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Old 09-10-2016, 11:43 AM   #15
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Rossland's Avatar
City: Buffalo
Country: US
Vessel Name: Almost Perfect
Vessel Model: Kadey-Krogen 48
Join Date: Dec 2015
Posts: 200
Here is another way of calculating.

Assuming that you agree that there is no point in having generating capacity greater than your shore power hookup, so if you have one 30A cord:

30A X 120V =3600. You should never operate a generator continuously at greater than 70% load, so 3600 divide by .7 = 5kw (rounded off).

The same calculations for a 50A cord = 8.5kw.

Note that this number is nearly the same as a couple of other recommendations .

We have a 5kw Onan generator connected to a Victron Multiplus inverter/charger, and a single 30A shore power cord. There is a control panel which allows us to dial the max amps drawn from the generator or shore power. (usually set at 30, but sometimes less). If the electrical load exceeds this number, the inverter makes up the difference from the batteries, then recharges the batteries when the load drops.

A comparative test of small marine generators is here:
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