its simple if just keeping charged you need about 10 watts per 100 amps of battery. if you need to charge the battery after use you need about 25 to 25 watts per 100 amps, which will charge the battery over a week.
if you go over the 10 watts per 100 amps you need a charge controller.
03-17-2011 10:47 PM
Those small units don't do much, usually 1/4-1/2 amp at best.
You need at least a 15-20 watt panel (1.1-1.5 amps) per avg. size (Group 27/31) battery for it to be somewhat effective.
You also need a Blocking Diode (some panels come with that) so it doesn't discharge at night.
I have the Harbor Freight 45 watt kit and it's marginal w/ a 4D battery. I really need another kit to be very effective along w/ my 125 watt Wind Turbine.
03-17-2011 09:20 PM
solar trickle chargers
Any suggestions from anyone? I saw one at west marine the other day that was about $25 and had alligator clips to attach to the battery terminals. We have a boat that is largely for weekend day trips and gets left on the mooring on weekends, so we just need a top-off during the week.