On Fri, 20 Aug 2010 12:11:21 -0700, Darryl Ramm wrote:

Although it obviously varies widely a typical power consumption number
for a glider avionics is roughly around 0.8 amp (as Evan noted his is)
for what I am guessing is a typical setup of C302 style computer, a PDA,
and VHF radio. Owners should measure and calculate the loads in the
glider and estimate the battery capacity needed or run time available
from the batteries they have. Do not just divide the nominal "Ah
capacity" by amp load, especially at higher loads, you need to use the
discharge curves data from a manufacturer to estimate the available run
time of a battery at a particular load (most good VRLA batteries are
close enough to use another manufacturers spec sheet for a similar sized
battery).

I'd seriously suggest a visit to your local RC model shop to look at
battery chargers. $60 - $100 gets you a cycling charger that can not only
peak charge a partially discharged SLA battery without harming it, but
can measure its capacity. Record the measured capacity every year and bin
the battery when it shows a 30% drop and you may even save money.

Slinging an SLA battery every three years is common wisdom here, yet last
winter my three year old batteries still had 90% of their nominal
capacity. Bin them? I think not!

FWIW these batteries have always been charged with a peak charger.

PS; sorry for hi-jacking the thread, but it seemed appropriate.

--
martin@ | Martin Gregorie
gregorie. | Essex, UK
org |