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I notice in the MayFly schematic near the diode for the “v_solar” input a “20V-1A” note. The MCP73831 charge management controller data sheet lists 6 volts as the upper limit for Vdd. I assume I need to pre-regulate solar power down to 5 or 6 volts; is that correct? What does the “20V-1A” note mean?
“20V-1A” is just the rating of the protection diode on the PC board. When choosing a solar panel for the Mayfly, you should only connect ones that are listed as 6 volt panels, and do not use a 9-volt or 12-volt panel.