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 -- Brian Gilbert Marine Media M17 "Tiny Dancer" (ex "Stargazer") (423)876-9990 3404 Hartford Drive Chattanooga, TN 37415 www.sailingsmall.com on 7/18/05 7:49 PM, montgomery_boats-request@mailman.xmission.com at montgomery_boats-request@mailman.xmission.com wrote:

I am going to add a small solar panel on top of the hatch cover - is there an electric wizard in the group, I was told today that to protect the battery from boiling dry, I should solder in place a 14.4 volt zenner diode between the solar panel and the battery to prevent overcharging when at the dock or on trailer for a few weeks. Apart from the back-feed diode which is also needed when no charge controller is used.

Thanks, MC