Today's Message Index:
----------------------
1. 05:14 AM - Re: crowbar method (Eric M. Jones)
2. 06:39 AM - Re: Re: crowbar method (Robert L. Nuckolls, III)
3. 06:55 AM - Re: Re: crowbar method (Robert L. Nuckolls, III)
4. 10:43 AM - The fatwire ground blues . . . (Robert L. Nuckolls, III)
5. 11:10 AM - Re: [luscombe-silvaire] Need help with Apollo GPS (Jim Ivey)
6. 11:17 AM - Bad Alternator ground on V-Tail! (Ronald J. Parigoris)
7. 12:00 PM - Re: Bad Alternator ground on V-Tail! (Robert L. Nuckolls, III)
8. 12:38 PM - Re: Re: I've got a secret (RV Builder (Michael Sausen))
9. 01:47 PM - Re: Re: crowbar method (Charlie England)
10. 02:01 PM - I'm happy...:) (Hinde, Frank George (Corvallis))
11. 02:39 PM - Re: Re: crowbar method (Robert L. Nuckolls, III)
12. 04:10 PM - Crowbar CB "problem" (Troy Scott)
13. 04:38 PM - Re: Crowbar CB "problem" (Fiveonepw@AOL.com)
14. 08:26 PM - Re: Diode orientation (Charlie Brame)
15. 08:40 PM - Two Mags & One Input to Electric Tach (r falstad)
16. 10:48 PM - CAD software (Steve Sampson)
17. 11:31 PM - Official Usage Guideline [Please Read] [Monthly Posting] (dralle@matronics.com)
Message 1
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| Subject: | Re: crowbar method |
--> AeroElectric-List message posted by: "Eric M. Jones" <emjones@charter.net>
--> AeroElectric-List message posted by: Charlie England
<ceengland@bellsouth.net>
Eric M. Jones wrote:
>--> AeroElectric-List message posted by: "Eric M. Jones"
><emjones@charter.net>
>
>--> AeroElectric-List message posted by: Charlie England
>ceengland@bellsouth.net
>
>
>>>Others have posted on this topic who can speak with much more authority
>>>
>>>
>than I, but it seems to me that saying that a breaker isn't designed to
>open a circuit when there's a short flies in the face of all logic. It
>seems to me, that's why it's there in the 1st place. It isn't there to
>protect some device from moderate over-current; the mfgr of the device
>has the responsibility to do that. The breaker is there to protect
>downstream wire from melting/burning in the case of gross over-current
>conditions (shorts). Would anyone maintain that we should go find some
>high tech alternative for our house breakers because they aren't
>designed to open the circuit if someone shorts out a circuit by
>accidentally cutting into a lamp cord with a pair of scissors?
>
>Charlie--A short circuit can produce high currents limited only by the
>circuit impedance. This impedance can be very very low. That's the problem.
>At 14.5 volts, a short of 0.001 ohms is 14500 amps. Of course your 5A
>circuit breaker would emit gamma rays at this current. (I'm not kidding).
>Lucky for us, in the real world the circuit breaker will probably not have
>to handle such a current, but the crowbar/CB combination WILL suffer damage
>as currently designed. Bob and Paul argued the exact current---but in
>summary it depends on where the battery is and what the battery is.
>
>
>>>Aren't the crowbar circuits being discussed designed to short across the
>>>
>>>
>supply to the field winding of the alternator? Following the 'not
>designed for the job' argument, is another solution needed for a
>traditional alternator field breaker in its traditional role considering
>that a wire between the breaker & the alternator might inadvertently rub
>against the chassis somewhere & short to ground? If the breaker is
>unsuitable for a crowbar circuit, it is just as unsuitable to open the
>same circuit if there is an insulation failure on the wire & it touches
>a grounded portion of the airframe.
>
>Negatory, the normal length of wire between the CB and the alternator or
>regulator will reduce the current by resistance and inductance a little
>bit,
>and that is enough to allow the 5A breaker to work as designed. In the case
>of the OVP/CB, this grounding can be a very large current. (but it depends
>on layout....). Also real short circuits are rarely "slammed down hard to
>ground".
>
>
>>>I haven't seen anyone say that repeated trips of the breaker due to hard
>>>
>>>
>shorts is a good thing. Most breakers aren't designed for high cycling
>counts; they are just there to protect against the (hopefully) rare
>catastrophic event. If there is repeated cycling, the problem needs to
>be fixed, not designed around with some high tech circuit. If I have
>hundreds of trip events of a circuit breaker & it eventually fails to
>protect the circuit, I'm probably getting what I deserve. On the other
>hand, if it won't protect against at least a few catastrophic short
>events over the life of the a/c, I've wasted my money on that
>high-dollar breaker.
>
>Correcto. And since breakers don't have "History Recorders" on them, it's
>hard to know. Even the first trip can be a problem operated outside of the
>manufacturers specs. Maybe you'll get lucky. Or maybe you'll be in
>Huatabampo Mexico (a very nice town, but not many replacement parts).
>
>But Eric, if the crowbar is after the alternator field breaker, all the
>wire between the battery & the breaker & >load mentioned in your argument
>is still there (or not there). If the breaker is in danger from the
>crowbar, it >follows that it is in danger from an inadvertent short
>circuit. Yet alternator field circuit breakers seem to have >survived as a
>design since the dawn of alternators in a/c.(If I could be convinced that
>this 'slam down' technique >really is dangerous, why do I need dozens of
>extra components to solve the problem? Why not just use one of >those
>gadgets with inverse temperature coefficient used to soft start
>incandescent lamps (sorry; I forget the >name of the device> in series with
>the crowbar?)Charlie
Charlie, I have decided that this whole issue would be easier if I released
the design of my Linear OVM. (email me if you want the PDF). A kit-built
version is still unlikely but perhaps Bob or somone will make something
similar.
The circuit breaker current is limited by the impedance (the combined
resistance and inductance and other contributions to reducing the current).
This is highly dependent on wiring layout.
>>why do I need dozens of extra components to solve the problem?..........
Which parts would you like me to remove (as Mozart might have said)? And why
is my income tax form so complicated?
The devil is in the details. Yes, there are other ways to do this. A
thermistor might be one way. To lower the peak current throught the CB, even
a loop of wire will help.
Regards,
Eric M. Jones
www.PerihelionDesign.com
113 Brentwood Drive
Southbridge MA 01550-2705
(508) 764-2072
"Everything you've learned in school as "obvious" becomes
less and less obvious as you begin to study the universe.
For example, there are no solids in the universe. There's
not even a suggestion of a solid. There are no absolute con-
tinuums. There are no surfaces. There are no straight lines."
- R. Buckminster Fuller
Message 2
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| Subject: | Re: crowbar method |
--> AeroElectric-List message posted by: "Robert L. Nuckolls, III" <nuckollsr@cox.net>
>
>
>But Eric, if the crowbar is after the alternator field breaker, all the
>wire between the battery & the breaker & load mentioned in your argument
>is still there (or not there). If the breaker is in danger from the
>crowbar, it follows that it is in danger from an inadvertent short
>circuit. Yet alternator field circuit breakers seem to have survived as
>a design since the dawn of alternators in a/c.
>
>(If I could be convinced that this 'slam down' technique really is
>dangerous, why do I need dozens of extra components to solve the
>problem? Why not just use one of those gadgets with inverse temperature
>coefficient used to soft start incandescent lamps <sorry; I forget the
>name of the device> in series with the crowbar?)
The trade name for these devices is Polyswitch. These are
the same devices that EXPBus and Greg Richter have embraced
as their circuit protectors of choice. See:
http://www.circuitprotection.com/polyswitch.asp
These are simply replacements for breakers and fuses and have
no ability to sense and react to an ov condition.
There were two major drivers in design goals for the development
of the crowbar system 25 years ago. (1) replace expensive/troublesome
relays with a solid state device and (2) reduce if not eliminate all
increase of power pathway resistance between the bus and a
voltage regulator.
Popular voltage regulators of the time did not have separate
bus sense and field power leads. This opens the door for voltage
regulator instability (bouncing ammeter syndrome) as aging
of components between regulator and bus increase the series
resistance to the point where the regulator becomes unstable.
(I'm working on an article that addresses this phenomenon
in response to an AeroElectric List posting concerning
a bouncing ammeter).
Many articles have been written about the cure for bouncing
ammeter syndrome wherein the writer speaks to replacement of
some component as being the cure . . . when in fact, resistance
of ALL components in the power pathway contribute to the effect
and replacing one of them simple reduces TOTAL resistance to
some value below the threshold of instability.
In a nutshell, the article I'm working on suggests that 30+
year old airplanes that present with the bouncing ammeter
syndrome will benefit from complete replacement of all ohmic
(pressure joints) in wiring between the bus and the regulator.
Total refurbishment will put the airplane back into a factory
new condition for this pathway offers a high probability
of 30 more years of stable operation. Replacing but one of
several contributors to the problem will 'cure' the
instability for a relatively short time.
Crowbar ov protection was an ideal solution to part of this
problem because it inserted NO series resistance into the pathway
it controlled. Further, its parts count was quite low and
the design problems with system integration for controlling
nuisance trips were achievable.
Folks have suggested there was no good reason for doing
ov protection this way . . . but had they read any of the
history of the philosophy and understood all the design goals
then perhaps the reasoning would have been clear.
Unusual? Yes, but it was not considered and adopted as
a passing fad. There were reasons traded off with system
integration issues to be solved. And except for instances
where individuals with agendas inserted themselves into
the relationship between honorable suppliers and customers
who were entitled their money's worth, the concept has
performed well in the field.
Bob . . .
Message 3
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| Subject: | Re: crowbar method |
--> AeroElectric-List message posted by: "Robert L. Nuckolls, III" <nuckollsr@cox.net>
>
>Charlie--A short circuit can produce high currents limited only by the
>circuit impedance. This impedance can be very very low. That's the problem.
>At 14.5 volts, a short of 0.001 ohms is 14500 amps. Of course your 5A
>circuit breaker would emit gamma rays at this current. (I'm not kidding).
>Lucky for us, in the real world the circuit breaker will probably not have
>to handle such a current, but the crowbar/CB combination WILL suffer damage
>as currently designed. Bob and Paul argued the exact current---but in
>summary it depends on where the battery is and what the battery is.
The battery is but ONE of many contributors to source impedance.
Judicious use of crowbar ov protection demands that one not
design for worst case fault currents during the crowbar event
and by inference (if nothing else) our wiring diagrams suggest
far less than worse case installations.
Nowhere do we suggest that the system should be assembled with
a .003 ohm circuit breaker and zero lead lengths between the
bus and the crowbar device. So the hypothesized 700, 500
and/or 14,500 amp current flows simply never happen. The
biggest 24 volt batteries we install at RAC will only dump
about 3000 amps with a dead short on their terminals . . .
so be wary of writers who toss around really big numbers
to impress . . . they don't happen in real life.
Which leaves us debating whether one should design the system
to avoid damaging a breaker (which has yet to be demonstrated)
during what should be a very rare event or should we concentrate
on getting a failed alternator disconnected first and worry
about circuit breaker life later?
By the way, a runaway alternator disconnected from the bus
by opening a b-lead contactor will continue to run to its
own destruction. So, if the ovp system has to operate for
a real ov event in an automotive alternator installation,
overstress to the circuit breaker is going to be a trivial
concern.
I'll suggest that one not even consider the battery's
source impedance in controlling crowbar fault current.
ASSUME zero source impedance. Now, build enough loop
resistance into the system by simply following the
installation instructions and you'll be just fine.
Bob . . .
Message 4
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| Subject: | The fatwire ground blues . . . |
--> AeroElectric-List message posted by: "Robert L. Nuckolls, III" <nuckollsr@cox.net>
>Comments/Questions: I am implementing your dual alt/batt/buss system on my
>GA-III. I fried a ground wire(lots of smoke)due to a loose battery ground
>connection while cranking the starter! The fried wire went to the fuel
>flow sensor mounted on the engine block. The starter return current tried
>to use the smaller wire due to a loose battery ground connector to the
>Alt-Battery. Should the sensors(Vision Micro) mounted on the engine block
>(fuel flow, fuel press, oil temp, oil press) have ground wires that
>connect to the engine block? These wires can be potential return paths for
>heavy starter current with a loose (-) battery connection.
I'm not sure I visualize exactly what happened
here. My recommendation is that all high current grounds
like crankcase and battery(-) leads come to a firewall
ground stud as illustrated in Chapter 5 of the 'Connection.
Your experience is not uncommon. Folks on the airport we
owned had two wire-smoking incidents similar to yours
for the 6 months we had the business!
Careful adherence to the ground architectures described
in Chapter 5 will reduce noise and possibly prevent a
recurrence . . . IF you are mindful of doors that open
every time you unhook a 'fat' wire and being careful that
they're all put back before you attempt to operate the
system . . . ESPECIALLY crank the engine.
Bob . . .
Message 5
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| Subject: | RE: [luscombe-silvaire] Need help with Apollo GPS |
--> AeroElectric-List message posted by: "Jim Ivey" <jim@jimivey.com>
Back on the list. I was bumped while in OSH for some reason. Catching up
and saw Bill's request on the Apollo unit. So if you're not interested
don't bother reading the "too much information" below:
Bill:
The 360 GPS is updated with a DOS-based transfer program provided on the
program diskette. I have both. The program is very, very basic and merely
loads the new dataset into the unit. It is not Windows and has not been
updated since about 1996. Works fine. You are, however, offered the option
of saving existing user waypoints first to restore them after a new database
is loaded. The software does not show any of the display on the unit
itself. When the GPS was initially purchased it came with a computer
interface connector to be located on the panel somewhere so updates would
not require the removal of the unit. If your unit is used it may not have
this remote serial connector. Also, many avionics shops skipped this step.
If you don't have that then you may have to remove the unit in order to
update. Pin-Out diagrams are included in the installation manual. When you
order a database update from Garmin AT it will arrive on a second diskette
the program will load.
However, the unit does output about 3 different versions of serial data. I
send moving-map serial data to my EDM800 engine monitor and it uses that
information in fuel calculations. You can also use this output to run a
third-party software such as Anwywhere Map, AirGator, Mountainscope or even
the likes of an Aspen Avionics AT300 multifunction display. Check with the
software manufacturer. Use the pin-out diagram to make your own cable or
hire your local avionics tech to do it for you (be sure they use shielded
cable for serial cable and ground shield at source end). The Apollo (UPSAT,
GarminAT?) kit cables are strictly set up for database updates and do not
contain the wires for data output for other devices.
In summary, if you need to update the database use the diskette and cable as
described. To use the unit as a GPS source for a laptop you will need
somebody else's software and a custom cable. At that point you may like to
buy a stand-alone GPS engine like a Garmin 35 or Traker Blue (if you use
Bluetooth and don't want wires all over the cockpit).
Call the Garmin AT guys in Salem, Oregon and talk to them at 1-800-525-6726
ext.3991. They are very knowledgeable and nice and will talk to you about
your unit. They can also tell whether it has been updated to the advanced
display (easy to read) or not just by the serial number. It was a sobering
day for me when Garmin bought UPSAT. You'd be lucky if the unit is
supported beyond another year or so.
I can send a copy of the software diskette but don't have an extra data
cable for you. As for the database it has encryption so it can only be
loaded on one serialized unit ... no sharing possible.
Jim Ivey
P.S. Despite the 360 unit's slow frequency response to command inputs, most
knowledgeable technicians will tell you that the GPS 360 (or 920 handheld)
had the most reliable and accurate GPS engine ever produced. Antiquated in
GPS years, but bulletproof. I own 2 and would like to have 3. If you buy
one on eBay or Trade-A-Plane get the serial no. before bidding and call the
factory to see if it has all the updates and what the repair history is.
-----Original Message-----
From: luscombe-silvaire@yahoogroups.com
[mailto:luscombe-silvaire@yahoogroups.com] On Behalf Of WRBYARS@aol.com
Subject: [luscombe-silvaire] Need help with Apollo GPS
Greetings to All,
I'm in a bit of a dilemma with my Apollo 360 GPS Moving Map Unit, (round
unit installed in the panel) which was installed with the latest data in
1997.
This unit can be upgraded by using a lap top computer with an "upgrade card"
in the floppy drive, connected to the GPS with a serial cable, according to
the Installation Guide.
Does anyone have a recent "up grade card", and cable to connect up with that
they would sell, loan, rent, whatever?
Here is the info that the "Guide" gives on these items.
PC Interface Kit (564-0052), which includes a program diskette (31/2"),the
data cable (500-0263), and a reference guide.
Data Cable (500-0263), a 25 pin on the GPS end, to a 9 pin dsub COM port on
the PC.
Also does anyone know if the GPS unit, when hooked up to a color lap top,
will display the same info on the lap top that is on the "Mother" unit on
the panel, and although the original unit display is in black & white, would
the lap top display the info in color? If it will, then the "co-pilot"/
passenger could have a larger, in color, view, to assist the pilot with.
Sorry this is so long, however I know there is a lot of Very Knowledgeable
folks out there on the list, and I very much need your help.
Thanks
Bill
_____
=09
* Visit your group "luscombe-silvaire
<http://groups.yahoo.com/group/luscombe-silvaire> " on the web.
* To unsubscribe from this group, send an email to:
luscombe-silvaire-unsubscribe@yahoogroups.com
<mailto:luscombe-silvaire-unsubscribe@yahoogroups.com?subjectUnsubscribe>
<http://docs.yahoo.com/info/terms/> .
_____
Message 6
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| Subject: | Bad Alternator ground on V-Tail! |
--> AeroElectric-List message posted by: "Ronald J. Parigoris" <rparigor@suffolk.lib.ny.us>
I was working on Europa build over weekend, and a guy with a V-Tail across way
was working
on his V-Tail. No alternator output.
I will note I helped him change it about 6 months ago, and he was having a hard
job
fitting it in place. It ended up whoever rebuilt it, or made it got paint on the
flange, I
helped him cover up everything, and did a shoeshine with a cut piece of 1 x 42
belt
sander.
OK till now. No charge. he went after all connectors, and it seemed to work. then
after
fuel it quit. he started to show me and it worked again!
There was play between the 2 halves of the alternator! It was safety wired, but
I suspect
whoever did the painting got carried away, and got it on the mating surfaces inside
the
alternator. Once the paint wore away due to vibration and heat, things got loose.
The hold
down screws were heavily corroded as they were making that intermittent connection
between
the 2 halves sometimes, and the stacked pieces of metal between the 2 halves were
pretty
corroded as well.
The screws looked 50 years old, when I am pretty certain they were new 6 months
ago.
Ron Parigoris
Message 7
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| Subject: | Re: Bad Alternator ground on V-Tail! |
--> AeroElectric-List message posted by: "Robert L. Nuckolls, III" <nuckollsr@cox.net>
At 02:13 PM 8/1/2005 -0400, you wrote:
>--> AeroElectric-List message posted by: "Ronald J. Parigoris"
><rparigor@suffolk.lib.ny.us>
>
>I was working on Europa build over weekend, and a guy with a V-Tail across
>way was working
>on his V-Tail. No alternator output.
>
>I will note I helped him change it about 6 months ago, and he was having a
>hard job
>fitting it in place. It ended up whoever rebuilt it, or made it got paint
>on the flange, I
>helped him cover up everything, and did a shoeshine with a cut piece of 1
>x 42 belt
>sander.
>
>OK till now. No charge. he went after all connectors, and it seemed to
>work. then after
>fuel it quit. he started to show me and it worked again!
>
>There was play between the 2 halves of the alternator! It was safety
>wired, but I suspect
>whoever did the painting got carried away, and got it on the mating
>surfaces inside the
>alternator. Once the paint wore away due to vibration and heat, things got
>loose. The hold
>down screws were heavily corroded as they were making that intermittent
>connection between
>the 2 halves sometimes, and the stacked pieces of metal between the 2
>halves were pretty
>corroded as well.
>
>The screws looked 50 years old, when I am pretty certain they were new 6
>months ago.
Good detective work. Thanks for giving us the story.
They say the devil is in the details . . . and I can
attest to that. Worked a problem a few years ago on a
pitch trim system where many $millions$ in warranty and
untold cost in customer dissatisfaction was rooted on
a material change of brake material from asbestos (EPA
strikes again!) to cork.
Bob . . .
Message 8
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| Subject: | Re: I've got a secret |
--> AeroElectric-List message posted by: "RV Builder (Michael Sausen)" <rvbuilder@sausen.net>
No kidding. Man, has it been 6 months already. How time flies between mud slinging
contests. The delete key was invented for a reason folks. Oh ya, and
thanks to everyone who has contributed to filling the archives with this meaningless
crap by not adding:
DO NOT ARCHIVE
-----Original Message-----
From: owner-aeroelectric-list-server@matronics.com [mailto:owner-aeroelectric-list-server@matronics.com] On Behalf Of Gerry Holland
Subject: Re: AeroElectric-List: Re: I've got a secret
--> AeroElectric-List message posted by: Gerry Holland
--> <gholland@gemini-resourcing.com>
What on earth is this all about!
I presume it's all fallout from Paul Messinger e-mail that gotten a negative response.
Does anyone know....or care!
>
> (oh no Riley don't filter! No one cares what you do)
>
>
> Riley:
>
> I thought we got rid of you.
>
> You deserve an award, for the most useless & hateful post.
>
> You post insults, trivial opinion or an unimportant & useless, I'll 2nd that.
>
> It's was much nicer with out you; Please just turn your computer off and go.
>
> Have a nice day, Dick
> Thanks George
Message 9
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| Subject: | Re: crowbar method |
--> AeroElectric-List message posted by: Charlie England <ceengland@bellsouth.net>
Robert L. Nuckolls, III wrote:
>--> AeroElectric-List message posted by: "Robert L. Nuckolls, III" <nuckollsr@cox.net>
>
>
>
>
>>But Eric, if the crowbar is after the alternator field breaker, all the
>>wire between the battery & the breaker & load mentioned in your argument
>>is still there (or not there). If the breaker is in danger from the
>>crowbar, it follows that it is in danger from an inadvertent short
>>circuit. Yet alternator field circuit breakers seem to have survived as
>>a design since the dawn of alternators in a/c.
>>
>>(If I could be convinced that this 'slam down' technique really is
>>dangerous, why do I need dozens of extra components to solve the
>>problem? Why not just use one of those gadgets with inverse temperature
>>coefficient used to soft start incandescent lamps <sorry; I forget the
>>name of the device> in series with the crowbar?)
>>
>>
>
> The trade name for these devices is Polyswitch. These are
> the same devices that EXPBus and Greg Richter have embraced
> as their circuit protectors of choice. See:
>
>http://www.circuitprotection.com/polyswitch.asp
>
> These are simply replacements for breakers and fuses and have
> no ability to sense and react to an ov condition.
>
>
> <> snip
> <>
> Bob . . .
Actually, I was talking about retaining the standard crowbar circuit &
breaker & just adding a single component (the gadget that is
occasionally used to avoid large inrush current in incandescent lights)
in series with the crowbar contacts that would force a ramp up of
current through the trip threshold of the breaker instead of the dreaded
'slam dunk' overcurrent Eric's worried about. I only mentioned it to
show that some elaborate multicomponent top secret circuit isn't needed.
The primary point of my post was that if a breaker can handle rare 'slam
dunk' overcurrents due to faulty wiring, it can also handle the crowbar
circuit. I see no need for any additional components.
Charlie
Message 10
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--> AeroElectric-List message posted by: "Hinde, Frank George (Corvallis)" <frank.hinde@hp.com>
With my all electric airplane (Lycoming with Emags and elctric fuel
pumps only) I have found that by using a simple com radio (backup to GNS
430) in receive mode and transponder I can get my total current draw
down to a shade under 8 amps which fits nicely into the SD-8 backup.
Using Bob's 3 buss design I can easily save my battery reserve to do the
approach/run the lights for when I land.
The above assumes I run only one fuel pump (I have one in each wing
root) and one Emag.
Having a Pmag on a dual alternator systems seems like two layers of
redundancy to me...Do we agree?
Thanks
Frank
Message 11
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| Subject: | Re: crowbar method |
--> AeroElectric-List message posted by: "Robert L. Nuckolls, III" <nuckollsr@cox.net>
>
>
>Actually, I was talking about retaining the standard crowbar circuit &
>breaker & just adding a single component (the gadget that is
>occasionally used to avoid large inrush current in incandescent lights)
>in series with the crowbar contacts that would force a ramp up of
>current through the trip threshold of the breaker instead of the dreaded
>'slam dunk' overcurrent Eric's worried about. I only mentioned it to
>show that some elaborate multicomponent top secret circuit isn't needed.
>
>The primary point of my post was that if a breaker can handle rare 'slam
>dunk' overcurrents due to faulty wiring, it can also handle the crowbar
>circuit. I see no need for any additional components.
>
>Charlie
Aha! Understand. It's been proposed that adding a resistor
in series with the crowbar module would mitigate the
crowbar fault current . . . which is correct. However,
It runs contrary to some original design goals.
One of the neat things about the crowbar technique is that
supply voltage to the alternator regulator is clamped off at
about 2 volts immediately after the SCR triggers. This means
that the ov condition is cooling off even before the
breaker opens. Adding this resistor would increase parts
count, adds a mechanical issue for packaging (see photos)
http://www.aeroelectric.com/Pictures/OVM-14_A.jpg
http://www.aeroelectric.com/Pictures/OVM-14_B.jpg
http://www.aeroelectric.com/Pictures/OVM-14_B.jpg
Finally, added resistance would have increased excitation
voltage available to the regulator while the breaker was
deciding to trip . . . and it takes longer to decide
due to reduced fault current. This would have reduced
effectiveness of the system while offering no benefits
I could demonstrate.
Adding the mitigation resistance any place else would
have driven up the bus-to-regulator pathway resistance.
This was root cause of numerous regulator instability
problems.
Your supposition is correct. The breaker in B&C's test
stand for their regulators has experienced thousands
of crowbar events (150 A or so in 14v mode, 300A in
24v mode) and last time I checked with Tim, the breaker
in place today was the one I installed there about
15 years ago. Granted, it's a high-end product equal
to the miniature breakers used in the majority of our
aircraft at RAC.
As I pointed out in an earlier post, this class of
breaker is routinely qualified in test situations where
potential interrupt currents are limited only by
resistance of the breaker itself (28v/.04 = 700A).
I suspect this is where the original 700A figure came from
and was proffered as a "worst case" condition. Thing
is, the product is never installed in a way that this
condition can be realized.
Bob . . .
Message 12
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| Subject: | Crowbar CB "problem" |
--> AeroElectric-List message posted by: "Troy Scott" <tscott1217@bellsouth.net>
Bob, Charlie, Eric, All,
If there's really a concern about the possible inappropriateness or lack of
reliability of a common CB in the Crowbar OVP application, why not just use
a fuse? It could be located in an easy-to-reach spot. We could carry a few
spares..... What's the big deal?
Regards,
Troy
Message 13
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| Subject: | Re: Crowbar CB "problem" |
--> AeroElectric-List message posted by: Fiveonepw@aol.com
In a message dated 08/01/2005 5:11:36 PM Central Standard Time,
tscott1217@bellsouth.net writes:
why not just use
a fuse?
>>>
One advantage of breaker is notification of OV event- you'll see it popped
out...
Mark
Message 14
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| Subject: | Re: Diode orientation |
--> AeroElectric-List message posted by: Charlie Brame <chasb@satx.rr.com>
Bob,
Thanks for the reply. You, and others, pointed out that the small band,
regardless of the color, indicates the "cathode" end. That solved my
problem - the various colors had me confused. As you surmised, the
Navaid manual uses a "comic book" wiring diagram.
As to the need to hook the comm to the autopilot, I quote from the
Navaid manual:
" The diode installed in series with the push-to-talk line,
together with the wire connected from the PTT switch to pin 7, are used
to kill the signal to the servo while the PTT switch is depressed. This
prevents the servo from jumping around due to the presence of high level
RFI on the servo power lines. The servo stays engaged during the voice
transmission, but it does not move until normal operation is restored by
releasing the mike button."
The manual goes on to say that a metal airplane with shielded wires
probably will not have a RFI problem, but that a composite airplane with
unshielded wires probably will. My RV is metal, of course, but I have an
obvious RFI problem with my unshielded trim indicator circuitry, so I
figured connecting the diode as shown was good insurance.
Charlie
RV-6A N11CB
San Antonio
-------------------------------------------------------
> Time: 08:08:11 PM PST US
> From: "Robert L. Nuckolls, III"
> Subject: Re: AeroElectric-List: Diode orientation
>
> --> AeroElectric-List message posted by: "Robert L. Nuckolls, III"
>
>
> At 10:20 AM 7/30/2005 -0500, you wrote:
>
> >--> AeroElectric-List message posted by: Charlie Brame
> >
> >Bob, et al,
> >
> >My Navaid installation manual recommends a diode between the Navaid pin
> >7 and the Comm PTT circuit. The Navaid schematic shows a black and white
> >diode with a large white area and a small black stipe on one end. The
> >white area is oriented toward the Comm unit and the black stripe
> >oriented toward the PTT circuit. However, the diode I received from B&C
> >is mostly black with a small grey stripe at one end.
> >
> >Can I assume that the large black end of the diode equates to the large
> >white end on the Navaid schematic?
>
>
> The descriptions you're making for the parts and wiring
> diagram are don't give us a clear image of the instructions.
>
> Most wire lead diodes have a "band" on one end and the color
> of the band is insignificant. It will be some color that
> contrasts with the body color of the diode itself.
>
> The banded end corresponds to the "cathode". In a diode's
> schematic, the "bar" touched by the arrowhead is the
> cathode while the arrowhead itself is the anode. Electrons
> flow through a diode in opposition to direction of arrow.
> See:
>
> http://www.aeroelectric.com/Pictures/Diode_Wiring_2.jpg
>
> Some folks are confused when they see diodes used for two
> different tasks like "steering" as shown in -A- and -B-
> and spike clipping as shown in -C- and -D-.
>
> Do you have a real schematic of the wiring were the
> bar and arrowhead are seen in the classic diode symbol
> . . . or is it a comic book wiring diagram that shows
> only pictures? Sounds like you're working with the latter.
>
> In this case, go by which end has a band on it irrespective
> of color. Do they say what this diode is supposed to do?
> I'm mystified by the need hook any part of your comm transceiver
> to the autopilot.
>
> Bob . . .
>
>
Message 15
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| Subject: | Two Mags & One Input to Electric Tach |
--> AeroElectric-List message posted by: "r falstad" <bobair8@msn.com>
I would like to use a Radio Shack submini DPDT switch so my Westach/Westberg Mfg.
electric tach can read RPM on each magneto. I'm thinking of running a single
conductor shielded 18 AWG wire from each mag switch (the same wire I'm going
to use for the "P" leads) to the DPDT switch. I'll terminate the conductors
and the shields separately for each side of the switch so when I throw it, I
won't have the shield from the other "P" lead making contact as I would have to
do if I used a SPDT switch.
Does this sound like it will work?
Best regards,
Bob
Message 16
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--> AeroElectric-List message posted by: "Steve Sampson" <SSampson.SLN21@london.edu>
Bob - before my machine crashed i had some simple software to read and modify Z-11
for instance. I had downloaded it from a reference on your web site. Cant
find it now. Can you point me to the downloads.
Thanks, Steve.
Message 17
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| Subject: | Official Usage Guideline [Please Read] [Monthly Posting] |
DNA: do not archive
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Dear Lister,
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Thank you,
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Matronics Email List Administrator
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