A simple battery charger based on SCR is shown here.Here the SCR rectifies the AC mains voltage to charge the battery.When the battery connected to the charger gets discharged the battery voltage gets dropped.This inhibits the forward biasing voltage from reaching the base of the transistor Q1 through R4 and D2.This switches off the transistor.When the transistor is turned OFF,the gate of SCR (H1) gets the triggering voltage via R1 & D3.This makes the SCR to conduct and it starts to rectify the AC input voltage.The rectified voltage is given to the battery through the resistor R6(5W).This starts charging of the battery.
When the battery is completely charged the base of Q1 gets the forward bias signal through the voltage divider circuit made of R3,R4,R5 and D2.This turns the transistor ON.When the Q1 is turned ON the trigger voltage at the gate of SCR is cut off and the SCR is turned OFF.In this condition a very small amount of charge reaches the battery via R2 and D4 for trickle charging.Since the charging voltage is only half wave rectified ,this type of charger is suitable only for slow charging.For fast charging full wave rectified charging voltage is needed.
Circuit diagram with Parts list.
- Assemble the circuit on a good quality PCB or common board.
- The transformer T1 can be 230V primary, 18V /3A secondary step down transformer.
- The voltage of the battery at which the charging should stop can be set by the POT R4.
- The battery can be connected to the charger circuit by using crocodile clips.