Firmware 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.

Noteworthy features:

• High-side switching with N-Channel MOSFETs:
  • Gate voltage is provided by a charge pump which doubles the battery voltage.
  • The MOSFETs are controlled using GPIOs.
• 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.
• 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.
• 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

Calibration

The sensing hardware should be quite accurate, but some minor error always remains. They can be compensated via the parameters in src/calibration.h.

To adjust those parameters, first set all CAL_FACTORs to 1000, recompile and flash the firmware. Then watch the RS485 output, which contains all measurements in a line starting with MEAS. Apply a known current/voltage for each measurement and calculate:

                          Actual value
CAL_FACTOR = 1000 * -----------------------
                    Value shown by firmware

Round to the nearest integer and replace the 1000 in src/calibration.h by the calculated value.

Customization

All customizable parameters can be adjusted in src/config.h.

License

The code in this repository (except submodules) is licensed under the MIT license.