Today I am going to focus on lead acid battery charger circuit that uses IC LM 317. The main purpose of the IC is to provide correct charging voltage for this battery. A battery should be charged with a tenth of its Ah value. This charging circuit is made based on this fact.

R1, R4, Q1 and R5 are used to control the battery’s charging current. Potentiometer can on the other hand be used in setting the charging current. The current passing through R1 will increase as the battery gets charged. This changes the conduction at Q1.

The voltage at output of LM 317 increases since collector of Q1 is linked to adjust pin of IC LM 317. When the battery is completely charged, the charger circuit will reduce the charging current. This mode is known as trickle charging mode.

Below is the battery charger circuit drawing with its parts listed clearly.

Points to note

  • For effective use, the battery should be connected to the circuit in a series with a mm. To attain the required charging current adjust R5. Charging current is equal to (1/10)* Ah value of battery.
  • Input to the IC should be at least 18V for attaining correct charging power at the output. LM 317 data sheet explains this better.
  • Fix LM 317 with a heat sink.
  • This is a stable voltage and current limited charger and can be used for SLA batteries. Set maximum voltage of 13.8 volts with R5 and maximum charge current at 1.5A which is limited by R1.
  • However this charger works better on Lead acid batteries compared to SLA battery.
  • It is impossible to have an infinite charging current since the battery will blow.
  • The limit for cycle use is 13.8 volt, for standby use while 15.2 is for boost charge.

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