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.

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

On Tue, 14 Jun 2005 18:11:11 -0700, ContestID67 wrote:

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.

We installed two batteries with changeover switches, so we have a warning
when one battery is flat (like a the reserve tap on a motorbike fuel tank).

But our Volkslogger runs off a separate circuit which is connected to both
batteries via low voltage drop electronic diodes. It draws current from
which ever battery has the highest voltage.

I have tested it and cannot reset the Volkslogger without unplugging both
batteries. (But I can measure the battery voltage on any one battery with
the VL battery test function simply by unplugging the other. The voltage
reading is that after the diode loss, slightly less than what the rest of
the panel sees - unfortunately I can only do this on the ground)


Ian

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.

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 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

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

Switches of any kind provide the opportunity for user error and as a
mechanical device are subject to mechanical failure too.

If you are using so much electrical power that you don't have enough
battery for a long flight then you have a separate issue of not enough
batteries. If you find yourself short on power during a flight then you
can always selectively turn off equipment that you don't need. Best
plan is to have plenty of supply and always start with charged batteries
on any flight of importance. Failure to start with fully charged
batteries simply shows a lack of preparation and no amount of switches
will cure that problem.



T o d d P a t t i s t wrote:
"Andy" wrote:


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.


And even if you don't have a problem, this method tends to
draw down the two batteries equally. I like to use only
one, keeping the second as a reserve in case I forget to
charge the first, or so I can reduce electrical consumption
if the first battery is used up early in the flight.


Short term power loss does not invalidate the flight log.


If you want to prevent the short term power loss during
switchover, you can use a "make before break" switch, or you
can use a switch to briefly put them in parallel before
switching over.