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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING Automatic charger. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Chargers, batteries, galvanic cells To prolong the battery life of nickel-cadmium or nickel-metal hydride batteries, it is recommended to discharge the battery before each charge. It is inconvenient to do this without a special device, and neglecting the discharge can lead to the appearance of the "memory" effect. The charger described below automatically performs both discharging and charging functions. The charger is designed to charge batteries consisting of 7-10 sealed alkaline batteries in a mode close to that indicated on the battery label. The manufacturer guarantees the battery life (the number of charge-discharge cycles) and the preservation of its rated capacity under the following operating conditions: discharge to a final voltage of at least 1 V and charge with a current equal to one tenth of the rated capacity in ampere-hours for 15 hours In the proposed device, the discharge is carried out to a final voltage corresponding to 1,05 V for each battery cell. The charging current is 0,8 nominal, the charging time is about 17 hours, the capacity of the rechargeable batteries is from 0,1 to 1 Ah. The diagram of the device is shown in the figure. It is very simple to operate the device - just connect the battery to terminals X1, X2, turn on the SA1 "Network" toggle switch and press the SB1 "Start" button. When the power supply is interrupted, the device goes into standby mode and when the mains voltage appears, the process continues
The battery is discharged by a stable current generator to the final voltage, at which the EMF on the "weakest" battery drops to 1,05 V. When the final voltage is reached, the stable current generator is connected in series with the battery to the power source, providing charging current. At the same time, a timer is started, which stops charging after 17 hours 4 minutes. The charger is powered by AC 220 V. The power supply is a full-wave rectifier VD1 with quenching capacitors C1, C2, C3 and a current-limiting resistor R1. The voltage smoothed by capacitors C4 and C5 is supplied to the series-connected zener diodes VD2 and VD4 with a stabilization voltage of 10 V. The first voltage is used to power the main part of the device, and the second to power the current generator in battery charging mode. Current generator - parametric. It is assembled on transistors VT5, VT6, LED HL2 and resistors R17, R18. Transistor VT5 sets the current through the HL2 LED, which, in addition to indicating the current through the battery, performs the function of a low-voltage stabistor. Transistor VT6 is connected according to the emitter follower circuit. The required current is set with a tuning resistor R17. After the relays K1 and K2 are activated, the current generator is connected in parallel to the battery and discharges it, and when the relay windings are de-energized, the current generator is connected in series with the battery to the power source - it is charging. Chip DD2 works simultaneously as a crystal oscillator at a frequency of 32768 Hz and a frequency divider. At the output S2 of the microcircuit, the frequency is 2 Hz, at the output M - 1/60 Hz. The device works as follows. Connect the battery to terminals X1 and X2. Turn on the toggle switch SA1, and press the button SB 1 "Start". When the right contacts of the button are closed, the voltage is supplied to the circuit C13R21 and then to the input R of the trigger DD3.2. At its inverted output, a high level occurs. Also, a high level through the diode VD6 is supplied to the circuit C8R6 and the input R of the counter DD1, turning it into the zero state. When the left contact group of the SB1 button is closed, current flows through the relay windings K1 and K2, the relays are activated (contacts 2 and 3 close) and the current generator is connected in parallel with the battery. The process of discharging the battery begins, as evidenced by the glow of the HL3 LED. The voltage value on the engine of the resistor R15 is more than necessary for direct bias of the emitter junction of the transistor VT4 and the HL4 LED used as a low-voltage stabistor. Transistor VT4 is open, its collector and input D of trigger DD3.1 are low. Clock pulses with a frequency of 2 Hz are fed to the input C of the DD3.1 trigger and put it into a state in which the direct output is low and the inverse output is high. This high level through the diode VD7 comes to the input R of the counter DD1 and to the base of the composite transistor VT7VT8, opening it. The current through the open transistors and windings of the K1 K2 relay keeps the contacts of these relays in the triggered state, in which the current generator is connected in parallel to the battery and discharges it. As the battery discharges, the voltage on the engine of the resistor R15 becomes insufficient to keep the transistor VT4 open. It closes, and a high level occurs at its collector and input D of the trigger DD3.1. With the arrival of the next clock pulse to the input C of the trigger DD3.1, a low level appears on its inverse output, and a high level on the direct one. The composite transistor VT7VT8 closes, the relay windings K1 and K2 are de-energized, their contacts return to the position in which the current generator is connected in series with the battery to a 25 V power source for charging. At the same time, a low level appears at the input R of the counter DD1, and it starts counting pulses with a frequency of 1/60 Hz coming to its input C from the output M of the counter DD2. A high level from the direct output of the trigger DD3.1 is supplied to the input S of the trigger DD3.2, while the voltage at its inverted output becomes zero, the diode VD10 opens and the flow of pulses to the input C of the trigger DD3.1 stops. The conversion factor of the DD1 counter is 1024, the input frequency is 1/60 Hz (one pulse per minute). When the 1024th pulse arrives (after 17 hours 4 minutes), a high level appears at the output 2 of the counter DD1, which opens the transistors VT2 and VT3. The composite transistor VT3 shunts the power supply, and the charging process stops. However, not the entire device is de-energized. The current from a charged battery, equal to 30 μA, begins to flow through the VD5 diode, the R2 resistor and the back-connected emitter junction of the VT1 transistor, which acts as a low-current zener diode with a stabilization voltage of 6,3 V. This voltage feeds the DD1, DD3 microcircuits and keeps them in a state, in where they were at the time of bypassing the power supply. The ability to store information in the absence of mains voltage allows you to allow interruptions in the process of discharging and charging due to a lack of voltage in the supply network. The VD11 diode is designed to protect the charger - when the battery is connected in the wrong polarity, the VD11 diode opens and the FU2 fuse blows. The device uses MBGCH capacitors (C1-C3) for a voltage of 500 V. Relays K1 and K2 are reed switches RES55A with passport RS4.569.600-02. Resistor R1 - C5-42V, R15, R17 - SPZ-19a. Zener diodes VD2, VD4 and transistor VT6 are placed on duralumin heat sinks with an area of 20 cm2 each. The device's compactly assembled circuit board is housed in a metal box that protects it from powerful electromagnetic and electrostatic fields that can cause false alarms. Since the device has a transformerless power supply from the mains, care should be taken when setting up and operating. At the time of establishment, it is desirable to connect the device to the network through an isolating transformer. Setting up the device consists in establishing the required charging and discharging current and determining the moment the device switches from the discharge mode to the charging mode. First, set the slider of the resistor R17 to the lowest position according to the diagram, and R15 to the highest position. Connect an incompletely discharged battery to contacts XI, X2 through a milliammeter and turn on the device in the network. Press the "Start" button - the battery begins to discharge through the current generator. The required discharge current is set by rotating the slider of the resistor R17. Turn off the milliammeter, connect the battery directly to the contacts X1, X2 and press the "Start" button - the discharge continues. Periodically monitor the voltage on each battery of the battery. When a value of 1,05 V is reached on any of them, the discharge is stopped by smooth rotation of the slider of the resistor R15 down the circuit. In this case, the device switches to charging mode, the HL3 LED goes out. The output of the device is galvanically connected to the network, as a result of which it is possible to connect or disconnect the battery only in the off position of the SA1 toggle switch. Author: Sh.Gizatullin, Tomsk
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