Solar tester update: it works!

[Part 1] [Part 2]

Did a real world test using a 17x17cm panel for the test cell. With a CN3791 charger board it took about 5.5 hours to charge a 18650 cell from 3v to 4.03v (which is the point this charger stops at). The panel produced 3.3W at peak sun (2W average over the charging phase), it actually maxed my current sensor at about 725mA which I was not expecting. Maybe I should try replacing the shunt resistor to get a wider range...

After the charge phase it started the measurement: discharging the cell through a 10W load resistor. This thing gets pretty hot even at 2.5W, in hindsight I should have probably had it on a separate small board. But everything seems fine anyway: at 3v it stops discharge and starts to charge the cell again, this time up to the programmed storage voltage (3.6v). It was evening at this point so I'll continue tomorrow.

Next: persisting settings and cycle state in flash memory, maybe Bluetooth communication for logging cycle data to PC. Also testing different charger modules and panels.