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post #21 of Old 03-14-2011
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Cranking amps are for starting batteries. What you need to know is the "Group Size" of the batteries, or the Amp Hour capacity of them, nominally at the 20-hour discharge rate.

I'm guessing they are group 24 or group 27 with a nominal capcaity around 75AH each when new. If you only cycle them 50%, that means you are working around a 75AH useable capacity for the "bank".

How often you will draw them down, how fast you want to charge have to run the numbers for an energy budget. Odds are that one 50A or 55A solar panel with a simple charge controller would work out pretty well for the minimal power needs you have. FWIW, if you invest in an MPPT controller, which may be overkill for you, they actually squeeze about 10-15% more effective power out of a solar panel, so they're actually useful.

Anything smaller, and a couple of gray days after a deeper than usual discharge is going to leave you looking for extension cords. Typically, in a full 12-hour day of bright sun, you'll get about four hours worth of "rated" full output fro a solar panel. (i.e. pretend the day is only 4 hours long but the panel is working at full output for those four hours.)
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