[quote author=sain link=topic=2868.msg42588#msg42588 date=1142904690] actually its pretty easy to do - you just use an opamp as a voltage comparator - comparing the battery voltage and a reference voltage. The reference voltage should be whatever you want the battery charged up to (use a voltage divider off a constant 12v src). The output from the op amp is fed into a transistor which switches the constant current source charger on and off. I'll find the schematic for the one I built eventually - its somewhere on a spindle of backups cds. In the meantime you can figure it out from that description, it'll make a useful exercise [/quote] This was from afromans forums, afro and i tested the charger and verifed that it works amazing w/o spending liek 20 bucks on a another charger, But i need help building wat sain said, i wanted to know could i make my voltage source automatically cutoff when the battery is finished charging. I could ask afroman and see if he could help, (becuase he has all the brains, i just got a big electronic workroom, flame free, and i test his experiments,) but afroman isnt reply to me on aim. SO i came to yall to see what yall think about it.