Automatic safety charger circuit diagram

The circuit of this charger is simple but fully functional.
1． Constant current pulse charging. The battery charging circuit is shown in Figure 1. Due to the capacitive reactance of capacitor C, the charging of the battery is constant. In Figure 1, half-wave 50Hz charging is used. Under the condition of 220V, the charging current of each channel is I≈34C (I unit mA, C unit μF). Select the appropriate capacitor to get the appropriate charging current, generally one-tenth of the battery capacity.
2． Trickle charging. After the battery is fully charged, trickle charging is maintained to keep the battery fully charged.
3. Pressure limiting protection. SR1 and W1 protect battery E1, and SR2 and W2 protect battery E2. When the battery voltage reaches the set value, the thyristor SR triggers conduction and stops charging. LED1 is used as the instruction of E1, and LED2 is used as the instruction of E2. When the LED lights up, the battery is being charged, and when it dims (glows), it indicates that the battery charging has ended.
4. Temperature protection. The trigger voltage of the thyristor SR decreases as its temperature increases, thus causing the voltage at which the battery stops charging to decrease. Protect the battery from over-temperature within a certain range. For more accurate temperature protection, the protection circuit in Figure 2 can be connected in parallel to ends B and C in Figure 1.
5. Number of rechargeable batteries. This circuit can charge 1 to multiple batteries by adjusting W appropriately. It is recommended to charge with a single battery for better effect (when charging in series, some will not be overcharged and some will not be fully charged). The two photoelectric circuits are independent of each other, so different types of batteries with different capacities can be charged at the same time. If you are charging a battery block, you can use the charger in Figure 3. The charging current is I≈68C, and the effect is the same as above.
6. Low power consumption. Since the capacitor consumes reactive power, the power consumption of this circuit is <0.5W, and there are no heat-prone components such as transformers and adjustment tubes . The whole machine can be integrated with the battery clip, and is small, lightweight and compact.
Component selection and debugging. Capacitor C is a CL21 polyester capacitor with a withstand voltage of >400V. The capacity of the thyristor is about 1A. Use high-brightness light-emitting diodes, use small trimmer resistors for W, and use positive-temperature thermistors for RT. ND is a neon lamp for power display and zero and live wire identification. Touch terminal A. If the brightness of ND remains unchanged or weakens, the wiring is correct. If the brightness increases, terminal D is the live wire. This means that the battery clip and the metal part of the battery may easily cause electric shock to the human body. The power plug should be plugged in reverse.
The debugging in Figures 1 and 3 is the same. W1 and W3 go down, W2 goes up to the bottom, then go back a little. Install the battery and it can be charged. At this time, the luminous tube should light up. When the Ni-Gd and Ni-mH batteries are charged to 1.5V (single), just adjust W to trigger the SR and the light-emitting tube goes out (glow). In Figure 2, the thermistor RT should be close to the battery. When charging, hold RT tightly with your fingers and adjust W4 from up to down until both light-emitting tubes dim. Each component can be fixed with hot melt glue. During production, the author used the control handle of a remote control toy car as the casing. The components were connected directly or soldered with wires, so this charger circuit did not use a printed circuit board.