On 12/1/2013 12:31 PM, Dr. William J. Schmidt, II wrote:
Which products do you use? I use their 60 watt panel.
What is needed to prevent overcharge. Nothing. I don't use a battery.
What does less than full sun do to the capacity. Full sun for full output
is a fallacy. Even 50% sun through overcast gives full output. Buy a
bigger panel, bigger than you need and it works almost until dusk.
Let's not oversimplify things. "Works almost until dusk" depends on far
too many variables, including the load current.
I disagree with virtually all of this, and so does all of the
scientifically-based work I've seen on the subject. Full sun on a bare
solar panel produces fairly high output voltage, but voltage falls as
the load draws current from the cell. The output of a pair of my 55W
industrial-grade solar panels varies from about 100 mA near dusk, to 300
mA in the shade, to 2A in partial sun, to 7A or more in full sun. Output
current also varies with the angle of incidence (greatest when
perpendicular) and temperature (greater at lower temperature). These
charging currents can be increased 20-40% by the use of a good MPPT
charge controller. I'm using a Genasun. GV1012, which can be bought
here http://kansaswindpower.net/charge_controls.htm for $125, in a
system with four 55W panels and two 210Ah 6V batteries. It is RF-quiet.
Most charge controllers make noise, including a Blue Skies MPPT unit I
recently encountered.
A battery IS needed to protect electronics (like a KX3) from
over-voltage, as might exist in bright sun on a big panel and a load of
only a few hundred mA (KX3 in RX only), and if you want to operate after
the sun has gone down. You don't need a BIG battery to do this -- a 7Ah
12V battery is small enough to drag up a long trail, and it will let you
stay on the air much of the night QRP.
I do agree that we can use only our brain as a charge controller if
we're careful to monitor battery voltage and not overcharge it. All the
Elecraft rigs I know of include a voltmeter, so that's easy to do, and a
careful study of the battery manufacturer's data sheet will tell you
when to stop.
73, Jim K9YC
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