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.
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.