On Wed, 17 Mar 2004 18:52:35 GMT, Ronny wrote:

Is there anyone here doing this? I have a 26' cruiser with a Mermaid
Marine A/C unit (6500) btu. I only want to use the air on the water for
about 4 to 6 hours a day and maybe an occasional over night stay. I am
looking at a Prosine 2.5 and will probably use 2 or 4 optima batteries.
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The Prosine 2.5 is a good unit and it will definitely supply enough
starting current *IF* you have a big enough battery bank, and *IF*
your battery cables are properly sized.

There are two big IFs there.

First the battery bank: Your A/C draws about 7 amps at 120 volts.
That will translate to 70 amps at 12 volts. 70 amps for 6 hours is
420 amp-hours, which will require a deep cycle capacity of 840 hours
in order to follow the 50% maximum discharge rule. You will need 8
golf cart batteries in series-parallel, weighing about 500 pounds,
and costing about $500 USD. That is the cheapest way to get the kind
of capacity you need, but not necessarily the best way because of
technical issues with 8 batts in series-parallel. You are also going
to have issues finding that kind of space on a 26 foot boat, not to
mention the weight implications. Anything less than 500 pounds of
lead acid batteries will be inadequate regardless of type or
configuration.

The second IF is easier to resolve but frequently overlooked. You
will need BIG cables between the inverter and battery, or voltage drop
will be excessive during the high current compressor start. I'd
recommend something like 2/0 cable with professionaly crimped and
sealed end connectors. West Marine has the cable at about $6 per foot
but it's a bear to work with.