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From: amirza@silver.ucs.indiana.edu (anmar mirza)
Newsgroups: sci.energy,sci.electronics,sci.physics
Subject: Re: solar cells
Message-ID: <1990Dec31.174455.25630@bronze.ucs.indiana.edu>
Date: 31 Dec 90 17:44:55 GMT
References: <1990Dec28.210436.10601@zoo.toronto.edu> <939@venice.SEDD.TRW.COM> <1146@blenny.UUCP>
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Organization: Indiana University, Bloomington
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In article <1146@blenny.UUCP> stevek@blenny.UUCP (Stephen Kogge) writes:
>
>	One point on the curve. I have a 30W (18" X 30") array. It charges
>a car battery that I keep outside. Here in Maryland it cannot produce enough
>total charge to keep 1 2.4W 12 volt fan running all the time.
>	My meters show ~2 Amps (24W) in full sunlight. The array does
>not track the sun and from about 3pm on the charge drops off to a few
>milliamps. During the winter I have to watch the voltage on the battery and
>let it charge with no load for a few days. In the summer I end up putting
>a car battery charger on the battery a couple of times.
>
That sounds strange, each day your fan will only draw 4.8 Ah, and
since even in Maryland you get around 3 hours peak sunlight average,
that would give you around 6 Ah average daily (more in summer, less
in winter).  Sounds like even a worst case summer scenario (cloudy for
a week) shouldn't deplete your battery from full charge. Maybe the
battery is old? Car batteries really aren't good for that application,
they don't like the cycle rate. Try a marine style deep cycle battery,
that should give better performance. If you don't want to run right
out and buy a new battery, test your battery by seeing how long it'll
run your fan from a full charge, till the voltage drops to around 11
volts, then calculate how much capacity your battery has. If it has
less than 20-30 Ah, then that may be your problem.




--
Anmar Mirza   # If a product is good, # I speak only my   # Space, humans next
EMT-A         # they will stop making # opinions on these # goal in the race 
N9ISY (tech)  # it. Unless it is      # subjects, IU has  # for immortality.
Networks Tech.# designed to kill.     # it's own.         # --- me