I have a 9000 mah battery in my Duo Discus. Would it be better to have two
2400 mah batteries in parallel (same weight) or just stick with the 9000? I
have an automatic redundancy switch in one of my other scale planes, but it
only switches if the primary pack goes bad. I have a 3000 mah primary and a
2400 mah secondary. Have flown 10+ hours and it never switched over.
Tested (static on the ground) the switch with a 150 mah pack and it switched
over in 66 min to the secondary.
Tom
----- Original Message -----
From: "Martin Usher" <[EMAIL PROTECTED]>
To: <soaring@airage.com>
Sent: Monday, March 06, 2006 12:23 PM
Subject: Re: [RCSE] Re: Redundancy for Scale ("Two or more batteries")
I suppose you could say that two batteries in parallel are as good as
whatever battery's the oldest / weakest. There's no point in doing this
unless the batteries are identical (age as well as characteristics) and
then all you're really doing is making one big battery -- that is, without
some kind of isolation circuit you're not getting redundancy. (You're
actually increasing the chances of failure because you're introducing extra
places where things can go wrong.)
So Bill Swingle's right.......don't waste your time, just use one
relatively new, good quality battery. The world won't end if you use two
smaller ones but you won't gain anything except a false sense of security.
I wouldn't obsess over everything being brand new, though. Electronics
failure rates are usually described as a 'bathtub' curve -- new stuff has
a higher probability of failing for a short time, then everything's stable
for quite a long time and finally things start to fail as they get to the
end of their life. This curve is messed up these days because modern
electronics is so well made that infant mortality is rare for consumer
products but the principle is still valid. So I'd take a battery that's
been used successfully over a couple of months over a new one any time.
(I'd be wary of switches, though -- the ones that you buy are pretty
reliable (they actually have two sets of contacts) but they're still quite
cheaply made. Its easy to buy good quality switches.)
Martin Usher
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