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scc_ron(at)yahoo.com
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 Posted: Sat Jan 27, 2007 9:00 am Post subject: Avionics Master - Yes or No? |
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I'm confused....
I believe the general consensus has been that an Avioics Master is unnecessary with "modern" avionics/radios we are using today. However, I just had to send in my Comm radio (XCOM - transmits but won't receive now) for repair because the technician told me that starting the engine with the radio on was a definate no-no, and (in doing so) I messed up the computer inside the radio that now needed to be reset on the bench.
He also informed me he'd seen many transponders/navs etc that get damaged by the "20 volt spike" that occurs on start-up. I do sometimes have to reset my Dynon after start-up because it gets all goofy and unreadable. Is it time to rewire my Avionics Master back in? I sure don't want more of this to have to deal with/pay for.
Tell me what you think....
Ron
[quote][b]
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Bret Smith
Joined: 09 Jan 2006
Posts: 178
Location: Mineral Bluff, GA
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| Posted: Sat Jan 27, 2007 10:43 am Post subject: Avionics Master - Yes or No? |
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Ron, doesn't your XCOM and transponder have their own on-off power switch? Is the technician saying that simply having power direct to the unit during start-up is capable of damaging the unit?
Bret Smith
RV-9A (91314)
Mineral Bluff, GA
www.FlightInnovations.com
From: owner-aeroelectric-list-server(at)matronics.com [mailto:owner-aeroelectric-list-server(at)matronics.com] On Behalf Of Ron Patterson
Sent: Saturday, January 27, 2007 11:59 AM
To: aeroelectric-list(at)matronics.com
Subject: Avionics Master - Yes or No?
I'm confused....
I believe the general consensus has been that an Avioics Master is unnecessary with "modern" avionics/radios we are using today. However, I just had to send in my Comm radio (XCOM - transmits but won't receive now) for repair because the technician told me that starting the engine with the radio on was a definate no-no, and (in doing so) I messed up the computer inside the radio that now needed to be reset on the bench.
He also informed me he'd seen many transponders/navs etc that get damaged by the "20 volt spike" that occurs on start-up. I do sometimes have to reset my Dynon after start-up because it gets all goofy and unreadable. Is it time to rewire my Avionics Master back in? I sure don't want more of this to have to deal with/pay for.
Tell me what you think....
Ron
[quote]
href="http://www.matronics.com/Navigator?AeroElectric-List">http://www.matronics.com/Navigator?AeroElectric-List
href="http://forums.matronics.com">http://forums.matronics.com
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Bret Smith
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Gilles.Thesee(at)ac-greno
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john(at)ballofshame.com
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| Posted: Sat Jan 27, 2007 11:58 am Post subject: Avionics Master - Yes or No? |
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I'm not even going to go into the the whole avionics master yes/no
argument. XCOM claims that they test to DO-160D. We can mince words
and say that they didn't claim they met the specification, only that
they tested to it....but let's assume they meet spec (there is a LOT of
stuff in this document, btw. If you know someone who's a member of
RTCA, have a read through it). It should simply shrug off a 20V "spike".
This is trivial to test. Find a buddy with a scope (portable fluke
would be sweet) and put it on the bus as you crank. Set it to trigger
at 16 volts and see what you get. Tell your EE friend you're looking
for transients above 16 volts. He'll know just what to do.
Your Dynon is most likely getting confused because of because of low
voltage, not high. Once again, easy to show with a scope (or even just
a VOM if it's not too noisy while you're cranking). You'll probably see
the bus drop below 10V. Notice, though, that it's brains don't get
"scrambled", whatever that means.
The tech you talked is just confused. My guess is that the most likely
killer of solid state electronics during engine start is poor design
somewhere in the electronic itself that would allow a low voltage
situation (such as you expect to get on engine starts at least SOME of
the time) to take switching transistors out of saturation. When it's
saturated, the resistance, and therefore the heat generated, is next to
nothing. Same when the "switch" is off. When the transistor is
partially on, as might happen in a low voltage situation, the transitor
essentially behaves as a resistor and both restricts current and
dissapates enourmous amounts of heat. Enormous in this case means "WAY
more than the designer intended". He intended 0". This is how I
typically used to blow stuff up, anyway.  Maybe Bob can weigh in
here since he had more experience with avionics before I was born than
I'll ever have in a lifetime. It's just a guess.
Avionics master won't hurt things, and will keep you from having to
reboot your Dynon (and maybe protects whatever it is the XCOM can't deal
with, although it was probably just flaky to begin with) but really,
things just shouldn't be blowing up regardless. Should and do are two
different things, I guess.
Sorry for rambling. My fingers have a life of their own sometimes.
-John
www.ballofshame.com
Ron Patterson wrote:
| Quote: | I'm confused....
I believe the general consensus has been that an Avioics Master is
unnecessary with "modern" avionics/radios we are using today. However,
I just had to send in my Comm radio (XCOM - transmits but won't
receive now) for repair because the technician told me that starting
the engine with the radio on was a definate no-no, and (in doing so) I
messed up the computer inside the radio that now needed to be reset on
the bench.
He also informed me he'd seen many transponders/navs etc that get
damaged by the "20 volt spike" that occurs on start-up. I do sometimes
have to reset my Dynon after start-up because it gets all goofy and
unreadable. Is it time to rewire my Avionics Master back in? I sure
don't want more of this to have to deal with/pay for.
Tell me what you think....
Ron
*
*
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jetboy
Joined: 22 Jul 2006
Posts: 233
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| Posted: Sat Jan 27, 2007 1:31 pm Post subject: Re: Avionics Master - Yes or No? |
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Ron I agree with the replies youve had and that if the radio was anywhere close to DO-160 spec there would be no issue. A friend has just got his Xcom back for the 3rd time and it seems to be fixed now. The dealer also loaned him a replacement which had the same fault and had to be sent away. The problem we experienced was identified by the company as a software issue and repaired under warranty though there has been no announcment about it yet on their website. Maybe it will go away.
he problem we had was a condition that could occur where although the receiver was getting a signal (witnessed by the RX indication) there would be no audio delivered to the headsets. There would be no noise even if the squelch control was adjusted to make noise. Usually the audio would start working if the transmitter was operated. But the receiver could go to sleep at any time, and repowering the radio didnt help. sometimes you cannot power these down without pulling a fuse. Then you will end up with a glitched radio as described.
You will be told you need an avionics master. And reminded about the requirement for a capacitor. My friends installation, being a Rotax 912, already has the capacitor, installed across the regulator. Xcom wiring for the capacitor suggests installation after the avionics master, IMHO this is incorrect practice as it will exceeed the ratings for the switch, with excessive inrush currents.
In my aircraft, I have no avionics master and routinely leave the radios / transponder on during startup. Yes, in the 60's the new transistorised radios were susceptible and flying schools taught to start up with everything turned off then go thru and set all the units on. Most of the radios failed because the volume controls wore out.
In summary, if you become aware of sleepy rx on the Xcom the factory should know about it, you just have to get past the 'must be a faulty installation" barrier - oh, and dont forget to clean the headset connections.
Ralph
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Ralph - CH701 / 2200a |
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khorton01(at)rogers.com
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| Posted: Sat Jan 27, 2007 2:56 pm Post subject: Avionics Master - Yes or No? |
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Bob Nuckolls posted a summary of some of the DO-160 requirements in a
message titled "DO-160 in a nutshell", back in May 2001.
A device that has passed the DO-160 tests for power should function
normally with bus voltages from 13 to 15v, and should still function
acceptably down to 10.5v. It should not be damaged by power drop
outs to 0v. It should be able to handle 20v for 1 second, and 40v
for 0.1 second.
So, if the XCOM has passed the DO-160 tests, as they claim, then it
should survive just fine being on during engine start and shut down.
Kevin Horton
On 27 Jan 2007, at 14:57, John Coloccia wrote:
| Quote: |
<john(at)ballofshame.com>
I'm not even going to go into the the whole avionics master yes/no
argument. XCOM claims that they test to DO-160D. We can mince
words and say that they didn't claim they met the specification,
only that they tested to it....but let's assume they meet spec
(there is a LOT of stuff in this document, btw. If you know
someone who's a member of RTCA, have a read through it). It should
simply shrug off a 20V "spike".
This is trivial to test. Find a buddy with a scope (portable fluke
would be sweet) and put it on the bus as you crank. Set it to
trigger at 16 volts and see what you get. Tell your EE friend
you're looking for transients above 16 volts. He'll know just what
to do.
Your Dynon is most likely getting confused because of because of
low voltage, not high. Once again, easy to show with a scope (or
even just a VOM if it's not too noisy while you're cranking).
You'll probably see the bus drop below 10V. Notice, though, that
it's brains don't get "scrambled", whatever that means.
The tech you talked is just confused. My guess is that the most
likely killer of solid state electronics during engine start is
poor design somewhere in the electronic itself that would allow a
low voltage situation (such as you expect to get on engine starts
at least SOME of the time) to take switching transistors out of
saturation. When it's saturated, the resistance, and therefore the
heat generated, is next to nothing. Same when the "switch" is
off. When the transistor is partially on, as might happen in a low
voltage situation, the transitor essentially behaves as a resistor
and both restricts current and dissapates enourmous amounts of
heat. Enormous in this case means "WAY more than the designer
intended". He intended 0". This is how I typically used to blow
stuff up, anyway. Maybe Bob can weigh in here since he had
more experience with avionics before I was born than I'll ever have
in a lifetime. It's just a guess.
Avionics master won't hurt things, and will keep you from having to
reboot your Dynon (and maybe protects whatever it is the XCOM can't
deal with, although it was probably just flaky to begin with) but
really, things just shouldn't be blowing up regardless. Should and
do are two different things, I guess.
Sorry for rambling. My fingers have a life of their own sometimes.
-John
www.ballofshame.com
Ron Patterson wrote:
> I'm confused....
> I believe the general consensus has been that an Avioics Master is
> unnecessary with "modern" avionics/radios we are using today.
> However, I just had to send in my Comm radio (XCOM - transmits but
> won't receive now) for repair because the technician told me that
> starting the engine with the radio on was a definate no-no, and
> (in doing so) I messed up the computer inside the radio that now
> needed to be reset on the bench.
> He also informed me he'd seen many transponders/navs etc that get
> damaged by the "20 volt spike" that occurs on start-up. I do
> sometimes have to reset my Dynon after start-up because it gets
> all goofy and unreadable. Is it time to rewire my Avionics Master
> back in? I sure don't want more of this to have to deal with/pay for.
> Tell me what you think....
> Ron
> *
> *
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nuckollsr(at)cox.net
Guest
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| Posted: Sat Jan 27, 2007 2:58 pm Post subject: Avionics Master - Yes or No? |
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At 08:59 AM 1/27/2007 -0800, you wrote:
| Quote: | I'm confused....
I believe the general consensus has been that an Avioics Master is
unnecessary with "modern" avionics/radios we are using today. However, I
just had to send in my Comm radio (XCOM - transmits but won't receive now)
for repair because the technician told me that starting the engine with
the radio on was a definate no-no, and (in doing so) I messed up the
computer inside the radio that now needed to be reset on the bench.
|
The radio has an ON/OFF switch, no? If the radio
is indeed sensitive to ANYTHING real or imagined
that MIGHT happen during starting . . . it's pretty
easy to have it turned off at the time
| Quote: |
He also informed me he'd seen many transponders/navs etc that get damaged
by the "20 volt spike" that occurs on start-up.
|
As far as I've been able to determine, the start-up "spikes"
are a figment of someone's imagination . . . we helped start
that rumor back in the 60's when Cessna put the avionics
master in. After years of hunting the elusive "snipe spike"
during startup, I've quite looking. Virtually every time I've
had 'scopes or high speed data acquisition systems tied to
everything from S.E. Cessnas to Bizjets, I have yet to capture
the elusive start up spike. I've yet to see anyone else's
trophy either. It's a phenomenon very long on discussion and
promulgation but exceedingly lacking in repeatable experiment.
| Quote: | I do sometimes have to reset my Dynon after start-up because it gets all
goofy and unreadable.
|
This is probably due to some sensitivity to brownout, not
over voltage transient. The curves below were plotted of
the battery terminals of two cars sitting in my driveway.
Note the short term drop to very low voltage while the battery
is subject to 1000A or so of starter inrush currents. Note
further the LOWER voltage taken from the terminals of the
Saturn . . . which has a PM starter. Higher inrush currents,
lower voltage.
http://www.aeroelectric.com/Pictures/Curves/95_GMC_Safari_1.gif
http://www.aeroelectric.com/Pictures/Curves/95_GMC_Safari_3.gif
http://www.aeroelectric.com/Pictures/Curves/99_Saturn_SL1.jpg
http://www.aeroelectric.com/Pictures/Curves/99_Saturn_SL1_2.gif
Note that none of these traces show UPWARD transients. Further,
the time that the voltage stays below 9v is short. Tens of
milliseconds. . . but PLENTY of time for a microprocessor to
wander off into the weeds.
One might properly state that an avionics master switch left
off during start and turned on only after start would fix
the to problems cited. So would judicious use of the radio's
own power switch.
I've often noted that devices confused by the startup
brownout phenomenon were not designed to live in the real
world of vehicular DC power systems. We don't have to fuss
with things on our cars . . .
At the time I was handling Microair, they were unwilling to
upgrade their products to take the 20V, 1-second surge. I don't
know about brown-out tolerance. Was unable to do tests myself
and didn't get any feedback from customers. But that one
reason out of several I decided not to continue my relationship
with them.
The short answer is that I can deduce no value for having
an AMS that cannot be equally addressed by using the device's
own power switch . . . and buying into the notion that startup
events are potentially harmful to a device is founded on suspect
science.
| Quote: | Is it time to rewire my Avionics Master back in? I sure don't want more
of this to have to deal with/pay for.
|
If it worries you and having the switch would mitigate the worries,
then why not? My father is paying $thousands$ for some treatments
that I believe are pure snake oil but he believes they're helpful.
In his case, he can afford it and if he's happy with the results,
then I'm not going to get inside that loop.
Bob . . .
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nuckollsr(at)cox.net
Guest
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| Posted: Sat Jan 27, 2007 9:16 pm Post subject: Avionics Master - Yes or No? |
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At 05:51 PM 1/27/2007 -0500, you wrote:
| Quote: |
Bob Nuckolls posted a summary of some of the DO-160 requirements in a
message titled "DO-160 in a nutshell", back in May 2001.
|
yes. that piece is still on the website at:
http://aeroelectric.com/articles/do160.html
Bob . . .
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