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Old 12-19-2013, 11:31 PM   #5
Senior Member
City: Gig Harbor
Country: USA
Vessel Name: Selah
Vessel Model: Ocean Alexander 40
Join Date: Dec 2011
Posts: 219
You will lose efficiency at some undefined level when you take shore-power 120 VAC, turn it into 12VDC with a charger, then turn that back into 120 VAC with the inverter so it would be more efficient to power the refrig from shore power. That efficiency loss may or may not be a practical consideration depending on your total shore-power use and your rates.

Don't know if you want to get into it, but the transfer relay question brings up the issue of switching the grounded neutral between the inverter and shore-power. If you manually pull the refrig plug from the inverter and plug it into an outlet supplied by the generator or shorepower and don't mix the systems at all you avoid that concern. If you use a transfer switch you probably want to address that. Some inexpensive truck or auto inverters do not play well with marine distribution systems -- for example I have a Samlex that won't turn on if the neutral is grounded externally. "Marine" inverters may or may not switch the neutral and they may or may not have transfer relays that pick up generator or shore power, and that info may not be easy to find, so it can be a frustrating search. Magnum makes a line that does both, and I am fairly sure that Victron's inverters do also, but I can't confirm that.

We could also do the public math to figure out how the 30A charger will have to run each day to power the refrigerator, but you didn't ask that. I think you may want a higher-capacity charger like Dave says.
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