Today's Message Index:
----------------------
1. 01:45 AM - Re: Rochester dual indicator (bouguy)
2. 05:13 AM - Re: LEDs for strobes and position lights (Speedy11@aol.com)
3. 05:51 AM - Re: Do you suppose this is why elephants are afraid of them? (Harley)
4. 07:12 AM - Re: B&C alterator problem (Robert L. Nuckolls, III)
5. 07:12 AM - Re: LEDs for strobes and position lights (Eric M. Jones)
6. 07:16 AM - Re: Re: Rochester dual indicator (Robert L. Nuckolls, III)
7. 09:45 AM - Landing Light Pops Breaker (Dennis Johnson)
8. 10:29 AM - Re: 30 Amp switch? (Ernest Christley)
9. 10:29 AM - Re: 30 Amp switch? (Ernest Christley)
10. 11:12 AM - Re: Landing Light Pops Breaker (Joemotis@aol.com)
11. 05:20 PM - Re: Landing Light Pops Breaker (Robert L. Nuckolls, III)
12. 07:04 PM - Re: Landing Light Pops Breaker (Vernon Little)
13. 07:42 PM - Re: Landing Light Pops Breaker (Robert L. Nuckolls, III)
14. 08:49 PM - Search for Gremlins ()
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Subject: | Re: Rochester dual indicator |
Hi Bob ,
these instruments are not old and are 2 1/4 standard dimensions ;
they are not embedded in a cluster ; look at the attachement .
so if i need to change them there will be no problem !
they are fitting the latest C172 i have seen .
if you may have information on senders it will be great ;
if not i will try to find another solution , but for the time i
try to save money .
thanks for your help ,
Boullu guy .
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=199046#199046
Attachments:
http://forums.matronics.com//files/rochester_17_08_08_003_105.jpg
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Subject: | Re: LEDs for strobes and position lights |
Corvairkelso,
It sounds like you solved the mounting problem. I've been experimenting for
some time with various LEDs for position and taxi light but with little
success on a mounting solution. I finally gave up and bought the high dollar
Whelen units. I found it wasn't worth my $time$ to continue the experiment.
Do you have and photos posted for us to see?
Stan Sutterfield
In response to a previous question about using LED for position lights and
strobe, check www.luxeonstar.com. I have used their rebel stars in the white
tri-emitter powered by their power supply, called a buck puck successfully.
The buck pucks imput 12 volts fine and output a fixed current, 700ma in my
case. I am using a group of five stars, for about 1400 lumens per side.
Luneon III stars are available in both red and green for position lights.
Mounting was a challenge, finally using NAPA 549SWD surface mount dome light as
a
container for them. I used the lambertain style, which is 140 degree of
coverage
**************Looking for a car that's sporty, fun and fits in your budget?
Read reviews on AOL Autos.
(http://autos.aol.com/cars-Volkswagen-Jetta-2009/expert-review?ncid=aolaut00030000000007 )
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Subject: | Re: Do you suppose this is why elephants are afraid |
of them?
>>As if bird's nests weren't bad enough,<<
I know that all too well...luckily it was my car, not my plane. But the
incident has me being sure that every exposed hole is taped over or
plugged whenever I leave the hangar now! My left wing is being painted
here in my garage at home, but, since this is where the chipmunks live,
even that has tape over the aileron rod hole and the tunnel where the
wiring to the wing tip goes. Both ends of it!
Two years ago, I started logging 16 mpg tanks of gas instead of the
usual 20-21 in my Mazda RX8. Found a chipmunk had crawled up the air
intake tube and tore apart the air filter to make a nice comfy, little
home! The car had only been idle for three days, so they can work pretty
fast!
Besides the well matted down filter material, it was full of seeds and
other edibles that chippies like to munch on while relaxing after a hard
day of hunting for new homes. Luckily, nothing got THROUGH the filter,
and it was just a matter of vacuuming out the filter box and replacing
the filter. This incident did give me the opportunity to finally replace
the factory filter with a K&N. To prevent future critter visits I also
mounted a piece of 1/2 wire cloth over the air inlet.
Guess that's why they suggest you plug all the holes in your plane
before you leave it for any length of time...who knows what little
critter's real estate agent might sell him on the comfortable, protected
little spaces in our planes!
Harley
------------------------------------------------------------------------
>
> As if bird's nests weren't bad enough, now we have . . .
>
> http://tinyurl.com/5vmasm
>
> Bob . . .
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Subject: | Re: B&C alterator problem |
At 10:39 PM 8/16/2008 -0700, you wrote:
>
>Bob and others -
>I have a newly purchased RV8 with a B&C 40 amp alternator and automotive
>style blade fuses. Good grounding with a firewall mounted ground bus
>which is then routed to the engine. The digital ammeter indicates a
>running load of 6-7 amps. The battery is a Concorde dry cell mounted on
>the firewall. On two separate occasions the 15 amp alternator field fuse
>has blown without any additional or noted transient loads being placed on
>the alternator. The builder had this happen to him also and he thought it
>was the battery so he replaced it. The new, year old Concorde battery has
>great cranking power so I am not looking at this as a potential
>problem. The only other problem I have noted is when using all of the
>lights, strobes, fuel pump and electric flaps the main 40 amp C/B popped
>once. Ignoring this as an overload my real problem appears to be the
>field fuse. Why does the 15 amp field fuse blow and what's the smartest
>way to diagnose this problem? Thank you. JBB
The first problem is that the original builder did not
understand the physics of the system he/she was crafting
and chose not to study and understand why the z-figures
were designed the way they are.
A 40A breaker on a 40A alternator is UNDERSIZED. The
nameplate rating of an alternator is for worst-case
conditions. I.e. minimum rpm for full output and max
ambient operating temperature. Under less stressful
conditions, the alternator may deliver 15 to 25%
more current.
This says that the 60A breaker on the b-lead of 60A
alternators in 100,000 GA aircraft is DESIGNED to
nuisance trip. Suggest you replace the 40A breaker
with a 30-50A current limiter out on the firewall.
There should not be a field fuse with an LR series
regulator. These us crowbar OV protection and are
designed to work downstream of a breaker only. Is
the recommended 5A breaker also installed? IF so,
the wiring between the breaker and the bus needs
little if any protection. The z-figures recommend
a fusible link . . . exceedingly robust compared
to the fuse.
Now we need to figure out what's irritating the
OV protection system. Do I presume correctly that
the regulator also came from B&C (LR3 series?) or
is there some other combination of regulator/ov
in place?
I'll assume that since the field protection is being
nuisance tripped, there is some form of crowbar
ov protection in place. The ov protection may
be an older version that was sensitive to some
forms of normal bus transients. The designs at
both B&C and AeroElectric Connection were modified
to eliminate that condition . . . the system you're
working with may need to be updated.
This is not a condition unique to 'crowbar' ov
protection. EVERY ov protection system has some
form of comparator between bus voltage and
some stable reference. When a setpoint is exceeded,
it sends a signal to some form of disconnect
device (relay, transistor, scr, etc). There is
a dynamic component to ov protection too . . .
voltage excursions above the setpoint are allowed
as long as they do not exceed certain time
intervals. It's the fine tuning of the dynamic
sensitivity that makes some products prone to
nuisance trips. I've probably designed two dozen
or more OV protection systems in my career, I've
only had to re-tune two of them. In one case,
the transient condition generated by the aircraft
was greater than the Mil-STD-704 guidelines
to which the product was crafted.
Tell us what regulator/ov combination is installed.
If an LR3, what's the manufacturing date? If
an AEC crowbar module, what colors of wires does
it have. Older versions are red/black, newer
are orange/black.
Bob . . .
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Subject: | Re: LEDs for strobes and position lights |
A remarkable coincidence perhaps--I just listed a bunch of these on Ebay:
LuxDrive Powerpuck LED pwr supply 700 ma
Ebay item number: 180278091883
or: http://tiny.cc/aujh1
I used these for my white LED tail light but changed to linear regulators. My loss
is your gain.
"it's faster horses, younger women, older whiskey, and more money...."
--Cowboy Poet Tom T. Hall
--------
Eric M. Jones
www.PerihelionDesign.com
113 Brentwood Drive
Southbridge, MA 01550
(508) 764-2072
emjones@charter.net
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=199072#199072
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Subject: | Re: Rochester dual indicator |
At 01:39 AM 8/17/2008 -0700, you wrote:
>
>Hi Bob ,
>
>these instruments are not old and are 2 1/4 standard dimensions ;
>they are not embedded in a cluster ; look at the attachement .
>
>so if i need to change them there will be no problem !
>
>they are fitting the latest C172 i have seen .
>
>if you may have information on senders it will be great ;
>if not i will try to find another solution , but for the time i
>try to save money .
Understand. I was not aware that Rochester was still
building for Cessna . . . but it doesn't surprise me.
I guess I should have picked up on the magnitude of
the S-number you quoted. When I worked there, the
current production products were in the 1000's range.
I'll see what I can find out about these parts.
Bob . . .
----------------------------------------)
( . . . a long habit of not thinking )
( a thing wrong, gives it a superficial )
( appearance of being right . . . )
( )
( -Thomas Paine 1776- )
----------------------------------------
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Subject: | Landing Light Pops Breaker |
The April issue of EAA's Sport Aviation magazine had a "technical"
column about an airplane that regularly popped the landing light circuit
breaker. The author said he found several high resistance connections
in the circuit and solved the problem by cleaning those connections and
making them low resistance. The current issue, August, has an excellent
letter to the editor that questions how a high resistance connection
(presumably not at the circuit breaker's terminals) could cause a high
amperage condition that would trip the breaker.
When I read the original article, I also didn't understand how a high
resistance connection could increase the amperage in a landing light
circuit and just figured that it was yet another example of bad advice
in a Sport Aviation "technical" article. I enjoy the magazine, but I
have found so much faulty technical information in it that I don't pay
much attention to their technical articles.
However, the author's response to the question reiterated that a high
resistance connection can increase the amperage enough to cause the
circuit breaker to trip.
I'm a beginner on things like this, but I've studied Bob's book and this
newsgroup since beginning my homebuilt project five years ago, and
cannot understand how the author could be right. However, I've learned
from this list that some components try to consume constant power and
that reducing the voltage to them increases the current in order to keep
the power constant. But I think a tungsten filament landing light is a
simple resistor (although very temperature sensitive). I think if I put
a resistor in series with a landing light, the amps would go down, not
up, and the amount of light produced would decrease.
So what's the truth? And why?
Best,
Dennis
Lancair Legacy, 150 hours, did all my own wiring (also assembly,
body-work, paint, instrument panel, etc)
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Subject: | Re: 30 Amp switch? |
Bob White wrote:
>
> On Sat, 16 Aug 2008 11:39:08 -0400
> Ernest Christley <echristley@nc.rr.com> wrote:
>
>
>
>> On another completely unrelated note, mpja.com has some nice
>> panel-mounted temp guages for $3.95 that have a remote probe. The
>> supplied battery will cost that much at the corner drug store. One for
>> OAT, one for carb temp and half a dozen more for various temps that I'd
>> want to measure, and I'd still not be into serious money.
>>
>>
>>
> Not so fast Ernest. I found that item, at least I guess it's the right
> one. "Requires 1 "LR1130" button cell. (Not included)", so you've
> probably doubled your cost. :)
>
> Bob W.
>
>
Hmmm? I paid 3.95, and it included the button cell. Taped to the side
of the LCD so that it wouldn't be run down when I got it. Go figure.
YMMV.
--
http://www.ernest.isa-geek.org
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Subject: | Re: 30 Amp switch? |
Dale Rogers wrote:
>
> Ernest Christley wrote:
>> <echristley@nc.rr.com>
>>
>> On another completely unrelated note, mpja.com has some nice
>> panel-mounted temp guages for $3.95 that have a remote probe. The
>> supplied battery will cost that much at the corner drug store. One
>> for OAT, one for carb temp and half a dozen more for various temps
>> that I'd want to measure, and I'd still not be into serious money.
>
> Ernest, was that item # 16370 ME?
> Dale R.
>
16370-MI in the catalogue I'm looking at.
--
http://www.ernest.isa-geek.org
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Subject: | Re: Landing Light Pops Breaker |
That's easy, how about if the landing light is turned on and is pulling
maximum amps on a cold filament,
meanwhile that high resistance connection upstream is starting to get hot
and arc and spark...Those values added together are greater than the circuit
breakers rating..
Joe Motis
Do not archive
**************Looking for a car that's sporty, fun and fits in your budget?
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Message 11
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Subject: | Re: Landing Light Pops Breaker |
At 09:38 AM 8/17/2008 -0700, you wrote:
>The April issue of EAA's Sport Aviation magazine had a "technical" column
>about an airplane that regularly popped the landing light circuit
>breaker. The author said he found several high resistance connections in
>the circuit and solved the problem by cleaning those connections and
>making them low resistance. The current issue, August, has an excellent
>letter to the editor that questions how a high resistance connection
>(presumably not at the circuit breaker's terminals) could cause a high
>amperage condition that would trip the breaker.
>
>When I read the original article, I also didn't understand how a high
>resistance connection could increase the amperage in a landing light
>circuit and just figured that it was yet another example of bad advice in
>a Sport Aviation "technical" article. I enjoy the magazine, but I have
>found so much faulty technical information in it that I don't pay much
>attention to their technical articles.
Understand . . . and agree. I quit writing for S.A. some
years ago after an article I reviewed for Jack Cox wound up
getting published anyhow. See:
http://aeroelectric.com/articles/rules/review.html
S.A. used to be the flagship publication of EAA and
dedicated to the best we know how to do. Sadly, it
now seems to be a cash cow for advertising sales
and a venue where wanna-be's get published. When
you have a high-volume, directed-market technical
publication that won't even pay a rudimentary writer's
fee or seek peer review of articles . . . well . . .
what you see is what you get.
>
>However, the author's response to the question reiterated that a
>high resistance connection can increase the amperage enough to
>cause the circuit breaker to trip.
>
Good for you! I don't know how many times I've seen
words in ostensibly authoritative works that suggest
"cleaning and re-tightening" junctions in order to
cure a variety of ills . . . including the opening of
breakers or fuses. See bottom of page 4 and top of
5 on . . .
http://www.aeroelectric.com/articles/richter/response_2.pdf
and upper left corner of page 2
http://www.aeroelectric.com/articles/Wired_for_Disaster.pdf
These words are written by folks who's esteem in
our society has been artificially elevated for
reasons other than their understanding of physics
and practical processes.
Unless a high resistance junction is showing signs
of impending failure due to heating . . . then its
effects are limited simply to increasing path resistance.
An increase in path resistance LOWERS overall power
consumed by devices on that pathway . . . but indeed
may concentrate power dissipation (heating) in a
localized area (joints, worn contacts) that precipitate
a failure at that location . . . but it certainly doesn't
cause breakers to open. Unless . . .
Here's a case where a switch failure DID first manifest
itself by opening a breaker . . . when it was TURNED
OFF. See:
http://www.aeroelectric.com/articles/Anatomy_of_a_Switch_Failure/Anatomy_of_a_Switch_Failure.html
Of course, this was a double failure . . . the switch
had not yet failed to conduct in the closed position
. . . but heating effects induced a second failure.
A distortion of the internal parts that ultimately
produced the short that tripped the breaker.
We've studied on these pages how an increased path
resistance contributes to instability of the voltage
regulator on alternators where field supply current
and bus voltage sense share the same pathway.
But aside from this demonstrable effect, I'm aware
of no other case where increased path resistance
due to real or imagined join degradation will cause
breakers or fuses to nuisance trip.
>I'm a beginner on things like this, but I've studied Bob's book and this
>newsgroup since beginning my homebuilt project five years ago, and cannot
>understand how the author could be right. However, I've learned from this
>list that some components try to consume constant power and that reducing
>the voltage to them increases the current in order to keep the power
>constant. But I think a tungsten filament landing light is a simple
>resistor (although very temperature sensitive). I think if I put a
>resistor in series with a landing light, the amps would go down, not up,
>and the amount of light produced would decrease.
Correct. The resistance of the lamp will decrease as
it gets dimmer . . . but not in inverse proportion
to decrease in voltage . . . i.e. current draw
STILL goes down, total power consumed still goes
down, just not like it would if a simple resistive
load were involved.
>So what's the truth? And why?
You were pretty close to it when your skepticism
based on what you understood raised some flags . . .
and you asked questions. With respect to the original
article: if one assumes the author of the original
article was not lying, then SOMETHING he did caused
the problem to go away. He may have moved some
wiring that cleared an intermittent short . . . but
believed that cleaning the connections was what
really did it. We'll never know since the "crime scene"
was not properly processed and is now probably compromised
to a degree that true root cause is no longer discoverable.
But a goodly portion of 135,000 EAA members will join him
in his erroneous beliefs.
Bob . . .
Message 12
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Subject: | Landing Light Pops Breaker |
Bob, and others.
There are a class of devices that can cause increased current with increased
resistance in the power circuit.
Some devices use switching power supplies which are constant-power devices.
What this means is that if input voltage increases, the current drain
decreases and vice versa. This negative resistance effect can cause
instability, and designers need to take it into consideration.
The best example I have is that my strobe power circuit had a faultly
(resistive) switch which caused current in the circuit to increase, and
tripped the breaker. The strobe supply was attempting to make up for the
voltage drop in the switch by increasing it's drain current. The fix was to
replace the switch and the burned terminals. I had two switches fail in
similar manners in different within the first year of operation of my RV-9A.
One was returned to the vendor for failure analysis, but I never heard back.
I first experienced this type of problem when designing switch mode power
supplies for cyclotron equipment. Everything worked fine until battery
internal resistances increased, then voltage/current oscillations would
start. Cheap fix was to put a fixed load on the input of the power supply
and waste a lot of energy to stabilize the load. Not recommended for
aircraft!
Vern Little
-----Original Message-----
From: owner-aeroelectric-list-server@matronics.com
[mailto:owner-aeroelectric-list-server@matronics.com] On Behalf Of Robert L.
Nuckolls, III
Sent: August 17, 2008 5:16 PM
Subject: Re: AeroElectric-List: Landing Light Pops Breaker
--> <nuckolls.bob@cox.net>
At 09:38 AM 8/17/2008 -0700, you wrote:
>The April issue of EAA's Sport Aviation magazine had a "technical"
>column
>about an airplane that regularly popped the landing light circuit
>breaker. The author said he found several high resistance connections in
>the circuit and solved the problem by cleaning those connections and
>making them low resistance. The current issue, August, has an excellent
>letter to the editor that questions how a high resistance connection
>(presumably not at the circuit breaker's terminals) could cause a high
>amperage condition that would trip the breaker.
>
>When I read the original article, I also didn't understand how a high
>resistance connection could increase the amperage in a landing light
>circuit and just figured that it was yet another example of bad advice in
>a Sport Aviation "technical" article. I enjoy the magazine, but I have
>found so much faulty technical information in it that I don't pay much
>attention to their technical articles.
Understand . . . and agree. I quit writing for S.A. some
years ago after an article I reviewed for Jack Cox wound up
getting published anyhow. See:
http://aeroelectric.com/articles/rules/review.html
S.A. used to be the flagship publication of EAA and
dedicated to the best we know how to do. Sadly, it
now seems to be a cash cow for advertising sales
and a venue where wanna-be's get published. When
you have a high-volume, directed-market technical
publication that won't even pay a rudimentary writer's
fee or seek peer review of articles . . . well . . .
what you see is what you get.
>
>However, the author's response to the question reiterated that a high
>resistance connection can increase the amperage enough to cause the
>circuit breaker to trip.
>
Good for you! I don't know how many times I've seen
words in ostensibly authoritative works that suggest
"cleaning and re-tightening" junctions in order to
cure a variety of ills . . . including the opening of
breakers or fuses. See bottom of page 4 and top of
5 on . . .
http://www.aeroelectric.com/articles/richter/response_2.pdf
and upper left corner of page 2
http://www.aeroelectric.com/articles/Wired_for_Disaster.pdf
These words are written by folks who's esteem in
our society has been artificially elevated for
reasons other than their understanding of physics
and practical processes.
Unless a high resistance junction is showing signs
of impending failure due to heating . . . then its
effects are limited simply to increasing path resistance.
An increase in path resistance LOWERS overall power
consumed by devices on that pathway . . . but indeed
may concentrate power dissipation (heating) in a
localized area (joints, worn contacts) that precipitate
a failure at that location . . . but it certainly doesn't
cause breakers to open. Unless . . .
Here's a case where a switch failure DID first manifest
itself by opening a breaker . . . when it was TURNED
OFF. See:
http://www.aeroelectric.com/articles/Anatomy_of_a_Switch_Failure/Anatomy_of_
a_Switch_Failure.html
Of course, this was a double failure . . . the switch
had not yet failed to conduct in the closed position
. . . but heating effects induced a second failure.
A distortion of the internal parts that ultimately
produced the short that tripped the breaker.
We've studied on these pages how an increased path
resistance contributes to instability of the voltage
regulator on alternators where field supply current
and bus voltage sense share the same pathway.
But aside from this demonstrable effect, I'm aware
of no other case where increased path resistance
due to real or imagined join degradation will cause
breakers or fuses to nuisance trip.
>I'm a beginner on things like this, but I've studied Bob's book and
>this
>newsgroup since beginning my homebuilt project five years ago, and cannot
>understand how the author could be right. However, I've learned from this
>list that some components try to consume constant power and that reducing
>the voltage to them increases the current in order to keep the power
>constant. But I think a tungsten filament landing light is a simple
>resistor (although very temperature sensitive). I think if I put a
>resistor in series with a landing light, the amps would go down, not up,
>and the amount of light produced would decrease.
Correct. The resistance of the lamp will decrease as
it gets dimmer . . . but not in inverse proportion
to decrease in voltage . . . i.e. current draw
STILL goes down, total power consumed still goes
down, just not like it would if a simple resistive
load were involved.
>So what's the truth? And why?
You were pretty close to it when your skepticism
based on what you understood raised some flags . . .
and you asked questions. With respect to the original
article: if one assumes the author of the original
article was not lying, then SOMETHING he did caused
the problem to go away. He may have moved some
wiring that cleared an intermittent short . . . but
believed that cleaning the connections was what
really did it. We'll never know since the "crime scene"
was not properly processed and is now probably compromised
to a degree that true root cause is no longer discoverable.
But a goodly portion of 135,000 EAA members will join him
in his erroneous beliefs.
Bob . . .
Message 13
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Subject: | Landing Light Pops Breaker |
At 07:02 PM 8/17/2008 -0700, you wrote:
><rv-9a-online@telus.net>
>
>Bob, and others.
>There are a class of devices that can cause increased current with increased
>resistance in the power circuit.
>Some devices use switching power supplies which are constant-power devices.
>What this means is that if input voltage increases, the current drain
>decreases and vice versa. This negative resistance effect can cause
>instability, and designers need to take it into consideration.
Sure . . . but let's put this into perspective. These are
not unlike the oscillating voltage regulators we discussed
earlier. But let's consider a system designed to run on 14v
at 3A (42w input) and protected with a 5A breaker. If series
resistance of a switch or other joint dropped say 2 volts,
then the system would compensate and current would rise
to 42/12 = 3.5A
From the outside looking in, things would appear normal
but the high resistance location would now be dissipating
2 x 3.5 = 7 watts! This is probably 4 or 5 times more than
the power it took to slowly toast the switch in the failure
analysis I cited. The situation would not last long . . . and
still wouldn't pop the breaker.
Suppose we have a 28v 42w system that runs 1.5A. Hmmm . . .
I suppose we could protect that line with a 2A breaker
but those things are expensive . . . the 22AWG feeder
is still happy at 5A breaker. But yeah, let's say a
3A breaker. Now some high resistance condition that would
push the 3A breaker has to drop 14v at 3A or 42 watts
of dissipation! It's toasted in a hurry . . .
>The best example I have is that my strobe power circuit had a faultly
>(resistive) switch which caused current in the circuit to increase, and
>tripped the breaker. The strobe supply was attempting to make up for the
>voltage drop in the switch by increasing it's drain current. The fix was to
>replace the switch and the burned terminals. I had two switches fail in
>similar manners in different within the first year of operation of my RV-9A.
>One was returned to the vendor for failure analysis, but I never heard back.
I recall that you sent an S700-2-10 switch back to B&C
for loose terminals. In that case, voltage excursions caused
by the loose terminals were probably upsetting the regulation
stability so badly as to cause a true ov condition that tripped
the system and opened the breaker. Breaker popping was a
secondary effect and not caused directly by an increased load
by a constant power device.
Were you the one that sent me the strobe switch cited
in the failure analysis I posted?
http://www.aeroelectric.com/articles/Anatomy_of_a_Switch_Failure/Anatomy_of_a_Switch_Failure.html
Again, breaker popping was a secondary effect
of the overheating of the switch that deformed the contact
support teeter-totter. These switches are normally good
for 10A or more in the closed state . . . but this switch
obviously failed at the pivot bridge as indicated by
heating patterns . . . this was happening with no more
than 1/2 volt of drop internal to the switch. So if your
strobe needed 5A average at 14v it would need only 5.2
amps at the "reduced" voltage. Yet the 5A at 1/2 volt
was 2.5 watts of heating on the switch's innards. Not
enough to 'smoke' it but enough to heat the components
to eventual failure but it took a number of hours but didn't
cause smoke in the cockpit.
>I first experienced this type of problem when designing switch mode power
>supplies for cyclotron equipment. Everything worked fine until battery
>internal resistances increased, then voltage/current oscillations would
>start. Cheap fix was to put a fixed load on the input of the power supply
>and waste a lot of energy to stabilize the load. Not recommended for
>aircraft!
That was a true negative resistance problem but those
generally happen under conditions that are far below those
needed to trip breakers that have any headroom at all.
Your perception of the behavior of constant-power systems
is accurate but increased resistance situations sufficient
to put a switch at risk are too small to be a likely
cause of breaker popping.
Bob . . .
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Subject: | Search for Gremlins |
8/17/2008
To reply to the author, write to "F. Tim Yoder" <ftyoder@yoderbuilt.com>
Report on this weekends search for Gremlins;
I spent several hours under the panel checking all the ground buss
connections, breaker and switch grounds. I loosened the connections to the
amp, volt, oil temp and oil pressure gauges, wiggled the terminals and re
tightened. I did the same thing to the alternator and removed the regulator
spades and replaced them.I removed the radio, cleaned the connectors and re
installed it. I checked the ground straps from the engine to the motor
mount. I spent some time looking for something,anything wrong.
I started the plane and found that I had not ran off any Gremlins. When I
turn on the Alt. the oil pressure dropped from 75# to 60# then settled on
70#, this takes about one second. As soon as I turn off the Alt. the oil
pressure goes back to 75#. With the radio and Alt. on the oil pressure
needle drops a needle width when I key the radio. Again, with the Alt. off
keying the radio does not effect the oil pressure gauge which was back to
75#.
I did not fly so I didn't have any radio issues. I think I need to find the
cause of the apparent load on the oil pressure gauge first.
Oh, the Amp. meter is a little positive at idle and the voltage is showing
a charge of about 14.4V and 13.5V with at Alt. off.
I'll appreciate any suggestions.
Thanks again, Tim
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