Charger circuit for any small batteries. Practical diagrams of universal battery chargers. Charger Threshold and Hysteresis Calibration
Power supplies
N. HERTZEN, Berezniki, Perm region.
Radio, 2000, No. 7
At today's prices, you can literally go broke powering small-sized equipment from galvanic cells and batteries. It is more profitable to spend one time and switch to using batteries. In order for them to serve for a long time, they must be used correctly: not discharge below the permissible voltage, charge with a stable current, and stop charging on time. But if the user himself has to monitor the fulfillment of the first of these conditions, then it is advisable to assign the fulfillment of the other two to the charger. This is exactly the device that is described in the article.
During development, the task was to construct a device with the following characteristics:
Wide intervals of change in charging current and voltage automatically stop charging (APC). providing charging of both individual batteries used to power small-sized equipment, and batteries composed of them with a minimum number of mechanical switches;
- close to uniform scales of the regulators, allowing you to set the charging current and voltage of the APP with acceptable accuracy without any measuring instruments;
- high stability of the charging current when the load resistance changes;
- relative simplicity and good repeatability.
Described Charger fully meets these requirements. It is intended for charging D-0.03 batteries. D-0.06. D-0.125. D-0.26. D-0.55. TsNK-0.45. NKGC-1.8. their imported analogues and batteries made from them. Up to the set threshold for switching on the APP system, the battery is charged with a stabilized current, independent of the type and number of elements, and the voltage on it gradually increases as it charges. After the system is triggered, the previously set constant voltage is stably maintained on the battery, and the charging current decreases. In other words, the battery does not recharge or discharge, and it can remain connected to the device for a long time.
The device can be used as a power supply for small-sized equipment with adjustable voltage from 1.5 to 13 V and protection against overload and short circuit in the load.
The main technical characteristics of the device are as follows:
Charging current at the limit "40 mA" - 0...40, at the limit "200 mA" - 40...200 mA;
- instability of the charging current when the load resistance changes from 0 to 40 Ohms - 2.5%;
- the limits of regulation of the APP response voltage are 1.45... 13 V.
Charger circuit
A current source on the transistor \L"4 is used as a charging current stabilizer. Depending on the position of the switch SA2, the load current In is determined by the ratios: I N = (U B - U BE)/R10 and I H = (U B - U BE )/(R9 + R10), where U B is the voltage at the base of transistor VT4 relative to the positive bus, V; U BE is the voltage drop at its emitter junction, V; R9, R10 are the resistances of the corresponding resistors, Ohms.
From these expressions it follows that. changing the voltage at the base of transistor VT4 with variable resistor R8. the load current can be adjusted over a wide range. The voltage across this resistor is maintained by a constant zener diode VD6, the current through which, in turn, is stabilized by field-effect transistor VT2. All this ensures the instability of the charging current specified in the technical specifications. The use of a voltage-controlled stable current source made it possible to change the charging current down to very small values, to have a close to uniform scale of the current regulator (R8) and to simply switch the limits of its regulation.
APZ system. triggered after reaching the maximum permissible voltage on the battery or battery, includes a comparator on the op-amp DA1, an electronic switch on the transistor VT3, and a zener diode VD5. current stabilizer on transistor VT1 and resistors R1 - R4. The HL1 LED serves as an indicator of charging and its completion.
When a discharged battery is connected to the device, the voltage on it and the non-inverting input of the op-amp DA1 is less than the exemplary one on the inverting one, which is set by variable resistor R3. For this reason, the voltage at the output of the op-amp is close to the voltage of the common wire, transistor VT3 is open, a stable current flows through the battery, the value of which is determined by the positions of the variable resistor R8 slider and switch SA2.
As the battery charges, the voltage at the inverting input of op-amp DA1 increases. The voltage at its output also increases, so transistor VT2 leaves the current stabilization mode, VT3 gradually closes and its collector current decreases. The process continues until then. until the zener diode VD6 ceases to stabilize the voltage across resistors R7, R8. As this voltage decreases, transistor VT4 begins to close and the charging current quickly decreases. Its final value is determined by the sum of the self-discharge current of the battery and the current flowing through resistor R11. In other words, from this moment on, the charged battery maintains the voltage set by resistor R3, and the current necessary to maintain this voltage flows through the battery.
The HL1 LED indicates that the device is connected to the network and two phases of the charging process. In the absence of a battery, resistor R11 is set to a voltage determined by the position of the slider of variable resistor R3. Very little current is required to maintain this voltage, so HL1 glows very dimly. At the moment the battery is connected, the brightness of its glow increases to maximum, and after the automatic protection system is activated at the end of charging, it abruptly decreases to the average between those mentioned above. If desired, you can limit yourself to two levels of glow (weak, strong), for which it is enough to select resistor R6.
The device parts are mounted on a printed circuit board, the drawing of which is shown in Fig. 2. It is made by cutting through foil and is designed for the installation of permanent resistors MLT, trimmer (wire) PPZ-43. capacitors K52-1B (C1) and KM (C2). Transistor VT4 is installed on a heat sink with an effective thermal dissipation area of 100 cm 2. Variable resistors R3 and R8 (PPZ-11 group A) are fixed on the front panel of the device and are equipped with scales with corresponding marks.
Switches SA1 and SA2 are of any type; however, it is desirable that the contacts used as SA2 be designed for switching current of at least 200 mA.
Network transformer T1 must provide an alternating voltage of 20 V on the secondary winding at a load current of 250 mA.
Field-effect transistors KPZZV can be replaced with KPZZG - KPZOZI, bipolar KT361V - with transistors of the KT361 series. KT3107, KT502 with any letter index (except A), and KT814B - to KT814V. KT814G. KT816V. KT816G. Zener diode D813 (VD5) must be selected with a stabilization voltage of at least 12.5 V. Instead, it is permissible to use D814D or any two low-power zener diodes connected in series with a total stabilization voltage of 12.5... 13.5 V. It is possible to replace PPZ-11 (R3. R8) with variable resistors any type of group A, and PPZ-43 (R10) - a tuned resistor of any type with a dissipation power of at least 3 W.
Setting up the device begins with selecting the brightness of the HL1 LED. To do this, switch switches SA1 and SA2, respectively, to the “13 V” and “40 mA” positions. and the variable resistor R8 slider is in the middle, connect a resistor with a resistance of 50... 100 Ohms to sockets XS1 and XS2 and find this position for the resistor R3 slider. in which the brightness of the HL1 glow changes. Increasing the difference in the brightness of the glow is achieved by selecting resistor R6.
Then the boundaries of the regulation intervals for the charging current and voltage of the automatic protection zone are set. By connecting a milliammeter with a measurement limit of 200...300 mA to the output of the device. move the slider of resistor R8 to the lower (according to the diagram) position, and switch SA2 to the “200 mA” position. By changing the resistance of the tuning resistor R10, the device needle is deflected to 200 mA. Then move the R8 slider to the upper position and select the resistor R7 to achieve a reading of 36...38 mA. Finally, switch SA2 to the “40 mA” position. return the slider of the variable resistor R8 to the lower position and select R9 to set the output current within 43...45 mA.
To adjust the boundaries of the APZ voltage regulation interval, switch SA1 is set to the “13 V” position, and a DC voltmeter with a measurement limit of 15...20 V is connected to the output of the device. By selecting resistors R1 and R4, readings of 4.5 and 13 V are achieved at the extremes positions of the resistor R3. After this, moving SA1 to the “4.5 V” position, in the same positions of the R3 slider, set the instrument arrow to the 1.45 and 4.5 V marks by selecting resistor R2.
During operation, the APZ voltage is set at the rate of 1.4... 1.45 V per battery being charged.
If the device is not intended to be used to power radio equipment, the indication of the end of charging by the extinguishing of the LED can be replaced by its blinking, for which it is enough to introduce hysteresis into the comparator - supplement the device with resistors R12, R13 (Fig. 3). and remove resistor R6. After such modification, when the set value of the APZ voltage is reached, the HL1 LED will go out and the charging current through the battery will completely stop. As a result, the voltage across it will begin to drop, so the current stabilizer will turn on again and the HL1 LED will light up. In other words, when the set voltage is reached, HL1 will begin to blink, which is sometimes more visual than a certain average brightness. The nature of the battery charging process remains unchanged in both cases.
A diode bridge can withstand currents greater than an ampere. The filter capacitor is electrolytic with a capacity of 470 µF and a voltage of 25-50V. A transformer can be taken with a power of 20-40 watts and having the voltage we need on the secondary winding.The battery charging current is set according to the formula:
I = (0.5 … 0.7) / R2
It is advisable to set resistor R2 variable (to be able to adjust the maximum initial charge current). The KREN12A stabilizer (LM317) allows you to regulate the output charging voltage over a wide range (from 1.5 to 35 V).
As the voltage on it will approach the voltage of the stabilizer and, accordingly, the current through the transistor (lower in the circuit) will begin to decrease. This will cause it to gradually close and the LED will gradually go out. To control the charging process, it is convenient to use a dial indicator at the output. Recording level indicators from old tape recorders are well suited for this.
Charging does not require any settings and, if assembled correctly, starts working immediately. When a discharged battery is connected to the terminals, the LED lights up and the instrument needle deviates towards the end of the scale, depending on the type of battery. Using variable resistor R3 we set the maximum charging current. As charging progresses, the brightness of the LED will gradually decrease, and the arrow of the device will approach the beginning of the scale. When fully charged, when the voltages at the battery and the charger output are equal, the current through the battery will become zero. This will eliminate any risk of overcharging the battery.
Instead of variable resistor R4, it is more convenient to use a switch with a set of pre-selected resistances. Then you only need to set the switch to the desired charge voltage.
By selecting the resistance of the lower row of resistors, we set the voltage we need at the output. This way it is easy to select any voltage.The charger is assembled on a small board measuring 2.5 x 3 cm.
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 heatsink 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.
Andrey Baryshev, Vyborg
This article describes the manufacture of a simple device designed to safely charge any small batteries. By “safety” here we mean the ability to manually set the charging current recommended for each specific type of battery, as well as automatically reduce the output current to zero after the battery is fully charged to its rated voltage. Such a charger (charger), of course, cannot serve as a full replacement for a “branded” charger, which is developed for a specific type of battery and ensures its optimal charging mode. But it’s convenient to have on hand if you often have to use different types of batteries, but there are no special “chargers” for these batteries. The charger allows you to charge batteries of different types, with a nominal voltage starting from 1.2 V (“tablets”, “finger-type”), cell phone batteries of various models (voltage 3.7...4.5 V), as well as 9 and 12-volt batteries. The charging current can be up to 500 mA and higher, it depends only on the power of the elements used in the circuit.
Principle of operation
As a rule, the battery charging current recommended by the manufacturer is 1/10 of the nominal nameplate capacity CA, which is measured in A/h (ampere/hour) and indicated on its case. That is, for example, for a battery with a capacity of 700 mAh, the optimal charge current will be 70 mA. Since the current will decrease during charging, its initial value can be set slightly higher than recommended in order to speed up the charging process (if necessary). But this should be done within moderate limits to prevent the battery from overheating. It is recommended to set the maximum value of the initial charging current to no more than (0.2 - 0.3) C A.
The proposed circuit provides for manual setting of the value of this current and the possibility of its visual display and control during the charging process using an LED and a small built-in pointer device.
The schematic diagram of the charger is shown in Fig. 1.
The direct rectified voltage is supplied from rectifier Br1 to the current limiter circuit with an indication unit assembled on transistors VT1, VT2 and LED VD1. Then, through the voltage stabilizer on the DA1 chip, the charging current is supplied to the battery connected to pins J1 and J2. In this case, the adjustable voltage stabilizer on the DA1 microcircuit (MC) allows you to change the circuit stabilization voltage using switch S1 in accordance with the operating voltage of the connected battery. If the battery is discharged and its voltage is less than the value of the stabilization voltage of the circuit, a current begins to flow through resistor P1, the value of which will be greater, the greater the degree of discharge of the battery. At the beginning of charging, the voltage across this resistor will exceed 0.6 V, transistor VT2 will open, and VT1, on the contrary, will close, limiting the output current of the circuit. Resistor R2 in the base circuit of transistor VT2 protects it from overload, and the LED in its collector circuit serves as an indicator and lights up during the charging process. When the battery is fully charged and its voltage is equal to the stabilization voltage of MS DA1, the current through resistor P1 will drop and transistor VT2 will close, which will lead to the LED going out and transistor VT1 to fully open. In this case, the voltage on the battery being charged will not exceed the stabilization voltage value of MS DA1 (set by switch S1) and this will protect the battery from overcharging. Thus, the variable resistor P1 is a kind of “current sensor”, by changing the resistance of which you can set the initial maximum charging current.
Construction and details
The circuit can be powered from any small-sized transformer with a voltage on the secondary winding of 12 ... 20 V. Here, for example, a transformer from the “charging” for old types of cell phones is suitable (in the “charging” of new types, as a rule, pulse circuits are used that do not have such step-down transformer). The alternating voltage from this transformer is rectified by the diode bridge Br1 and then smoothed by the capacitor C1 (these elements can also be taken from the same “charging” as the transformer). Capacitance C1 can be 470 µF or more, the voltage of all capacitors in the circuit is not lower than 36 V. Rectifier bridge diodes - any rectifier with a current of 0.5 A (KD226, etc.), you can use a diode bridge of the KTs403 type. Transistors VT1, VT2 - medium or high power, n-p-n type (for example KT815, KT817, KT805 with any letter or imported analogs of type). The permissible collector current of such transistors allows the charge current to be set to 1.5 A, but at currents of more than 200 mA, these transistors must be installed on small heat sinks. The LED can be any low-power one, for example AL307. Microcircuit DA1 is an adjustable voltage stabilizer or a domestic analogue of KR142EN12A (taking into account pinout). Such stabilizers allow you to regulate the output voltage over a wide range - from 1.25 to 35 V. Instead of smoothly adjusting the output voltage, in this case it is more convenient to use a discrete switch with several positions corresponding to the nominal values of the batteries that are supposed to be charged by this charger. For example: 1.2 V - 2.4 V - 3.6 V - 3.9 V - 9 V - 12 V. In the version of the charger shown here, a small-sized flip switch with 6 fixed positions is used for this purpose. The required voltage values are set during setup by selecting resistors R9 ... R14, the values of which range from tens of Ohms to several kOhms.
The charge current, in addition to the LED, can be controlled using an additional dial microammeter connected at the output of the circuit in series with the load (battery). For this purpose, for example, a dial indicator of the recording level of old tape recorders or something similar is suitable. You can, of course, do without it by making a circuit with given fixed values of the charging current. Then, instead of the variable resistor P1, you will need to use a set of constant resistances, switchable depending on the desired value of the charging current. In this case, you will need an additional switch. But using a separate pointer device for these purposes will make working with the charger much more convenient, and the charging process itself will be clearly displayed throughout its entire duration. In addition, the VD1 LED will completely go out when the current through it drops below 10-15 mA (depending on the type), and this will not correspond to a full charge of the connected battery, through which a small current will still flow. Therefore, it is better to navigate by the arrow of the device.
The charger for the version with the LM317 MS is assembled on a small printed circuit board measuring 25 × 30 mm (Fig. 2). When using other types of MS, you should take into account the location of their pins, it may differ.
The memory can be assembled in a small case of suitable dimensions, for example, from a network adapter. The arrangement of parts in the body of this option is shown in Fig. 3.
Settings
Setting up the proposed charger circuit begins with setting the required charging voltages at the output. To do this, instead of a battery, a resistance of about 100 Ohms is connected to terminals J1 and J2 (with a power of at least 5 W, preferably a wire one, otherwise it will get very hot!). Set switch S1 to the extreme position corresponding to the battery being connected, for example, “1.2 V”. By selecting resistor R9, we achieve a voltage at the output terminals that is 15 - 20% greater than the rated voltage of the battery being charged. That is, in this case, we set the output to about 1.4 V. Then we switch S1 to the next position (for example, “2.4 V”) and by selecting resistor R10 we set the output to about 2.8 V... And so on, for all the required values. The maximum voltage that can be set in this way is determined by the maximum value of the output voltage of MS DA1, and the input voltage of the circuit (at the collector VT1) must exceed the output voltage by at least 3 V to ensure normal stabilization of the microcircuit.
After setting all the required output voltage values, you should calibrate the pointer device - microammeter. To do this, we connect a tester or ammeter in series with it, and to the output terminals - a variable resistance (wire, high power) of the order of 100 Ohms and, by changing its value, we achieve at the output the maximum current value for which our charger will be designed (for example , 300 mA). Instead of variable resistance, sets of constant resistances can be used here. Then we select a shunt - a resistance, which we solder between the contacts of our dial indicator. It must be selected so that at the selected maximum current the needle points to the end of the scale. This resistance (it can be seen in Fig. 3) for the applied dial indicator of the “M476” type was 1 Ohm. In this case, the full deflection of the needle to the end of the scale will correspond to a charge current of 300 mA. The scale can be graduated - markings corresponding to currents from 0 to 0.5 A can be applied, but this is not necessary. In practice, it will be quite sufficient to determine the approximate value of the current.
Working with memory
Set switch S1 to the position corresponding to the rated voltage of the battery that needs to be charged.
When a discharged battery is connected to terminals J1, J2, the LED lights up and the instrument needle deviates towards the end of the scale. Using variable resistor P1, we set the maximum charging current for a given battery. As the battery charges, the brightness of the LED will gradually decrease, and the arrow of the device will approach the beginning of the scale. At the last stage of charging, the LED will go out, but it is better to judge that the battery is fully charged by looking at the arrow of the device - when it is at “zero” (that is, at the very beginning of the scale). After this, the battery can remain in the charger for as long as desired - it will not be overcharged.
If you have a “battery” of batteries (several pieces connected in parallel or in series), then it is better to charge each of the batteries separately, and not in a group. Because the internal resistance of each of them, although slightly, differs from the others, and this can lead to overcharging or undercharging of individual battery elements, which will negatively affect its overall capacity. For example, to charge 4 finger batteries, it is better to make four modules (boards) connected to each battery separately. The transformer, rectifier (diode bridge) and smoothing electrolytic capacitor can be common, but designed for the total load power.
To comment on materials from the site and gain full access to our forum, you need |