A
short-circuit proof battery charger will provide an average charging
current of about 8A to a 12V lead-acid storage battery. The Charger
circuit has an additional advantage, it will not function nor will it be
damaged by improperly connecting the battery to the circuit. With 220V
at the input , the circuit comences to function when the battery is
properly attached.The
battery provides the current to charge the timing capacitor C1 used in
the PUT relaxation oscillator.When C1 charges to the peak point
voltage the PUT , the PUT fires turning the SCR on , which in turn
applies charging current to the battery. As the battery charges , the
battery voltage increases slightly which increases the peak point
voltage of the PUT. The voltage on C1 increases until the zener voltage
of D1 is reached , which clamps the voltage on C1 , and thus prevents
the PUT oscillator from oscillating and charging ceases. The maximum
battery voltage is set by potentiometer R2 which sets the peak point
firing voltage pf the PUT . In the circuit shown , the charging voltage
can be set from 10 V to 14 V - the Lower limit being set by D1 and the
upper limit by T1.
Part List :
Resistor
R1 = 10K
R2 = 50K trim
R3 = 47K
R4 = 1K
Capacitor
C1 = 0.1uF
Diode , SCR , PUT
B1 = MDA990-1
D1 = 1N5240 10V
SCR = 2N5164
PUT = MPU131
Transformer , Inductor
T1 = Stepdown 220V to 14V
T2 = 11Z12 1:1
