Power supply considerations

[Zebra100]

Morning all. First post, so be gentle with me...

I'm just about to take delivery of my first dev kit, a Heltec ESP32 v4/SX1262 with GPS module and I'm thinking of making a solar node.

Question: Is the best option directly connecting the solar panel and Li-ion battery to the power inputs on the ESP32, or are there better option for powering the board?

Also, any other tips or advice would be greatly appreciated.

[jamesgarcia8390-sketch]

Don't wire either to the header pins, your V4 already has the charging handled on board. There's two SH1.25 connectors, the battery one takes a bare 3.3-4.2V Li-ion cell and the solar one wants 4.7-6V, so a small 5V panel, not a 12V one. The onboard PMIC does the charging and undervoltage protection, which is exactly the bit that fails when people wire a raw panel straight to the cell, an unprotected cell overcharges and swells. Just note USB and the 5V pin can't both be connected at once per the datasheet.

The thing that'll actually kill a solar node is the GPS, not the ESP32. The board sleeps under 20 µA on battery but the GPS pulls tens of mA and will flatten a small cell overnight, so gate it off except while it's getting a fix. And size the panel around the LoRa TX burst, a few hundred mA up to 750 mA at full power, not around the sleepy average