Do I understand correctly, you did this test without using the 120v side powered up with the common items a RV camper would be using, such as my use; Laptop, Direct TV DVR, LED Television and various other items on, such as LED Table Lamp? What would be the point of doing a test if the batteries are not having a draw on them that is then depleting the batteries, creating a load that the convertor then would activate the battery charging mode of the convertor? This is the real test of a real time test of the "loop" process. So, your test is not real time test. Sorry, but that is how my system runs, real time, not just DC loads.
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