Finally got the big 50A transfer relay system built.
The big relays need 120VAC to operate the coils, so I used 2 of the same 2A solid state relays that we used on the grid charger to turn them on and off. The SSR feature opto isolated dc inputs that will operate from 3 to 32 VDC. After doing some measurements, the opto input seems to be current regulated at 10 ma, so it was easy to get another series led to act as an indicator with no need for a resistor. Will power the optos with 12VDC
Since we still needed 120VAC for the relay power, I put another SPDT switch so the ac can either come from the inverter output or the grid input.
I used a 9 pin connector (grid charger) for the source control lines and 12V power, which will run to the load management computer box.
The mounting location for this transfer box is not very accessable so I had to fully wire the box before it is mounted.