Today's Message Index:
----------------------
1. 07:56 AM - Re: Strobe Lights (glen matejcek)
2. 08:30 AM - NASCAR 2007 Crash- Reset Circuit Breaker (Richard Dudley)
3. 08:30 AM - Hey Bob, Why no FL or ANL on the main and bat bus feeds? (Brantel)
4. 08:52 AM - Re: Strobe Lights (Ernest Christley)
5. 09:09 AM - NASCAR 2007 Crash - reset circuit breaker (Richard Dudley)
6. 10:07 AM - Switches and Relays (jayb)
7. 01:06 PM - Re: NASCAR 2007 Crash- Reset Circuit Breaker (Robert L. Nuckolls, III)
8. 01:24 PM - Re: Switches and Relays (Robert L. Nuckolls, III)
9. 04:42 PM - Re: Switches and Relays (jayb)
10. 05:49 PM - Re: Switches and Relays (Vern Little)
11. 08:49 PM - Re: Switches and Relays (B Tomm)
Message 1
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Subject: | RE: Strobe Lights |
Hi All-
Many good points on lights and threat detection. I'd like to add that,
like many on this list, I've had a lot of opportunity to look for traffic
at night. The number of times I've seen strobes and the distance at which
I've seen I've seen strobes is many times that of seeing a red beacon. How
many times have we looked at a night sky and seen an airliner's strobes and
never seen the beacon?
Also, as Matt observed, motion is a key element of visual perception,
especially with faint light. I suspect "change in the light' is the real
issue, and is why wig wags are so attractive to the eye. Strobes,
obviously, have that characteristic. They certainly can have the
shortcomings that were pointed out, namely low duty cycle, no inherent
direction vector, and potential confusion with ground based strobes. To
address all those issues, Whelen makes strobes called "Comet Flash" that
will fire 4 times, IIRC, in very rapid succession. This quadruples the
duty cycle and creates a visual 'trail' for the eye. These factors
identify the lights as being airborne, and are both attention getting and
impart a direction vector to the light. These strobes can be configured to
fire in opposition, as with a wig-wag system, which I believe further
doubles the duty cycle of the strobes.
At the time I was shopping for external lighting, the Whelens were by far
and away the brightest strobes on the market, as well as the most
expensive. As much as I like to get the best bang for my limited bucks, I
consider hairy-chested anti-collision strobe lights a high priority. It's
a long and unique story, but my pucker factor would have been a whole lot
lower one hazy afternoon had the other plane had strobes on...
The particular Whelen's I bought have strobe, white, and red or green
lights all in one wing tip unit. This way, I have 2 white tail lights and
no tail mounted lights at all. None of the cost, installation, maint, or
drag associated with the beacon and discrete tail lights. The only down
side I can think of is that when viewed from behind, someone might mistake
my little, slow aircraft for a large aircraft that is five or six times
farther away and moving faster.
As an aside, Beech used to supply at least their airliners with white
anti-collision beacons. They were certainly more effective / obnoxious
than red beacons while on the ground, but I really don't know if they were
any more effective aloft. Also, there were several TC'd aircraft in my
deep dark past that had strobes in lieu of a beacon. Mostly Grumman, but
there may have been a Cessna or piper in there as well.
YMMV, FWIW, etc.
glen matejcek
aerobubba@earthlink.net
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Subject: | NASCAR 2007 Crash- Reset Circuit Breaker |
Bob,
The FAA's conclusion of the causes of the NASCAR crash in 2007 was
published in the Orlando Sentinel today:
http://www.orlandosentinel.com/news/local/seminole/orl-planecrash2909jan2
9,0,4517645.story
It is a great example that supports of your rationale for fuses vs
circuit breakers.
Regards,
Richard Dudley
-6A (with fuses) sold
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Subject: | Hey Bob, Why no FL or ANL on the main and bat bus feeds? |
Bob,
Why no over current protection on the battery and main bus feeds?
Unfused wires with a huge current source make me nervous even if they are fairly
short.
What would be the wrong in using a ANL on the main bus and either an ANL or a fuseable
link on the battery bus?
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=227502#227502
Message 4
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Subject: | Re: Strobe Lights |
Matt Prather wrote:
> Where I'm going with is that when I go shopping for anti-collision
> lighting, I won't be looking at strobes. Instead I'll want some system
> that might look to the eye more like the old incandescent lights, except
> brighter, cooler running, and more reliable. LED's are the obvious source
> of illumination, especially today with their remarkable efficiency.
>
>
Matt, you make a good case, but I think the better option is to go with
both. The strobe is to draw the eye of the other pilot to your general
direction. The wig-wag is to get him (or her) to hone in on your exact
position. I don't always necessarily need to know exactly where
something is at. "A tower is to the right, hang a little to the left"
is usually more precision than necessary, and I wouldn't use 'precision
guidance' around phrases like "Traffic at 2 o'clock". The strobe is
just a heads up that there is something in that general direction, and I
think a quick flash does that better than a steady burning light.
Message 5
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Subject: | NASCAR 2007 Crash - reset circuit breaker |
Bob,
The NTSB conclusions, published today, include the re-setting of a
circuit breaker of an already suspicious circuit as likely contributor.
This is a clear reinforcement of the philosophy for use of fuses (to be
replaced only on the ground) instead of circuit breakers.
Regards,
Richard Dudley
-6A (all fuses), sold
Message 6
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Subject: | Switches and Relays |
Is there a general rule of thumb regarding max current load through a switch before
it is prudent to add a relay to handle switching higher current loads (similar
to S704-1 12v/20A)? Maybe this is spelled out in an AEC doc, but if so I
couldn't find it.
A couple of components which might require relay switch protection come to mind
including: pitot heat, landing lights, standard nav lights, and maybe fuel pump...
each appear to draw 5A or more in steady state.
The AN5812 heated pitot might be a strong relay usage contender as it has a hefty
initial current spike followed by a sizable current draw (see AEC article "Gauging
Pitot Heater Performance" 15 Feb 2005).
1N5400 (3A/50v) diodes are commonly used on Z-diagram contactors across the low
current coil side to suppress current spikes. Similar best practice would seem
to follow for S704-1 type relays too?
The 1N5400 diode seems like it would be good candidate. Are mil-spec components
advised or is the local Radio Shack sufficient?
I'm all for sweating through the load analysis and thinking things out in advance
so as to not end up with arc welded switches later.
Thanks,
Jay
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=227517#227517
Message 7
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Subject: | Re: NASCAR 2007 Crash- Reset Circuit Breaker |
At 10:03 AM 1/29/2009, you wrote:
>Bob,
>
>The FAA's conclusion of the causes of the NASCAR crash in 2007 was
>published in the Orlando Sentinel today:
><http://www.orlandosentinel.com/news/local/seminole/orl-planecrash2909jan29,0,4517645.story>http://www.orlandosentinel.com/news/local/seminole/orl-planecrash2909jan29,0,4517645.story
>
>It is a great example that supports of your rationale for fuses vs
>circuit breakers.
>
>Regards,
>
>Richard Dudley
Hmmmmm . . . it's not clear from this story that
the outcome would have been any different had
the airplane been fitted with fuses.
Both fuses and breakers are crafted with the
hard-fault in mind. I.e. a pretty solid short
or overload that causes a current several times
greater than the protection rating.
We've had some discussions on the List concerning
what I call soft faults. I've had several occasions
to study the difference and have delivered a number
of explanatory presentations to folks in my industry.
The "hard" fault is generally over in tens of
milliseconds but 10 seconds max. And while the current
flow is high, the total ENERGY dissipated in highly
stressed components is relatively low compared
with . . .
Soft faults are those events that DO NOT stress the
over current protection very hard. Examples of this
condition made big news in SwissAir 111 accident
a few years back were it was decided that prolonged
arcing at or below the breaker trip calibration set
un-qualified insulation on fire.
Here are some excerpts from a presentation I gave
on the topic where some folks were agonizing over
the existence of a 10AWG feeder downstream of an
8AWG feeder protected by a 50A breaker.
http://www.aeroelectric.com/articles/Hard_vs_Soft_Faults.pdf
This airplane was built in 1977.
http://www.ntsb.gov/ntsb/GenPDF.asp?id=NYC07MA162&rpt=p
I'm sure the Cessna west-side guys were using the same
wire as us east-side guys . . . Mil-W-16867 type
BN (nylon over pvc). . . Tefzel didn't get a good
grip in local aircraft fabrication for several more
years.
What's more, this insulation was 30+ years old
at the time of the accident. It seems the pilot
might have thought a previous day's smoke event
was limited to the radar or associated wiring when
the first problem abated after a breaker was pulled.
The airplane was so totally destroyed by fire that
we can only guess as to root cause and successive
events. But it's not a far reaching hypothesis to
suggest that the first event may have damaged other
wires in a bundle placing them at risk for continued
failures beyond those associated with the radar
system.
When we see an accident where an electrically
induced fire is suspected, it's almost a 100% bet
that the failure was a soft fault that dumped a lot
of energy without exceeding the ratings of the
fuses or breakers.
Given the nature of modern insulations I'll suggest
likelihood of this type event repeating in your
OBAM aircraft is exceedingly small. Tefzel is about
as close to an ideal insulating material as we've
ever seen. From eye witness descriptions if this
incident we can assume that the problem was less
electrical and more a function of flammable materials
continuing to burn.
The accident stories noted that their last
transmission was interrupted mid sentence. I can
only guess that they were already in a lot of
trouble with an electrical system that was still
energized.
When you smell smoke, the best advice is to shut
down the electrical system in its entirety and
continue with hand-helds as needed to a no-sweat
landing.
If you really NEED stuff on the e-bus, wait until
you know the smoke event is over before bringing
the e-bus back on through the alternate feed. Turn
of any un-needed, e-bus powered accessories before
powering it back up. Be ready to kill it if smoke
resumes.
Bob . . .
Message 8
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Subject: | Re: Switches and Relays |
At 11:33 AM 1/29/2009, you wrote:
>
>Is there a general rule of thumb regarding max current load through
>a switch before it is prudent to add a relay to handle switching
>higher current loads (similar to S704-1 12v/20A)? Maybe this is
>spelled out in an AEC doc, but if so I couldn't find it.
What particular situation drives this consideration?
Aside from pitot heaters, toe heaters, and klieg lights
for landing and taxi, you're unlikely to overload the
plain vanilla switches offered by most suppliers. See:
http://aeroelectric.com/articles/Switch_Ratings.pdf
>A couple of components which might require relay switch protection
>come to mind including: pitot heat, landing lights, standard nav
>lights, and maybe fuel pump... each appear to draw 5A or more in steady state.
>
>The AN5812 heated pitot might be a strong relay usage contender as
>it has a hefty initial current spike followed by a sizable current
>draw (see AEC article "Gauging Pitot Heater Performance" 15 Feb 2005).
Yes, this is an excellent application for a relay . . .
especially a solid state relay.
>1N5400 (3A/50v) diodes are commonly used on Z-diagram contactors
>across the low current coil side to suppress current spikes. Similar
>best practice would seem to follow for S704-1 type relays too?
Yeah, except that the lead wires on a 5400 series
device are pretty hefty and may be difficult to
install as shown in . . .
http://www.aeroelectric.com/Pictures/Relays/s704inst.jpg
>The 1N5400 diode seems like it would be good candidate. Are mil-spec
>components advised or is the local Radio Shack sufficient?
The lowly silicon diode rectifier is the oldest
semiconductor device in the marketplace. It's so easy
to make a really good diode that nobody even bothers
to offer parts screened to military specs. Finally
the electrical stresses on spike catcher diodes is
measured in MILLIJOULES . . . a sneeze in a thunderstorm.
Anything from this list of parts offered by RadioShack
and many others can be considered to your tasks.
http://www.aeroelectric.com/Pictures/Misc/RS_Diodes.jpg
>I'm all for sweating through the load analysis and thinking things
>out in advance so as to not end up with arc welded switches later.
I've never seen an arc welded switch that's been
"overloaded". Switches fail open after they burn
for a host of reasons not the least of which is
mechanical inadequacies at riveted joints.
What are the current ratings for systems you're
considering?
Bob . . .
----------------------------------------)
( . . . a long habit of not thinking )
( a thing wrong, gives it a superficial )
( appearance of being right . . . )
( )
( -Thomas Paine 1776- )
----------------------------------------
Message 9
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Subject: | Re: Switches and Relays |
Bob,
Thanks for the reply.
The biggest current users on my panel are AN5812 pitot heat (~8A steady state after
the initial inrush spike is done), landing lights (~4A each), Whelen strobes
(~7A total), NAV lights (~6A total) and boost fuel pump (~5A).
My take away from reading the AEC Switch article is that there's no need to protect
panel switches except those used to operate the high current starter and
battery contactors.
The entire topic really boils down to this paragraph:
"The heaviest currents handled by panel switches are landing/
taxi lights (which have their own special inrush values
-see "lamp" ratings in table above), and pitot heat. For most
14-volt airplanes this is about 8 amps. Everything else drops
rapidly from there. I can also tell you that switching an
8-amp landing light with a 4-amp "lamp" rated switch is not
an automatic formula for welding. The 200% "overload" will
indeed reduce the life of the switch. However, let us suppose
the switch was originally rated for 10,000 cycles (a low
estimate) and the reduction was to 10% of rated life(also
very low) . . . How long will it take you to put 1000 cycles
on your landing light switch? "
Does anyone have the definitions of an "Electrical Code Rating" as referenced in
the Microswitch Catalog table? The table would probably make better sense then.
There's a reference to switch cycle life above, but switches aren't typically sold
with that information easily obtained up front. Maybe someone has a link to
a good website as that info could be useful.
I must be missing something. People must be buying S704-1 relays as B&C sells them
and you reference them in several docs... but what are they using them for
if there's really no utility in it?
Jay
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=227591#227591
Message 10
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Subject: | Re: Switches and Relays |
I've looked at this in some detail. Since I've had multiple switch failures
(long Carling switch thread), I have looked at relays for switching heavy
loads.
In my new A/C (Harmon Rocket), this thinking has led me to a bank of relays
controlled by grounded switches. I need a bunch of relays for the trim
systems and other stick-grip switches anyway, so I went all the way with all
of my electrical loads switched with relays. While not strictly necessary,
it allowed me to place the relays and breakers off-panel where the heavy
gauge wiring runs were shorter. This saves many dozens of feet of heavy
wiring running back and forth to the panel.
Most of the switches on the panel are grounded to activate the corresponding
relay. This allows me to use a single 22 AWG wiring for each relay control.
I can also use lighter weight toggle switches on the panel, which also
happen to be cheaper. The lighter weight switches and shorter heavy gauge
wiring runs should roughly balance out the relay weights.
Another benefit of this approach is that rotary switches can be used instead
of toggles. For example, I plan one rotary switch for my main lights:
OFF-WIGWAG-PULSE-LDG-TAXI-BOTH. This takes one position on my panel and is
configured to drive my two lamp relays as necessary (left and right wingtip
lamps). Also, I plan on connectorizing the panel... it's a lot simpler with
fewer light gauge wires.
So an architecture based on relays has other benfits other than protecting
switches. These benefits must be weighed against the complexity and
potential failure modes of relays compared to switches. Sometimes, you just
want to experiment!
Vern Little
----- Original Message -----
From: "jayb" <jaybrinkmeyer@yahoo.com>
Sent: Thursday, January 29, 2009 9:33 AM
Subject: AeroElectric-List: Switches and Relays
>
>
> Is there a general rule of thumb regarding max current load through a
> switch before it is prudent to add a relay to handle switching higher
> current loads (similar to S704-1 12v/20A)? Maybe this is spelled out in an
> AEC doc, but if so I couldn't find it.
>
> A couple of components which might require relay switch protection come to
> mind including: pitot heat, landing lights, standard nav lights, and maybe
> fuel pump... each appear to draw 5A or more in steady state.
>
> The AN5812 heated pitot might be a strong relay usage contender as it has
> a hefty initial current spike followed by a sizable current draw (see AEC
> article "Gauging Pitot Heater Performance" 15 Feb 2005).
>
> 1N5400 (3A/50v) diodes are commonly used on Z-diagram contactors across
> the low current coil side to suppress current spikes. Similar best
> practice would seem to follow for S704-1 type relays too?
>
> The 1N5400 diode seems like it would be good candidate. Are mil-spec
> components advised or is the local Radio Shack sufficient?
>
> I'm all for sweating through the load analysis and thinking things out in
> advance so as to not end up with arc welded switches later.
>
> Thanks,
> Jay
>
>
> Read this topic online here:
>
> http://forums.matronics.com/viewtopic.php?p=227517#227517
>
>
>
Message 11
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Subject: | Switches and Relays |
Bob,
Speaking of switch failures,
I think you had mentioned that you would test the practicality and function
of adding JB weld to switch rivets to see if it would prevent them from
loosening without a downside. Any progress there?
Bevan
RV7A wiring
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