[Public-list] Solar Panel

[George Dinwiddie]

Peter Staehling wrote:
> George's comment about "equalizing charge" has me
> wondering about whether I can charge both batteries
> with one panel.  I assume "equalizing charge" means
> that it independently charges both batteries at the
> same time.  Is that right?

No, an equalizing charge is a charge phase of higher voltage (after the 
battery has basically been recharged to capacity).  This is to equalize 
the voltages in the cells (which inside the battery are connected in 
series) in spite of their differing impedances.  The chemistry of 
lead-acid batteries is quite complicated in real life.  And 
manufacturing differences can have an effect.  The various flavors of 
lead-acid batteries: wet cell, gel cell, absorbed electrolyte (aka AGM 
or absorbed glass mat) have slightly differenet characteristics and 
charging regimens.  I've even found a considerable difference, in 
practice, between the gel-cells manufactured by Sonnenschein in Germany 
and those made under license, but purportedly by the same process, in 
the US.

There's lots of information available on the web, but you have to keep 
in mind that much of it is only partial truth, not telling all the 
variances, and some of it is very misleading.  It's worth reading a 
number of sources so you can factor out some of the real trash, but 
you'll still be stuck with some myths and obsolete information.

For example, Mike earlier recommended placing the batteries on wood to 
insulate them from a concrete floor during the winter.  Once upon a 
time, this was important, as the damp floor would provide significant 
leakage with the old batteries, draining them more quickly.  Today's 
plastics provide much better insulation, and while that advice won't 
hurt anything, I doubt it will buy you much, either.

Some basic truths:

  A battery that's kept charged will last longer than one that isn't. 
It's also freeze-protected to a lower temperature.

  Wet cells do best with a relatively sophisticated charging regimen. 
This used to be a real chore, but with todays multi-stage microprocessor 
controlled chargers, it's much less so.

  Gel cells do best with a simpler charging regimen, and are designed 
for a basic constant-voltage charge.  This is a good think if you're 
charging with a stock alternator.

  Gel cells are considerably more expensive than wet cells (though you 
can find some fairly expensive wet cells).  The good ones make up for 
this with longevity, simplicity, and resistance to abuse.  (I had a pair 
of Sonnenscheins for 10 years.  One of them was discharged to 8 volts 
one winter, and left that way for a month of freezing weather, and 
continued to be useful for house lights for another 5 years, though it 
wasn't a very good starting battery anymore.)  The ones that are easily 
available in the US, today, do not IMO fall into the category of "good 
ones."

  - George

-- 
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   When I remember bygone days                         George Dinwiddie
   I think how evening follows morn;            gdinwiddie at alberg30.org
   So many I loved were not yet dead,           http://www.Alberg30.org
   So many I love were not yet born.
                                             'The Middle' by Ogden Nash
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