Electric vehicle battery charging protection circuit diagram

This protection circuit can not only prevent undercharging and overcharging, but also automatically cut off the power if the charger does not switch to green light for ten hours to prevent serious errors. And the charging time can also be automatically recorded with a quartz clock. In this way, the battery capacity change can be grasped, and whether the charger does not switch to green light occurs, so as to decide whether to send it to the maintenance point for processing. The circuit principle is shown in the figure below. Press the AN button to get power. At the beginning, Q10 and Q13 of CD4060 are both 0V, and the output of U2C and U2D NAND gates of CD4011 is high level, so Q2 transistor 8050 is turned on, J is attracted and self-held, and the charger starts charging. 555 generates a pulse with a period of 8.789 seconds as a timing reference and is added to the CD4060 count. When charging, the voltage of about 1.8V taken from the red light of the charger is added to the base of transistor Q1 through the plug to turn it on, and the output of U12A of CD4011 is high level, and the output of U2B is low level. Therefore, if the red light is always on, even if Q10 becomes high after counting 512 pulses, the relay J will not be disconnected. Only when Q13 becomes high after counting 4096 pulses (10 hours), U2C outputs 0V, Q2 is cut off, relay J is powered off and charging stops, and the circuit itself stops working. If the red light turns green after charging for a period of time, the voltage on the base of Q1 is less than the voltage required for conduction, so it is cut off, its output becomes high, U2A output becomes low, and U2B output becomes high. At the same time, the rising edge of U2B is added to the RST reset terminal of CD4060 through capacitor C3, so that it starts counting from zero. When counting to 512 pulses (1 hour and 15 minutes), Q10 becomes high, U2D output becomes 0V, Q2 is cut off, J is powered off, and the charging stop circuit also stops working. This plays a role in preventing undercharging and overcharging, and automatically turning off the power if the green light does not change for more than ten hours, so it can be called a charging protector . LED 1 is on, indicating that the red light voltage of the charger has been taken out and connected normally. LED2 is on every few seconds, indicating that the 555 is working normally. It is used to observe the pulse cycle during debugging. LED3 is on, indicating that the relay is energized and in the charging state, and the voltage of about 1.8V taken from it can be used as the power supply of the quartz clock (remove the 1.5V battery), so that it can record the time used for charging. During debugging, first temporarily connect the 12th foot of U2D to the 7th foot Q4 of CD4060, without connecting the red light voltage of the charger, and see if the relay can be disconnected normally when LED2 is on for 9 times (8 cycles). If there is a "pop" sound but it is not disconnected, it is necessary to connect a capacitor of about 0.01μ from the 12th foot of CD4060 to the ground to eliminate the erroneous reset pulse generated by electromagnetic interference on the 12th foot when the relay is disconnected. The erroneous reset will cause the transistor Q2 to be turned on immediately after disconnection because Q10 and Q13 become 0V, and the relay is energized again. The parallel capacitor should not be too large, otherwise it will affect the effect of normal reset, and it cannot be guaranteed that the counting starts from zero when the green light is on. C3 cannot have leakage, and 1u monolithic capacitor or glass glaze capacitor can be used. Adjust RP1 so that the 8 oscillation cycles of 555 are about 70 seconds. After adjustment, connect the 12th foot of CD4011 and NAND gate U2D to the 15th foot Q10 of CD4060 and it will be successful. For a charger with a constant current charge of 1.8A, 18AH can be charged in 10 hours. For batteries within 14AH, even if charging starts from the lowest allowable voltage, considering the efficiency of electrochemical conversion, it needs to be charged to 14×1.2=16.8AH, so the green light will be on in no more than 10 hours. It is reasonable to set 10 hours as the protection time. If the original charger is still used and replaced with a large-capacity battery such as 20AH, the green light will be on for more than 10 hours if charging starts from the lowest allowable voltage and considering the conversion efficiency. If 10 hours is still used as the protection time, undercharging will occur. This requires adjusting RP to lengthen the pulse period of 555 so that the protection time is greater than the time required to light the green light. For example, if the relay is turned off 1 hour and 30 minutes after the green light comes on, the protection power-off time will automatically become 8×1.5=12 hours. Using a charging protector, you can charge without supervision and extend the battery life and save electricity.