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Fully charging 2 AA batteries using solar panels that are in a 5" by 3.25" configuration... - Page 2

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Posted by H. Dziardziel on August 23, 2005, 2:10 am
On Sun, 21 Aug 2005 23:25:55 -0400, they call me frenchy

For a reference and initial engineering estimate those are fine
with the understanding one should use actual specs from the solar
cell manufacturer.and note that such specs are optimal  maximum
output in full direct sun.  Actual cell output is always much less
and the voltage-current ouput curve will usually not be a good
match for the application for the simplest cell configuration
based on their maximum.outputs.

Not quite, the panel needs to supply a certain voltage and current
for the application.  So, _if_ the panel can output 3V, a 465mW
the panel _might_ do so at 155mA.  Check the specs and again keep
in mind specs are for rarely acheived ideal sun and load

NiCad and NiMh cells, when charged at the standard C/10 rate,
require about 40% to 60% overcharge due to electrochemical
charging inefficiency,   The higher the charge rate the lower this
ineffciency.  50% for these small capacity cells (1000mAh or
2500mAh)  at C/10, is 100mA or 250mA is ckose enough.

So, the 1000mAh cells need 1500mA for a full charge.  Take a look
at any AA or AAA cell, this standard rate is usually printed on
consumer packaged cells.

Solar cell output fall drastically under such conditions so that
will need some spec and area sun research.  Just reducing cell mAh
may not be enough since the solar panel voltage may be too low
under those conditions to charge any capacity NiCd NiMh unless the
panel has reserve capacity.  Eg, a maximum 6V output through a
regulator-charger circuit to match the nominal two series cell 3V
charging voltage..  This would allow for low sun conditions.

Good luck

Posted by they call me frenchy on August 23, 2005, 10:18 pm
On Tue, 23 Aug 2005 11:10:12 +0900, H. Dziardziel

I did not know this.  Obvously I need to put myself through a crash
course in battery chemistry and charge/discharge ethics.  Can you
recommend a resource that you particularly like?  Like an application
PDF from Sanyo or Panasonic or similar?

Excellent point about the solar panel voltage falling too low to
charge under non-sunny conditions.  Likewise, I need to read
application notes/manuals on solar battery charging circuits.  The
more regulation I include, the higher the hi-volume cost.  As usual,
this will be an engineering balancing act.

Thanks again for your input and it would be great to get a few
recommendations for reference texts from you, because you obviously
know what you are talking about!

Steve French aka frenchy

Posted by Paul on August 24, 2005, 12:19 am
 A google search of "NiMH charging" brought me:
among other hits. Amazing what you can find when you look.

Posted by H. Dziardziel on August 24, 2005, 9:49 am
 On Tue, 23 Aug 2005 18:18:35 -0400, they call me frenchy

Look for the various application and charging manuals:

Excellent overall sources:

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