Configure inverter via Sunsynk Connect app
My inverter is in the loft, and difficult to get to. I gather that Sunsync Connect can be used to manage the configuration, so that would be the ideal method.
However, the documents all cover operation via the front panel, and the app looks inconsistent. So a little confusion arises.
Second, any change seems ineffective. Silly question, but is some sort of restart required to activate changes?
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Well, the green, white and black leads coming out of the USB cable are the -, + and GND and so should go to pins 1, 2 and 3 as you suggest. The pin numbering is left to right looking into the inverter as shown on this page:
https://solar-assistant.io/help/deye/configuration
If you're using the Solar Assistant card image for the Pi, the driver is included, If you're using other software or Linux distribution, it would probably be installed already, but I guess you might need to add a driver.
Oh, and careful if you're stripping those wires: they're quite delicate.