I agree with the theory, but what IS happening is what I described.
With solar disconnected 12.8V is showing at Solar + bare terminal.
With cable attached from solar + , charger is happy to output 27V (set) @ about 2A (set for 1A
) to start batteries. Blocking diode between solar + and charger input (fitted correct way around).
MPP250 otherwise works as expected, so either internal fault or Manual includes the now popular "alternate truth".
I have AliExpress "Blocking Diode 15amp 45V High Surge Current Capability 15SQ045 High Quality For DIY Solar Cells Panel". Any problem using one to stop reverse current ? Solar is 2 x 150W seried.