Battery A/B switches are very old old old school. If you have two or
more batteries for your avionics, eliminate the switches and use a low
voltage drop diode on each battery. This set up will always pull from
the best battery.

In the event you have a melt down in between the batteries and the
recorder then having an additional battery of some sort wired to the
recorder with another diode is a good option. The CAI 302 provides for
this feature as part of it's design.

ContestID67 wrote:
At a recent contest we got to talking about powering flight recorders
(and computers, etc) and how to survive a mid-flight power failure and
still get a log file. There are a couple of lines of thought.

1) Don't worry about it. The systems are pretty good these days and if
you wire things up right you won't have a failure.

2) Use two batteries with an A/B switch. This requires the recorder to
be able to survive the failure until you flip the switch. Some can
handle short power outages, others cannot. I have no test data to
suggest how long of an outage they can handle while a good battery is
switched in.

3) Place a separate backup battery on the recorder itself. Many
recorders have that feature. If this is a computer you may loose
functionality (vario, moving map) while retaining recording.

While my experience fall into #1, I am currently using #2 and thinking
about #3.

What are your thoughts?

Thanks, John