MC, Might it not be easier to just buy a flexible solar panel with a charge controller built in? This is what I got and it has worked very well for me. http://www.e-marine-inc.com/products/solar_panels/batcharge11.html I use an electric trolling motor on my M-15, though admitidly not a lot and and this panel and controller seem to be working very well. I have yet to use a plug in battery charger since I hooked this panel up. Rik Brian Gilbert wrote:
Hi MC:
I'm certainly no wizard, but I know what the zenier diode is for. It's like a one-way valve for electricity. Without it, reverse current will flow back into the panel at night, heating the cells and draining the battery.
It doesn't protect from overcharging, but it does drop the useable voltage a bit.
To keep from cooking your battery, you need to size the panel to your battery bank. Unfortunately, I can't remember off the top of my head how to size the panel, but Spurr's Boatbook devotes an entire chapter on the subject. I think that the basic jist of things is that small panels are really only good for keeping up with the self-discharge of the battery. Bigger panels are needed to replace current... sometimes you need a lot of panel to refill the battery if your electrical demands are high.
Hope this helps BG