On Jul 4, 8:32*pm, Eric Greenwell wrote:
jb92563 wrote:
I use one of these:
http://www.harborfreight.com/cpi/cta...emnumber=44768
View the product manual for details.
At 1.5 watt it keeps a small motorcycle battery charged indefinately
for powing a typical instrument panel with radio and audio varios etc.
a 5 watt panel might be too much and will need a good charge reulater
so as not to cook the battery.
You need to measure your current drain before getting too excited about
solar panels. A PDA can draw 300-400 ma; for a 5 hour flight, that's 1.5
to 2 amphours. A 5 watt panel can put out, at most, about 300 ma with
perfect alignment to the sun. On a glider in flight, it will likely
supply an average of maybe 100 ma. Do the math.
Sitting on the ground, it will still not be perfectly aligned with the
sun, so even when you count the amps over a full day, it might not keep
up with the PDA, and you still have a radio, vario, gps, maybe more.
Result: 1.5 watt is quite inadequate for the typical glider, and you
need solar panels that can put out at least twice the normal current
drain to just keep up. Of course, if you fly only 2 or 3 hours a day,
you can get by with smaller panels.
The reason pilots are willing to pay the big bucks for the Strobl solar
panels is they put out a lot of current for their size, so they can
actually keep up with the typical radio, vario, gps, PDA, and (with four
panels) a transponder.
An alternative is to charge your glider battery from another 12 volt
panel, using a Multiplex Ln-5014 DC-DC charger (or similar). Much
cheaper, and you don't need to install solar panels on the glider. The
DC charger battery can be charged by an AC charger or small solar panels
during the day.
--
Eric Greenwell - Washington State, USA
* Change "netto" to "net" to email me directly
* "Transponders in Sailplanes"http://tinyurl.com/y739x4
* * * Sections on Mode S, TPAS, ADS-B, Flarm, more
* "A Guide to Self-launching Sailplane Operation" atwww.motorglider.org
And even a 5W panels are very small and may be no use.
You've also got to think what problem you are trying to solve, and it
if is really a problem.
AGM/VRLA batteries (i.e. what almost ll glides use) have such a low
self-discharge rate (~1% or so per month) they don't need to be left
on a trickle charger. The claims about trickle chargers/battery
maintaniers are really for cars or motorbikes not used frequently
where there alarm system or other components keeps a constant small
load on the battery and/or the flooded lead acid battery discharges at
a higher rate (~ order of magnitude or higher) than our batteries do.
Further what people think some of these small panels or trickle
chargers can do and what they actually do is often different. One
apparently common point of confusion is for people to run down their
battery and then hook it up to a small panel and then go fly a few
days later and look at the voltage and think "wow this little thing
has really charged well". In reality what they are likely seeing is a
spurious effect called surface charge. Put a decent load on the
battery and the voltage will sag within tens of seconds. Then they
wonder why the battery is not lasting - it was just not fully charged.
I've seen this in club gliders where there is no possible way the
small solar panels can keep up with the load and people keep futzing
around with small panels to thinking they are helping by "topping off"
or "maintain" the battery or whatever. Those batteries should really
be put on a proper AC charger for an AGM battery, or hooked up to a
*large* solar panel and charge controller (60W, 100W, 200W, pick your
poison but it's not going to be 1 W or 10W) and maybe secondary
battery (like Eric suggests) and DC to DC charger to quickly charge
them back to full capacity. An AGM battery sitting around at low state
of charge will damage the battery eventually so you want to get it
back to near full charge quickly.
A charge controller is really not needed on a 5W or 10W or so panel.
And these really small panels may not be the right thing to use at
all.
Darryl