Hardware for the LNSC-2420 Solar Charger

The LNSC-2420 is a PWM-based solar charge regulator for 24 V systems supporting up to 20 A charging current.

WARNING

The version 1.0 currently in the repository contains a mistake will destroy the driver MOSFETs (the power MOSFETs are safe)! Do not build it as-is!

This notice will be removed once the design is fixed.

Noteworthy Features

• High-side switching with N-Channel MOSFETs:
  • Gate voltage is provided by a charge pump which doubles the battery voltage.
  • Using N-Channel MOSFETs allows to drastically reduce the Rds_on compared to P-Channel MOSFETs, resulting in lower loss.
  • High-side switching allows to have a shared ground connection between solar panel, battery and all devices connected as load.
• Current and voltage measurement:
  • The solar current, load current, solar voltage, battery voltage and charge pump output voltage are measured using the internal ADC of the STM32F030.
  • The voltages are measured via high-resistance voltage dividers which are buffered using ultra-low-power OpAmps.
• Low power usage:
  • The charge pump is disabled if both power FETs are off.
  • Additionally, the microcontroller is put into deep sleep (Stop Mode) if no solar power is available and the battery voltage is in undervoltage protection.
  • During normal operation (with LEDs on), the controller itself consumes below 300 mW.
  • In deep sleep, power consumption is below 25 mW.
• LED status display:
  • 6 LEDs show the internal charging and discharging state.
  • The LEDs are controlled using Charlieplexing (i.e. only 3 GPIOs are needed)
• Protections:
  • Solar panel reverse current
  • Battery overvoltage
  • Battery undervoltage
  • Load current limit

License

The design in this repository is licensed under the CERN Open Hardware Licence Version 2 - Permissive (CERN-OHL-P.