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Fast Charger for Car Battery

This high-current fast charger is designed for 12V car batteries, providing rapid charging while ensuring safe operation. It uses an AC transformer, rectification, voltage regulation, and a relay control circuit to manage the charging process.

Power Supply

  • AC Transformer: 13-0-13 V
  • Rectifier: 35A bridge rectifier for high-current DC output
  • Voltage regulation and control using 7805 and LM311 relay circuit

Circuit Operation

  • The transformer steps down mains voltage to ~13V AC, which is rectified to DC by the 35A rectifier.
  • The 7805 voltage regulator provides a stable reference for the LM311 relay circuit.
  • The LM311 comparator and relay control the charging current and switch the charger to float mode when the battery reaches the desired voltage.
  • The charger provides high current for rapid charging while preventing overcharge damage.

Key Features

  • Fast charging for 12V car batteries
  • High-current rectifier for rapid charging (35A)
  • Automatic voltage regulation using 7805 and LM311
  • Relay-controlled float mode to maintain full charge safely
  • Simple, reliable design suitable for automotive use

Construction Notes

  • Use proper heatsinks for the rectifier and 7805 regulator to handle high currents.
  • Ensure correct wiring and polarity when connecting the battery.
  • Include a fuse or circuit breaker for safety (matching the maximum charging current).
  • Keep wiring short and use thick conductors to minimize voltage drops at high current.
  • Optionally, mount the charger in a ventilated enclosure or add a fan to dissipate heat.

fast charger for 12v car batteries

Make sure RL support draw current to battery. When battery is full charged RL turn off circuit.