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.
1-Assemble the circuit on a good quality
PCB or common board.
2-The transformer T1 can be 230V
primary, 18V /3A secondary step down
3-The voltage of the battery at which the
charging should stop can be set by the
4-The battery can be connected to the charger circuit by using crocodile clips.