piclist 1999\03\09\122445a >
Thread: Solar Panel / Battery hybrid power for palmtop
picon face BY : Mike Keitz email (remove spam text)

On Tue, 9 Mar 1999 06:51:35 -0800 WIL REEDER <KILLspamteachtech.....spam.....BC.SYMPATICO.CA>

> a 12v panel may be the most cost effective,
>maybe you want to mount up cells to make your own custom panel. You
>probably end up with better than 1 square foot for your panel and more
>you go with amorphous.

Always use a larger panel and battery than you think you need.  Panels
with an open-circuit voltage of about 17V are common and a good match for
charging a 12V lead-acid battery without a regulator.  In a small system
like this one, you're better off to buy more / larger panels than to try
and get a few percent more power using a regulator.

For any sort of high-performance application (and wanting this much power
from a portable system is high-performance), don't use amorphous panels.
They only output their specified power in full sunlight, and fall off
very rapidly with less light.  Crystalline ones will continue to produce
useful power on cloudy days, which in most areas happen quite frequently.
I'd go farther and say don't use amorphous panels, period, but for those
few who happen to live in a desert and can get the panels for almost
free, they may be practical.

>The batteries, I'm assuming gel, love to be equalized fairly often and
>there is evidence that shows prolonged life with pulsed charging.

The most important thing for battery life is to not overdischarge.  The
load should turn itself off when the battery voltage drops to 10.5V (for
a 12V nominal battery).  Second most important is to keep the battery
temperature in the "room temperature" range, hard to do when it is set
out in the sun.  Probably overcharging won't be much of a problem, when
it does happen it will act as an equalize.  If you use a battery type
that is commonly found as inexpensive surplus, it won't be too bad to
replace it every couple of years.  Don't expect a sealed lead-acid to
work more than 5 years even if you treat it perfectly.

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See also: www.piclist.com/techref/power/batterys.htm?key=battery
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