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The circuit enables two nickel-cadmium batteries to automatically disconnect the charging or discharging circuit when charging to 3V or discharging to 1î€34V, effectively preventing overcharging or overdischarging.
The circuit is shown in the drawing. The voltages after the rectification of D1 and D2 are supplied to the battery for charging, and the voltages after the rectification of D3 to D6 are supplied to the comparison and control circuit. The TL082 constitutes a comparison circuit. The 2 pin is supplied with a constant voltage as a reference reference by the LM317 output, and the 3-pin voltage is derived from the battery. After the voltage comparison of the 2 and 3 feet is controlled, the 1 pin output controls the opening and closing of the BG, and then the relay is used to control the charging or discharging circuit.
1î€ Charging process: Put the switch S in the “1†position, the battery is placed in the battery clip, and the power is turned on. At this time, the voltage of the 2 pin of the TL082 is 3V, and the voltage of the 3 pin is less than 3V, and the 1 pin outputs a negative voltage. When BG is cut off, no current flows through J, the normally closed contact J1 is closed, and the power supply charges the battery through R8, S2, and J1. When the battery voltage rises to more than 3V, the output voltage of pin 1 of TL082 is positive, so that BG is turned on. When J is powered, J1 is turned off and charging is completed. At this time, pin 3 of TL082 provides a higher voltage by R8 and S2 to maintain the conduction of J until the power is turned off. LED2 is used for charging indication.
2î€Discharge process: When the battery is charged three or four times, a discharge is required to eliminate the memory effect. Before discharging, put switch S in the "2" position, then put the battery and turn on the power. Since the output voltage of the LM317 is set to 1î€3V at this time, the battery voltage is higher than this value. After the TL082 is compared, a positive voltage is output to turn on the BG. After the J is turned on, the normally open contact J2 is closed (and J1 is disconnected). The battery is discharged through J2, S3, and R10, and LED3 is lit at the same time. When the battery voltage drops to nearly 1î€3V, the TL082 output voltage is inverted to negative, BG is turned off to make J2 open, the discharge is over, and LED3 is extinguished.
After the power is discharged, the switch S is placed in the "1" position to be charged.
Switch S selects the band switch with four sets of contacts, R2, R3 preferably do not use adjustable resistors, so as to avoid the contact failure affecting the voltage of the constant voltage source. Capacitor C3 must not be connected, otherwise the relay will appear "jitter" after charging.
Pay attention to the operation sequence when using, put the battery, and put the switch S in the corresponding position, then turn on the power, otherwise it will be misjudged as charging is completed and there is no charging phenomenon. Wuhu North Luo Yunzhong
Experiment review:
The device is low in cost, simple and easy to perform, and after actual testing, it is considered to be able to perform the functions of automatic charging and discharging of its battery. However, this device has a small drawback, that is, LED2 does not indicate that the battery is full. Therefore, the author suggests a slight modification on the original circuit to control LED2 through T, so that when the battery is fully charged, LED2 will automatically go out.
According to the author's understanding, it is rare to see such a charger that can automatically charge and discharge (memory) in the market, and it is relatively expensive. Therefore, the device has certain market potential.
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