On 1/16/2011 5:00 PM, Ed wrote:
and I'm
beginning to suspect that the battery is not being fully topped off.

I've had a solar trickle charger set up that thought would work, but
now I'm not so sure. I use a Powerfilm rollable R15-300 ( 0.3 A, 15.4
V ) with a Morningstar Sunguard controller. The reason I use the
rollable is that I can bungee it onto the top/side of the glider so
wind doesn't become too much of a problem since it shapes itself to
the fuselage and has a fair approximation to the angle needed for
direct sun exposure.

I bought a new battery last year, but this doesn't seem to keep it
topped off enough to get the full cranking RPM I need. Before I start
blaming losses in the charging system, I was wondering if any of the
electrical engineering types might have some words of wisdom about the
adequacy of my setup. The 0.3 A is only achieved in full sun with
direct alignment, and given the curve of the Powerfilm on the fuselage
and the periodic cloudiness of the Pac NW I'm wondering if this setup
is just underpowered. Even after several weeks of summer sun I usually
find that the battery is only about 12.4 volts or so, and not at the
12.7 volts I need. I haven't found much on the web about solar
charging batteries of this size.

Alternatively, are there other strategies for tie down charging such
as DC to DC or inverters to enable the AC charger? The battery is not
easy to replace, so swapping it out is a bit of a hassle, but
possible. If nothing else, I thought this might encourage a thoughtful
discussion on battery care and maintenance in the field. Any words of
wisdom?

Your current (a little battery pun, hehe) solution is totally
inadequate. You should have about 13.2 volts on the battery, measured
soon after you remove the charger.

You don't say how many amphours you use in a flight, and if you want to
fly several days in a row. Amusing you fly several days in a row, and
the drain is 5 amphours or less, a 20 watt panel (aligned with the
morning sun) with a good regulator would be enough. Using more amphours
- use a bigger panel.

A DC/DC converter can work well, also. I use a Multiplex LN5014 hobby
charger, run by a 12 amphour SLA battery to replace the 6 or so amphours
I use in flight. My solar panel can be plugged into the glider at the
same time, in parallel. The LN5014 plus battery charges the glider
overnight; the solar panel takes over in the morning. The LN5014 should
be disconnected in the morning and it's battery put on charge, so it's
ready to charge again that evening.

You can also use a 12 volt battery to run an inverter, then plug your AC
charger into the inverter. The inefficiencies in the setup mean you
probably need a battery twice the size you did for the LN5014 DC/DC
charger. You still need to show up at the airport to put the inverter
battery on charge.

Some people use a "hybrid" system. One example: a solar panel on the
trailer charges a deep cycle 12 volt RV battery (typically around 120
amphours); the RV battery runs an inverter; the inverter runs your usual
AC charger. This system is elegant, but it's inexpensive, it's big
battery lets it coast through cloudy spells, and since the solar panel
is charging it, you don't have to tend to it. Because the panel charges
it all day long, the panel can be horizontal and not aimed in a
particular direction. Plug the charger output into the glider whether
it's in the trailer or tied down (yes, long extension cord!) and forget it.

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