I elaborated a little on your test. I still don’t understand how or why you might want to do this, but I learned a few things about my system by the exercise.
I have a WFCO 8955 converter, ProWatt 2000 (PSW) inverter and four GC2 batteries. The converter has been moved from the power distribution panel at the aft end of the trailer to a location right next to the batteries at the fwd end of the trailer. I was able to simulate the external power source by removing one end of the wire that connects the converter to the battery bank. This allowed the bank to power the inverter only. The converter could then power the systems, but not charge the batteries. The solar power could charge the batteries but not power the 12-volt systems. The external power cord was plugged directly into the inverter with the manual transfer switch set to shore power.
I performed the test with four variations for comparison.
1. Normal operation with link connected with solar
2. Normal operation with link connected w/o solar
3. External power with link disconnected with solar
4. External power with link disconnected w/o solar
The bank was allowed to recharge between the tests.
Since the battery bank was fully charged and the sky intermittently cloudy, the solar contributed very little except to hold the battery voltage slightly higher until the demand exceeded the output of the panels. The results of those two tests were eliminated from the chart below.
I was surprised at the flat voltage output of the converter without a battery in the system. With no loads the voltage was 13.69. With a nearly 100 amp combined load on the external battery bank (20 amp DC through the converter) it was still at 13.66. The voltage was 13.26 measured at the distribution panel so I have a 400 millivolt loss in the long wire from the converter to the panel at 20 amps.
To make the voltage variation a little more visible I cropped the chart so the high amp draw isn’t shown when I turned on the toaster. The amp draw when wired as a normal system was 86.7. When wired as an external power supply, it was 96.8 amps so the “cost” of powering the DC through the converter at that high total demand through the inverter was 10.1 amps.
