Chargers for lead batteries. Automatic device for charging lead-acid batteries. Output voltage selection
In amateur radio practice, you often encounter the problem of powering portable devices. Fortunately, everything has already been invented and created for us a long time ago, all that remains is to use a suitable battery, for example, sealed lead-acid batteries, which have gained enormous popularity and are quite affordable.
But here another problem arises: how to charge them? I also encountered this problem, but since this issue has already been resolved a long time ago, I want to share my charger design.
In search of a suitable circuit, I came across an article by S. Malakhov with two options for universal chargers, one on a pair of KR142EN22, and the second on a single L200C chip, so I decided to repeat it. Why L200C? Yes, there are plenty of advantages: in order to save space, printed circuit board, it’s easier to wire the board, you only need one heatsink, there is protection against overheating, polarity reversal, and short circuit, and the cost is cheaper than two KR142EN22.
I made virtually no changes to the scheme, everything is simple and quite workable, thanks to the author.
It consists of an adjustable voltage and current controller made in a TO-220-5 (Pentawatt) housing, a rectifier and a set of resistors in the current-setting circuit.
At first I used a filament TN36-127/220-50 as a transformer, but given its insufficient output current of 1.2A, I later replaced it with a TN46- 127/220-50 with an output current of 2.3A.
These transformers are convenient with a set of 6.3V windings, combining which you can obtain the required voltage. Moreover, the third and fourth secondary windings have a 5V tap (pins 12 and 15). The author recommends connecting a 12 V winding for the charging mode of 6 volt batteries, and another additional 8 V for the charging mode of 12 volt batteries. In this mode, the voltage drop will be approximately equal to 5 - 6 Volts. I decided to reduce this drop a little and connected a 10V winding for the six-volt mode, and an additional 6.3V winding for the twelve-volt mode, thereby reducing the voltage drop to 2-3 Volts. A smaller voltage drop facilitates thermal conditions, but this drop should not be made too small; the voltage drop across the microcircuit must be taken into account. If suddenly the charger becomes unstable, you can switch the windings and apply more voltage.
Charger for lead-acid batteries in the author's version it is equipped with an ammeter and a voltmeter, but since we live in the era of modern technology, I decided to install a modern panel with an ampere-voltmeter. Such panels can be purchased at radio stores; I ordered them from our Chinese brothers for only 5 American rubles. The panel allows you to measure current from 0.01 to 9.99 Amperes and voltage from 0.1 to 99.9 Volts, made on an STM8 microcontroller, although it requires additional power, which I took directly from the output of the diode bridge. It should be taken into account that the current is measured using the negative bus.
Switching the charging current in the author's version is done with a biscuit switch, but such switches are quite expensive and difficult to access, so I decided to use cheap PS22F11 push-button switches, which reduced the cost of the design and gave one advantage: using buttons you can combine current-limiting resistors, selecting the optimal charge current. With all switches turned off, the charging current is 0.15A.
I made the printed circuit board small-sized, for LUT, all the elements of the charger are located tightly, but in principle, you can remake it to your taste.
The author recommends installing a cooling radiator with dimensions of 90x60mm, but I came across a radiator from a computer cooler, with dimensions of 60x80mm and very developed fins. The microcircuit was secured to the radiator using a plastic insulator through a thermally conductive dielectric substrate.
In principle, I have described all the nuances and differences between my version and the author’s, let’s move on to the body.
Having searched the shelves and stocks for a suitable case for Charger for lead-acid batteries I didn’t find it, but in this case, radio amateurs do it simply, take the case from the ATX computer power supply. They are easy to get, they can be found for pennies when they are not working, the case is comfortable, strong, and has a power connector.
I picked up a power supply with a solid side wall, gutted all the contents, leaving only the connector and power switch. I laid out all the structural elements inside, marked and drilled holes and cut out a window for the indicator panel.
Then all that remains is to assemble and connect. For connection I used wires from the same computer unit nutrition.
Of the obvious disadvantages of using such a case.
The transformer turned out to be too big and the top cover did not close tightly, although it can still be tightened with a screw, albeit with deformation.
- since the body is iron, vibration from the transformer is transmitted to it, which causes extra hum.
- a hole in the body from which a braid of wires came out.
To give an attractive appearance It was decided to print a false panel on thick paper with inscriptions for buttons, etc.
The setting comes down to adjusting the output voltage for both modes using trimming resistors, in fact, everything is the same as in the author’s version, I set the charging voltage for a 6V battery to 7.2 Volts, and for a 12V battery to 14.5 Volts.
By connecting a 4.7 Ohm resistor and a power of 5-10 W instead of a battery, we control the charging current and, if necessary, select resistors. When assembling the board, I recommend soldering all the solder tracks to increase their cross-sectional area and reduce resistance; if you route your board, make these tracks as thick as possible to minimize their resistance. There is nothing to worry about if your charge current is greater than the calculated one; batteries can be charged with a current greater than 0.1 of the rated capacity (0.1C), safely up to 0.2 of the rated capacity (0.2C).
After assembly and configuration Charger for lead-acid batteries ready for use and capable of charging almost all types of lead-acid batteries with a voltage of 6 or 12 Volts and an operating current of 1.2 to 15 Amps.
At the end of charging, the current supplied to the battery is equal to the self-discharge current; the battery can remain in this mode for a very long time and still retain and maintain its charge.
In this article I will tell you how to use an AT/ATX computer power supply and homemade block control to make a fairly “smart” charger for lead-acid batteries. These include the so-called. “UPS”, automobile and other batteries of wide application.Description
The device is intended for charging and training (desulfation) lead-acid batteries with a capacity of 7 to 100 Ah, as well as for approximate assessment of their charge level and capacity. The charger has protection against incorrect connection of the battery (reversal of polarity) and against short circuit of accidentally abandoned terminals. It uses microcontroller control, thanks to which safe and optimal charging algorithms are implemented: IUoU or IUIoU, followed by “topping up” to a 100% charging level. Charging parameters can be adjusted to a specific battery (customizable profiles) or you can select those already included in the control program. Structurally, the charger consists of an AT/ATX power supply, which needs to be slightly modified, and a control unit on the ATmega16A MK. The entire device is freely mounted in the housing of the same power supply. The cooling system (standard PSU cooler) turns on/off automatically.
The advantages of this memory are its relative simplicity and the absence of labor-intensive adjustments, which is especially important for beginner radio amateurs.
]1. Charging mode - “Charge” menu. For batteries with capacities from 7Ah to 12Ah, the IUoU algorithm is set by default. This means:
- first stage - charging with a stable current of 0.1C until the voltage reaches 14.6V
- the second stage is charging with a stable voltage of 14.6V until the current drops to 0.02C
- the third stage is maintaining a stable voltage of 13.8V until the current drops to 0.01C. Here C is the battery capacity in Ah.
- fourth stage - “finishing”. At this stage, the voltage on the battery is monitored. If it drops below 12.7V, the charge starts from the very beginning.
For starter batteries (from 45 Ah and above) we use the IUIoU algorithm. Instead of the third stage, the current is stabilized at 0.02C until the battery voltage reaches 16V or after about 2 hours. At the end of this stage, charging stops and “topping up” begins. This is the fourth stage. The charging process is illustrated by graphs in Fig. 1 and Fig. 2.
2. Training mode (desulfation) - “Training” menu. Here is the training cycle:
10 seconds - discharge with a current of 0.01C, 5 seconds - charge with a current of 0.1C. The charge-discharge cycle continues until the battery voltage rises to 14.6V. Next is the usual charge.
3. Battery test mode. Allows you to approximately estimate the degree of battery discharge. The battery is loaded with a current of 0.01C for 15 seconds, then the voltage measurement mode on the battery is turned on.
4. Control-training cycle (CTC). If you first connect an additional load and turn on the “Charge” or “Training” mode, then in this case, the battery will first be discharged to a voltage of 10.8 V, and then the corresponding selected mode will be turned on. In this case, the current and discharge time are measured, thus calculating the approximate capacity of the battery. These parameters are displayed on the display after charging is complete (when the message “Battery charged” appears) when you press the “select” button. As an additional load, you can use a car incandescent lamp. Its power is selected based on the required discharge current. Usually it is set equal to 0.1C - 0.05C (10 or 20 hour discharge current).
Moving through the menu is carried out using the “left”, “right”, “select” buttons. The “reset” button exits any operating mode of the charger to the main menu.
The main parameters of charging algorithms can be configured for a specific battery; for this, there are two customizable profiles in the menu - P1 and P2. The configured parameters are saved in non-volatile memory(EEPROM).
To get to the settings menu, you need to select any of the profiles, press the “select” button, select “settings”, “profile parameters”, profile P1 or P2. Having selected the desired parameter, press “select”. The left or right arrows will change to up or down arrows, indicating that the parameter is ready to be changed. Select the desired value using the “left” or “right” buttons, confirm with the “select” button. The display will show “Saved”, indicating that the value has been written to the EEPROM.
Setting values:
1. “Charge algorithm.” Select IUoU or IUIoU. See graphs in Fig. 1 and Fig. 2.
2. “Battery capacity”. By setting the value of this parameter, we set the charging current at the first stage I=0.1C, where C is the battery capacity V Ah. (Thus, if you need to set the charge current, for example, 4.5A, you should select a battery capacity of 45Ah).
3. "Voltage U1". This is the voltage at which the first charging stage ends and the second begins. The default value is 14.6V.
4. "Voltage U2". Only used if the IUIoU algorithm is specified. This is the voltage at which the third stage of charging ends. Default is 16V.
5. “2nd stage current I2”. This is the current value at which the second charging stage ends. Stabilization current at the third stage for the IUIoU algorithm. The default value is 0.2C.
6. “End of charge I3.” This is the current value upon reaching which charging is considered complete. The default value is 0.01C.
7. "Discharge current". This is the value of the current that discharges the battery during training with charge-discharge cycles.
Selection and modification of the power supply.
In our design we use a computer power supply. Why? There are several reasons. Firstly, this is an almost ready-made power unit. Secondly, this is also the body of our future device. Thirdly, it has small dimensions and weight. And, fourthly, it can be purchased at almost any radio market, flea market and computer service centers. As they say, cheap and cheerful.
Of all the variety of power supply models, the best fit for us is an ATX format unit with a power of at least 250 W. You just need to consider the following. Only those power supplies that use the TL494 PWM controller or its analogues (MB3759, KA7500, KR1114EU4) are suitable. You can also use an AT format power supply, but you will only have to make a low-power standby power supply (standby) for a voltage of 12V and a current of 150-200mA. The difference between AT and ATX is in the initial startup scheme. The AT starts up independently; power for the PWM controller chip is taken from the 12-volt winding of the transformer. In ATX for initial nutrition The microcircuit is served by a separate 5V source, called the “standby power supply” or “standby power supply”. You can read more about power supplies, for example, here, and converting a power supply into a charger is well described here.
So, there is a power supply. First you need to check it for serviceability. To do this, we disassemble it, remove the fuse and instead solder a 220 volt incandescent lamp with a power of 100-200 W. If there is a switch on the back panel of the power supply mains voltage, then it should be set to 220V. We turn on the power supply to the network. The AT power supply starts up immediately; for ATX you need to short-circuit the green and black wires on the large connector. If the light does not light, the cooler is spinning, and all output voltages are normal, then we are lucky and our power supply is working. Otherwise, you will have to start repairing it. Leave the light bulb in place for now.
To convert the power supply into our future charger, we will need to slightly change the “piping” of the PWM controller. Despite the huge variety of power supply circuits, the TL494 switching circuit is standard and can have a couple of variations, depending on how current protection and voltage limits are implemented. The conversion diagram is shown in Fig. 3.
It shows only one output voltage channel: +12V. The remaining channels: +5V, -5V, +3.3V are not used. They must be turned off by cutting the corresponding tracks or removing elements from their circuits. Which, by the way, may be useful to us for the control unit. More on this a little later. Elements that are installed additionally are indicated in red. Capacitor C2 must have an operating voltage of at least 35V and is installed to replace the existing one in the power supply. After the TL494 “piping” is shown in the diagram in Fig. 3, we connect the power supply to the network. The voltage at the power supply output is determined by the formula: Uout=2.5*(1+R3/R4) and with the ratings indicated on the diagram it should be about 10V. If this is not the case, you will have to check the correct installation. At this point the alteration is completed, you can remove the light bulb and replace the fuse.
Scheme and principle of operation.
The control unit diagram is shown in Fig. 4.
It is quite simple, since all the main processes are performed by the microcontroller. It is recorded in his memory control program, which contains all the algorithms. The power supply is controlled using PWM from the PD7 pin of the MK and a simple DAC based on elements R4, C9, R7, C11. The measurement of battery voltage and charging current is carried out using the microcontroller itself - a built-in ADC and a controlled differential amplifier. The battery voltage is supplied to the ADC input from the divider R10R11. The charging and discharging current are measured as follows. The voltage drop from the measuring resistor R8 through dividers R5R6R10R11 is supplied to the amplifier stage, which is located inside the MK and connected to pins PA2, PA3. Its gain is set programmatically, depending on the measured current. For currents less than 1A, the gain factor (GC) is set equal to 200, for currents above 1A GC=10. All information is displayed on the LCD connected to ports PB1-PB7 via a four-wire bus. Protection against polarity reversal is carried out on transistor T1, signaling of incorrect connection is carried out on elements VD1, EP1, R13. When the charger is connected to the network, transistor T1 is closed at a low level from the PC5 port, and the battery is disconnected from the charger. It connects only when you select the battery type and charger operating mode in the menu. This also ensures that there is no sparking when the battery is connected. If you try to connect the battery in the wrong polarity, the buzzer EP1 and the red LED VD1 will sound, signaling a possible accident. During the charging process, the charging current is constantly monitored. If it becomes equal to zero (the terminals have been removed from the battery), the device automatically goes to the main menu, stopping the charge and disconnecting the battery. Transistor T2 and resistor R12 form a discharge circuit, which participates in the charge-discharge cycle of the desulfating charge (training mode) and in the battery test mode. The discharge current of 0.01C is set using PWM from the PD5 port. The cooler automatically turns off when the charging current drops below 1.8A. The cooler is controlled by port PD4 and transistor VT1.
Details and design.
Microcontroller. They are usually found on sale in a DIP-40 or TQFP-44 package and are labeled as follows: ATMega16A-PU or ATMega16A-AU. The letter after the hyphen indicates the type of package: “P” - DIP package, “A” - TQFP package. There are also discontinued microcontrollers ATMega16-16PU, ATMega16-16AU or ATMega16L-8AU. In them, the number after the hyphen indicates the maximum clock frequency of the controller. The manufacturing company ATMEL recommends using ATMega16A controllers (namely with the letter “A”) and in a TQFP package, that is, like this: ATMega16A-AU, although all of the above instances will work in our device, as practice has confirmed. Case types also differ in the number of pins (40 or 44) and their purpose. Figure 4 shows circuit diagram control unit for MK in DIP housing.
Resistor R8 is ceramic or wire, with a power of at least 10 W, R12 - 7-10 W. All others are 0.125W. Resistors R5, R6, R10 and R11 must be used with a permissible deviation of 0.1-0.5%. It is very important! The accuracy of measurements and, consequently, the correct operation of the entire device will depend on this.
It is advisable to use transistors T1 and T1 as shown in the diagram. But if you have to select a replacement, then you need to take into account that they must open with a gate voltage of 5V and, of course, must withstand a current of at least 10A. Suitable, for example, are transistors marked 40N03GP, which are sometimes used in the same ATX format power supplies, in a 3.3V stabilization circuit.
Schottky diode D2 can be taken from the same power supply, from the +5V circuit, which we do not use. Elements D2, T1 and T2 are placed on one radiator with an area of 40 square centimeters through insulating gaskets. Buzzer EP1 - with a built-in generator, for a voltage of 8-12 V, the sound volume can be adjusted with resistor R13.
LCD indicator – WH1602 or similar, on the controller HD44780, KS0066 or compatible with them. Unfortunately, these indicators may have different pin locations, so you may have to design a printed circuit board for your instance
Program
The control program is contained in the “Program” folder. The configuration bits (fuses) are set as follows:
Programmed (set to 0):
CKSEL0
CKSEL1
CKSEL3
SPIEN
SUT0
BODEN
BODLEVEL
BOOTSZ0
BOOTSZ1
all others are unprogrammed (set to 1).
Setup
So, the power supply has been redesigned and produces a voltage of about 10V. When connecting a working control unit with a firmware MK to it, the voltage should drop to 0.8..15V. Resistor R1 sets the contrast of the indicator. Setting up the device involves checking and calibrating the measuring part. We connect a battery or a 12-15V power supply and a voltmeter to the terminals. Go to the “Calibration” menu. We check the voltage readings on the indicator with the readings of the voltmeter, if necessary, correct them using the “<» и «>" Click "Select". Next comes the current calibration at KU=10. With the same buttons "<» и «>“You need to set the current reading to zero. The load (battery) is automatically switched off, so there is no charging current. Ideally, there should be zeros or very close to zero values. If so, this indicates the accuracy of resistors R5, R6, R10, R11, R8 and the good quality of the differential amplifier. Click "Select". Similarly - calibration for KU=200. "Choice". The display will show “Ready” and after 3 seconds. the device will go to the main menu.
Calibration is complete. Correction factors are stored in non-volatile memory. It is worth noting here that if, during the very first calibration, the voltage value on the LCD is very different from the voltmeter readings, and the currents at any KU are very different from zero, you need to use (select) other divider resistors R5, R6, R10, R11, R8, Otherwise, the device may malfunction. With precise resistors (with a tolerance of 0.1-0.5%), the correction factors are zero or minimal. This completes the setup. If the voltage or current of the charger at some stage does not increase to the required level or the device “pops up” in the menu, you need to once again carefully check that the power supply has been modified correctly. Perhaps the protection is triggered.
And finally, a few photos.
Arrangement of elements in the power supply housing:
The finished design might look like this:
So:
or even like this:
ARCHIVE:Download
CHARGER DIAGRAMS
FOR (sealed, maintenance-free) BATTERIES.
BATTERIES AGM TECHNOLOGY(Absorbent Glass Mat) - the difference between these batteries and classic ones is that they contain not liquid, but absorbed electrolyte, this gives a number of changes in the properties of the battery.
Sealed, maintenance-free batteries produced using AGM technology work perfectly in buffer mode, i.e. in recharging mode, in this mode they last up to 10-15 years (battery 12V). If they are used in a cyclic mode (i.e. constantly charged and discharged by at least 30% -40% of capacity), then their service life is reduced. Almost all sealed batteries can be mounted on their sides, but the manufacturer usually recommends mounting the batteries in the "normal", vertical position.
AGM batteries general purpose Usually used in low-cost UPS (uninterruptible power supply) and backup power supply systems, that is, where the batteries are mainly in recharging mode, and sometimes, during power outages, release stored energy.
AGM batteries usually have a maximum allowed charge current of 0.3C, and a final charge voltage of 14.8-15V.
Flaws:
Should not be stored in a discharged state, the voltage should not fall below 1.8V;
Extremely sensitive to excess charge voltage;
Batteries made using this technology are often confused with batteries made using GEL technology (which have a jelly-like electrolyte, which has a number of advantages).
GEL TECHNOLOGY BATTERIES(Gel Electrolite) - contain an electrolyte thickened into a jelly-like state, this gel does not allow the electrolyte to evaporate, oxygen and hydrogen vapors are retained inside the gel, react and turn into water, which is absorbed by the gel. Almost all of the vapor is thus returned to the battery, and this is called gas recombination. This technology allows the use of a constant amount of electrolyte without adding water for the entire service life of the battery, and its increased resistance to discharge currents prevents the formation of “harmful” indestructible lead sulfates.
Gel batteries have approximately 10-30% longer service life than AGM batteries and are better able to withstand cyclic charge-discharge modes; they also tolerate deep discharge less painfully. Such batteries are recommended for use where it is necessary to ensure a long service life at deeper discharge conditions.
Due to their characteristics, gel batteries can remain discharged for a long time, have low self-discharge, and can be used in a residential area and in almost any position.
Most often, such batteries with a voltage of 6V or 12V are used in computer backup power supplies (UPS), security and measuring systems, flashlights and other devices that require autonomous power supply. The disadvantages include the need to strictly adhere to charging modes.
As a rule, when charging such batteries, the charge current is set at 0.1C, where C is the battery capacity, and the charging current is limited and the voltage is stabilized and set within 14-15 volts. During the charging process, the voltage remains practically unchanged, and the current decreases from the set value to 20-30 mA at the end of the charge. Similar batteries are produced by many manufacturers, and their parameters may differ, primarily in terms of the maximum permissible charging current, so before use it is advisable to study the documentation of a specific battery.
To charge batteries manufactured using GEL and AGM technology, it is necessary to use a special charger with appropriate charge parameters that differ from the charge of classic batteries with liquid electrolyte.
Next, a selection of various schemes for charging such batteries is proposed, and if you take it as a rule to charge the battery with a charging current of about 0.1 of its capacity, then we can say that the proposed chargers can charge batteries from almost any manufacturer.
Fig. 1 Photo of a 12V battery (7.2A/h).
Charger circuit on L200C chip which is a voltage stabilizer with a programmable output current limiter. 
Fig.2 Charger diagram.
The power of resistors R3-R7 that sets the charging current should be no less than indicated in the diagram, or better yet more.
The microcircuit must be installed on a radiator, and the lighter its thermal regime, the better.
Resistor R2 is needed to adjust the output voltage within 14-15 volts.
The voltage on the secondary winding of the transformer is 15-16 volts.
Everything works like this - at the beginning of the charge the current is high, and towards the end it drops to a minimum; as a rule, manufacturers recommend just such a small current for a long time to preserve battery capacity.
Fig.3 Board of the finished device.
Circuit diagram of a charger based on integrated voltage stabilizers KR142EN22, uses “constant voltage charging with current limitation” and is designed to charge various types of batteries. 
The circuit works like this: first, a rated current is supplied to a discharged battery, and then, as charging proceeds, the voltage on the battery increases, but the current remains unchanged; when the set voltage threshold is reached, its further growth stops, and the current begins to decrease.
By the time charging is completed, the charging current is equal to the self-discharge current; in this state, the battery can remain in the charger for as long as desired without recharging.
The charger is designed as a universal charger and is designed to charge 6 and 12-volt batteries of the most common capacities. The device uses integrated stabilizers KR142EN22, the main advantage of which is the low input/output voltage difference (for KR142EN22 this voltage is 1.1V).
Functionally, the device can be divided into two parts, a maximum current limiting unit (DA1.R1-R6) and a voltage stabilizer (DA2, R7-R9). Both of these parts are made according to standard designs.
Switch SB1 selects the maximum charging current, and switch SB2 selects the final voltage on the battery.
At the same time, when charging a 6V battery, section SB2. 1 switches the secondary winding of the transformer, reducing the voltage.
To reduce charging time, the initial charging current can reach 0.25C (some battery manufacturers allow a maximum charging current of up to 0.4C).
Details:
Since the device is designed for long-term continuous operation, you should not save on the power of current-setting resistors R1-R6, and in general it is advisable to select all elements with a reserve. In addition to increasing reliability, this will improve the thermal conditions of the entire device.
It is advisable to take multi-turn tuning resistors SP5-2, SP5-3 or their analogues.
Capacitors: C1 - K50-16, K50-35 or imported analogue, C2, SZ, you can use metal film type K73 or ceramic K10-17, KM-6. It is advisable to replace imported 1N5400 (3A, 50V) diodes, if there is free space in the case, with domestic ones in metal cases such as D231, D242, KD203, etc.
These diodes dissipate heat quite well with their housings, and when operating in this device their heating is almost unnoticeable.
The step-down transformer must provide maximum charging current for a long time without overheating. The voltage on winding II is 12V (charging 6-volt batteries). The voltage on winding III, connected in series with winding II when charging 12-volt batteries, is 8V.
In the absence of KR142EN22 microcircuits, you can install KR142EN12, but you must take into account that the output voltage on the secondary windings of the transformer will have to be increased by 5V. In addition, you will have to install diodes that protect the microcircuits from reverse currents.
Setting up the device should begin by setting resistors R7 and R8 to the required voltages at the output terminals of the device without connecting a load. Resistor R7 sets the voltage within 14.5...14.9V for charging 12-volt batteries, and R8-7.25...7.45V for 6-volt ones. Then, by connecting a load resistor with a resistance of 4.7 Ohms and a power of at least 10 W in the charging mode of 6-volt batteries, check the output current with an ammeter in all positions of switch SB1.
OPTION OF DEVICE FOR BATTERY CHARGING 12V-7.2AH,the circuit is the same as the previous one, only switches SB1, SB2 with additional resistors are excluded from it and a transformer without taps is used. 
We set it up in the same way as described above: First, using resistor R3 without connecting a load, set the output voltage within 14.5...14.9V, and then, with a connected load, by selecting resistor R2, set the output current to 0.7... 0 ,8A.
For other types of batteries, you will need to select resistors R2, R3 and a transformer in accordance with the voltage and capacity of the battery being charged.
Charging parameters should be selected based on the condition I = 0.1C, where C is the battery capacity, and the voltage is 14.5...14.9V (for 12-volt batteries).
When working with these devices, first set the required values of charging current and voltage, then connect the battery and connect the device to the network. In some cases, the ability to select the charging current allows you to speed up the charge by setting the current to more than 0.1C. So, for example, a battery with a capacity of 7.2A/h can be charged with a current of 1.5A without exceeding the maximum permissible charging current of 0.25C.
Integrated voltage stabilizer KR142EN12 (LM317) allows you to create a simple source of stable current,
The microcircuit in this connection is a current stabilizer and, regardless of the connected battery, produces only the calculated current - the voltage is set “automatically”. 
Advantages of the proposed device.
Not afraid of short circuits; it doesn’t matter the number of elements in the battery being charged and their type - you can charge sealed acid 12.6V, lithium 3.6V and alkaline 7.2V. The current switch should be turned on as shown in the diagram - so that resistor R1 remains connected during any manipulation.
The charging current is calculated as follows: I (in amperes) = 1.2V/R1 (in Ohms). To indicate the current, a transistor (germanium) is used, which allows visual observation of currents up to 50 mA.
The maximum voltage of the battery being charged must be 4V less than the supply (charging) voltage; in case of charging with a maximum current of 1A, the 142EN12 microcircuit should be installed on a radiator that dissipates at least 20W.
A charging current of 0.1 of the capacity is suitable for all types of batteries. To fully charge a battery, it must be given 120% of its rated charge, but before that it must be completely discharged. Therefore, charging time in the recommended mode is 12 hours.
Details:
Diode D1 and fuse F2 protect the charger from improper connection of the battery. Capacitance C1 is selected from the ratio: for 1 Ampere you need 2000 uF.
Rectifier bridge - for a current of at least 1A and a voltage of more than 50V. The transistor is germanium due to the low opening voltage B-E. The values of resistors R3-R6 determine the current. The KR142EN12 microcircuit is replaceable with any analogues that can withstand the specified current. Transformer power - at least 20W.
SIMPLE CHARGER FOR LM317, the diagram is as in the description (Datasheet), we add only some elements, and we get a charger. 
The VD1 diode is added so that the charged battery does not discharge in case of loss mains power, a voltage switch has also been added. The charge current is set to around 0.4A, transistor VT1-2N2222 can be replaced with KT3102, switch S1 has any two positions, transformer 15V, diode bridge with 1N4007
The charging current is set (1/10 of the battery capacity) using resistor R7, calculated by the formula R = 0.6/I charge.
In this example it is R7=0.6/0.4=1.5Ohm. Power 2 W.
Setup.
We connect to the network, set the required voltages, for a 6V battery the charging voltage is 7.2V-7.5V, for a 12V battery – 14.4-15V, set by resistors R3, R5, respectively.
CHARGER WITH AUTOMATIC SHUT OFF for charging a 6V sealed lead battery, with minimal modifications it can also be used to charge other types of batteries, with any voltage, for which the condition for the end of the charge is to reach a certain voltage level.
In this device, battery charging stops when the terminal voltage reaches 7.3V. The charge is carried out with an unstabilized current, limited at 0.1C by resistor R5. The voltage level at which the device stops charging is set by the zener diode VD1 accurate to tenths of a volt.
The basis of the circuit is an operational amplifier (op-amp), connected as a comparator, and connected by an inverting input to a reference voltage source (R1-VD1), and not by an inverting input to the battery. As soon as the voltage on the battery exceeds the reference voltage, the comparator switches to the single state, transistor T1 opens and relay K1 disconnects the battery from the voltage source, while simultaneously applying a positive voltage to the base of transistor T1. Thus, T1 will be open and its state will no longer depend on the voltage level at the output of the comparator. The comparator itself is covered by positive feedback (R2), which creates hysteresis and leads to a sharp, abrupt switching of the output and opening of the transistor. Thanks to this, the circuit is free from the disadvantage of similar devices with a mechanical relay, in which the relay makes an unpleasant rattling sound due to the fact that the contacts are balancing at the switching boundary, but switching on has not yet occurred. In the event of a power outage, the device will resume operation as soon as it appears and will not allow the battery to be overcharged. 
A device assembled from serviceable parts begins to work immediately and does not require configuration. The operational amplifier indicated in the diagram can operate in the supply voltage range from 3 to 30 volts. The shutdown voltage depends only on the parameters of the zener diode. When connecting a battery with a different voltage, for example 12V, the zener diode VD1 must be selected according to the stabilization voltage (for the voltage of a charged battery - 14.4…15V).
CHARGER FOR SEALED LEAD ACID BATTERIES.
The current stabilizer contains only three parts: an integrated voltage stabilizer DA1 type KR142EN5A (7805), an LED HL1 and a resistor R1. The LED, in addition to working as a current stabilizer, also serves as an indicator of the battery charging mode. The battery is charged using constant current. 
The alternating voltage from transformer Tr1 is supplied to the diode bridge VD1, the current stabilizer (DA1, R1, VD2).
Setting up the circuit comes down to adjusting the battery charging current. The charging current (in amperes) is usually chosen to be ten times less than the numerical value of the battery capacity (in ampere-hours).
To configure, instead of the battery, you need to connect an ammeter with a current of 2...5A and select the resistor R1 to set the required charge current using it.
The DA1 chip must be installed on the radiator.
Resistor R1 consists of two series-connected wirewound resistors with a power of 12W.
DUAL MODE CHARGER.
The proposed charger circuit for 6V batteries combines the advantages of two main types of chargers: constant voltage and constant current, each of which has its own advantages. 
The circuit is based on a voltage regulator based on LM317T and a controlled zener diode TL431.
In direct current mode, resistor R3 sets the current to 370 mA, diode D4 prevents battery discharge through LM317T when the mains voltage disappears, resistor R4 ensures that transistor VT1 is unlocked when mains voltage is applied.
The controlled zener diode TL431, resistors R7, R8 and potentiometer R6 form a circuit that determines the battery charge to a given voltage. LED VD2 is a network indicator, LED VD3 lights up in constant voltage mode.
SIMPLE AUTOMATIC CHARGER, designed for charging batteries with a voltage of 12 volts, designed for continuous round-the-clock operation with power supply from a 220V mains voltage, the charge is carried out at low pulse current(0.1-0.15 A).
When the battery is connected correctly, the green light on the device should light up. If the green LED does not light up, the battery is fully charged or the line is broken. At the same time, the red indicator of the device (LED) lights up. 
The device provides protection against:
Short circuit in the line;
Short circuit in the battery itself.
Incorrect battery polarity connection;
The adjustment consists of selecting resistances R2 (1.8k) and R4 (1.2k) until the green LED disappears, with a battery voltage of 14.4V.
CHARGER provides a stabilized load current and is intended for charging motorcycle batteries with a nominal voltage of 6-7V. The charge current is smoothly regulated within 0-2A by variable resistor R1.
The stabilizer is assembled on a composite transistor VT1, VT2, a zener diode VD5 fixes the voltage between the base and emitter of the composite transistor, as a result of which transistor VT1, connected in series with the load, maintains almost D.C. charge, regardless of the change in battery emf during charging. 
The device is a current generator with a large internal resistance, so it is not afraid of short circuits, the voltage is removed from resistor R4 feedback by current, limiting the current through transistor VT1 at short circuit in the load circuit.
CHARGER WITH CHARGING CURRENT CONTROL based on a titistor phase-pulse power regulator, does not contain scarce parts, and if the elements are known to be good, does not require adjustment.
The charging current is similar in shape to pulse current, which is believed to help extend battery life.
The disadvantage of the device is fluctuations in the charging current when the voltage of the electric lighting network is unstable, and like all similar thyristor phase-pulse regulators, the device interferes with radio reception. To combat them, you should provide a network LC filter, similar to those used in network pulse blocks nutrition. 
The circuit is a traditional thyristor power regulator with phase-pulse control, powered from winding II of the step-down transformer through the diode bridge VD1-VD4. The thyristor control unit is made on an analogue of the unijunction transistor VT1,VT2. The time during which capacitor C2 charges before switching the unijunction transistor can be adjusted by variable resistor R1. When the engine is in the extreme right position according to the diagram, the charging current will be maximum and vice versa. Diode VD5 protects the control circuit from reverse voltage that occurs when thyristor VS1 is turned on.
The device parts, except the transformer, rectifier diodes, variable resistor, fuse and thyristor, are located on the printed circuit board.
Capacitor S1-K73-11 with a capacity of 0.47 to 1 µF or K73-16, K73-17, K42U-2, MBGP. Any diodes VD1-VD4 for a forward current of 10A and a reverse voltage of at least 50V. Instead of the KU202V thyristor, KU202G-KU202E will be suitable; powerful T-160, T-250 will also work normally.
We will replace the KT361A transistor with KT361V KT361E, KT3107A KT502V KT502G KT501Zh, and KT315A with KT315B-KT315D KT312B KT3102A KT503V-KT503G. Instead of KD105B, KD105V KD105G or D226 with any letter index will be suitable.
Variable resistor R1 - SGM, SPZ-30a or SPO-1.
Network step-down transformer of the required power with a secondary winding voltage from 18 to 22V.
If the voltage of the transformer on the secondary winding is more than 18V, resistor R5 should be replaced with another of higher resistance (at 24-26V up to 200 Ohms). In the case when the secondary winding of the transformer has a tap from the middle or two identical windings, then it is better to make the rectifier using two diodes according to a standard full-wave circuit.
When the secondary winding voltage is 28...36V, you can completely abandon the rectifier - its role will simultaneously be performed by the thyristor VS1 (rectification is half-wave). For this option, it is necessary to connect a KD105B or D226 separating diode with any letter index (cathode to the board) between pin 2 of the board and the positive wire.
In this case, only those that allow operation with reverse voltage, for example, KU202E.
BATTERY PROTECTION FROM DEEP DISCHARGE.
Such a device, when the voltage on the battery decreases to the minimum permissible value, automatically turns off the load. The devices can be used where batteries are used and where there is no constant monitoring of the battery condition, that is, where it is important to prevent processes associated with their deep discharge.
Slightly modified diagram of the original source: 
Service functions available in the scheme:
1. When the voltage drops to 10.4V, the load and control circuit are completely disconnected from the battery.
2. The comparator operating voltage can be adjusted for a specific battery type.
3. After an emergency shutdown, restarting is possible at a voltage above 11V by pressing the "ON" button.
4. If there is a need to turn off the load manually, just press the "OFF" button.
5. If the polarity is not observed when connecting to the battery (polarity reversal), the control device and the connected load are not turned on.
As a tuning resistor, resistors of any value from 10 kOhm to 100 kOhm can be used.
The circuit uses operational amplifier LM358N, the domestic analogue of which is KR1040UD1.
Voltage stabilizer 78L05 for 5V voltage can be replaced with any similar one, for example, KR142EN5A.
Relay JZC-20F for 10A 12V, it is possible to use other similar relays.
The KT817 transistor can be replaced with a KT815 or another similar one of appropriate conductivity.
You can use any low-power diode that can withstand the current of the relay winding.
Momentary buttons of different colors, green for turning on, red for turning off.
The setup consists of setting the required voltage threshold for turning off the relay; the device, assembled without errors and from serviceable parts, begins to work immediately.
THE FOLLOWING DEVICE for protecting 12v batteries with a capacity of up to 7.5A/H from deep discharge and short circuit with automatic shutdown its output from the load. 
CHARACTERISTICS
The battery voltage at which the shutdown occurs is 10± 0.5V.
The current consumed by the device from the battery when turned on is no more than 1 mA
The current consumed by the device from the battery when turned off is no more than 10 µA
The maximum permissible direct current through the device is 5A.
The maximum permissible short-term (5 sec) current through the device is 10A
Turn-off time in case of a short circuit at the device output, no more than - 100 μs
OPERATING ORDER OF THE DEVICE
Connect the device between the battery and the load in the following sequence:
- connect the terminals on the wires, observing the polarity (red wire +), to the battery,
- connect to the device, observing the polarity (the positive terminal is marked with a + sign), the load terminals.
In order for voltage to appear at the output of the device, you need to briefly short-circuit the negative output to the negative input. If the load is powered by another source besides the battery, then this is not necessary.
THE DEVICE OPERATES AS FOLLOWS;
When switching to battery power, the load discharges it to the response voltage of the protection device (10± 0.5V). When this value is reached, the device disconnects the battery from the load, preventing further discharge. The device will turn on automatically when voltage is supplied from the load side to charge the battery.
If there is a short circuit in the load, the device also disconnects the battery from the load. It will turn on automatically if a voltage of more than 9.5V is applied from the load side. If there is no such voltage, then you need to briefly bridge the output negative terminal of the device and the negative terminal of the battery. Resistors R3 and R4 set the response threshold.
1. PRINTED BOARDS IN LAY FORMAT(Sprint Layout) -
The charger is a 14.2 V parametric voltage stabilizer with a field-effect transistor control element. Gate circuit powerful field effect transistor VT1 is powered from a separate 30 V source.
Schematic diagram of the charger
To obtain an output voltage of 14.2 V, it is necessary to apply a stabilized voltage of about 18 V to the gate of transistor VT1, since the cutoff voltage of the field-effect transistor IRFZ48N reaches 4 V. The voltage at the gate is formed by the parallel stabilizer DA1, fed through resistor R2 from a voltage source of 30 V. Stabilist VD3 introduced to compensate for changes in the EMF of a fully charged battery when the external temperature changes.
If you connect a discharged battery to the charger (an indicator of a deeply discharged battery is an emf of less than 11 V at its terminals), then transistor VT1 will go from the active stabilization mode to a fully open state due to the large difference between the voltage at the gate and at the source: 18 V - 11 V = 7 V, this is 3 V more than the cutoff voltage of 7 V - 4 V = 3 V.
Three volts is enough to open the IRFZ48N transistor. The open channel resistance of this transistor will become negligible. Therefore, the charging current will be limited only by resistor R3 and will be equal to:
(23 V - 11 V) / 1 Ohm = 12 A.
This is the calculated current value. In practice, it will not exceed 10 A due to the voltage drop on the secondary winding of the transformer and on the diodes of the VD2 bridge, while the current will pulsate at twice the network frequency. If the charging current nevertheless exceeds the recommended value (0.1 of the battery capacity), it will not damage the battery, since it will soon begin to decrease quickly. As the battery voltage approaches the stabilization voltage of 14.2 V, the charging current will decrease until it stops altogether. The device can remain in this state for a long time without the risk of overcharging the battery.
Lamp HL1 indicates that the device is connected to the network, and HL2 signals, firstly, that fuse FU2 is working properly and, secondly, that the battery being charged is connected. In addition, the HL2 lamp serves as a small load, making it easier to accurately set the output voltage.
The device must use a network transformer with an overall power of at least 150 W. Winding II should provide a voltage of 17...20 V at a load current of 10 A, and winding III - 5...7 V at 50...100 mA. The IRFZ48N transistor can be replaced with an IRFZ46N. If the device is used to charge batteries with a capacity of no more than 55 Ah, then the IRFZ44N transistor (or the domestic one KP812A1) is suitable.
We will replace the GBPC15005 rectifier bridge with four diodes D242A, D243A or similar. Instead of KD243A, it is possible to use a KD102A or KD103A diode. Resistor R3 is made of nichrome wire with a diameter of at least 1 mm. It is wound onto a ceramic rod, and each of the terminals is clamped under an M4 screw with a nut and a soldering tab. The resistor should be mounted so that nothing interferes with its natural cooling by air flow.
The KS119A stabilizer will replace four KD522A diodes connected in series according to. Instead of TL431, its domestic analogue KR142EN19A is suitable. Resistor R6 should be selected from the SP5 series.
Transistor VT1 must be installed on a heat sink with a useful area of 100...150 cm 2. The thermal power during the charging process will be distributed between the transistor and resistor R3 as follows: at the initial moment, when the transistor is open, all the thermal power will be released on resistor R3; by the middle of the charging cycle, the power will be distributed equally between them, and for the transistor this will be a maximum heating (20...25 W), and by the end the charging current will decrease so much that both the resistor and the transistor will remain cold.
After assembling the device, it is only necessary to set the threshold voltage at the output to 14.2 V using trimming resistor R6 before connecting the battery.
The device described in the article is simple and easy to use. However, it must be borne in mind that not all batteries have an emf of 14.2 V when charged. Moreover, during their service life it does not remain constant due to destructive changes in the battery plates. This means that if the charger is adjusted as the author recommends, some batteries will be undercharged, while others will be overcharged and may “boil”. The EMF also depends on the temperature of the battery.
Therefore, for each battery instance, it is necessary to first determine the optimal value of its EMF by controlled charging until the first signs of “boiling” and, taking into account the temperature, set this value in the charger. It is also advisable in the future to periodically (at least once a year) check the EMF and adjust the threshold voltage setting of the charger.
V. Kostitsyn
Radio 3-2008
www.radio.ru
The need for a charger for lead-acid batteries arose a long time ago. First charger was also made for a 55Ah car battery. Over time, maintenance-free gel batteries of various denominations appeared in the household, which also needed charging. Provide a separate charger for each battery, at least, unreasonable. Therefore, I had to pick up a pencil, study the available literature, mainly the Radio magazine, and, together with my comrades, come up with the concept of a universal automatic charger (UAZU) for 12-volt batteries from 7AH to 60AH. I present the resulting design to your judgment. Made in iron more than 10 pcs. with various variations. All devices work flawlessly. The scheme can be easily repeated with minimal settings.
The power supply from an old AT format PC was immediately taken as a basis, since it has a whole complex positive qualities: small size and weight, good stabilization, power with a large margin, and most importantly, a ready-made power unit, to which it remains to screw the control unit. The idea of the control unit was suggested by S. Golov in his article “Automatic charger for a lead-acid battery,” Radio magazine No. 12, 2004, special thanks to him.
I will briefly repeat the battery charging algorithm. The whole process consists of three stages. At the first stage, when the battery is completely or partially discharged, it is permissible to charge with a high current, reaching 0.1:0.2C, where C is the battery capacity in ampere-hours. The charging current must be limited above the specified value or stabilized. As charge accumulates, the voltage at the battery terminals increases. This voltage is controlled. Upon reaching the level of 14.4 - 14.6 volts, the first stage is completed. At the second stage, it is necessary to maintain the achieved voltage constant and control the charging current, which will decrease. When the charge current drops to 0.02C, the battery will gain a charge of at least 80%, we proceed to the third and final stage. We reduce the charge voltage to 13.8 V. and we support it at this level. The charge current will gradually decrease to 0.002:.001C and stabilize at this value. This current is not dangerous for the battery; the battery can remain in this mode for a long time without harm to itself and is always ready for use.
Now let's actually talk about how this is all done. The power supply from the computer was chosen based on the consideration of the greatest distribution of the circuit design, i.e. The control unit is made on the TL494 microcircuit and its analogues (MB3759, KA7500, KR1114EU4) and slightly modified:
The 5V, -5V, -12V output voltage circuits were removed, the 5 and 12V feedback resistors were sealed off, and the overvoltage protection circuit was disabled. On the fragment of the diagram, the places where the circuits are broken are marked with a cross. Only the 12V output part is left; you can also replace the diode assembly in the 12V circuit with an assembly removed from the 5-volt circuit; it is more powerful, although not necessary. All unnecessary wires were removed, leaving only 4 black and yellow wires, 10 centimeters long, for the output of the power unit. We solder 10 cm long wires to the 1st leg of the microcircuit; this will be the control. This completes the modification.
In addition, the control unit, at the request of numerous people who want to have such a thing, implements a training mode and a protection circuit against battery reverse polarity for those who are especially inattentive. And so BU:
Main nodes:
parametric reference voltage stabilizer 14.6V VD6-VD11, R21
A block of comparators and indicators that implement three stages of battery charging DA1.2, VD2 first stage, DA1.3, VD5 second, DA1.4, VD3 third.
Stabilizer VD1, R1, C1 and dividers R4, R8, R5, R9, R6, R7 forming the reference voltage of the comparators. Switch SA1 and resistors provide changing the charging mode for different batteries.
Training block DD K561LE5, VT3, VT4, VT5, VT1, DA1.1.
Protection VS1, DA5, VD13.
How it works. Let's assume that we are charging a 55Ah car battery. Comparators monitor the voltage drop across resistor R31. At the first stage, the circuit works as a current stabilizer; when turned on, the charging current will be about 5A, all 3 LEDs are lit. DA1.2 will hold the charge current until the voltage on the battery reaches 14.6 V., DA1.2 will close, VD2 will turn off red. The second stage has begun.
At this stage, the voltage of 14.6 V on the battery is maintained by the stabilizer VD6-VD11, R21, i.e. The charger operates in voltage stabilization mode. As the battery charge increases, the current drops and as soon as it drops to 0.02C, DA1.3 will operate. The yellow VD5 will go out and the transistor VT2 will open. VD6, VD7 are bypassed, the stabilization voltage drops abruptly to 13.8 V. We moved on to the third stage.
Then the battery is recharged with a very small current. Since by this moment the battery has gained approximately 95-97% of its charge, the current gradually decreases to 0.002C and stabilizes. On good batteries may drop to 0.001C. DA1.4 is configured to this threshold. The VD3 LED may go out, although in practice it continues to glow faintly. At this point, the process can be considered complete and the battery can be used for its intended purpose.
Training mode.
When storing a battery for a long time, it is recommended to periodically train it, as this can extend the life of old batteries. Since the battery is a very inertial thing, charging and discharging should last several seconds. In the literature there are devices that train batteries at a frequency of 50Hz, which has a sad effect on its health. The discharge current is approximately a tenth of the charge current. In the diagram, switch SA2 is shown in the training position, SA2.1 is open SA2.2 is closed. The discharge circuit VT3, VT4, VT5, R24, SA2.2, R31 is turned on and the trigger DA1.1, VT1 is cocked. A multivibrator is assembled on elements DD1.1 and DD1.2 of the K561LE5 microcircuit. It produces a meander with a period of 10-12 seconds. The trigger is cocked, element DD1.3 is open, pulses from the multivibrator open and close transistors VT4 and VT3. When open, transistor VT3 bypasses diodes VD6-VD8, blocking charging. The battery discharge current goes through R24, VT4, SA2.2, R31. The battery takes 5-6 seconds to receive a charge and the same time is discharged with a low current. This process lasts for the first and second charging stages, then the trigger fires, DD1.3 closes, VT4 and VT3 close. The third stage takes place in normal mode. There is no need for additional indication of the training mode, since the LEDs VD2, VD3 and VD5 are flashing. After the first stage, VD3 and VD5 flash. At the third stage, VD5 lights up without blinking. In training mode, the battery charge lasts almost 2 times longer.
Protection.
In the first designs, instead of a thyristor, there was a diode that protected the charger from reverse current. It works very simply; when turned on correctly, the optocoupler opens the thyristor, and you can turn on charging. If it is incorrect, the VD13 LED lights up, swap the terminals. Between the anode and cathode of the thyristor you need to solder a non-polar capacitor of 50 μF 50 volts or 2 back-to-back electrolytes 100 μF 50 V.
Construction and details.
The charger is assembled in the power supply unit from the computer. The BU is manufactured using laser-iron technology. The printed circuit board drawing is attached in an archive file, made in SL4. Resistors MLT-025, resistor R31 - a piece of copper wire. Measuring head PA1 may not be installed. It was just lying around and was adapted. Therefore, the values of R30 and R33 depend on the milliammeter. Thyristor KU202 in plastic design. The actual execution can be seen in the attached photos. The monitor power connector and cable were used to turn on the battery. The charging current selection switch is small-sized with 11 positions, resistors are soldered to it. If the charger will only charge car batteries You don’t have to install the switch by simply soldering a jumper. DA1 - LM339. Diodes KD521 or similar. The PC817 optocoupler can be supplied with another one with a transistor actuator. The BU scarf is screwed to an aluminum plate 4 mm thick. It serves as a radiator for the thyristor and KT829, and LEDs are inserted into the holes. The resulting block is screwed to the front wall of the power supply unit. The charger does not heat up, so the fan is connected to the power supply via a KR140en8b stabilizer, the voltage is limited to 9V. The fan rotates more slowly and is almost inaudible.
Adjustment.
Initially, we install a powerful diode instead of the thyristor VS1, without soldering in VD4 and R20, we select zener diodes VD8-VD10 so that the output voltage, without load, is 14.6 volts. Next, we solder VD4 and R20 and select R8, R9, R6 to set the response thresholds of the comparators. Instead of a battery, we connect a 10 Ohm wirewound variable resistor, set the current to 5 amperes, solder in a variable resistor instead of R8, turn it at a voltage of 14.6 V, the VD2 LED should go out, measure the introduced part of the variable resistor and solder in a constant one. We solder in a variable resistor instead of R9, setting it to approximately 150 Ohms. We turn on the charger, increase the load current until DA1.2 operates, then begin to reduce the current to a value of 0.1 ampere. Then we reduce R9 until the comparator DA1,3 works. The voltage across the load should drop to 13.8V and the yellow VD5 LED will go out. We reduce the current to 0.05 ampere, select R6 and extinguish VD3. But it is best to carry out adjustments on a good, discharged battery. We solder in the variable resistors, set them a little larger than those indicated in the diagram, connect the ammeter and voltmeter to the battery terminals and do this in one go. We use a battery that is not very discharged, then it will be faster and more accurate. Practice has shown that virtually no adjustment is required if you select R31 accurately. Additional resistors are also easy to select: with the appropriate load current, the voltage drop across R31 should be 0.5V, 0.4V, 0.3V, 0.2V, 0.15V, 0.1V and 0.07V.
That's all. Yes, also, if you short-circuit the VD6 diode with one half and the VD9 zener diode with an additional two-pole toggle switch, you will get a charger for 6-volt helium batteries. The charge current must be selected with the smallest switch SA1. On one of the collected ones, this operation was successfully carried out.
