i want to use circuit from bottom of this page http://www.diyaudio.com/forums/showthread/t-41858.html to build a 10 amp lead acid battery charger. my battery is 100AH. the page has high amp voltage regulator circuit but there is no overcharge protection. is there any way to add overcharge protection?

 

Did not see the circuit on the page, but the normal way to charge a lead acid battery is to charge at constant current with voltage regulation kicking in at about 13.8 volts, where the current goes to 0. Or think of it as a 13.8 volt supply with current limiting.

 

here is the circuit. R1 is 0.82ohm 3W. R2, R3 is 0.1ohm 10W. this circuit has current control but does not have automatic cut off when battery is fully charged. i need a automatic cut off with this circuit.

 

... the normal way to charge a lead acid battery is to charge at constant current ...

On the contrary, the usual and recommended way to charge a lead-acid battery is from a constant voltage source, for a 12v battery often around 13.8. The actual voltage should be chosen after consulting the manufacturer's data.

This method will give an initially high charge current which automatically decreases as the charges. Once the battery's voltage has reached that of the charger's output, current will be reduced to zero.