Nickel-cadmium battery automatic charger and discharger circuit

This circuit can make two nickel-cadmium batteries automatically disconnect the charging or discharging circuit when charging to 3V or discharging to 1.34V, effectively preventing overcharging or overdischarging. See attached diagram for circuit. The rectified voltages of D1 and D2 are supplied to the battery for charging, and the rectified voltages of D3 to D6 are supplied to the comparison and control circuits. TL082 constitutes a comparison circuit, its pin 2 is provided by the LM317 output to provide a constant voltage as a reference, and the voltage of pin 3 comes from the battery. After comparing the voltages of pins 2 and 3, the output of pin 1 controls the on and off of BG, and then controls the charging or discharging circuit through the relay. 1. Charging process: Set the switch S to the "1" position, place the battery in the battery clip, and turn on the power. At this time, the voltage of pin 2 of TL082 is 3V, while the voltage of pin 3 is less than 3V, and pin 1 outputs negative voltage. 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 greater than 3V, the output voltage of pin 1 of TL082 is positive, turning on BG. After J is powered, J1 is turned off, and charging is completed. At this time, pin 3 of TL082 is provided with a higher voltage by R8 and S2 to maintain J's conduction until the power is turned off. LED2 is used for charging indication. 2. Discharge process: After the battery has been charged three or four times, it must be discharged once to eliminate the memory effect. Before discharging, first put the switch S in the "2" position, then put in the battery and turn on the power. Since the output voltage of LM317 is set to 13V at this time, the battery voltage is higher than this value. After comparison, TL082 outputs a positive voltage to turn on BG. After J is powered, the normally open contact J2 closes (at the same time J1 opens) , the battery is discharged by J2, S3, and R10, and LED3 is lit at the same time. When the battery voltage drops to nearly 1.3V, the TL082 output voltage flips to negative, BG is cut off to disconnect J2, the discharge is completed, and LED3 goes out. After discharging, put the switch S in the "1" position to continue charging. Switch S is a band switch with four sets of contacts. It is best not to use adjustable resistors for R2 and R3 to avoid poor contact that affects the voltage of the constant voltage source. Capacitor C3 must not be left unconnected, otherwise the relay will "jitter" after charging. When using, pay attention to the operating sequence, put the battery in, and put the switch S in the corresponding position before turning on the power. Otherwise, it will be mistakenly judged as charging and the battery will not charge. Hubei Luo Yunzhong's experiment comments: This device is low-cost and simple to make. After actual testing, it is believed that it can complete the automatic charging and discharging functions of its battery. However, there is a small flaw in this device, that is, LED2 does not indicate that the battery is fully charged. Therefore, the author recommends making slight changes to the original circuit and controlling LED2 through T, so that when the battery is fully charged, LED2 can automatically turn off. According to the author's understanding, chargers that can automatically charge and discharge (eliminate memory) like this are rare and relatively expensive on the market. Therefore, this device has certain market potential.