Simple Lead Acid Battery Charger

The above pictured schematic diagram is just a standard constant current model with a added current limiter, consisting of Q1, R1, and R4. The moment too much current is flowing biases Q1 and drops the output voltage. The output voltage is: 1.2 x (P1+R2+R3)/R3 volt. Current limiting kicks in when the current is about 0.6/R1 amp. For a 6-volt battery which requires fast-charging, the charge voltage is 3 x 2.45 = 7.35 V. (3 cells at 2.45v per cell). So the total value for R2 + P1 is then about 585 ohm. For a 12 V battery the value for R2 + P1 is then about 1290 ohm.
Simple Lead Acid Battery Charger - schematic

For this power supply to work efficiently, the input voltage has to be a minimum of 3V higher than the output voltage. P1 is a standard trimmer potentiometer of sufficient watt for your application. The LM317 must be cooled on a sufficient (large) coolrib. Q1 (BC140) can be replaced with a NTE128 or the older ECG128 (same company). Except as a charger, this circuit can also be used as a regular power supply.

Leave Comment

characters left:

New Circuits