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Old 20-07-2016, 15:45   #1
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Join Date: Oct 2010
Boat: Morris Justine 36'
Posts: 134
planning energy requirements

Can people please help me anticipate energy requirements for my Moris Justine 36?

I am considering switching from engine driven refrigeration to 12V with solar. I have two Group 31 batteries which were new in 2007 and still charge to 14.1 V and do not drop below 12.5 in a day's usage. I have a 90 Amp alternator and a Balmar regulator. I have never seen my energy use exceed 5A at any given moment. During the day I currently run an autopilot, chartplotter, AIS and rarely might use radar. At night energy usage seems to be mostly lights as we have foot pumpsfor water, iPod for entertainment, a portable inverter that charges phones--all with low energy requirements. We have a manual windlass and no electric winches. We currently run the engine one hour per day in Maine. We are considering the switch because the current engine-driven fridge needs a new condenser and because running the engine for an hour per day is onerous for us. We prefer to just sail and anchor. We plan to go to the tropics. The insulation is 4". A five pound block of ice is gone in 4 days.

I am considering the Sea Frost air and water cooled with 2 plates. I would want to add enough solar so that on at least 75% of the days I would not need to use the engine to charge my batteries. I do not cover enough ground to have a hydro generator and do not particularly want wind. How much solar will I need, do I need a bigger battery bank or alternator, other things I am not thinking about? Thanks.
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Old 20-07-2016, 20:14   #2
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Join Date: Jun 2013
Location: canada
Posts: 1,274
Re: planning energy requirements

if you have batteries from 2007 they are defiantly due to be changed and amazing they still work. especially car sized batteries. are they gel?

adding more batteries by itself will not help you.
a large battery bank helps if you charge at dock, leave dock for a few days - week. come back to dock. fully recharge. go again for another week.
or if you have very large charge capabilitys on board.

90a external reg alt for a 35' boat with minimal loads sounds ok. you'd have a tough time getting 90a into a pair of batteries anyways. what do you normally get from your alt while running? I doubt you are even maxing it out. you'd need a bigger bank to use a bigger alt.

fridges probably draw ~60ah a day. depending on size and outside temp. 200w of solar would make this up. 300-400w of solar and you'd probably never run the engine.
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