Emergency power duration and handling

[selimnairb]

Original report by Brian Calder (Bitbucket: brian_r_calder, ).

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The super-capacitor intended to hold up the power line after main power is gone is current (2.3.0) not doing what’s intended. That is, the power is held up, but not to the level required for the 3.3V LDO to continue to operate successfully and keep the ESP32 module on. What’s observed is that the system drops voltage quickly, and then plateaus; the ESP32 brownout detector triggers long before the firmware can shut things down.

The system therefore needs either a bigger capacitor, or a better LDO, or both.