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NiCd / NiMH Battery Charger with LM317T

This compact charger is designed for NiCd and NiMH rechargeable batteries using the LM317T adjustable voltage regulator. A BC547B transistor provides current control, and an LED indicator shows the charging status.

Circuit Operation

  • The LM317T regulates the output voltage to safely charge 1.2V NiCd or NiMH cells.
  • The BC547B transistor acts as a current limiter, ensuring the battery receives a safe and constant charging current.
  • The LED indicates when charging is in progress or complete, providing a simple visual feedback for the user.
  • Charging current can be set based on the battery capacity, typically around 1/10 of the battery’s Ah rating.

Key Features

  • Suitable for NiCd and NiMH batteries
  • LM317T regulator for stable voltage output
  • BC547B transistor for current limiting
  • LED indicator for charging status
  • Adjustable current for safe battery charging
  • Simple and reliable design for hobby or small-scale applications

Construction Notes

  • Use a heatsink on the LM317T to dissipate heat during charging.
  • Ensure correct battery polarity to avoid damage.
  • Use low-tolerance resistors to maintain precise charging current.
  • Keep wiring short and use sufficient conductor thickness for reliable charging.
  • Optionally, adjust the charging current with a potentiometer to match different battery capacities.