Hi Jim!

Agreed.. On cruising boats, these are much used, called "battery
isolaters" ..

My boat has 3 banks of batteries, and these isolators keep the
"storage (s)" separate, but allow all 3 banks to be charged from any
or multiple sources...

Dave


On Thu, 15 Jun 2006 23:38:05 -0500, "Jim Macklin"
wrote:

A set of relays and diodes would allow the installation of a
second battery and a great deal of redundancy at fairly low
cost and weight. The standard alternator would charge both
batteries, only the second battery would be connected to the
essential bus of lights and avionics. A battery failure
kills the alternator on most aircraft and thus kills the
entire system. Having two isolated batteries give
redundancy as long as the bus is able to shed load.

Beech uses self-exciting alternators [and a generator will
produce power w/o a battery (but it isn't well filtered)].
On a Beech you can turn the battery OFF and still operate.
But in most Cessna and Piper aircraft the battery must be ON
for the alternator to function. A second battery and
modified bus can give redundancy. Load shedding can be
automatic or manual. You need to have diodes to control
current flow.