README.md
This is a solar battery charger and power module. In this tscircuit version, the core circuit is in index.circuit.tsx:109.
What It Does
- Takes power from a solar panel on SLPWR1 / “Solar Panel”.
- Uses a BQ24650 solar buck charger controller to charge a battery using MPPT-style input voltage regulation. TI describes this
part as a standalone 1-6 cell buck charger with solar input and programmable MPPT; it supports 5-28 V solar input and
resistor-set charge voltage/current.
- The resistor values in this design set roughly:
- Solar input regulation / MPPT point: about 17.8 V, so it expects a panel whose useful operating voltage is around 18 V.
- Main charge voltage: about 12.6 V, consistent with a 3-cell Li-ion/LiPo pack.
- Charge current: likely about 2 A, assuming the usual BQ24650 sense formula with RSR1 = 0.02 ohm.
- Provides a regulated VOUT rail using an LT1129-3.3 LDO, so VOUT is intended to be a switched/controlled 3.3 V output.
- Includes an STC3117 fuel-gauge/monitor IC connected to SDA, SCL, and ALM so a host MCU can read battery status and receive
low-battery/fault alarms.
- Includes an MCP73113 single-cell Li-ion charger section tied to BATD, so the reference appears to include support for a small
single-cell/backup battery path as well.
How To Use It
- Connect the solar panel to the board’s Solar Panel connector, SLPWR1.
- pin1 = VCC
- pin2 = GND
- Connect the battery pack to the Battery Connector, SLPWR2.
- In this local design, it is wired as BATD and CS, not simply BAT+ and GND, so verify the original reference schematic
before powering hardware.
- Use the edge pads:
- VIN: raw external input pad in this layout.
- GND: common ground.
- VOUT: regulated output, apparently 3.3 V.
- ON_OFF: controls the LT1129 shutdown pin, enabling/disabling VOUT.
- nCE: charger enable/control input.
- SDA / SCL: I2C lines for the STC3117 battery monitor.
- ALM: alarm output from the STC3117.
Devices Required
- An assembled PCB for this design.
- A solar panel suitable for the BQ24650 input, practically around 18 V Vmp / 21 V nominal open-circuit class, and within the
BQ24650’s 5-28 V operating range.
- A compatible rechargeable battery pack. Based on the divider values, the main charger target is about 12.6 V, so this looks
like a 3S Li-ion/LiPo battery pack. Use a protected pack or add a proper BMS.
- A load that runs from the VOUT rail, likely 3.3 V, within the LT1129 current/thermal limits.
- Optional host MCU if you want to use SDA, SCL, ALM, ON_OFF, and nCE.
Important caveat: before building or applying power, compare this tscircuit port against the original GitHub reference
schematic. The local net names around BATTERY, BATD, CS, and VIN_RAW are easy to misuse, and battery charger mistakes can
damage cells or create a fire risk.
Sources: local circuit files, the referenced GitHub project, TI BQ24650 product page, Microchip MCP73113 page, ST STC3117 page,
and Analog Devices LT1129 page.
