Electric bicycle 36V battery charger circuit - Power Circuit - Circuit Diagram

3. If the two output terminals of the charger are short-circuited, the trigger circuit of the thyristor SCR in the charger cannot function properly, so the thyristor remains off and there will be no output current. 4. If the battery’s positive and negative poles are reversed during use, the thyristor trigger circuit will also reverse, preventing any trigger signal from reaching the thyristor. As a result, the thyristor stays off and the output current becomes zero. 5. Pulse charging is employed to prolong the battery's lifespan. After full-wave rectification, the low-voltage alternating current becomes pulsating direct current. The thyristor turns on only when its peak voltage surpasses the battery voltage, and it turns off during the valley region of the pulsating DC voltage, ceasing to charge the battery. Therefore, the current flowing into the battery is a pulsating direct current. 6. Fast charging ensures automatic stop once the battery is fully charged. Initially, when the battery voltage is low, the charging current is high. As the battery approaches full capacity (when the voltage reaches approximately 44V for a 36V battery), the charging voltage gets closer to the peak value of the pulsating DC output voltage, causing the charging current to decrease gradually until it transitions into a trickle charge. When the battery voltage reaches the peak value of the rectified output, the charging process stops. Tests show that a three-section electric vehicle battery (36V, 12V/12Ah in series) can be fully charged within just a few hours using this charger. 7. The circuit design is straightforward, making it easy to fabricate and maintain.

Second, the Circuit Principle:
The AC220V mains supply is stepped down by transformer T1 and then delivered to the charging circuit after full-wave rectification by diodes D1-D4. Once the output terminals are correctly connected to the battery pack, if the peak value of each half of the rectified output ripple voltage exceeds the battery's output voltage, the thyristor SCR is triggered to conduct by the collector current of Q. The battery is then charged via the thyristor. When the pulsating voltage approaches the battery voltage, the thyristor turns off, halting the charging process. Adjusting R4 can change the turn-on voltage of transistor Q. Generally, R4 can be adjusted from large to small to enable Q-switching and trigger the thyristor (conduction). In the diagram, the LED D5 serves as a power indicator, while D6 functions as a charging indicator. Third, Component Selection: A control transformer such as the BK200 type can be used for the power transformer, with an output voltage set at the 36V gear. Alternatively, a 4090 type toroidal transformer with a 200V rating can be used, selecting a secondary voltage of 22Vx2 or 20Vx2 in series configuration. The 4090 type toroidal transformer used by the author has a secondary voltage of 24Vx2, 12Vx2, and 0-6-23V. If the 24Vx2 section is connected in series (resulting in 48V), the output voltage is too high, leading to excessive charging current (for a 36V electric vehicle battery). During charging, the average charging current measured by the on-column ammeter is about 1.5-1.8A, which is the average value. At this point, the peak current can reach 5-7A or more. To reduce the transformer output voltage, the remaining 12V×2 and 0-6V sets of coils can be connected in series in the primary coil, reducing the secondary output voltage to 40V at no load and 36V under full load (when the average charging current is 1.2A), which meets expectations. Since the 4090 toroidal transformer costs around 23 yuan, it helps reduce production costs. Additionally, fans can wind their own transformers. Furthermore, the rectified full bridge D1-D4 in the circuit can be chosen as an 8-10A square full bridge with a circular mounting hole in the middle, which can be mounted on an aluminum plate for heat dissipation. The thyristor can be sealed with a 10A/100V gold unidirectional thyristor, fixed on the same heat dissipation aluminum plate as the rectifier bridge nut. The parameters of the transistor Q are Vceo≥60V, IM=1A, and可以选择2SB536, B564, B1008, B1015 or 2SA684, A720 and other tubes. R6 is used for current-limiting protection. If the secondary output voltage of the transformer is appropriate, the charging current (average value) does not exceed 1.5A, and the resistor can be omitted. If the charger is used for batteries of other voltages (such as 24V, 12V, etc.), the secondary output voltage of the transformer can be selected as 22V-26V, 12V-14V, etc., and the resistance of R2 and R5 should be appropriately reduced. A toggle switch can also be used to control the secondary AC voltage and resistance conversion, allowing the charger to have a wider range of applications.