car battery. They are more complex in circuit design and require certain installation skills. Therefore, if you do not have special skills, it is better to buy a factory unit.
Pulse chargers
Pulse chargers have a number of advantages:
The operating principle of pulse devices is based on the conversion AC voltage household power supply to DC using a VD8 diode assembly. Then constant pressure converted into pulses of high frequency and amplitude. Pulse transformer T1 again converts the signal into DC 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, when assembled correctly the unit begins to work without additional adjustment. This device provides a charging current of up to 10 Amps.
When charging the battery using a homemade device, you must:
- place the device and battery on a non-conductive surface;
- comply with electrical safety requirements ( use gloves, a rubber mat, and tools with an electrical insulating coating);
- 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.
Who has not encountered in their practice the need to charge a battery and, disappointed in the lack of a charger with the necessary parameters, was forced to purchase a new charger in a store, or reassemble the necessary circuit?
So I have repeatedly had to solve the problem of charging various batteries when there was no suitable charger at hand. Accounted for a quick fix collect something simple, in relation to a specific battery.
The situation was tolerable until the need for mass preparation and, accordingly, charging the batteries arose. It was necessary to produce several universal chargers - inexpensive, operating in a wide range of input and output voltages and charging currents.
The charger circuits proposed below were developed for charging lithium-ion batteries, but it is possible to charge other types of batteries and composite batteries (using the same type of cells, hereinafter referred to as AB).
All presented schemes have the following main parameters:
input voltage 15-24 V;
charge current (adjustable) up to 4 A;
output voltage (adjustable) 0.7 - 18 V (at Uin=19V).
All circuits were designed to work with power supplies from laptops or to work with other power supplies with DC output voltages from 15 to 24 Volts and were built on widespread components that are present on the boards of old computer power supplies, power supplies of other devices, laptops, etc.
Memory circuit No. 1 (TL494)
The memory in Scheme 1 is a powerful pulse generator operating in the range from tens to a couple of thousand hertz (the frequency varied during research), with an adjustable pulse width.
The battery is charged by current pulses limited feedback, formed by the current sensor R10, connected between the common wire of the circuit and the source of the key on field effect transistor VT2 (IRF3205), filter R9C2, pin 1, which is the “direct” input of one of the error amplifiers of the TL494 chip.
The inverse input (pin 2) of the same error amplifier is supplied with a comparison voltage, regulated by a variable resistor PR1, from a reference voltage source built into the chip (ION - pin 14), which changes the potential difference between the inputs of the error amplifier.
As soon as the voltage value on R10 exceeds the voltage value (set by variable resistor PR1) at pin 2 of the TL494 microcircuit, the charging current pulse will be interrupted and resumed again only at the next cycle of the pulse sequence generated by the microcircuit generator.
By thus adjusting the width of the pulses on the gate of transistor VT2, we control the battery charging current.
Transistor VT1, connected in parallel with the gate of a powerful switch, provides the necessary discharge rate of the gate capacitance of the latter, preventing “smooth” locking of VT2. In this case, the amplitude of the output voltage in the absence of a battery (or other load) is almost equal to the input supply voltage.
With an active load, the output voltage will be determined by the current through the load (its resistance), which allows this circuit to be used as a current driver.
When charging the battery, the voltage at the switch output (and, therefore, at the battery itself) will tend to increase over time to a value determined by the input voltage (theoretically) and this, of course, cannot be allowed, knowing that the voltage value of the lithium battery being charged should be limited to 4.1V (4.2V). Therefore, the memory uses a threshold device circuit, which is a Schmitt trigger (hereinafter - TS) on an op-amp KR140UD608 (IC1) or on any other op-amp.
When the required voltage value on the battery is reached, at which the potentials at the direct and inverse inputs (pins 3, 2 - respectively) of IC1 are equal, a high logical level (almost equal to the input voltage) will appear at the output of the op-amp, causing the LED indicating the end of charging HL2 and the LED to light up optocoupler VH1 which will open its own transistor, blocking the supply of pulses to output U1. The key on VT2 will close and the battery will stop charging.
Once the battery is charged, it will begin to discharge through the reverse diode built into VT2, which will be directly connected in relation to the battery and the discharge current will be approximately 15-25 mA, taking into account the discharge also through the elements of the TS circuit. If this circumstance seems critical to someone, a powerful diode (preferably with a low forward voltage drop) should be placed in the gap between the drain and the negative terminal of the battery.
The TS hysteresis in this version of the charger is chosen such that the charge will begin again when the voltage on the battery drops to 3.9 V.
This charger can also be used to charge series-connected lithium (and other) batteries. It is enough to calibrate the required response threshold using variable resistor PR3.
So, for example, a charger assembled according to scheme 1 operates with a three-section serial battery from a laptop, consisting of dual elements, which was mounted to replace the nickel-cadmium battery of a screwdriver.
The power supply from the laptop (19V/4.7A) is connected to the charger, assembled in the standard case of the screwdriver charger instead of the original circuit. The charging current of the “new” battery is 2 A. At the same time, transistor VT2, working without a radiator, heats up to a maximum temperature of 40-42 C.
The charger is switched off, naturally, when the battery voltage reaches 12.3V.
The TS hysteresis when the response threshold changes remains the same as a PERCENTAGE. That is, if at a shutdown voltage of 4.1 V, the charger was turned on again when the voltage dropped to 3.9 V, then in this case the charger was turned on again when the voltage on the battery decreased to 11.7 V. But if necessary, the hysteresis depth can change.
Charger Threshold and Hysteresis Calibration
Calibration occurs using an external voltage regulator (laboratory power supply).The upper threshold for triggering the TS is set.
1. Disconnect the upper pin PR3 from the charger circuit.
2. We connect the “minus” of the laboratory power supply (hereinafter referred to as the LBP everywhere) to the negative terminal for the battery (the battery itself should not be in the circuit during setup), the “plus” of the LBP to the positive terminal for the battery.
3. Turn on the charger and LBP and set the required voltage (12.3 V, for example).
4. If the end of charge indication is on, rotate the PR3 slider down (according to the diagram) until the indication goes out (HL2).
5. Slowly rotate the PR3 engine upward (according to the diagram) until the indication lights up.
6. Slowly reduce the voltage level at the output of the LBP and monitor the value at which the indication goes out again.
7. Check the level of operation of the upper threshold again. Fine. You can adjust the hysteresis if you are not satisfied with the voltage level that turns on the charger.
8. If the hysteresis is too deep (the charger is switched on at a too low voltage level - below, for example, the battery discharge level), turn the PR4 slider to the left (according to the diagram) or vice versa - if the hysteresis depth is insufficient, - to the right (according to the diagram). When changing depth of hysteresis, the threshold level may shift by a couple of tenths of a volt.
9. Make a test run, raising and lowering the voltage level at the LBP output.
Setting the current mode is even easier.
1. We turn off the threshold device using any available (but safe) methods: for example, by “connecting” the PR3 engine to the common wire of the device or by “shorting” the LED of the optocoupler.
2. Instead of the battery, we connect a load in the form of a 12-volt light bulb to the output of the charger (for example, I used a pair of 12V 20-watt lamps to set up).
3. We connect the ammeter to the break of any of the power wires at the input of the charger.
4. Set the PR1 engine to minimum (to the maximum left according to the diagram).
5. Turn on the memory. Smoothly rotate the PR1 adjustment knob in the direction of increasing current until the required value is obtained.
You can try to change the load resistance towards lower values of its resistance by connecting in parallel, say, another similar lamp or even “short-circuiting” the output of the charger. The current should not change significantly.
During testing of the device, it turned out that frequencies in the range of 100-700 Hz were optimal for this circuit, provided that IRF3205, IRF3710 were used (minimum heating). Since the TL494 is underutilized in this circuit, the free error amplifier on the IC can be used to drive a temperature sensor, for example.
It should also be borne in mind that if the layout is incorrect, even a correctly assembled pulse device will not work correctly. Therefore, one should not neglect the experience of assembling power pulse devices, described repeatedly in the literature, namely: all “power” connections of the same name should be located at the shortest distance relative to each other (ideally at one point). So, for example, connection points such as the collector VT1, the terminals of resistors R6, R10 (connection points with the common wire of the circuit), terminal 7 of U1 - should be combined almost at one point or through a straight short and wide conductor (bus). The same applies to drain VT2, the output of which should be “hung” directly onto the “-” terminal of the battery. The terminals of IC1 must also be in close “electrical” proximity to the battery terminals.
Memory circuit No. 2 (TL494)
Scheme 2 is not very different from Scheme 1, but if the previous version of the charger was designed to work with an AB screwdriver, then the charger in Scheme 2 was conceived as a universal, small-sized (without unnecessary adjustment elements), designed to work with composite, sequentially connected elements up to 3, and with singles.
As you can see, in order to quickly change the current mode and work with different numbers of elements connected in series, fixed settings have been introduced with trimming resistors PR1-PR3 (setting the current), PR5-PR7 (setting the end of charging threshold for different quantities elements) and switches SA1 (selection of charging current) and SA2 (selection of the number of battery cells to be charged).
The switches have two directions, where their second sections switch the mode selection indication LEDs.
Another difference from the previous device is the use of a second error amplifier TL494 as a threshold element (connected according to the TS circuit) that determines the end of battery charging.
Well, and, of course, a p-conductivity transistor was used as a key, which simplified the full use of the TL494 without the use of additional components.
The method for setting the end of charging thresholds and current modes is the same, as for setting up the previous version of the memory. Of course, for a different number of elements, the response threshold will change multiples.
When testing this circuit, we noticed stronger heating of the switch on the VT2 transistor (when prototyping I use transistors without a heatsink). For this reason, you should use another transistor (which I simply didn’t have) of appropriate conductivity, but with better current parameters and lower open-channel resistance, or double the number of transistors indicated in the circuit, connecting them in parallel with separate gate resistors.
The use of these transistors (in a “single” version) is not critical in most cases, but in this case, the placement of the device components is planned in a small-sized case using small radiators or no radiators at all.
Memory circuit No. 3 (TL494)
Added to memory in diagram 3 automatic shutdown AB from charger with switching to load. This is convenient for checking and studying unknown batteries. The TS hysteresis for working with a battery discharge should be increased to the lower threshold (for switching on the charger), equal to the full battery discharge (2.8-3.0 V).
Charger circuit No. 3a (TL494)
Scheme 3a is a variant of scheme 3.
Memory circuit No. 4 (TL494)
The charger in scheme 4 is no more complicated than previous devices, but the difference from the previous schemes is that the battery here is charged with direct current, and the charger itself is a stabilized current and voltage regulator and can be used as a module laboratory source nutrition, classically built according to the “Datashit” canons.
Such a module is always useful for bench tests of both batteries and other devices. It makes sense to use built-in devices (voltmeter, ammeter). Formulas for calculating storage and interference chokes are described in the literature. I’ll just say that I used ready-made various chokes (with a range of specified inductances) during testing, experimenting with a PWM frequency from 20 to 90 kHz. I didn’t notice any particular difference in the operation of the regulator (in the range of output voltages 2-18 V and currents 0-4 A): minor changes in the heating of the key (without a radiator) suited me quite well. The efficiency, however, is higher when using smaller inductances.
The regulator worked best with two series-connected 22 µH chokes in square armored cores from converters integrated into laptop motherboards.
Memory circuit No. 5 (MC34063)
In diagram 5, a version of the PWM controller with current and voltage regulation is made on the MC34063 PWM/PWM chip with an “add-on” on the CA3130 op amp (other op amps can be used), with the help of which the current is regulated and stabilized.
This modification somewhat expanded the capabilities of the MC34063, in contrast to the classic inclusion of the microcircuit, allowing the function of smooth current control to be implemented.
Memory circuit No. 6 (UC3843)
In diagram 6, a version of the PHI controller is made on the UC3843 (U1) chip, CA3130 op-amp (IC1), and LTV817 optocoupler. The current regulation in this version of the charger is carried out using a variable resistor PR1 at the input of the current amplifier of the U1 microcircuit, the output voltage is regulated using PR2 at the inverting input IC1.
There is a “reverse” reference voltage at the “direct” input of the op-amp. That is, regulation is carried out relative to the “+” power supply.
In schemes 5 and 6, the same sets of components (including chokes) were used in the experiments. According to the test results, all of the listed circuits are not much inferior to each other in the declared range of parameters (frequency/current/voltage). Therefore, a circuit with fewer components is preferable for repetition.
Memory circuit No. 7 (TL494)
The memory in diagram 7 was conceived as a bench device with maximum functionality, therefore there were no restrictions on the volume of the circuit and the number of adjustments. This version of the charger is also made on the basis of a PHI current and voltage regulator, like the option in diagram 4.
Additional modes have been introduced into the scheme.
1. “Calibration - charge” - for pre-setting the end voltage thresholds and repeating charging from an additional analog regulator.
2. “Reset” - to reset the charger to charge mode.
3. “Current - buffer” - to switch the regulator to current or buffer (limiting the output voltage of the regulator in the joint supply of the device with battery voltage and the regulator) charge mode.
A relay is used to switch the battery from the “charge” mode to the “load” mode.
Working with the memory is similar to working with previous devices. Calibration is carried out by switching the toggle switch to the “calibration” mode. In this case, the contact of the toggle switch S1 connects the threshold device and a voltmeter to the output of the integral regulator IC2. Having set the required voltage for the upcoming charging of a specific battery at the output of IC2, using PR3 (smoothly rotating) the HL2 LED lights up and, accordingly, relay K1 operates. By reducing the voltage at the output of IC2, HL2 is suppressed. In both cases, control is carried out by a built-in voltmeter. After setting the PU response parameters, the toggle switch is switched to charge mode.
Scheme No. 8
The use of a calibration voltage source can be avoided by using the memory itself for calibration. In this case, you should decouple the TS output from the SHI controller, preventing it from turning off when the battery charge is complete, determined by the TS parameters. The battery will one way or another be disconnected from the charger by the contacts of relay K1. The changes for this case are shown in Figure 8.
In calibration mode, toggle switch S1 disconnects the relay from the positive power supply to prevent inappropriate operations. In this case, the indication of the operation of the TC works.
Toggle switch S2 performs (if necessary) forced activation of relay K1 (only when calibration mode is disabled). Contact K1.2 is necessary to change the polarity of the ammeter when switching the battery to the load.
Thus, a unipolar ammeter will also monitor the load current. If you have a bipolar device, this contact can be eliminated.
Charger design
In designs it is desirable to use as variable and tuning resistors multi-turn potentiometers to avoid suffering when setting the necessary parameters.
Design options are shown in the photo. The circuits were soldered impromptu onto perforated breadboards. All the filling is mounted in cases from laptop power supplies.
They were used in designs (they were also used as ammeters after minor modifications).
The cases are equipped with sockets for external connection of batteries, loads, and a jack for connecting an external power supply (from a laptop).
He designed several digital pulse duration meters, different in functionality and elemental base.
More than 30 improvement proposals for the modernization of units of various specialized equipment, incl. - power supply. For a long time now I have been increasingly involved in power automation and electronics.
Why am I here? Yes, because everyone here is the same as me. There is a lot of interest here for me, since I am not strong in audio technology, but I would like to have more experience in this area.
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