Rogue MPPT, 490W and charging mysteries

Almot wrote:

Amps dropping from 12 to 3 with mere 10% shade on ONE panel, alright, maybe, but then it goes into ABS 12A and REMAINS at 12A when shaded again. Marc says MPPT is slow - but MPPT drop from 12 A to 3A with enough sun to generate 12A is weird. And keeping 12A in shade again is weird. This looks like a "freeze" of software that you see in computers sometimes - rebooting (abruptly changing the light conditions in my case) brings things back to normal. In this case the firmware update might help. Will see if this happens again.

It wouldn't be all that unusual to see current drop like that with even a little shading on series panels. It also depends on what part of the panel was shaded. If there's three strings of cells per panel (as 3 diodes would suggest) and the ends of all three strings were shaded, then there's going to be a real bottleneck in that panel unless the bypass diodes start conducting, and probably very little to grab onto as far as MPP goes. So the controller's tracking is going to wander. In all the tests I've done, the controller will recover the MPP once moved out of the shade, which is probably what happened - right before it went to absorb.

If the controller "froze" it would reset itself because there's a failsafe (watchdog timer) that causes a reset if the code stops executing for any reason. All charging would have stopped and it would have restarted at the welcome screen.

I probably didn't read the manual well, since tried to tune-up VTRIM at different temps - which is of course difficult. Multimeter error by 0.1V to the lower side... maybe... It's a good multimeter, not $10. Tomorrow will borrow 2 other meters from 2 neighbors and see what happens.

It may not be your multimeter. I just like to run through all of the possibilities. The display could just be on "this side" or the other of where it should be because of its limited resolution and other factors mentioned.