Electric vehicle fast charger circuit design

　　Circuit principle: AC220V mains is stepped down by transformer T1, and after full-wave rectification by D1-D4, it is supplied to the charging circuit. When the output end is connected to the set battery to be charged according to the correct polarity, if the peak value of each half-wave of the rectified output pulsating voltage exceeds the output voltage of the battery, the thyristor SCR is triggered to conduct through the collector current of Q, and the current charges the battery through the thyristor. When the pulsating voltage is close to the battery voltage, the thyristor is turned off and charging stops. By adjusting R4, the conduction voltage of transistor Q can be adjusted. Generally, R4 can be adjusted from large to small until Q conduction can trigger the thyristor (conduction). In the figure, the light-emitting tube D5 is used as a power indicator, and D6 is used as a charging indicator.

　　Circuit features: After the output voltage is set (for example, 36V), if the charged battery plate falls off and disconnects, causing a group of batteries to be blocked or a short circuit occurs, the battery terminal voltage will decrease or become zero, and the charger will have no output current. If the charged battery voltage deviates from the set voltage, such as the set voltage is 36V, and a 24V, 12V, 6V battery is mistakenly connected, the charger will also have no output current. If the setting is 24V and the battery is mistakenly connected to a 36V battery, the charger output voltage is lower than the battery voltage, and therefore the battery cannot be charged. If the two output terminals of the charger are short-circuited, the trigger circuit of the thyristor SCR in the charger cannot work, so the thyristor does not conduct, and the output current is zero. If the positive and negative poles of the battery are mistakenly connected in reverse during use, the thyristor trigger circuit is reversely cut off, there is no trigger signal, the thyristor does not conduct, and the output current is zero. Pulse charging is used to extend the life of the battery. Since low-voltage AC becomes pulsating DC after full-wave rectification, the thyristor will only conduct when its peak voltage is greater than the battery voltage. When the pulsating DC voltage is in the trough area, the thyristor is reverse biased and cut off, and stops charging the battery, so the pulsating DC flows through the battery. Fast charging, automatic stop when fully charged. Since the voltage across the battery is low at the beginning of charging, the charging current is large. When the battery is about to be fully charged (the voltage at the end of a 36V battery can reach 44V), as the charging voltage is getting closer and closer to the peak value of the pulsating DC output voltage, the charging current will also become smaller and smaller, and automatically become a trickle charge. When the voltage across the battery is charged to the peak value of the rectifier output, the charging process stops. According to the test, three electric vehicle batteries of 36V (three 12V/12Ah in series) can be fully charged in just a few hours using this charger; the circuit is simple and easy to make, and almost no maintenance and repair is required.