Car battery charger

Given below, is a very simple circuit that can be used for charging car batteries. In this circuit there is facility for monitoring the charging current and voltage.

The circuit is based on the IC MC78T12ABT from Freescale.The IC is nothing but a 7812 in TO-3 package with 3A capacity. The transformer T1 steps down the mains voltage and diodes D1&D2 does the job of rectification. Capacitor C1 does the filtering and C2 acts as a decoupling capacitor. The ground terminal of IC1 is lifted to 2.1V using the diodes D3 , D4 and D5 . So the output from the IC1 will be a regulated 14.1V (12+2.1).The battery is charged via diode D6.The D6 blocks reverse flow of current from battery to charging circuit when the mains power is not available. Meter M1 shows the charging current and M2 shows the charging voltage.

Circuit diagram with Parts list.



  • The transformer T1 can be a 230V primary; 15-0-15V, 3A secondary step down transformer.
  • The meter M1 can be a 3A FSD ammeter.
  • Meter M2 can be a 20V FSD volt meter.
  • Fuse F1 can be a 1A fuse.