Solar charging question

On Jan 17, 10:35*am, Eric Greenwell wrote:
On 1/16/2011 8:55 PM, Ed wrote:

Thank you, Eric, this is a good start knowing that I have to upgrade a
bit.

The complicating factor is that the glider is tied down on the flight
line in the summer, far from the trailer. Whatever I come up with has
to be a self-contained, compact and secure solution which will either
fit in the glider or is weatherproof and resistant to wind. Most 20 W
panels make excellent weathervanes, and the only securing mechanism I
have is the tie down cable and eyes. Since I live an hour from the
airport I need a "set it and forget it" solution that charges while
I'm away. I don't often fly on back to back days, and I do get some
recharge from the alternator on launch as well, so I probably need to
make up only about 6-8 Ah.

For the typical soaring season, laying the panel flat on the ground
works well. It does require a bigger panel, compared to one that's
optimally aimed at the sun, but it's easier to secure. If you aren't
flying consecutive days, a 20 watt panel would probably suffice, but a
30 watt is much more expensive.



You've given me an interesting idea. I wonder if I could construct a
small aux battery box with a LN5014 DC/DC converter which I leave in
the glider to top off the battery after I leave. On return to the
airport I could remove the unit and charge it on the AC charger in the
hangar while I'm flying. If that few hours of recharge cycle time were
not enough it would be easy just to buy a second battery and swap them
out so that a fully charged one is always ready when I leave the
airport.

That plan would work fine. You do need a way to automatically disconnect
the LN5014 from the battery after 10-12 hours: while it will
automatically stop charging the glider battery when it's full, the
LN5014 continues to draw about 50 ma from the battery that powers it. A
12 hour mechanical timer (like you see on bathroom fans or heating
lamps, for example) between the LN5014 and the battery powering it would
do the trick.

So this leads to two more questions....

Is the LN5014 ok to leave attached for that long (ie., is it like a
charge controller which will shut the current off when the main
battery is recharged)? *If so, is it possible to do what you do with
respect to connecting my existing 300 mA solar panel and Morningstar
controller in parallel?

Yes, you could use them in parallel. You still need the timer switch to
disconnect the LN5014 from it's battery, or the battery will discharge
too far.

--
Eric Greenwell - Washington State, USA (change ".netto" to ".us" to
email me)

Again, thank you Eric for your thoughtful replies. I think I may have
found just what I need. I'll post the details in case someone else
might benefit.

If you go to http://www.powerstream.com/DC-input-chargers.htm and
click on the PST-BC1212-15DCDC Charger you can see this option. It
costs about twice as much as the LN5014, but I spoke with the engineer
who built it and he seems to think it will work well. We devised a
system where I can keep a source battery on the floor of the aircraft
which becomes the input of this converter. It needs to be about 1.5
times the Ah deficit that needs to be replaced (so for a 10 Ah boost
it needs to be at least 15 Ah). It doesn't run hot, so I can keep it
in the aircraft and not worry about weatherproofing. Interestingly,
this setup, run in reverse, allows me to take the source battery and
leave it in my car while I am flying, charging the source battery from
my car battery. The advantage I see to this product is that is it a
smart controller which will keep topping off the main aircraft battery
as needed and then stay in the background until the main battery needs
topping off again. If the source battery is large enough, even if I
don't get a complete recharge from my car I can always take it back to
the the hangar and bring it all the way back up with an AC charger. I
think I'm going to go in this direction since it was specifically
designed to do the very thing I am trying to accomplish. It does not
need to be attended while charging, so it looks as though it is the
'set it and forget it' solution I was looking for.

Andy, thanks for your post as well. Yes, the ultimate solution is
battery removal if all else fails, but the designer of this aircraft
made that difficult to do. It isn't just popping open a small battery
box -- it requires some disassembly of the front instrument panel and
the removeal of some tight clearance attachment hardware for the
terminals. I've done it enough times to know that it will be my
desperation solution if all else fails.