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NiCd Battery Charger with Solar Cells (MAX639)

This solar-powered NiCd battery charger uses 12 small BT2 solar cells and a MAX639 voltage supervisor IC to safely charge rechargeable NiCd batteries. It is ideal for trickle charging and small solar-powered applications.

Circuit Operation

  • The 12 BT2 solar cells generate low-voltage DC when exposed to sunlight, providing the charging current.
  • The MAX639 IC monitors the battery voltage and controls charging to prevent overcharge.
  • The charging current is limited by the solar panel output, making it safe for long-term connection to NiCd batteries.
  • The circuit provides automatic cutoff when the battery reaches full charge, resuming charging when the voltage drops.

Key Features

  • Solar-powered NiCd battery charger
  • Uses 12 BT2 solar cells for energy harvesting
  • MAX639 IC provides voltage monitoring and automatic cutoff
  • Safe trickle charging for long-term battery maintenance
  • Compact and eco-friendly design

Construction Notes

  • Ensure proper connection and orientation of all solar cells for maximum output.
  • Use low-resistance wiring to minimize voltage drop from the solar panel to the battery.
  • The MAX639 IC should be powered from the solar panel voltage or a small buffer capacitor to ensure stable operation.
  • Optionally, include a series resistor to limit charging current for small batteries.
  • Protect the battery from complete discharge when no sunlight is available by using a blocking diode in series with the solar panel.
Nicad battery Charger