The SCR gets triggered with a voltage at its Gate terminal through the resistor R1 and diode D1. It then starts rectifying the AC voltage, though only for the half cycle. As the DC current starts flowing to the battery through the resistor R2, the battery gets charged
A simple SCR-based battery charger is presented here. To charge the battery, the SCR rectifies the AC mains voltage. The battery voltage drops when the battery attached to the charger is depleted. Through R4 and D2, the forward biassing voltage is prevented from reaching the transistor Q1’s base. This turns the transistor off. When the transistor is turned off, the triggering voltage is applied to the gate of the SCR (H1) through R1 and D3. As a result, the SCR begins to conduct and correct the AC input voltage. The battery receives the rectified voltage via the resistor R6 (5W). The battery will now begin to charge.
When the battery is fully charged, the voltage divider circuit comprising R3, R4, R5, and D2 provides the forward bias signal to the base of Q1. This activates the transistor. The trigger voltage at the gate of the SCR is cut off when the Q1 is switched on, and the SCR is turned off. A very tiny amount of charge reaches the battery via R2 and D4 for trickle charging in this scenario. This sort of charger is only ideal for sluggish charging because the charging voltage is only half-wave rectified. Full-wave rectified charging voltage is required for fast charging.
Battery Charger Schematic Circuit diagram with Parts list:
Notes:
- Assemble the circuit on a high-quality PCB or a standard circuit board.
- The T1 step-down transformer can be 230V primary and 18V /3A secondary.
- The POT R4 can be used to set the voltage of the battery at which the charging should stop.
- Crocodile clips can be used to connect the battery to the charger circuit.
