Join Date: Mar 2003
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Power management is key
The bottom line to all the charging discussion is that you MUST know 1) your daily usage in amp/hours, 2) your usable battery capacity in amp/hour--most people use 50% of rated capacity, and 3) your charging capacity in amps per hour. So, you must figure out your usage first, and only then can you decide if you have enough battery capacity to live that way. If so, then you need to match your charging ability to that battery bank, i.e. you want to be able to replace used amp/hrs regularly without straining your charging setup. If you're talking about a boat at a mooring with a small bank that has nothing normally on, then a small solar panel will probably do to keep the battery charged. However, if you have a 1000ah battery bank and use 400ah a day, obviously even a wind generator won't get the job done and an auxilary generator (diesel) would be necessary or a high output alternator that you would run once a day. It's really hard to speak to your situation without having specifics.
One thing you might consider is a low-voltage cutoff switch for a high use device like a 12v fridge. It's basically a relay switch that keeps the power on as long as your battery voltage is above a certain level, then cuts off when it drops below that (only uses about 10 mA when in use). I have one on my boat wired only for the 12v fridge so that if I go away from the boat for longer than expected I won't come back to a dead battery bank. I even use this at the marina because sometimes even shorepower fails for a while.