Description.

Here is a simple but effective battery charger circuit using IC LM 317.The circuit can be used to charge 12Vlead acid batteries.The circuit is very simple and can be easily assembled on a general purpose PCB.

The heart of the circuit is IC LM 317 ,which is an adjustable voltage regulator IC.The pin 1 of the IC is the control pin which is used to control the charging voltage.The pin 2 is the output pin at which the charging voltage appears.The pin 3 is the input pin to which the regulated DC supply is given.

The charging voltage and current is controlled by the Transistor Q1,resistor R1 and POT R5.when the battery is first connected to the charging terminals ,the current through R1 increases.This in turn increases the current and voltage from LM 317.When the battery is fully charged the charger reduces the charging current and the battery will be charged in the trickle charging mode.

Circuit diagram with Parts list.

Notes.

• The input voltage to the circuit must be atleast 3V higher than the expected output voltage.LM 317 dissipates around 3V during its operation.Here I used 18V DC as the input.
• The charging voltage can be set by using the POT R5.
• The LM 317 must be mounted on a heat sink.
• All capacitors must be rated atleast 25V.
• You can use crocodile clips for connecting the battery to the charger.