just rechecked the powersonic manual....

at .1c a 12 volt battery will drop below 12 volts in about 5 hours...below
11.5 in about 6.........10.5 almost 10 hours

Cookie




At 17:41 24 September 2012, Eric Greenwell wrote:
On 9/24/2012 8:39 AM, Bob Cook wrote:
Actually it is not 10 hours worth....its about 4 hours worth.

The "rated" 9 AH is rated at .05C or 450 ma.

If you run at 800 ma, that's about .1C.....so you don't get half the
time,
you get way less than half...........

Also they rate the batteries as "dead" at 10.5 volts, but for glider
equipment, once you get down to 11.5 or so, stuff doesn't work well.

Actually anything under 12 volts means time to recharge.....below 10.5
volts and battery damage can occur.

For an 800 ma draw, the proper battery would be 16 AH.....this in
theory
would last 20 hours, and leave you at 10.5 volts.....probably 10 hours
to
stay above 11.5...

Hi Cookie - I agree it's a good rule of thumb to use batteries at the 20
hour rate, and I encourage pilots use it; however, it doesn't seem to be
the problem. Using a bigger battery is desirable in general, but may be
awkward to do in practice.

SLA data sheets show a 10% reduction in AH capacity at the 0.1C rate,
and if you restrict the voltage drop to 11.5 volts, you lose another
10%. That lowers his 9 AH to 7.2 AH, allowing a nominal 9 hour run time
at 800 ma. Since he is getting only 4 hours, something is dramatically
wrong. A full charge, then a discharge test at 800 ma can rule out
charger/battery problems, and it's easy, so that is where I would start.

Also, unless you have old "stuff", 11.5 volts is plenty of voltage to
run things, and he didn't mention any problems.

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