We offer the idea of making a charger for any lead-acid batteries from motorcycles or cars, with minimal effort. It was created on the basis of a 14 V / 5 A switching power supply. You can use almost any ready-made switching power supply with an output voltage of 12 - 15 V, which will undergo a little modification. By the way, a similar trick can be done from a computer PSU -
14 volt switching power supply Charger features
- voltage limit 14.2 V
- minimum output voltage (battery discharged) 6 V
- charging current switchable 0.8A / 3.5A
Additionally, you will need LED indicators: green and red, NPN transistor. The red LED indicates the battery is being charged, and the green LED indicates that the voltage limit has been reached (charging completed).
Warning: the power adapter contains voltages that are dangerous to life and health. Such refinement should be undertaken only by experienced electronics engineers who have experience with switching power supplies!
The modification concerns only the elements on the secondary side of the transformer.
The idea is based on correcting (if necessary) the output voltage of the power supply, adding a current limiter and LEDs informing about the charger's operating mode.
Refinement scheme
The original UPS diagram 
Refinement scheme UPS Upgrade Sequence
1) Selecting the output voltage.
Power adapters often use the TL431 to stabilize the output voltage. The output voltage sets the divider R1 and R2, where the voltage across R2 is always 2.5 V. The output voltage (in voltage stabilization mode, the battery is charged) is 2.5 V x (1 + R1 / R2). To get a voltage of 14.2 V, if the power supply provides 12 V, you need to increase R1 or decrease R2. This power supply outputs 14.1 V, so it was decided not to change the divider data.
2) Adding a green LED and resistor R4 in parallel with the optocoupler.
In the voltage regulation mode, TL431 controls the current of the optocoupler LED in order to obtain stabilization in this way. If the output voltage is too low, the TL431 closes and no current flows through the optocoupler. By putting a green LED, we get information about reaching the voltage stabilization mode, that is, the battery charge. During normal operation, the current of the optocoupler is only about 0.5 mA, that is, the green diode lights up weakly. To make its glow brighter, we connect a 220 Ohm resistor R4 in parallel with the optocoupler. It increases the current of the green diode to about 5 mA.
3) Adding a current limit hysteresis loop
Usually, the microcircuit that controls the operation of the converter is responsible for limiting the current. If there is a strong overload at the output, for example, during a short circuit, the controller is not able to start the PSU on its own. In the battery charging system, it is necessary to make this current limiting mode become the normal mode. To this end, we add the elements: R5 (power resistor), R6 (about 1 kOhm, protection of the base of the transistor in case of a short circuit of the output), transistor T1 and a red LED. The current limit value is ~0.65V/R5. The default resistor R5 is 0.82 ohm (0.8 A), which is connected in parallel with the switch, the 0.22 ohm / 5 V resistor (then the current will be 3.5 A). Resistors get quite hot - which is the biggest drawback of the accepted solution. Instead of limiting with a single transistor, an op amp or current mirror can be used.
Is it possible to use a PSU from a laptop?
Unfortunately, power supplies from laptops that give 19.5 V at the output are not suitable for rework. This is due to the fact that the voltage is produced by the auxiliary winding and the self-sustaining operation of the device. If we lower the voltage from 19.5 to 14.2 V, this will also reduce the auxiliary supply voltage of the converter controller chip. With 14.2 output, the system will work well, but if the voltage drops below 12 V (with a dead battery), the converter will not be able to start. With the same PSU, the start takes place even from 6 V - that is, there is a large margin.
Converted PSU to memory Possible improvements
In this article I will tell you how to make a rather “smart” charger for lead-acid batteries from an AT / ATX format computer power supply and a home-made control unit. These include the so-called. "UPS-ovye", automotive and other batteries of wide application.Description
The device is designed for charging and training (desulfation) of lead-acid batteries with a capacity of 7 to 100 Ah, as well as for an approximate assessment of their charge level and capacity. The charger has protection against incorrect switching on of the battery (polarity reversal) and against short circuits of accidentally thrown terminals. It uses microcontroller control, thanks to which safe and optimal charging algorithms are carried out: IUoU or IUIoU, followed by a “finishing” up to 100% charge level. Charging parameters can be adjusted for 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 whole device is freely mounted in the case 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 time-consuming adjustments, which is especially important for beginner radio amateurs.
]1. Charging mode - "Charge" menu. For batteries with a capacity of 7Ah to 12Ah, the IUoU algorithm is set by default. This means:
- the first stage is 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 to maintain a stable voltage of 13.8V until the current drops to 0.01C. Here C is the capacity of the battery in Ah.
- the fourth stage - "finishing". At this stage, the battery voltage is monitored. If it falls below 12.7V, the charge is turned on from the very beginning.
For starter batteries (from 45 Ah and above), we use the IUIoU algorithm. Instead of the third stage, current stabilization at the level of 0.02C is turned on until the battery voltage reaches 16V or after about 2 hours. At the end of this stage, charging stops and “finishing” begins. This is the fourth stage. The charging process is illustrated by graphs in Fig.1 and Fig.2.
2. Training mode (desulfation) - menu "Training". 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 - 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 switched 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 10.8V, and then the corresponding selected mode will turn on. In this case, the current and discharge time are measured, thus, the approximate capacity of the battery is calculated. These parameters are displayed on the display after charging is completed (when the message “Battery is charged” appears) by pressing 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 (current of 10 or 20 hour discharge).
Navigation through the menu is carried out using the buttons "left", "right", "select". The "reset" button exits from any mode of the memory 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 adjusted parameters are stored 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. After selecting the desired option, 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 with 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 in 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 stage of charging 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. The default is 16V.
5. "Current of the 2nd stage I2". This is the current value at which the second stage of charging ends. Stabilization current at the third stage for the IUIoU algorithm. The default value is 0.2S.
6. "End of charge I3". This is the value of the current, upon reaching which the charging is considered completed. The default value is 0.01S.
7. "Discharge current". This is the value of the current that discharges the battery during training with charge-discharge cycles.
Selection and alteration of the power supply.
In our design, we use a power supply from a computer. Why? There are several reasons. Firstly, this is an almost ready-made power unit. Secondly, this is 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 the variety of models of power supplies, we are best suited for an ATX format unit with a power of at least 250 watts. It is only necessary to take into account 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 PSU, you just have to make a low-power standby power supply (duty) 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 on its own, the power supply for the PWM controller chip is taken from the 12-volt winding of the transformer. In ATX, for the initial power supply of the microcircuit, a separate 5V source is used, called the “standby power supply” or “duty”. You can read more about power supplies, for example, here, and the conversion of a PSU 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, take out the fuse and instead solder a 220 volt incandescent lamp with a power of 100-200W. If there is a mains voltage switch on the rear panel of the PSU, then it must be set to 220V. We turn on the PSU in the network. The AT power supply starts immediately, for ATX you need to close the green and black wires on the large connector. If the light does not glow, the cooler rotates, and all output voltages are normal, then we are lucky and our power supply is working. Otherwise, you will have to repair it. Leave the bulb in place for now.
To convert the PSU into our future charger, we 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 the current protection and voltage limits are implemented. The alteration scheme is shown in Fig.3.
It shows only one channel of the output voltage: +12V. Other 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, can be useful to us for the control unit. More on this later. Items that are installed additionally are marked in red. Capacitor C2 must have an operating voltage of at least 35V and is installed instead of the existing one in the PSU. After the “strapping” of the TL494 is shown in the diagram in Fig. 3, we turn on the PSU in the network. The voltage at the PSU output is determined by the formula: Uout = 2.5 * (1 + R3 / R4) and, with the ratings indicated in the diagram, should be about 10V. If this is not the case, you will have to check the correct installation. This completes the alteration, you can remove the light bulb and put the fuse in place.
Scheme and principle of operation.
The diagram of the control unit is shown in Fig.4.
It is quite simple, since all the main processes are performed by the microcontroller. A control program is recorded in its memory, in which all algorithms are embedded. The power supply is controlled using PWM from the PD7 output of the MK and the simplest DAC on the elements R4, C9, R7, C11. Measurement of battery voltage and charging current is carried out by means of 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. Charging and discharging current are measured as follows. The voltage drop from the measuring resistor R8 through the R5R6R10R11 dividers is fed to the amplifying stage, which is located inside the MK and connected to the terminals PA2, PA3. Its gain is set by software, depending on the measured current. For currents less than 1A, the gain factor (KU) is set equal to 200, for currents above 1A, KU=10. All information is displayed on the LCD connected to the ports РВ1-РВ7 via a four-wire bus. Reverse polarity protection is made on the transistor T1, signaling the wrong connection - on the elements VD1, EP1, R13. When the charger is connected to the network, transistor T1 is closed low from the PC5 port, and the battery is disconnected from the charger. It is connected only when the type of battery and the mode of operation of the memory are selected in the menu. This also ensures that there is no sparking when the battery is connected. When you try to connect the battery in the wrong polarity, the buzzer EP1 and the red LED VD1 will work, signaling a possible accident. During the charging process, the charging current is constantly monitored. If it becomes equal to zero (the terminals were removed from the battery), the device automatically switches to the main menu, stopping the charge and disconnecting the battery. Transistor T2 and resistor R12 form a discharge circuit that 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 will automatically turn off when the charge current drops below 1.8A. The cooler is controlled by port PD4 and transistor VT1.
Details and design.
microcontroller. On sale, they are usually found in the DIP-40 or TQFP-44 package and are marked as follows: ATMega16A-PU or ATMega16A-AU. The letter after the hyphen indicates the package type: "P" - DIP package, "A" - TQFP package. There are also discontinued ATMega16-16PU, ATMega16-16AU or ATMega16L-8AU microcontrollers. In them, the number after the hyphen indicates the maximum clock frequency of the controller. The ATMEL manufacturer recommends using ATMega16A controllers (namely with the letter “A”) in the TQFP package, that is, these are: ATMega16A-AU, although all of the above instances will work in our device, which was confirmed by practice. Case types also differ in the number of pins (40 or 44) and their purpose. Figure 4 shows a schematic diagram of a control unit for an MK in a DIP package.
Resistor R8 - ceramic or wire, with a power of at least 10 W, R12 - 7-10W. All others - 0.125W. Resistors R5, R6, R10 and R11 must be used with a tolerance 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.
Transistors T1 and T1 are preferably used as indicated in the diagram. But if you have to select a replacement, then it must be borne in mind that they must be opened with a gate voltage of 5V and, of course, must withstand a current of at least 10A. Suitable, for example, transistors marked 40N03GP, which are sometimes used in the same ATX PSUs, in a 3.3V stabilization circuit.
The Schottky diode D2 can be taken from the same PSU, from the + 5V circuit, which we do not use. Elements D2, T1 and T2 are placed through insulating gaskets on one radiator with an area of 40 square centimeters. Buzzer EP1- with a built-in generator, for a voltage of 8-12 V, the sound volume can be adjusted with a resistor R13.
LCD display - WH1602 or equivalent, on HD44780, KS0066 controller or compatible. Unfortunately, these indicators may have different pinouts, so you may have to design a printed circuit board for your copy.
Program
The control program is contained in the “Program” folder. 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).
Adjustment
So, the power supply is redone and produces a voltage of about 10V. When a working control unit with a flashed MK is connected to it, the voltage should drop to 0.8..15V. Resistor R1 sets the contrast of the indicator. Adjustment of the device consists in checking and calibrating the measuring part. We connect the battery to the terminals, or a power supply with a voltage of 12-15V and a voltmeter. Go to the "Calibration" menu. We compare the voltage readings on the indicator with the readings of the voltmeter, if necessary, correct them with the buttons "<» и «>". We press "Select". Next comes the current calibration at KU=10. The same buttons<» и «>» you need to set zero current readings. The load (battery) is then automatically disconnected, so that there is no charge current. Ideally, there should be zeros or values very close to zero. If so, this indicates the accuracy of the resistors R5, R6, R10, R11, R8 and the good quality of the differential amplifier. We press "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 completed. 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 apply (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 carefully check once again that the power supply has been modified correctly. Perhaps the protection is working.
And finally, a few photos.
Arrangement of elements in the power supply case:
The finished design might look like this:
So:
or even like this:
ARCHIVE:Download
The charger is a 14.2 V parametric voltage regulator with a field-effect transistor control element. The gate circuit of a powerful field-effect transistor VT1 is powered by 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 the transistor VT1, since the cutoff voltage of the field-effect transistor IRFZ48N reaches 4 V. The voltage at the gate forms a parallel regulator DA1, fed through a resistor R2 from a source of 30 V. Stabistor VD3 introduced to compensate for changes in the EMF of a fully charged battery when the external temperature changes.
If a discharged battery is connected to the charger (the indicator of a deeply discharged battery is the EMF less than 11 V at its terminals), then the transistor VT1 will switch 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 - 11V = 7V, that's 3V more than the 7V cutoff voltage - 4V = 3V.
Three volts to open the IRFZ48N transistor is enough. The open channel resistance of this transistor will become negligible. Therefore, the charging current will be limited only by the resistor R3 and will become equal to:
(23 V - 11 V) / 1 ohm = 12 A.
This is the calculated value of the current. 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 mains frequency. If the charging current still exceeds the recommended value (0.1 of the battery capacity), then it will not damage the battery, as it will soon begin to decline rapidly. As the battery voltage approaches the stabilization voltage of 14.2 V, the charging current will decrease until it stops altogether. In this state, the device can be left for a long time without the risk of overcharging the battery.
The HL1 lamp indicates that the device is connected to the network, and HL2 signals, firstly, the health of the FU2 fuse and, secondly, the connection of a rechargeable battery. In addition, the HL2 lamp serves as a small load, making it easy to accurately set the output voltage.
The device must use a network transformer with an overall power of at least 150 W. Winding II must provide a voltage of 17 ... 20 V at a load current of 10 A, and winding III - 5 ... 7 V at 50 ... 100 mA. Transistor IRFZ48N can be replaced with IRFZ46N. If the device is used to charge batteries with a capacity of not more than 55 Ah, then the IRFZ44N transistor (or domestic. KP812A1) is suitable.
We will replace the GBPC15005 rectifier bridge with four D242A, D243A or similar diodes. 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 on a ceramic rod, and each of the leads is clamped under an M4 screw with a nut and a soldering lug. The resistor should be mounted in such a way that nothing interferes with its natural cooling by air flow.
The stabistor KS119A will replace four KD522A diodes connected in series according to. Instead of TL431, its domestic counterpart KR142EN19A will do. Resistor R6 should be selected from the SP5 series.
Transistor VT1 must be installed on a heat sink with a usable area of 100 ... 150 cm 2. Thermal power during charging will be distributed between the transistor and resistor R3 as follows: at the initial moment, when the transistor is open, all 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 the 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 of 14.2 V at the output with a 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 battery instances have an EMF equal to 14.2 V when charged. Moreover, it does not remain constant during the service life due to destructive changes in the battery plates. This means that if the charger is adjusted as recommended by the author, 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 instance of the battery, 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 setting of the threshold voltage of the charger.
V. Kostitsyn
Radio 3-2008
www.radio.ru
CHARGER
FOR ACID - LEAD FREE SLA BATTERIES CAPACITY 4 ... 17 Ah
Maintenance-free lead-acid batteries are now very widely used in various computer uninterruptible power supplies, burglar alarm systems, power tool power supplies, and even children's toys. Their advantage is ease of operation, the absence of liquid electrolyte and, accordingly, there is no need to monitor its level and density. To reduce the time to restore electrical capacity, these batteries are usually charged with a high current (fast charge mode), numerically reaching the nominal capacity. Due to the inability to top up the boiled-off electrolyte during its recharging, the requirements for the charging current of these batteries are very stringent - battery manufacturers require that the charging current ripple does not exceed 2.5% of the maximum current, and the charging current changes over time in a strictly defined way . These conditions are almost always met in uninterruptible power supplies containing complex switching power supplies. The pulse chargers with key transistors and a storage choke previously described in this section satisfy the same requirements. The considered schemes are quite difficult to repeat, and in everyday life the simplest small-sized chargers are often required, which are not the most optimal in terms of ensuring the development of the maximum battery life, but having small dimensions and high efficiency. Below is a diagram of such a device. The charging current of the battery is maintained stable at the level of 10% of the numerical value of the nominal capacity, which reduces the negative effect of the pulsed nature of this current, and charging stops when the voltage at the battery terminals reaches approximately 15V.
The required value of the charging current is achieved by selecting the resistance of the resistor R8. The values of the threshold voltages for switching off the charging process are determined by the ratio of the resistors R12/R6 and R12/R6||R2. When calculating the resistor values, it is assumed that when the maximum voltage on the battery is reached, the voltage at pin 16 of the DA1 chip should be 5.00V. During charging, the brightness of the HL1 LED changes, and when fully charged, the LED starts flashing, attracting attention.
The circuit is a modification of the previously described device. A thyristor is used as a regulating element, which makes it possible to simplify the circuit by eliminating large capacitors and chokes. All elements of the device, except for the power transformer, are located on a small printed circuit board 45 x 45 mm. 
The efficiency of the device is very high and the circuit elements, including the thyristor, do not require a radiator for cooling.
The proposed device can also be used to charge other types of batteries by adjusting the charging current and the cut-off threshold voltage. By replacing the power diodes and the transformer with more powerful ones and installing the thyristor on a small radiator, the circuit can also be used to charge car batteries. The resistance of the resistor R8 is reduced by 5-10 times. If there are no errors in the installation and the serviceability of the elements, the circuit starts working immediately. It is only necessary to adjust the charging current and the threshold voltage.
CHARGER DIAGRAM
FOR (sealed, maintenance-free) BATTERIES.
AGM TECHNOLOGY BATTERIES(Absorbent Glass Mat) - the difference between these batteries and the 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 manufactured using AGM technology work perfectly in buffer mode, i.e. in recharging mode, in this mode they serve up to 10-15 years (batteries-12V). If they are used in a cyclic mode (that is, constantly charge-discharge at least 30% -40% of the capacity), then their service life is reduced. Almost all sealed batteries can be mounted on their side, however the manufacturer generally recommends batteries be mounted in the "normal", upright position.
General purpose AGM batteries are commonly used in low-cost UPS (non-interruptible) and standby power systems, that is, where the batteries are mainly in recharge 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 that 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 accumulator, and this is called gas recombination. This technology allows the use of a constant amount of electrolyte without the addition of water for the entire life of the battery, and its increased resistance to discharge currents prevents the formation of "harmful" indestructible lead sulfates.
Gel batteries have about 10-30% longer life than AGM batteries and are better able to withstand charge-discharge cycling, and they are less painful to deep discharge. Such batteries are recommended for use where it is required to ensure a long service life with deeper discharge modes.
Due to their characteristics, gel batteries can be discharged for a long time, have a low self-discharge, they can be used in a residential area and in almost any position.
Most often, such batteries for a voltage of 6V or 12V are used in computer backup power supplies (UPS), security and measuring systems, flashlights and other devices that require independent power supply. The disadvantages include the need for strict adherence to charge modes.
As a rule, when charging such batteries, the charge current is set at 0.1C, where C is the capacity of the battery, 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 20-30mA at the end of the charge. Similar batteries are produced by many manufacturers, and their parameters may differ, and, above all, in terms of the maximum allowable charging current, therefore, before use, it is advisable to study the documentation of a particular battery instance.
To charge batteries manufactured using GEL and AGM technology, it is necessary to use a special charger with appropriate charging parameters, which are different from charging classic batteries with liquid electrolyte.
The following is a selection of various schemes for charging such batteries, and if we make it 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 (7.2Ah).
Charger circuit on the L200C chip which is a voltage stabilizer with a programmable output current limiter. 
Fig.2 Diagram of the charger.
The power of the resistors R3-R7 that set the charge current should be no less than that indicated in the diagram, and preferably more.
The microcircuit must be installed on a radiator, and the easier its thermal regime is, 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 large, and by the end it drops to the minimum, as a rule, manufacturers recommend just such an insignificant current for a long time to preserve the capacity of the battery.
Fig.3 Board of the finished device.
Scheme of the charger, which is based on integrated voltage stabilizers KR142EN22, uses “current-limiting constant voltage charging” and is designed to charge various types of batteries. 
The circuit works like this: first, a rated current is applied to a discharged battery, and then, as the battery is charged, the voltage on the battery increases, and the current remains unchanged, when the set voltage threshold is reached, its further growth stops, and the current begins to decrease.
By the end of charging, the charging current is equal to the self-discharge current, in this state the battery can be in the charger for as long as you like 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, the maximum current limiting unit (DA1.R1-R6) and the voltage regulator (DA2, R7-R9). Both of these parts are made according to standard schemes.
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 the charging time, the value of 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, then you should not save on the power of the current-setting resistors R1-R6, and in general it is advisable to choose all the elements with a margin. In addition to increasing reliability, this will improve the thermal regime of the entire device.
Trimmer resistors, it is desirable to take multi-turn SP5-2, SP5-3 or their analogues.
Capacitors: C1 - K50-16, K50-35 or an imported analogue, C2, SZ, metal-film type K73 or ceramic K10-17, KM-6 can be used. Imported diodes 1N5400 (3A, 50V), if there is free space in the case, it is advisable to replace with domestic ones in metal cases such as D231, D242, KD203, etc.
These diodes dissipate heat quite well with their cases, and when working in this device, their heating is almost imperceptible.
The step-down transformer must provide maximum charging current for a long time without overheating. The voltage on winding II is 12V (charging 6V 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 it must be taken into account that the output voltages 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.
Establishing the device should begin with setting resistors R7 and R8 to the required voltages at the output terminals of the device without connecting the load. Resistor R7 sets the voltage within 14.5 ... 14.9V to charge 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 10W in the mode of charging 6-volt batteries, the output current is checked with an ammeter for all positions of the switch SB1.
VARIANT OF THE DEVICE FOR CHARGING THE BATTERY12V-7.2AH,the circuit is the same as the previous one, only the 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, with the resistor R3 without connecting the load, the output voltage is set within 14.5 ... 14.9V, and then with the connected load, by selecting the resistor R2, the output current is set 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 the charging current and voltage, then connect the battery and plug the device into 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 allowable charging current of 0.25C.
Integrated voltage stabilizer KR142EN12 (LM317) allows you to create a simple source of stable current,
the microcircuit in such an inclusion is a current stabilizer and, regardless of the connected battery, it produces only the rated current - the voltage is set "automatically". 
Advantages of the proposed device.
Not afraid of short circuits; no matter the number of cells in the rechargeable battery and their type - you can charge acid sealed 12.6V and lithium 3.6V and alkaline 7.2V. The current switch should be turned on as shown in the diagram - so that during any manipulations, the resistor R1 remains connected.
The charging current is calculated as follows: I (in amps) = 1.2V/R1 (in ohms). To indicate the current, a transistor (germanium) was used, which makes it possible to visually observe currents up to 50 mA.
The maximum voltage of the rechargeable battery must be less than the supply (charging) voltage by 4V; in case of charging with a maximum current of 1A, the 142EN12 chip should be installed on a radiator that dissipates at least 20W.
Charging current 0.1 of the capacity is suitable for all types of batteries. To fully charge the battery, it must be given 120% of the nominal charge, but before that it must be completely discharged. Therefore, the charging time in the recommended mode is 12 hours.
Details:
Diode D1 and fuse F2 protect the charger from improperly turning on the battery. Capacitance C1 is selected from the ratio: 1 Ampere needs 2000 microfarads.
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 the resistors R3-R6 determine the current. The KR142EN12 microcircuit is interchangeable with any analogues that can withstand a given current. Transformer power - not less than 20W.
SIMPLE CHARGER FOR LM317, the scheme is as in the description (Datasheet), we add only some elements, and we get a charger. 
The diode VD1 is added so that the battery being charged is not discharged in the event of a loss of mains power, a voltage switch is also added. The charge current is set in the region of 0.4A, the VT1-2N2222 transistor can be replaced with KT3102, any S1 switch has two positions, a 15V transformer, a diode bridge on 1N4007
The charge current is set (1/10 of the battery capacity) using the resistor R7, calculated by the formula R = 0.6 / I charge.
In this example it is R7=0.6/0.4=1.5ohm. Power 2W.
Setting.
We connect it to the network, set the required voltages, for battery-6V the charge voltage is 7.2V-7.5V, for battery-12V it is 14.4-15V, it is set by resistors R3, R5, respectively.
CHARGER WITH AUTOMATIC SHUT OFF for charging a 6V sealed lead battery, with minimal changes, 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, the battery charge stops when the voltage at the terminals reaches 7.3V. The charge is carried out with an unstabilized current, limited at the level of 0.1C by resistor R5. The voltage level at which the device will stop charging is set by the Zener diode VD1 with an accuracy of tenths of a volt.
The basis of the circuit is an operational amplifier (op-amp), included as a comparator, and connected by an inverting input to a reference voltage source (R1-VD1), and not by an inverting one to the battery. As soon as the voltage on the battery exceeds the reference voltage, the comparator switches to a single state, the transistor T1 opens and the relay K1 disconnects the battery from the voltage source, simultaneously applying a positive voltage to the base of the 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, jumpy output switching and opening of the transistor. This eliminates the disadvantage of similar mechanical relay devices, where the relay makes an unpleasant rattling sound due to the contacts balancing at the switching boundary, but not switching on yet. 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 recharged. 
A device assembled from serviceable parts starts working immediately and does not need to be configured. The operational amplifier indicated in the diagram can operate in the supply voltage range from 3 to 30 volts. The cut-off voltage depends only on the parameters of the zener diode. When connecting a battery with a different voltage, for example 12V, the VD1 zener diode 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 regulator DA1 type KR142EN5A (7805), an HL1 LED and a resistor R1. The LED, in addition to working in a current stabilizer, also performs the function of an indicator of the battery charge mode. The battery is charged with direct current. 
AC voltage from transformer Tr1 is supplied to the diode bridge VD1, current stabilizer (DA1, R1, VD2).
Setting up the circuit is reduced to adjusting the battery charge current. The charging current (in amperes) is usually chosen ten times less than the numerical value of the battery capacity (in ampere-hours).
To set up, instead of a battery, you need to connect an ammeter for a current of 2 ... 5A and, by selecting a resistor R1, set the desired charge current through it.
Chip DA1 must be installed on the radiator.
Resistor R1 consists of two 12W wirewound resistors connected in series.
DUAL-MODE CHARGER.
The proposed 6V battery charger circuit combines the advantages of two main types of chargers: constant voltage and constant current, each of which has its own advantages. 
The basis of the circuit is a voltage regulator on the LM317T and a controlled zener diode TL431.
In constant current mode, resistor R3 sets a current of 370 mA, diode D4 prevents the battery from discharging through the LM317T when the mains voltage fails, resistor R4 ensures that the transistor VT1 is unlocked when the mains voltage is applied.
Controlled zener diode TL431, resistors R7, R8 and potentiometer R6 form a circuit that determines the charge of the battery to a given voltage. LED VD2 - 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 a voltage of 220V, the charge is carried out by a small pulsed current (0.1-0.15 A).
When the battery is properly connected, the device's green LED should light up. If the green LED is not lit, 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 is protected against:
Short circuit in the line;
Short circuit in the battery itself.
Incorrect battery polarity connection;
The adjustment consists in selecting the 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 designed to charge motorcycle batteries with a rated voltage of 6-7V. The charge current is continuously adjustable within 0-2A, with a variable resistor R1.
The stabilizer is assembled on a composite transistor VT1, VT2, the zener diode VD5 fixes the voltage between the base and emitter of the composite transistor, as a result of which the transistor VT1, connected in series with the load, maintains a practically constant charge current, regardless of changes in the battery EMF during charging. 
The device is a current generator with a high internal resistance, so it is not afraid of short circuits, the current feedback voltage is removed from the resistor R4, which limits the current through the transistor VT1 in the event of a short circuit in the load circuit.
CHARGER WITH CHARGING CURRENT CONTROL based on a thyristor phase-pulse power controller, does not contain scarce parts, and with known good elements does not require adjustment.
Charging current is close to pulsed in shape, which is believed to prolong battery life.
The disadvantage of the device is the fluctuations in the charging current with an unstable voltage of the electric lighting network, and like all similar thyristor phase-pulse controllers, the device interferes with radio reception. To combat them, a network LC filter should be provided, similar to those used in network switching power supplies. 
The circuit is a traditional thyristor power controller with pulse-phase control, fed from the winding II of the step-down transformer through the diode bridge VD1-VD4. The thyristor control unit is made on the analog of the unijunction transistor VT1, VT2. The time during which the capacitor C2 is charged before switching the unijunction transistor can be adjusted by the variable resistor R1. With the extreme right position of its engine 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 the thyristor VS1 is turned on.
The details of the device, except for the transformer, rectifier diodes, variable resistor, fuse and thyristor, are placed on the printed circuit board.
Capacitor C1-K73-11 with a capacity of 0.47 to 1 μF or K73-16, K73-17, K42U-2, MBGP. Any diodes VD1-VD4 for direct current 10A and reverse voltage of at least 50V. Instead of the thyristor KU202V, KU202G-KU202E will do, and the 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 do.
Variable resistor R1 - SGM, SDR-30a or SPO-1.
Network step-down transformer of required power with secondary winding voltage from 18 to 22V.
If the voltage at the transformer on the secondary winding is more than 18V, the resistor R5 should be replaced with another 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 on two diodes according to the standard full-wave circuit.
With a voltage of the secondary winding of 28 ... 36V, you can completely abandon the rectifier - its role will be simultaneously performed by the thyristor VS1 (rectification is half-wave). For this option, it is necessary to turn on a separating diode KD105B or D226 with any letter index (cathode to the board) between output 2 of the board and the positive wire.
In this case, only those that allow operation with reverse voltage, for example, KU202E, can be used as a thyristor.
BATTERY PROTECTION FROM DEEP DISCHARGE.
Such a device, when the voltage on the battery drops to the minimum allowable value, automatically turns off the load. The devices can be used where batteries are used, and where there is no constant monitoring of the state of the battery, that is, where it is important to ensure the prevention of processes associated with their deep discharge.
Slightly modified scheme of the original: 
Service functions available in the scheme:
1. When the voltage drops to 10.4V, the load and the control circuit are completely disconnected from the battery.
2. Comparator trigger voltages can be adjusted for specific battery types.
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 monitoring device and the connected load are not switched on.
As a trimming resistor, resistors of any value from 10 kOhm to 100 kOhm can be used.
The circuit uses an operational amplifier LM358N, the domestic analogue of which is KR1040UD1.
The voltage stabilizer 78L05 for a voltage of 5V can be replaced by 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 with the appropriate conductivity.
Any low-power diode that can withstand the current of the relay winding can be used.
Buttons without fixation of different colors, green for turning on, red for turning off.
Adjustment consists in setting the desired voltage threshold for switching off the relay, assembled without errors and from serviceable parts, the device starts working immediately.
NEXT DEVICE for protecting 12v batteries up to 7.5A/H from deep discharge and short circuit with automatic disconnection of its output from the load. 
CHARACTERISTICS
The voltage on the battery at which the shutdown occurs is 10 ± 0.5V.
The current consumed by the device from the battery in the on state, no more than - 1mA
The current consumed by the device from the battery in the off state, no more than - 10 μA
The maximum allowable direct current through the device is 5A.
The maximum allowable short-term (5 sec) current through the device - 10A
Turn-off time in case of a short circuit at the output of the device, no more than - 100 µs
HOW THE DEVICE WORKED
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 a voltage to appear at the output of the device, it is necessary to briefly close the negative output to the negative input. If the load is powered by another source other than the battery, then this is not necessary.
THE DEVICE WORKS AS FOLLOWS;
When switching to battery power, the load discharges it to the trip voltage of the protection device (10± 0.5V). When this value is reached, the device disconnects the battery from the load, preventing its further discharge. The device will turn on automatically when voltage is supplied from the load side to charge the battery.
In case of a short circuit in the load, the device also disconnects the battery from the load. It will turn on automatically if a voltage greater than 9.5V is applied from the load side. If there is no such voltage, then it is necessary to briefly bridge the output negative terminal of the device and the battery minus. Resistors R3 and R4 set the threshold.
1. PCB IN LAY FORMAT(Sprint Layout) -
