Hi Bruce,
Their are numerous methods used for sizing solar panel systems, and using
one of the common methods provides the following for your application as
follows :
Using a battery charging efficiency factor of 120%, and Portland Maine as
the location (winter average = 3.56 sun hours/day) . And designing for a
reserve capacity of 3 days (3 days of no sun), with a minimum battery
capacity of 50%.
If designing for continuous power applied to the preamp (24 hours per day)
: Required battery capacity = 18.7 Ah, Solar panel = 1.05 amps (almost a 20
watt panel).
If designing for 15 hours of continuous service (using a day/night
controller) : Required battery capacity = 11.7 Ah, Solar Panel = 0.66 amps
(approximately a 10 watt panel).
The above method is somewhat simplistic (does not take into account how
cold temperature impacts the capacity of the battery, etc.), nevertheless
it provides some reasonable numbers to put things into perspective.
I'm sure you will think the panel and battery are large, but that's what it
takes to handle continuous service during the winter when day light is
minimum.
Note : solar panels really operate like a constant current source versus a
constant voltage source, therefore a typical solar panel for 12 volt
battery charging will have an open circuit voltage of around 21 volts but
this is under a zero output current condition. The maximum output current
of a solar panel is when you have it's output short circuited but it's
current at max power is not much less than its short circuit current. An
easy way to characterize what kind of panel you have is to measure under
bright sunlight the short circuit current, and the open circuit voltage of
the panel.
Don (wd8dsb)
On Thu, Sep 25, 2014 at 2:55 PM, <k1fz@myfairpoint.net> wrote:
>
> Hi Don,
>
> Pre-amp requires 12-18 volts at 130ma. (low band DXing- nightime use)
>
> This solar charger puts out 20 volts that could be reduced to 15 volts
> with a three legged regulator. I was hoping to find a pre-assembled
> charger & battery, but may have to build one.
> http://www.harborfreight.com/15-watt-solar-battery-charger-68692.html
>
> 73
> Bruce-K1FZ
>
> What is the operating current and voltage of the preamp you plan to
> use? Since it sounds like the preamp will be powered on all the time this
> information will be key in the selection of the battery capacity and solar
> panel rating.
> Don (wd8dsb)
>
> On Thu, Sep 25, 2014 at 1:30 PM, wrote:
>
> Anyone using, or know of a source, for a compact battery with solar
> cell charger, to power a remote antenna pre-amp ?
> 73 Bruce-K1FZ
> www.qsl.net/k1fz/pennantnotes.html
>
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