Charger for small batteries. Charger circuits for car batteries. Simple automatic charger
I tried to insert into the title of this article all the advantages of this scheme, which we will consider, and naturally I did not quite succeed. So let's now look at all the advantages in order.
The main advantage of the charger is that it is fully automatic. The circuit controls and stabilizes the required battery charging current, monitors the battery voltage and when it reaches the desired level, it reduces the current to zero.
What batteries can be charged?
Almost everything: lithium-ion, nickel-cadmium, lead and others. The scope of application is limited only by the charge current and voltage.This will be enough for all household needs. For example, if your built-in charge controller is broken, you can replace it with this circuit. Cordless screwdrivers, vacuum cleaners, flashlights and other devices can be charged with this automatic charger, even car and motorcycle batteries.
Where else can the scheme be applied?
In addition to the charger, this circuit can be used as a charging controller for alternative energy sources, such as a solar battery.The circuit can also be used as a regulated power supply for laboratory purposes with short circuit protection.
Main advantages:
- - Simplicity: the circuit contains only 4 fairly common components.
- - Full autonomy: control of current and voltage.
- - LM317 chips have built-in protection against short circuits and overheating.
- - Small dimensions of the final device.
- - Large operating voltage range 1.2-37 V.
Flaws:
- - Charging current up to 1.5 A. This is most likely not a drawback, but a characteristic, but I will define this parameter here.
- - For currents greater than 0.5 A, it requires installation on a radiator. You should also consider the difference between input and output voltage. The greater this difference is, the more the microcircuits will heat up.
Automatic charger circuit
The diagram does not show the power source, but only the control unit. The power source can be a transformer with a rectifier bridge, a power supply from a laptop (19 V), or a power supply from a telephone (5 V). It all depends on what goals you are pursuing.The circuit can be divided into two parts, each of them functions separately. The first LM317 contains a current stabilizer. The resistor for stabilization is calculated simply: “1.25 / 1 = 1.25 Ohm”, where 1.25 is a constant that is always the same for everyone and “1” is the stabilization current you need. We calculate, then select the closest resistor from the line. The higher the current, the more power the resistor needs to take. For current from 1 A – minimum 5 W.
The second half is the voltage stabilizer. Everything is simple here, use a variable resistor to set the voltage of the charged battery. For example, for car batteries it is somewhere around 14.2-14.4. To configure, connect a 1 kOhm load resistor to the input and measure the voltage with a multimeter. We set the substring resistor to the desired voltage and that’s it. As soon as the battery is charged and the voltage reaches the set value, the microcircuit will reduce the current to zero and charging will stop.
I personally used such a device to charge lithium-ion batteries. It's no secret that they need to be charged correctly and if you make a mistake, they can even explode. This charger copes with all tasks.
To control the presence of charge, you can use the circuit described in this article -.
There is also a scheme for incorporating this microcircuit into one: both current and voltage stabilization. But in this option, the operation is not entirely linear, but in some cases it may work.
Informative video, just not in Russian, but you can understand the calculation formulas.
Who has not encountered in their practice the need to charge a battery and, disappointed in the lack of a charger with the necessary parameters, was forced to purchase a new charger in a store, or reassemble the necessary circuit?
So I have repeatedly had to solve the problem of charging various batteries when there was no suitable charger at hand. I had to quickly assemble something simple, in relation to a specific battery.
The situation was tolerable until the need for mass preparation and, accordingly, charging the batteries arose. It was necessary to produce several universal chargers - inexpensive, operating in a wide range of input and output voltages and charging currents.
The charger circuits proposed below were developed for charging lithium-ion batteries, but it is possible to charge other types of batteries and composite batteries (using the same type of cells, hereinafter referred to as AB).
All presented schemes have the following main parameters:
input voltage 15-24 V;
charge current (adjustable) up to 4 A;
output voltage (adjustable) 0.7 - 18 V (at Uin=19V).
All circuits were designed to work with power supplies from laptops or to work with other power supplies with DC output voltages from 15 to 24 Volts and were built on widespread components that are present on the boards of old computer power supplies, power supplies of other devices, laptops, etc.
Memory circuit No. 1 (TL494)
The memory in Scheme 1 is a powerful pulse generator operating in the range from tens to a couple of thousand hertz (the frequency varied during research), with an adjustable pulse width.
The battery is charged by current pulses limited by feedback formed by the current sensor R10, connected between the common wire of the circuit and the source of the switch on the field-effect transistor VT2 (IRF3205), filter R9C2, pin 1, which is the “direct” input of one of the error amplifiers of the TL494 chip.
The inverse input (pin 2) of the same error amplifier is supplied with a comparison voltage, regulated by a variable resistor PR1, from a reference voltage source built into the chip (ION - pin 14), which changes the potential difference between the inputs of the error amplifier.
As soon as the voltage value on R10 exceeds the voltage value (set by variable resistor PR1) at pin 2 of the TL494 microcircuit, the charging current pulse will be interrupted and resumed again only at the next cycle of the pulse sequence generated by the microcircuit generator.
By thus adjusting the width of the pulses on the gate of transistor VT2, we control the battery charging current.
Transistor VT1, connected in parallel with the gate of a powerful switch, provides the necessary discharge rate of the gate capacitance of the latter, preventing “smooth” locking of VT2. In this case, the amplitude of the output voltage in the absence of a battery (or other load) is almost equal to the input supply voltage.
With an active load, the output voltage will be determined by the current through the load (its resistance), which allows this circuit to be used as a current driver.
When charging the battery, the voltage at the switch output (and, therefore, at the battery itself) will tend to increase over time to a value determined by the input voltage (theoretically) and this, of course, cannot be allowed, knowing that the voltage value of the lithium battery being charged should be limited to 4.1V (4.2V). Therefore, the memory uses a threshold device circuit, which is a Schmitt trigger (hereinafter - TS) on an op-amp KR140UD608 (IC1) or on any other op-amp.
When the required voltage value on the battery is reached, at which the potentials at the direct and inverse inputs (pins 3, 2 - respectively) of IC1 are equal, a high logical level (almost equal to the input voltage) will appear at the output of the op-amp, causing the LED indicating the end of charging HL2 and the LED to light up optocoupler VH1 which will open its own transistor, blocking the supply of pulses to output U1. The key on VT2 will close and the battery will stop charging.
Once the battery is charged, it will begin to discharge through the reverse diode built into VT2, which will be directly connected in relation to the battery and the discharge current will be approximately 15-25 mA, taking into account the discharge also through the elements of the TS circuit. If this circumstance seems critical to someone, a powerful diode (preferably with a low forward voltage drop) should be placed in the gap between the drain and the negative terminal of the battery.
The TS hysteresis in this version of the charger is chosen such that the charge will begin again when the voltage on the battery drops to 3.9 V.
This charger can also be used to charge series-connected lithium (and other) batteries. It is enough to calibrate the required response threshold using variable resistor PR3.
So, for example, a charger assembled according to scheme 1 operates with a three-section serial battery from a laptop, consisting of dual elements, which was mounted to replace the nickel-cadmium battery of a screwdriver.
The power supply from the laptop (19V/4.7A) is connected to the charger, assembled in the standard case of the screwdriver charger instead of the original circuit. The charging current of the “new” battery is 2 A. At the same time, transistor VT2, working without a radiator, heats up to a maximum temperature of 40-42 C.
The charger is switched off, naturally, when the battery voltage reaches 12.3V.
The TS hysteresis when the response threshold changes remains the same as a PERCENTAGE. That is, if at a shutdown voltage of 4.1 V, the charger was turned on again when the voltage dropped to 3.9 V, then in this case the charger was turned on again when the voltage on the battery decreased to 11.7 V. But if necessary, the hysteresis depth can change.
Charger Threshold and Hysteresis Calibration
Calibration occurs using an external voltage regulator (laboratory power supply).The upper threshold for triggering the TS is set.
1. Disconnect the upper pin PR3 from the charger circuit.
2. We connect the “minus” of the laboratory power supply (hereinafter referred to as the LBP everywhere) to the negative terminal for the battery (the battery itself should not be in the circuit during setup), the “plus” of the LBP to the positive terminal for the battery.
3. Turn on the charger and LBP and set the required voltage (12.3 V, for example).
4. If the end of charge indication is on, rotate the PR3 slider down (according to the diagram) until the indication goes out (HL2).
5. Slowly rotate the PR3 engine upward (according to the diagram) until the indication lights up.
6. Slowly reduce the voltage level at the output of the LBP and monitor the value at which the indication goes out again.
7. Check the level of operation of the upper threshold again. Fine. You can adjust the hysteresis if you are not satisfied with the voltage level that turns on the charger.
8. If the hysteresis is too deep (the charger is switched on when the voltage level is too low - below, for example, the battery discharge level), turn the PR4 slider to the left (according to the diagram) or vice versa - if the hysteresis depth is insufficient, - to the right (according to the diagram). When changing depth of hysteresis, the threshold level may shift by a couple of tenths of a volt.
9. Make a test run, raising and lowering the voltage level at the LBP output.
Setting the current mode is even easier.
1. We turn off the threshold device using any available (but safe) methods: for example, by “connecting” the PR3 engine to the common wire of the device or by “shorting” the LED of the optocoupler.
2. Instead of the battery, we connect a load in the form of a 12-volt light bulb to the output of the charger (for example, I used a pair of 12V 20-watt lamps to set up).
3. We connect the ammeter to the break of any of the power wires at the input of the charger.
4. Set the PR1 engine to minimum (to the maximum left according to the diagram).
5. Turn on the memory. Smoothly rotate the PR1 adjustment knob in the direction of increasing current until the required value is obtained.
You can try to change the load resistance towards lower values of its resistance by connecting in parallel, say, another similar lamp or even “short-circuiting” the output of the charger. The current should not change significantly.
During testing of the device, it turned out that frequencies in the range of 100-700 Hz were optimal for this circuit, provided that IRF3205, IRF3710 were used (minimum heating). Since the TL494 is underutilized in this circuit, the free error amplifier on the IC can be used to drive a temperature sensor, for example.
It should also be borne in mind that if the layout is incorrect, even a correctly assembled pulse device will not work correctly. Therefore, one should not neglect the experience of assembling power pulse devices, described repeatedly in the literature, namely: all “power” connections of the same name should be located at the shortest distance relative to each other (ideally at one point). So, for example, connection points such as the collector VT1, the terminals of resistors R6, R10 (connection points with the common wire of the circuit), terminal 7 of U1 - should be combined almost at one point or through a straight short and wide conductor (bus). The same applies to drain VT2, the output of which should be “hung” directly onto the “-” terminal of the battery. The terminals of IC1 must also be in close “electrical” proximity to the battery terminals.
Memory circuit No. 2 (TL494)
Scheme 2 is not very different from Scheme 1, but if the previous version of the charger was designed to work with an AB screwdriver, then the charger in Scheme 2 was conceived as a universal, small-sized (without unnecessary adjustment elements), designed to work with composite, sequentially connected elements up to 3, and with singles.
As you can see, to quickly change the current mode and work with different numbers of elements connected in series, fixed settings have been introduced with trimming resistors PR1-PR3 (current setting), PR5-PR7 (setting the end of charging threshold for a different number of elements) and switches SA1 (current selection charging) and SA2 (selecting the number of battery cells to be charged).
The switches have two directions, where their second sections switch the mode selection indication LEDs.
Another difference from the previous device is the use of a second error amplifier TL494 as a threshold element (connected according to the TS circuit) that determines the end of battery charging.
Well, and, of course, a p-conductivity transistor was used as a key, which simplified the full use of the TL494 without the use of additional components.
The method for setting the end of charging thresholds and current modes is the same, as for setting up the previous version of the memory. Of course, for a different number of elements, the response threshold will change multiples.
When testing this circuit, we noticed stronger heating of the switch on the VT2 transistor (when prototyping I use transistors without a heatsink). For this reason, you should use another transistor (which I simply didn’t have) of appropriate conductivity, but with better current parameters and lower open-channel resistance, or double the number of transistors indicated in the circuit, connecting them in parallel with separate gate resistors.
The use of these transistors (in a “single” version) is not critical in most cases, but in this case, the placement of the device components is planned in a small-sized case using small radiators or no radiators at all.
Memory circuit No. 3 (TL494)
In the charger in diagram 3, automatic disconnection of the battery from the charger with switching to the load has been added. This is convenient for checking and studying unknown batteries. The TS hysteresis for working with a battery discharge should be increased to the lower threshold (for switching on the charger), equal to the full battery discharge (2.8-3.0 V).
Charger circuit No. 3a (TL494)
Scheme 3a is a variant of scheme 3.
Memory circuit No. 4 (TL494)
The charger in diagram 4 is no more complicated than the previous devices, but the difference from the previous schemes is that the battery here is charged with direct current, and the charger itself is a stabilized current and voltage regulator and can be used as a laboratory power supply module, classically built according to “datasheet” to the canons.
Such a module is always useful for bench testing of both batteries and other devices. It makes sense to use built-in devices (voltmeter, ammeter). Formulas for calculating storage and interference chokes are described in the literature. Let me just say that I used ready-made various chokes (with a range of specified inductances) during testing, experimenting with a PWM frequency from 20 to 90 kHz. I didn’t notice any particular difference in the operation of the regulator (in the range of output voltages 2-18 V and currents 0-4 A): minor changes in the heating of the key (without a radiator) suited me quite well. The efficiency, however, is higher when using smaller inductances.
The regulator worked best with two series-connected 22 µH chokes in square armored cores from converters integrated into laptop motherboards.
Memory circuit No. 5 (MC34063)
In diagram 5, a version of the PWM controller with current and voltage regulation is made on the MC34063 PWM/PWM chip with an “add-on” on the CA3130 op amp (other op amps can be used), with the help of which the current is regulated and stabilized.
This modification somewhat expanded the capabilities of the MC34063, in contrast to the classic inclusion of the microcircuit, allowing the function of smooth current control to be implemented.
Memory circuit No. 6 (UC3843)
In diagram 6, a version of the PHI controller is made on the UC3843 (U1) chip, CA3130 op-amp (IC1), and LTV817 optocoupler. The current regulation in this version of the charger is carried out using a variable resistor PR1 at the input of the current amplifier of the U1 microcircuit, the output voltage is regulated using PR2 at the inverting input IC1.
There is a “reverse” reference voltage at the “direct” input of the op-amp. That is, regulation is carried out relative to the “+” power supply.
In schemes 5 and 6, the same sets of components (including chokes) were used in the experiments. According to the test results, all of the listed circuits are not much inferior to each other in the declared range of parameters (frequency/current/voltage). Therefore, a circuit with fewer components is preferable for repetition.
Memory circuit No. 7 (TL494)
The memory in diagram 7 was conceived as a bench device with maximum functionality, therefore there were no restrictions on the volume of the circuit and the number of adjustments. This version of the charger is also made on the basis of a PHI current and voltage regulator, like the option in diagram 4.
Additional modes have been introduced into the scheme.
1. “Calibration - charge” - for pre-setting the end voltage thresholds and repeating charging from an additional analog regulator.
2. “Reset” - to reset the charger to charge mode.
3. “Current - buffer” - to switch the regulator to current or buffer (limiting the output voltage of the regulator in the joint supply of the device with battery voltage and the regulator) charge mode.
A relay is used to switch the battery from the “charge” mode to the “load” mode.
Working with the memory is similar to working with previous devices. Calibration is carried out by switching the toggle switch to the “calibration” mode. In this case, the contact of the toggle switch S1 connects the threshold device and a voltmeter to the output of the integral regulator IC2. Having set the required voltage for the upcoming charging of a specific battery at the output of IC2, using PR3 (smoothly rotating) the HL2 LED lights up and, accordingly, relay K1 operates. By reducing the voltage at the output of IC2, HL2 is suppressed. In both cases, control is carried out by a built-in voltmeter. After setting the PU response parameters, the toggle switch is switched to charge mode.
Scheme No. 8
The use of a calibration voltage source can be avoided by using the memory itself for calibration. In this case, you should decouple the TS output from the SHI controller, preventing it from turning off when the battery charge is complete, determined by the TS parameters. The battery will one way or another be disconnected from the charger by the contacts of relay K1. The changes for this case are shown in Figure 8.
In calibration mode, toggle switch S1 disconnects the relay from the positive power source to prevent inappropriate operations. In this case, the indication of the operation of the TC works.
Toggle switch S2 performs (if necessary) forced activation of relay K1 (only when calibration mode is disabled). Contact K1.2 is necessary to change the polarity of the ammeter when switching the battery to the load.
Thus, a unipolar ammeter will also monitor the load current. If you have a bipolar device, this contact can be eliminated.
Charger design
In designs it is desirable to use as variable and tuning resistors multi-turn potentiometers to avoid suffering when setting the necessary parameters.
Design options are shown in the photo. The circuits were soldered impromptu onto perforated breadboards. All the filling is mounted in cases from laptop power supplies.
They were used in designs (they were also used as ammeters after minor modifications).
The cases are equipped with sockets for external connection of batteries, loads, and a jack for connecting an external power supply (from a laptop).
He designed several digital pulse duration meters, different in functionality and elemental base.
More than 30 improvement proposals for the modernization of units of various specialized equipment, incl. - power supply. For a long time now I have been increasingly involved in power automation and electronics.
Why am I here? Yes, because everyone here is the same as me. There is a lot of interest here for me, since I am not strong in audio technology, but I would like to have more experience in this area.
Reader vote
The article was approved by 77 readers.
To participate in the voting, register and log in to the site with your username and password.Every car owner needs a battery charger, but it costs a lot, and regular preventive trips to a car service center are not an option. Battery service at a service station takes time and money. In addition, with a discharged battery, you still need to drive to the service station. Anyone who knows how to use a soldering iron can assemble a working charger for a car battery with their own hands.
A little theory about batteries
Any battery is a storage device for electrical energy. When voltage is applied to it, energy is stored due to chemical changes inside the battery. When a consumer is connected, the opposite process occurs: a reverse chemical change creates voltage at the terminals of the device, and current flows through the load. Thus, in order to get voltage from the battery, you first need to “put it down,” that is, charge the battery.
Almost any car has its own generator, which, when the engine is running, provides power to the on-board equipment and charges the battery, replenishing the energy spent on starting the engine. But in some cases (frequent or difficult engine starts, short trips, etc.) the battery energy does not have time to be restored, and the battery is gradually discharged. There is only one way out of this situation - charging with an external charger.
How to find out the battery status
To decide whether charging is necessary, you need to determine the state of the battery. The simplest option - “turns/does not turn” - is at the same time unsuccessful. If the battery doesn’t turn on, for example, in the garage in the morning, then you won’t go anywhere at all. The “does not turn” condition is critical, and the consequences for the battery can be dire.
The optimal and reliable method for checking the condition of a battery is to measure the voltage on it with a conventional tester. At an air temperature of about 20 degrees dependence of the degree of charge on voltage on the terminals of the battery disconnected from the load (!) is as follows:
- 12.6…12.7 V - fully charged;
- 12.3…12.4 V - 75%;
- 12.0…12.1 V - 50%;
- 11.8…11.9 V - 25%;
- 11.6…11.7 V - discharged;
- below 11.6 V - deep discharge.
It should be noted that the voltage of 10.6 volts is critical. If it drops below, the “car battery” (especially a maintenance-free one) will fail.
Correct charging
There are two methods of charging a car battery - constant voltage and constant current. Everyone has their own features and disadvantages:
Homemade battery chargers
Assembling a charger for a car battery with your own hands is realistic and not particularly difficult. To do this, you need to have basic knowledge of electrical engineering and be able to hold a soldering iron in your hands.
Simple 6 and 12 V device
This scheme is the most basic and budget-friendly. Using this charger, you can efficiently charge any lead-acid battery with an operating voltage of 12 or 6 V and an electrical capacity of 10 to 120 A/h.
The device consists of a step-down transformer T1 and a powerful rectifier assembled using diodes VD2-VD5. The charging current is set by switches S2-S5, with the help of which quenching capacitors C1-C4 are connected to the power circuit of the primary winding of the transformer. Thanks to the multiple “weight” of each switch, various combinations allow you to stepwise adjust the charging current in the range of 1–15 A in 1 A increments. This is enough to select the optimal charging current.
For example, if a current of 5 A is required, then you will need to turn on the toggle switches S4 and S2. Closed S5, S3 and S2 will give a total of 11 A. To monitor the voltage on the battery, use a voltmeter PU1, the charging current is monitored using an ammeter PA1.
The design can use any power transformer with a power of about 300 W, including homemade ones. It should produce a voltage of 22–24 V on the secondary winding at a current of up to 10–15 A. In place of VD2-VD5, any rectifier diodes that can withstand a forward current of at least 10 A and a reverse voltage of at least 40 V are suitable. D214 or D242 are suitable. They should be installed through insulating gaskets on a radiator with a dissipation area of at least 300 cm2.
Capacitors C2-C5 must be non-polar paper with an operating voltage of at least 300 V. Suitable, for example, are MBChG, KBG-MN, MBGO, MBGP, MBM, MBGCh. Similar cube-shaped capacitors were widely used as phase-shifting capacitors for electric motors in household appliances. A DC voltmeter of type M5−2 with a measurement limit of 30 V was used as PU1. PA1 is an ammeter of the same type with a measurement limit of 30 A.
The circuit is simple, if you assemble it from serviceable parts, then it does not need adjustment. This device is also suitable for charging six-volt batteries, but the “weight” of each of the switches S2-S5 will be different. Therefore, you will have to navigate the charging currents using an ammeter.
With continuously adjustable current
Using this scheme, it is more difficult to assemble a charger for a car battery with your own hands, but it can be repeated and also does not contain scarce parts. With its help, it is possible to charge 12-volt batteries with a capacity of up to 120 A/h, the charge current is smoothly regulated.
The battery is charged using a pulsed current; a thyristor is used as a regulating element. In addition to the knob for smoothly adjusting the current, this design also has a mode switch, when turned on, the charging current doubles.
The charging mode is controlled visually using the RA1 dial gauge. Resistor R1 is homemade, made of nichrome or copper wire with a diameter of at least 0.8 mm. It serves as a current limiter. Lamp EL1 is an indicator lamp. In its place, any small-sized indicator lamp with a voltage of 24–36 V will do.
A step-down transformer can be used ready-made with an output voltage on the secondary winding of 18–24 V at a current of up to 15 A. If you don’t have a suitable device at hand, you can make it yourself from any network transformer with a power of 250–300 W. To do this, wind all windings from the transformer except the mains winding, and wind one secondary winding with any insulated wire with a cross-section of 6 mm. sq. The number of turns in the winding is 42.
Thyristor VD2 can be any of the KU202 series with the letters V-N. It is installed on a radiator with a dispersion area of at least 200 sq. cm. The power installation of the device is done with wires of minimal length and with a cross-section of at least 4 mm. sq. In place of VD1, any rectifier diode with a reverse voltage of at least 20 V and withstanding a current of at least 200 mA will work.
Setting up the device comes down to calibrating the RA1 ammeter. This can be done by connecting several 12-volt lamps with a total power of up to 250 W instead of a battery, monitoring the current using a known-good reference ammeter.
From a computer power supply
To assemble this simple charger with your own hands, you will need a regular power supply from an old ATX computer and knowledge of radio engineering. But the characteristics of the device will be decent. With its help, batteries are charged with a current of up to 10 A, adjusting the current and charge voltage. The only condition is that the power supply is desirable on the TL494 controller.
For creating DIY car charging from a computer power supply you will have to assemble the circuit shown in the figure.
Step by step steps required to finalize the operation will look like this:
- Bite off all the power bus wires, with the exception of the yellow and black ones.
- Connect the yellow and separately black wires together - these will be the “+” and “-” chargers, respectively (see diagram).
- Cut all traces leading to pins 1, 14, 15 and 16 of the TL494 controller.
- Install variable resistors with a nominal value of 10 and 4.4 kOhm on the power supply casing - these are the controls for regulating the voltage and charging current, respectively.
- Using a suspended installation, assemble the circuit shown in the figure above.
If the installation is done correctly, then the modification is complete. All that remains is to equip the new charger with a voltmeter, an ammeter and wires with alligator clips for connecting to the battery.
In the design it is possible to use any variable and fixed resistors, except for the current resistor (the lower one in the circuit with a nominal value of 0.1 Ohm). Its power dissipation is at least 10 W. You can make such a resistor yourself from a nichrome or copper wire of the appropriate length, but you can actually find a ready-made one, for example, a 10 A shunt from a Chinese digital tester or a C5-16MV resistor. Another option is two 5WR2J resistors connected in parallel. Such resistors are found in switching power supplies for PCs or TVs.
What you need to know when charging a battery
When charging a car battery, it is important to follow a number of rules. This will help you Extend battery life and maintain your health:
The question of creating a simple battery charger with your own hands has been clarified. Everything is quite simple, all you have to do is stock up on the necessary tools and you can safely get to work.
Universal charger for small batteries
Using the proposed charger (CHD), it is possible to restore the functionality of almost all types of small-sized batteries used in everyday life with a rated voltage of 1.5 V (for example, STs-21, STs-31, STs-32D-0.26S, D-0.06 , D-0.06D, D-0.1, D-0.115, D-0.26D, D-0.55S, KNG-0.35D, KNGTs-1D, TsNK-0.2, 2D-0.25, ShKNG. -1D, etc.). The charger provides automatic disconnection from the network when the set charging time expires and when the permissible voltage on the battery is exceeded. The charger also provides an indication of the charging current value.
The electronic circuit of the universal charger is shown in Fig. 1; it consists of five different functional units:
- DC source;
- diagrams for setting the duration of charging time;
- circuits for automatically turning on and off the charger from the network;
- circuits for indicating the charging current value;
- power supply.
Rice. 1. Schematic diagram
Batteries can be charged using five different charging currents: 6, 12, 26, 55 and 100 mA. The charging current is selected using switches SA2—SA5, respectively, connecting one of the groups of resistors Rl—R4 in parallel to R5. For example, when charging batteries STs-21, STs-31, STs-32 for modern electronic wristwatches, a charging current of 6 or 12 mA is used. When charging with a current of 6 mA, switches SA2 -SA5 remain in the position shown in the diagram. With a charging current of 12 mA, resistor R4 is connected in parallel to resistor R5 using switch SA2. and at a current of 26 mA, resistor R3 is connected in parallel to resistor R5 using SA3, etc.
The functionality of batteries for electronic wristwatches is restored approximately 1...3 hours after connecting to the device, and if the voltage on the battery reaches 2.2...2.3 V, the charger is automatically disconnected from the network.
The circuit for automatically turning the charger on and off from the network is made using transistor VT4, diode VD3, electronic relay K1 and resistors R6, R7. The threshold voltage of 2.2...2.3 V is set using variable resistor R7. The voltage on the battery through diode VD1 and resistor R7 is supplied to the base of transistor VT4. When the voltage reaches a level of 2.2...2.3 V, the transistor opens and the voltage on relay K1 decreases, contact K disconnects the charger from the network. To turn on the charger, just briefly press SA1. After switching on SA1 for a short time, relay K1 is activated, its contacts K block the contacts of SA1 and the charger is connected to the network.
The circuit for setting the charging time is made on microcircuits DD4 K155LAZ, DD2, DD3 K155IE8, DD1 K155IE2. A low-frequency generator is built on logic elements DD4.1, DD4.2, resistors R9, R10 and capacitor C2. Using K155IE8 microcircuits, two input frequency divider counters with a division coefficient of 64 are made, and on the K155IE2 microcircuit - a counter-divider with a division coefficient of 10. The generator frequency can be changed using variable resistor R10. By changing the frequency of the generator, you can adjust the charging time from 2 to 20 hours. However, given that the charging time for almost all types of small batteries is 15 hours, it is advisable to rigidly set the charging time to 15 hours. The output signal warning of the end of the charging time is - logic level 1 is applied through diode VD2 and resistor R7 to the base of transistor VT4. The latter, opening through the contacts of relay K1, disconnects the charger from the network.
The charging current value indication circuit is made using the K155REZ PROM, digital semiconductor indicators HL1, HL2 ALS324B and resistors Rll-R19. In this case, it is necessary to first record the program given in table in the K155REZ EEPROM. 1.
Digital semiconductor indicators display one of five different values of the charging current, with the help of which the battery is being charged at that moment. It should be noted that when charging with a current of 100 mA, since it is a three-digit number, the number 98 is displayed on the indicators HL1, HL2.
Due to the fact that input E (pin 15) of the PROM is connected to a low-frequency generator through element DD4.3, the digital information on the indicators flashes at the frequency of the generator. This method of indicating the charging current value, firstly, reduces the current consumption of the indication circuit. Secondly, the flashing frequency can be used to roughly estimate the preset charging time.
Considering the relative complexity of the indication circuit for radio amateurs, it can be excluded from the memory. Then the DD5 chip, digital semiconductor indicators HL1, HL2, resistors Rll - R19 and the second group of switch contacts SA2 - SA5 are excluded from the circuit. And when using an indication circuit, the preliminary program in the K155REZ PROM can be written with the device described in.
The power supply is made according to a well-known circuit on the DA1 KP142EH5B chip. The microcircuit itself is secured to the transformer body using Moment glue or another method. In this case, there is no need to use a separate heat sink for the DA1 chip.
The device parts are mounted on a printed circuit board, which is placed in a polystyrene housing. The XP1 power plug is mounted on the body. The contacts for connecting disk batteries are made of household plastic clothespins (Fig. 2).
When the circuit elements are installed correctly, the device works immediately. The operation of the pulse generator is checked using the LED shown in dotted lines in Fig. 1. Then, to set the recovery time to 15 hours, using resistor R1, select a pulse repetition rate such that a negative pulse appears at the output of the DD3 chip (at pin 7) after 1.5 minutes. This can be controlled using an LED. The LED shown in dotted lines is disconnected from the generator output and connected during the time setting period to pin 7 of the DD3 chip.
The current consumed by the memory does not exceed 350 mA. To reduce power, instead of K155 series microcircuits, you can use K555 series microcircuits.
LITERATURE
1. Khorovits P., Hill W. The Art of Circuit Design. - M.: Mir, 1989, vol. 1.
2. Bondarev V., Rukovishnikov A. Charger for small-sized elements. - Radio, 1989, No. 3. p. 69.
3. Puzakov A. ROM in sports literature. - Radio, 1982. No. 1. p. 22-23.
4. Goroshkov B.I. Elements of radio-electronic devices. - M. Radio and communications, 1988.
