18 volt car battery charger, with automatic cu toff

This charger will quickly and easily charge most any lead acid battery. The charger delivers full current until the current drawn by the battery falls to 150 mA. At this time, a lower voltage is applied to finish off and keep from over charging. When the battery is fully charged, the circuit switches off and lights a LED, telling you that the cycle has finished.

Schematic

Parts

Part Total Qty. Description Substitutions R1 1 500 Ohm 1/4 W Resistor R2 1 3K 1/4 W Resistor R3 1 1K 1/4 W Resistor R4 1 15 Ohm 1/4 W Resistor R5 1 230 Ohm 1/4 W Resistor R6 1 15K 1/4 W Resistor R7 1 0.2 Ohm 10 W Resistor C1 1 0.1uF 25V Ceramic Capacitor C2 1 1uF 25V Electrolytic Capacitor C3 1 1000pF 25V Ceramic Capacitor D1 1 1N457 Diode Q1 1 2N2905 PNP Transistor U1 1 LM350 Regulator U2 1 LM301A Op Amp S1 1 Normally Open Push Button Switch MISC 1 Wire, Board, Heatsink For U1, Case, Binding Posts or Alligator Clips For Output

Notes

1. The circuit was meant to be powered by a power supply, which is why there is no transformer, rectifier, or filter capacitors on the schematic. There is no reason why you cannot add these.
2. A heatsink will be needed for U1.
3. To use the circuit, hook it up to a power supply/plug it in. Then, connect the battery to be charged to the output terminals. All you have to do now is push S1 (the "Start" switch), and wait for the circuit to finish.
4. If you want to use the charger without having to provide an external power supply, use the following circuit.
   
   

   Part	Total Qty.	Description	Substitutions
   C1	1	6800uF 25V Electrolytic Capcitor
   T1	1	3A 15V Transformer
   BR1	1	5A 50V Bridge Rectifier	10A 50V Bridge Rectifier
   S1	1	5A SPST Switch
   F1	1	4A 250V Fuse

5. The first time you use the circuit, you should check up on it every once and a while to make sure that it is working properly and the battery is not being over charged.