sizing solar panel

Udo Rumpf wrote:


Udo Rumpf wrote:

If I want to maintain a 12 volt 7amp/h Battery with a solar cell panel
what rating would I need during flight, if after 4 hrs I wanted to
have a usable, not full, charge in my 12 Volt battery.
Right now, my as good as new battery is useless after 4 hours.



This suggests you are drawing about 1.5 amps from your battery, which
is very high, even for a glider with a transponder. Is that right? Can
you reduce the drain safely by turning something off?

and what size would the panel be?


It would have be about a 1 amp maximum output panel just to be sure of
getting 0.5 amps on average, which would leave ~2 amphours to the
battery after a 4 hour flight. About 1+ hours of use would remain at
your 1.5 amp drain. That's a rather large solar panel to mount on
glider, or a rather expensive one.

If you are really drawing 1.5 amps and can't reduce it, I'd suggest
first putting in another (or bigger) battery. Cheaper and easier, I
think.


Eric,
As per manuals I draw about 1.1 amps without talking on the radio
I can fly for about 4 hours and I drop to 12 volts from fully charged
7 amp/h battery. Add an other 1.4 amps for transmit.

I seem to recall your radio stopped working properly at 12 volts, even
though the battery still has half it's capacity left at that point. The
easiest thing might be to go to a 14 volt system by adding a 2 volt
battery instead of a solar panel. That assumes the radio is working
correctly and it is incapable of working below 12 volts.

Before putting a lot of money into a 1 amp or so solar panel, I'd
consider getting a new radio, which will draw less current, and work
until the battery is exhausted (not to mention the other advantages).

--
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Eric Greenwell - Washington State, USA

www.motorglider.org - Download "A Guide to Self-launching Sailplane
Operation"