Well, here's the rest of the story.
The 1500w inverter beeped every time the fridge started and sometimes wouldn't start it at all. I noticed the overload light
was not coming on, just the alarm tone noise. Finally read the manual very carefully and realized a beep without the overload light
meant low voltage on the 12v side, not overload as I had incorrectly assumed. My battery meter showed 12.8v with no load but less than 11v when the inverter was drawing 85 amps. The 12v cables are 4 gage and the manual calls for 1/0 for runs of 4' or less so I first thought the wire was undersized causing the voltage drop. I checked a wire size calculator though and it showed I should should only see a 2% drop at that amperage with my 4 gage wire.
I then thought I might have a bad connection and removed, sanded and retightened the connectors one at a time. Son of a b..., I had a loose battery connection. Tightened it up and the inverter works like a charm. I put the old 600w unit back in and it starts the fridge perfectly. Don't I feel stupid for overlooking such a basic fault! Since the 12v system worked fine with low loads like lights
and the inverter powering phone and computer chargers I figured it must be good. Wrongo!
I've run the fridge now for 24 hrs starting with a fully charged 220 ah bank. Started the test in the afternoon with a warm empty fridge (at least 90 degrees in the trailer), low was around 65 at night and a high of 80 today. The fridge plus inverter overhead drew 69 ah, meter indicated 71% of battery capacity was left. This gives me a conservative two day run time on battery alone. If I dry camp with my Honda generator
, two hours a day charging will take care of 24 hours of refrigeration.
Over the course of the winter we have had several 4 to 8 hour drives and now that the inverter works, we can keep the fridge cold while on the road. Even 4 hours without power will cause the frost on the freezer compartment to melt.