Surviving Flight Recorder Power Failures

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

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

If you are using a volkslogger you must ensure you can power down the
VL so at power up it will go into PC mode for a few seconds. This
allows you to load a declaration or task from a program such as
Winpilot into the VL.

I agree that a couple of diodes are the way to go to place the
batteries in parallel without allowing one battery to cause problems
with the other. However the key is the voltage drop which is typically
0.6vdc for a power diode. Do you have a specific diode number that you
have been using?

I am using a 302. I could have a separate battery for recorder backup
but I would rather come up with a more generic solution for everyone
that powers everything.

I think the diode idea is a poor way to go unless there is full time
monitoring of both of both/all batteries. If one battery goes bad the
other will be discharged before you know you have a problem. This
solution offers no more redundancy than a single battery with twice the
capacity. With switched batteries the pilot has the option to minimize
current draw to conserve the second battery for essential equipment.
Short term power loss does not invalidate the flight log.

With a 302 the ideal solution is probably 2 switched main batteries and
a backup battery (factory option) for the 302 only.

I'm wired for 3 switched batteries but am only using 2.


Andy

On Thu, 16 Jun 2005 09:37:07 -0700, ContestID67 wrote:

I agree that a couple of diodes are the way to go to place the
batteries in parallel without allowing one battery to cause problems
with the other. However the key is the voltage drop which is typically
0.6vdc for a power diode. Do you have a specific diode number that you
have been using?

I used two IN5817's. I only use these to power a Volkslogger. The rest of
the panel is still controlled via "A/B" switches.

These are rectifying diodes with low forward voltage drop, especially at
low currents. In my setup I think I loose less than 0.2V but it is tricky
to measure. These are small diodes with a Max current rating of about 1A.
I don't think that you could power your whole panel through them. (Google
should find you a data sheet).

Having the switches for the heavy current items (transponder etc) is
useful. It is very difficult to test the health of a battery on the
ground. So you normally only discover that the battery is not up to
scratch when it dies while you are flying. At this stage it is nice to be
able to switch over to battery B.


Ian

How about cheap handheld GPS + cheap handheld PDA + SW for a completely
separate, fully redundant system? Cost about $400.

"ContestID67" wrote in message
oups.com...
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

One of the main points is to protect the recorder so that you retain
your all important log file. While what you propose will get you back
home, it won't produce a valid FAI log file.

I think there have only been a small handful of failures out there so
far.

If the electrical system is clean and put together well, then the
chance of a failure is probably too remote to worry about.

FAI and contests allow for a gap of several minutes, so a simple switch
for dual batteries is good enough if you're worried about the battry
running out on you - or you forget to charge one.

A simple A/B setup takes care of the most obvious situation of leaving
the master switch on overnight and running a battery down. The second
one is hopefully still full.

-Tom

X-no-archive: yes
In article .com, 5Z
writes
I think there have only been a small handful of failures out there so
far.

If the electrical system is clean and put together well, then the
chance of a failure is probably too remote to worry about.

FAI and contests allow for a gap of several minutes, so a simple switch
for dual batteries is good enough if you're worried about the battry
running out on you - or you forget to charge one.

As you say, most recorders will only start a new file after power has
been removed for about 5 minutes, which is provided for in the current
FR Specification.

However some earlier recorder, the Volkslogger for example, were
designed before this provision was written in, and will always start a
new file after a power-down, regardless of duration.

Even then, if it is 'beyond reasonable doubt' that there was no
intermediate landing, more than one file may be accepted.

Tim Newport-Peace

"Indecision is the Key to Flexibility."