On Sun, 23 Nov 2003 16:06:53 +0000, Hmseconomy wrote:

What's the minimum amps/volts output needed to trickle charge two marine
batteries to keep them up? Can a single small trickle charge panel charge two
batteries at the same time? What's the recommended connection method? Need a
diode to protect against overcharging (even with a minimum output panel?). Any
advice would be appreciated.

I'll start with an assumption that may be wrong, but...Assume a battery loses
50% of its charge in 3 months, and it's about 80AH. That means it loses about .4
AH per day. So it needs about .4 amps CONTINUOUSLY to keep it charged.

Now, since a solar panel only puts out anything about 50% of the time (assume
full sun all day) you would need an 800mA panel. But a "1 Amp" panel only puts
out close to 1 amp in full sun when the sun's directly perpendicular to the
cell, I'd put it a 60-70% "fudge factor" (more if you live in a cloudy area).
This means you need about a 1.3A panel per battery.

Note that most of these "trickle charge" solar panels only put out 200mA or so.

Also, a diode is so that the battery doesn't "backfeed" the panel, not to
prevent overcharging.

Based on this, I'd say you'd be safe with a 2A panel, paralleled to both
batteries (assuming there's no load on the batteries). I've used a 2A panel on
one 4D battery over the summer, and it seemed to work well. I doubt one of these
"trickle charge" panels would be useful for the long term.

Lloyd Sumpter
"Far Cove" Catalina 36