Automatic 12V Battery Charger

Charger can work with gel, AGM and acid 12 V batteries. Led Indicates when battery is fully charged.


C1    -   220uF 25V Electrolytic Capacitor   
D1    -    P600 Diode - 50V 5A or greater rectifier diode
D2    -    1N4004 Diode  
D3    -    5.6V Zener Diode

D4    -    LED

R1,R3 - 330 Ohm 1/4W Resistor   
R2    -    100 Ohm 1/4W Pot   
R4, R5 -82 Ohm 2W Resistor
R7, R8 -82 Ohm 2W Resistor   
R6    -   100 Ohm 1/4W Resistor   
R9    -   1K 1/4W Resistor   
Q1    -    BT136 TRIAC    (need heatsink)
Q2    -    BRX49 SCR   
T1    -    12V, 4A Transformer   
F1    -    3A Fuse   
S1    -    ON-OFF Switch, > 5A  at 110 or 220V

Misc- If circuit work on box then a fan is might be necessary.

automatic 12v battery charger

It's fully automatic and will charge at a rate up to 4 A until battery voltage reaches a preset point at wich it still switch a very low current float charge. If battery voltage drops again, charger willl begin charging until the voltage reaches the cut off point. We can be left connected a battery forever maintain full charge without causing damage.

If circuit is powered off, disconnect battery otherwise battery drain slowly to it.


R2 adjust proper charge voltage. Flood and Gel batteries charging at 13,8V otherwise AGM or GEL use 14,5 or 14,9. To adjust, turn on charger and a battery, R2 in midway, turn on charger. Monitor charge with a voltmeter until battery reaches proper end voltage then, adjust pot until led grow. Charger has set.