JS wrote:
snip
If you're recharging the batteries on the ground pre/post flight, use
at least a 25W panel (the bigger the better), and a charge controller.

Bigger is better only if you need the current, otherwise, it's just
bigger and more expensive.

* If you run a radio and vario, and fly less than 5 hours a day and put
out the panel when you land, then reorient it in the evening for the
morning sun, a 5 watt panel will likely be adequate.

* If you run a radio, vario, GPS logger, Ipaq, transponder with encoder,
and fly 6 or 7 hours a day, you'll need that 25 watt panel to fully
charge every day.

5 watt panel ~$100; 25 watt panel ~ $300. I fit the second case, but
opted for a 15 watt panel because I have a large battery, so I don't
have to fully recharge in one day. If I fly 3 days out of 4, the battery
stays charged.

Another option is to have two battery packs, one of which charges while
the other is flying. That charges it during the peak of the day, and so
it doesn't need nearly as big a panel. If you can change packs easily,
it's worth considering, as it's cheaper and more flexible.


--
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Eric Greenwell - Washington State, USA

www.motorglider.org - Download "A Guide to Self-launching Sailplane
Operation"