In *theory* the "standard" 7.5 AH battery will power your transponder for 8+
hours. Sealed Lead Acid batteries rarely achieve their advertised capacity in
ideal conditions even when new. Now age that battery for a year or two. Throw in
some repeated deep discharges. Now cold soak the battery for a few hours at
altitude. I think you'll find that your 7.5 AH battery has something more like 4
AH (or less) useable capacity. So you up the size of the battery to 12 AH. Yes
you can always find somewhere to put the additional equipment. However a real
problem is that there are a significant number of ships out there that are at
(or over) their max. allowable weight for non-lifting parts, and the 10+ lbs of
the additional battery and associated wiring is simply too much.
I think that ATC would much rather see you suddenly pop up on their radar when
approaching airspace than suddenly dissappear (from a dead battery) while in or
overflying their airspace.

RF

Bob Greenblatt wrote:

OK, I can't keep quiet on this any longer. I agree completely that adding a
transponder is likely to increase safety, that's why I did it. I think the
exemption is meaningless - we don't need one! If you are going to add a
transponder to your aircraft (and I urge you to do so) you ought to insure
that you have enough power to drive it and the rest of your electronics for
the duration of your expected flights. To do otherwise is simply
irresponsible.

A fully charged "standard" 7.5 AH battery will power one of the newer
transponders and encoders for more than 8 hours. And, that's here on the
east cost where the interrogations are almost constant. Why would anyone go
to the trouble of installing a transponder and encoder and not insure that
there is enough power to take advantage of it?

It's so simple to conform to the FARs (or CFRs or whatever they are) as they
presently exist. Attempting to achieve an exemption is misdirection of a lot
of energy better spent elsewhere.

So, put in a transponder and some extra batteries. There's always room. If
you can't find any think harder.

--
bobgreenblattATmsnDOTcom --fix this before responding