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, <k...@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 > > _________________ > Topband Reflector Archives - http://www.contesting.com/_topband > > > _________________ > Topband Reflector Archives - http://www.contesting.com/_topband > _________________ Topband Reflector Archives - http://www.contesting.com/_topband