Today's Message Index:
----------------------
1. 05:04 AM - Re: Re: Internally regulated alternator OVP protection (Steve Goldman)
2. 06:58 AM - Re: source for S700 series switches (Robert L. Nuckolls, III)
3. 07:45 AM - Battery Help ()
4. 08:09 AM - Re: Re: Internally regulated alternator OVP protection (Ken)
5. 08:12 AM - Re: Re: Internally regulated alternator OVP protection (Ken)
6. 09:18 AM - Re: Warning light press-to-test circuitry (Robert L. Nuckolls, III)
7. 09:43 AM - Re: Battery Help (Gerry Holland)
8. 10:32 AM - Re: Re: Internally regulated alternator OVP protection (George Braly)
9. 02:02 PM - Apex NC seminar June 4/5 (Robert L. Nuckolls, III)
10. 02:46 PM - "Optimum" antenna coax length for GPS? (Robert L. Nuckolls, III)
11. 02:58 PM - Re: Re: Master/Starter Contactor connection (Robert L. Nuckolls, III)
12. 03:20 PM - Re: Internally regulated alternator OVP protection (Eric M. Jones)
13. 03:31 PM - Re: Re: Internally regulated alternator OVP protection (George Braly)
14. 04:20 PM - off-topic - thick cessna windshield (rd2@evenlink.com)
Message 1
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| Subject: | Re: Internally regulated alternator OVP protection |
clamav-milter version 0.80j
on hestia
--> AeroElectric-List message posted by: Steve Goldman <steve@fatcatair.com>
gmcjetpilot@yahoo.com wrote:
>
> I have to assume when over voltage is sensed (17V) the IC will try to shut the
field (MOSFET) down. So if the OV is the symptom of a FET failure, than yes
it will detect a failure, but agreed this is not very predictive. Also the rotor
short protection (detection) although not a direct indication of the FET shorting
as I might have assumed, I wonder if a FET failure could appear as a field
short (ie increasing field current like a field short).
>
>
I would hope that this is not the only thing the OVP is trying to do. The reason
the
voltage is over spec is that the regulator, which is controlling that very same
transistor to modulate field currents, is not able to do its job.
For the OVP design to assume that the reason the OV condition exists is that the
rest of the
regulator itself is failing but that the hardest working component in the regulator
is still functional would be serious design mistake. It wouldn't be a mistake for
the OVP circuitry to try this, but it would be a mistake if it was its only recourse.
--
Steve
Message 2
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| Subject: | Re: source for S700 series switches |
--> AeroElectric-List message posted by: "Robert L. Nuckolls, III" <b.nuckolls@cox.net>
At 03:04 PM 4/29/2005 -0400, you wrote:
>--> AeroElectric-List message posted by: sportav8r@aol.com
>
>
>Besides B & C, where can I shop for S700 series / Carling / C&H
>switches? I'm compiling a vendor list before embarking on a total re-do
>of my panel (now that I've read the 'Connection)
>-Stormy
Get on the Internet . . . there are dozens of major parts houses
and thousands of minor sources. The big guys are Allied, Newark,
Digikey, Hosfelt, Mouser, Halted Specialties, etc.
Take care lest the $time$ you spend trying to optimize your
purchasing dollar dilute the value of dollar because of the
$time$ you spend.
At every opportunity to do a skunk works project for RAC,
I will order materials on my credit card from one of the
BIG guys and ask for overnight shipping. I don't even
wait until the whole list of parts are identified. I and
my techs will any quantity and kind of item as soon as
the need is identified.
On one particularly hurry-up project a few years ago
my local purchasing guy got wind of what I was doing and
wrote my boss a rather terse memo. He was upset that I
was "paying $15 overnight charges (and sometimes $5 extra
on orders under $25) just to get around the value
of his services". When the dust settled on the job, I
looked at all of our orders which totaled just over 20.
Assuming we paid the worst possible penalties for each
order, my shipping overhead for the task was about $400.
We had the parts delivered to my front doorstep so nothing
got lost in receiving and no RAC folks touched the parts
thus adding more overhead $time$. We figure it
costs RAC about $250 just to process the paper for one
minimal purchase order and even then, we can only purchase
materials from 'approved' suppliers. Some of my favorite
suppliers were not on RACs approved list.
Bottom line was that the shortest and least costly
distance between needing and receiving was my
credit card and keyboard. Every other 'service'
offered only made the task more difficult (it takes
as much no-value-added time to fill out a purchase
request as it did to place the order ourselves). It was
also risky (little packages get lost in the mountain
of incoming freight) and expensive in terms of other
$time$ adders (the receiving dock was 7 miles from my
lab). My boss apologized for upsetting the gentleman
but reminded him that our customer expected the very
best we could offer in terms of delivery and that the
'system', while useful for buying trainloads of rivets
and aluminum, simply did not make sense for the task at hand.
If you enjoy this kind of exercise, by all means, have
at it. This IS after all, just an expensive hobby.
However, if your task is to produce a product to your
design goals in with a minimum expenditure of total $time$
then $time$ spent to save $time$ may not be adding value
to your effort.
Bob . . .
Message 3
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--> AeroElectric-List message posted by: <bakerocb@cox.net>
AeroElectric-List message previously posted by: "Matt Prather"
<mprather@spro.net>
<<Is there any chance you could disect the battery pack you have and
repopulate
it with new batteries? Matt>>
4/30/2005
Hello Matt, Thanks for your input -- I'll suggest that to my friend. I know
that other people have used that method on other battery powered units such
as cordless drills, etc.
Some of the ni cad battery cases on the hand held avionics units are so well
put together / molded that dissecting them constitutes near destruction of
the battery case. From a volume and voltage aspect stuffing the right amount
of alkaline or other batteries inside the ni cad case and making the proper
electrical connections could be a challenge. Also some of the ni cad battery
cases are so integral to the shape of the hand held unit that the presence
of the designed battery case is essential to the handling / fastening / use
of the hand held unit.
I think my friend is actually lucky that he can power his Garmin GPS Comm
with a cigarette lighter cord. I don't have any such provision on my ICOM
IC-A4. Attaching a battery case with either the designed ni cad or alkaline
batteries appears to be the only option for operation of that unit.
OC
Message 4
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| Subject: | Re: Internally regulated alternator OVP protection |
--> AeroElectric-List message posted by: Ken <klehman@albedo.net>
I would tend to think that if such fusing really exists and is
intentional - it is there because the designer considers that the
possiblility of an uncontrolled alternator runaway is significant enough
to warrant it...
Ken
>-Internal alternators incorporate a fuse that prevents alternator from melt down
if an OV condition occurs, protecting the airframe, but it may not act fast
enough to prevent avionics equip damage.
>
>snip
>
>The ND I have, uses a current limit / fusing device; unfortunately its not a diode
as you speak of. From the Berkeley ref above, it points to the fact this
kind of device has a disadvantage in that they can withstand currents 10 times
their normal rating for prolonged time (a fraction of a second?). To get the
recommend 1ms failure the fuse cant have more than 4 times norm capacity. So as
an absolute back up to save your avionics from OV, it is not going to help much;
however, it will assure the alternator will die at some point, sooner than
later without catching on fire. Which is real important to anyone using a ND
alternator.
>
>
>snip
>
>
Message 5
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| Subject: | Re: Internally regulated alternator OVP protection |
clamav-milter version 0.80j on hestia
--> AeroElectric-List message posted by: Ken <klehman@albedo.net>
Hi Steve
Yes that is precisely the main point. There is no other part in there
that we know of capable of reducing the field current before the voltage
gets out of hand. It might be oversized, have temperature protection,
and not be highly stressed in the newer designs though...
Ken
Steve Goldman wrote:
>--> AeroElectric-List message posted by: Steve Goldman <steve@fatcatair.com>
>
>gmcjetpilot@yahoo.com wrote:
>
>
>
>>I have to assume when over voltage is sensed (17V) the IC will try to shut the
field (MOSFET) down. So if the OV is the symptom of a FET failure, than yes
it will detect a failure, but agreed this is not very predictive. Also the rotor
short protection (detection) although not a direct indication of the FET shorting
as I might have assumed, I wonder if a FET failure could appear as a field
short (ie increasing field current like a field short).
>>
>>
>>
>>
>I would hope that this is not the only thing the OVP is trying to do. The reason
the
>voltage is over spec is that the regulator, which is controlling that very same
>transistor to modulate field currents, is not able to do its job.
>
>For the OVP design to assume that the reason the OV condition exists is that the
rest of the
>regulator itself is failing but that the hardest working component in the regulator
>is still functional would be serious design mistake. It wouldn't be a mistake
for
>the OVP circuitry to try this, but it would be a mistake if it was its only recourse.
>
>
>
Message 6
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| Subject: | Re: Warning light press-to-test circuitry |
--> AeroElectric-List message posted by: "Robert L. Nuckolls, III" <b.nuckolls@cox.net>
At 10:45 PM 4/29/2005 -0400, you wrote:
>--> AeroElectric-List message posted by: Fiveonepw@aol.com
>
>In a message dated 04/29/2005 12:15:01 PM Central Standard Time,
>retasker@optonline.net writes:
>do I isolate the lamp for it's "everyday" purpose, but connect it to the
> >>>others for testing?
> >>>>
>
>Went through the same concern while planning my LED annunciator panel. Asked
>the same question on the A-list and Bob N. reminded me that during normal
>power up and engine start, most annunciators "should" activate in one
>fasion or
>another, telling you the lights are working plus provide real-world
>operational
>checks as well. (which is why they're there anyway!) Master on = oil p,
>alt, flaps, canopy and EIS warning all active, flaps up turns that one of,
>ditto
>for canopy latched. Engine start knocks out the rest for a clean annunciator
>for taxi. Put the items of interest on your checklist and launch. If any
>particular light does or does not light when appropriate, good time to
>shut down
>and investigate. Has worked very well for me after 175 hours...
I've been watching this thread and I believe the majority
of salient points have been covered. Thanks to all the participants.
I'll only add to the discussion with a review of the history
of press-to-test for lamp driven annunciators.
The P-t-T fixture has been around since WWII. There first were
single lamp holders with various colors for lenses and a MECHANICAL
shutter for dimming. Here's a modern, miniature version.
http://www.aeroelectric.com/Pictures/PTT_Dim_Fixture.jpg
I have one of ol' boss hogg fixtures from the WWII era
around here somewhere but couldn't put my hands on it in
time for this picture. Maybe later.
Anywho, this clever product allowed installation of individual
annunciator/indicator lamps as needed and provided dimming
and testing in the one package. Cool.
The thrust of wanting to test back then was that incandescent
lamps were known to burn out. They had limited service
lives. Further, since each fixture had but one lamp, it
was useful to be able to push the fixture to test lamp
integrity at any time.
Over the years, individual incandescent fixtures were
replaced with arrays of lighted screens with various
legends to inform/warn pilots of some activity. We
put TWO lamps into each fixture so as to eliminate
the possibility that loss of one lamp would mean loss
of that informative function.
Keep in mind that local PTT functions do but one thing,
prove integrity of the lamp. You can have wiring and
all manner of sensors and switches go bad such that
you loose one annunciator. Pressing a button to see
all the lights come on may be reassuring to some but
it tests only a tiny fraction of the whole system . . .
light bulbs.
When I design important electro-whizzies, there's a
test input pin that can be exercised with a push-button
on the panel. I use this input as a command to do
as much INTERNAL VERIFICATION OF FUNCTIONALITY as
possible. Hitting the PTT button and getting some
predictable behavior from the annunciator has much
a great deal more meaning and assurance of system
integrity.
In the mean time, very long lived LEDs have replaced
the limited life lamps for annunciation and indication.
But the PTT button for testing lamps seems to have
persisted. I'll suggest that unless a proposed PTT
system does more than illuminate LEDs, that adding
the PTT system reduces reliability (lots of extra
wiring, diodes, etc), increases $time$ to fabricate
and install the system and ultimately tells you
nothing of interest when you push the button.
Bob . . .
Message 7
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| Subject: | Re: Battery Help |
--> AeroElectric-List message posted by: Gerry Holland <gnholland@onetel.com>
> --> AeroElectric-List message posted by: <bakerocb@cox.net>
>
> AeroElectric-List message previously posted by: "Matt Prather"
> <mprather@spro.net>
>
> <<Is there any chance you could disect the battery pack you have and
> repopulate
> it with new batteries? Matt>>
>
> 4/30/2005
>
> Hello Matt, Thanks for your input -- I'll suggest that to my friend. I know
Hi!
> I don't have any such provision on my ICOM
> IC-A4. Attaching a battery case with either the designed ni cad or alkaline
> batteries appears to be the only option for operation of that unit.
I think you can. Use:
CP-12/L CIGARETTE LIGHTER CABLE WITH NOISE FILTER: Allows you to charge the
connected battery pack (13.5 to 16 V DC required). For charging ONLY -- the
transceiver cannot be simultaneously operated.
With both A4 and A5 it will charge and be usable to so dont know why it
carries that warning.
Or wire in a supply permanently to your aircraft using:
OPC-254/L DC POWER CABLE: Allows you to charge the connected battery pack
(13.5 to 16 V DC required).
Useful if you want the A4 as a backup and always to be charged when in
Aircraft. It is a pain that you cannot switch on whilst charging.
I have superceded my A4 with an A5 but did use the Cigarette lighter power
input with both.
Regards
Gerry
Message 8
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| Subject: | Re: Internally regulated alternator OVP protection |
--> AeroElectric-List message posted by: "George Braly" <gwbraly@gami.com>
After all of this, the one simple fact remains:
If the FET (or other transistor) switching the field fails in the normal way those
components fail (shorted) - - you will have an uncontrolled runaway alternator.
At this point, there is really not much more to be said about the issue. The
internally regulated automotive alternators have a known single point failure
mode that is unacceptable in normal aircraft design circles.
If people crashed when alternators failed - - it would be unacceptable for the
automotive world, too.
That is the distinction, and it makes all of the difference.
Regards, George
-----Original Message-----
From: owner-aeroelectric-list-server@matronics.com [mailto:owner-aeroelectric-list-server@matronics.com] On Behalf Of gmcjetpilot@yahoo.com
Subject: AeroElectric-List: Re: Internally regulated alternator OVP protection
--> AeroElectric-List message posted by: <gmcjetpilot@yahoo.com>
THANKS BOB, Great reply. The whole purpose of this discussion is not to worship
auto technology, but to know what you are praying for if you choose to sit in
that church pew.
One-liners: regarding auto alternators (voltage regulator) in your airplane:
-Power system test demonstrated 4.6 million hours MTBF (electronic)
-Expect a min 1/2 million hours MTBF (mean time between failure)
-Internal alternators incorporate a fuse that prevents alternator from melt down
if an OV condition occurs, protecting the airframe, but it may not act fast
enough to prevent avionics equip damage.
Bob, you asked 2 questions or clarifications:
>I didn't see that the IC knows anything about impending failures?
You are correct; nothing says it will predict a transistor is about to fail, as
I indicated. **However, the VR in the ND does have Over Voltage protection, as
do many I-VRs.**
If I have to make one point, internal VR do have OV protection. The question of
how effective or how they work is still up for debate. What does that mean?
I have to assume when over voltage is sensed (17V) the IC will try to shut the
field (MOSFET) down. So if the OV is the symptom of a FET failure, than yes it
will detect a failure, but agreed this is not very predictive. Also the rotor
short protection (detection) although not a direct indication of the FET shorting
as I might have assumed, I wonder if a FET failure could appear as a field
short (ie increasing field current like a field short).
>Where in the narrative do we find a feature that "senses impending overload"?
Predictive (impending) over load/temp may be overstating it. Besides the obvious
normal functions of any VR limiting voltage, there are references made to current
limiting and thermal-overload protection. I recall ND propaganda referring
to reducing alternator output in the event it becomes over heated, but I cant
find the specific technical reference, other than vague terms. Thermal protection
of what: IC, field driver transistor or alternator output rectifier? Many
ICs do have internal thermal shut down protection. Is that a function of alternator
over load? Could be. I found details that support thermal protection
and shut down of a power MOSFET by an IC for other applications, including stereos,
but nothing specific about this in alternator applications. Since FET failures
are preceded with increasing temp this could be somewhat predictive. Whether
any I-VR has thermal protection or not, I don't know, but it is well with
in the capabilities of off the shelf components
to do
this, just might not be cost effective for auto applications. (Keep your alternator
as cool as you reasonably can).
Quote: A power MOSFET contains thousands of parallel devices that are internal,
and you cannot individually protect them. This situation is similar to the well-known
phenomenon of secondary breakdown and you can take steps to avoid its
destruction. One way to overcome this problem is to directly sense the temperature
of the MOSFET by integrating the MOSFET with the controller, and the temperature
can be sensed directly on the FET die.
http://wind.eecs.berkeley.edu/~nesgaard/PATH%20Report%20on%20Power%20System%20Reliability.pdf
Data quoted for reliability of electronic components for individual components
and as a system. This ref is EXCELLENT, directly dealing with the topic at hand,
"power system reliability" (with an eye on protection of unbelievably advanced
automotive electronics which affects safety) Apparently auto technology in
the future will have active electronics with communication links, steering actuation
and collision avoidance using radar and Liar -Light Detection And Ranging!
Note: FIT (Failure In Time -billions hrs).
http://www.koaproducts.com/english/application/ap7.htm
The ND I have, uses a current limit / fusing device; unfortunately its not a diode
as you speak of. From the Berkeley ref above, it points to the fact this kind
of device has a disadvantage in that they can withstand currents 10 times
their normal rating for prolonged time (a fraction of a second?). To get the recommend
1ms failure the fuse cant have more than 4 times norm capacity. So as
an absolute back up to save your avionics from OV, it is not going to help much;
however, it will assure the alternator will die at some point, sooner than
later without catching on fire. Which is real important to anyone using a ND
alternator.
http://www.irf.com/technical-info/whitepaper/s30p5.pdf
Interesting very technical and over my head, but excelling graphical illustration
representing the internal flow inside a FET in failure modes. The main point
is a FET failure is not just one internal event, but also many secondary events.
Apparently the new L MOSFETs are more resilient, but my 25-year-old Pioneer
Stereo (65watt x 2), with MOSFET transistors is still kicking.
Thanks Bob, for giving your insight. When it comes to little alternators with I-VR,
first I can trust that it will NOT cause danger to the aircraft. However
equipment damage "avionics" is *possible* as you and others have stated. With
that said, understanding of *how possible* will help make an informed choice.
I can accept the risk of using a I-VR without extra OV protection since MTBF
is between 200,000-500,000 hours. If I had $30,000 of avionics I would also consider
using additional OV protection, it is more insurance. However, depending
on your design goals, a stand alone I-VR alternator can provide a very good
level of reliability and simplicity. Also, use of standard auto parts may help
on the road if you need to replace it.
Thanks George
---
---
Message 9
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| Subject: | Apex NC seminar June 4/5 |
--> AeroElectric-List message posted by: "Robert L. Nuckolls, III" <b.nuckolls@cox.net>
Due to a blessedly temporary crash of the gray matter soft-drive,
we pulled the plug prematurely on the Apex NC seminar on June 4/5.
I've spoken with and/or e-mailed all the folks who were signed up for
that program to let them know that we've had a successful re-boot
and the REAL go/no-go date for the program is May 14th. So if
anyone on the list was planning to attend and had not yet made their
reservations, I beg your indulgence and understanding. I'll encourage
you to get signed up before the 14th and we just might pull this
one off after all!
See: http://aeroelectric.com/seminars/ApexNC.html
Thanks!
Bob . . .
Message 10
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| Subject: | "Optimum" antenna coax length for GPS? |
--> AeroElectric-List message posted by: "Robert L. Nuckolls, III" <b.nuckolls@cox.net>
Comments/Questions: Bob, I have a Falco (all wood) with a Northstar M600
GPS, using RG-58 cable. I am replacing it with a Northstar M3 IFR GPS. The
M600 installation manual specifies the shortest possible antenna link
should be used.
The M3 manual says that RG-58 cable has a 23 dB loss per 100 ft @ 1500MHz
and the cable should be at least 10 ft and no longer than 50 ft. I am
planning on using RG-400 cable.
What is the dB cable loss per 100 ft for the RG-400, and based on the
RG-58 recomendation of at least 10 ft, what would you recommend as the
optimum cable length. The antenna is located on the glare shield so the
actual distance is pretty short - Appx 4 ft.
FYI, the folks at CMC told me that the cable would be "impotent" if too
short! The dictionary says impotent is "lacking in power, strength, or
vigor", so I definitely do not want an impotent antenna cable.
I cannot imagine where these guys are coming from. There's no
basis in physics where I can deduce the need for an "opitimum"
cable length. There ARE some GPS applications where multiple
antennas are use for ATTITUDE sensing in vehicles. This case
requires cables to be MATCHED to each other in very tight
tolerances but here too, it's not so much a matter of 'optimum'
length as it is 'same' length.
The relative differences between 142/400 and 58 can be seen at:
http://www.aeroelectric.com/articles/coaxloss.pdf
For the very short run you cite, these differences are
insignificant with respect to loss.
I do recommend RG-142 or RG-400 . . . not so much for their
losses over the 4' run you anticipate but for their advanced
materials and fabrication.
Bob . . .
-----------------------------------------
( Experience and common sense cannot be )
( replaced with policy and procedures. )
( R. L. Nuckolls III )
-----------------------------------------
Message 11
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| Subject: | Re: Master/Starter Contactor connection |
bar
--> AeroElectric-List message posted by: "Robert L. Nuckolls, III" <b.nuckolls@cox.net>
bar
At 06:16 PM 4/28/2005 -0400, you wrote:
>--> AeroElectric-List message posted by: <kbob@cox.net>
>
>Mathew,
>I did the exact thing you did...built a one bar strap to connect the
>relay. When the RV plans show a 2 bar! Further checking into resistance
>and load carrying of the copper bar eased my mind. Yes - I will loose a
>tiny bit of voltage when cranking. But so will the terminal ends, the
>other starter wires, the contactor, etc. It won't crank long enough to
>heat the bar up. So I just left it.
Oh, now I think I understand the original question about one or two
piece straps. Van must show two thin straps in sandwich. If one were
attempting to get the same cross section of copper in the jumper strap
as, say 4AWG copper: 4AWG = .204" diam or 3.14 x 0.1 x 0.1 or .031 square
inches. So a 3/4" wide copper strap would need to be .031/.75 = 0.041"
thick.
The K&S Engineering hobby metals centers found in many hobby and
hardware stores offers a .75 x .064" brass strip (#247) at
http://www.ksmetals.com/HobbyMerchandisers/metal_center.asp#
This would be great stuff from which to fabricate your jumper
straps between accessories with boss-hogg terminals on them.
Bob . . .
Message 12
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| Subject: | Re: Internally regulated alternator OVP protection |
--> AeroElectric-List message posted by: "Eric M. Jones" <emjones@charter.net>
--> AeroElectric-List message posted by: "George Braly" <gwbraly@gami.com>
>After all of this, the one simple fact remains:
>If the FET (or other transistor) switching the field fails in the normal
way those
>components fail (shorted) - - you will have an uncontrolled runaway
alternator.
>At this point, there is really not much more to be said about the issue.
The
>internally regulated automotive alternators have a known single point
failure
>mode that is unacceptable in normal aircraft design circles.
>If people crashed when alternators failed - - it would be unacceptable for
the
>automotive world, too.
>That is the distinction, and it makes all of the difference.
>Regards, George
Elegantly stated George, but I can't agree.
Chopping the alternator with a Kilovac relay is a pretty good plan. And
there are other solutions. We need to know more about what goes on inside
some of the internally regulated alternators that are out there. In the
meantime the solution using the White_Rodgers_Emerson_Stancor Type 70
contactor is probably not a good plan to isolate the internally regulated
alternator because it won't kill the arc (If you poke a hole in the
contactor top and fill it with oil--then it will work as planned). I have
some technical types looking at the Type 70--but it reminds me of
technological archeology. So far my sources say "no way", but can't seem to
get the bottom file drawer open to show me the old data....
I think the option of using an external regulator complicates the design and
introduces problems that many do not recognize. I'll bet I could find ten
failed-in-flight alternators from people on this list and not a single
internally regulated runaway. It's all those wires and connections and parts
that cause failures--not the field FETs or transistors.
I confess---the concept of single-point failure just seems to me---vague and
even illusory---the kind of safety pronunciamento a committee might make.
Sure, I see that the concept has merit, but I try not to examine it closely
because I am certain that I will find it bogus.
We tend to defend against monsters from our past. I put dual batteries and
dual alternators into that category. The contactor, switch and related
wiring is probably less reliable than one good battery and one good
alternator bolted tight. And two of something tends not get get
inspected....because we have a backup anyway.
Bob was right that a press-to-test-switch is unnecessary with LEDs. Lots of
things are just like that and they are hard to see.
Regards,
Eric M. Jones
www.PerihelionDesign.com
113 Brentwood Drive
Southbridge MA 01550-2705
Phone (508) 764-2072
Email: emjones@charter.net
"The man who carries a cat by the tail
learns something that can be learned
in no other way."
--Mark Twain
Message 13
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| Subject: | Re: Internally regulated alternator OVP protection |
--> AeroElectric-List message posted by: "George Braly" <gwbraly@gami.com>
Eric,
I didn't say there were other add-on "fixes" that could be devised to avoid the
damage to the aircraft from the single point failure mode that is inherent in
the automotive internal regulator.
But that is the point. You are having to create a "work around" for a problem
that should not require a "work around".
And the work around still leaves the alternator vulnerable to a very high voltage
long term (minutes to hours depending on how long it takes to get the engine
shut down) melt down - - assuming the Kilovac disconnect works gracefully and
as absolutely it is intended to work.
Regards, George
-----Original Message-----
From: owner-aeroelectric-list-server@matronics.com [mailto:owner-aeroelectric-list-server@matronics.com] On Behalf Of Eric M. Jones
Subject: AeroElectric-List: Re: Internally regulated alternator OVP protection
--> AeroElectric-List message posted by: "Eric M. Jones" <emjones@charter.net>
--> AeroElectric-List message posted by: "George Braly" <gwbraly@gami.com>
>After all of this, the one simple fact remains:
>If the FET (or other transistor) switching the field fails in the normal
way those
>components fail (shorted) - - you will have an uncontrolled runaway
alternator.
>At this point, there is really not much more to be said about the issue.
The
>internally regulated automotive alternators have a known single point
failure
>mode that is unacceptable in normal aircraft design circles.
>If people crashed when alternators failed - - it would be unacceptable for
the
>automotive world, too.
>That is the distinction, and it makes all of the difference.
>Regards, George
Elegantly stated George, but I can't agree.
Chopping the alternator with a Kilovac relay is a pretty good plan. And
there are other solutions. We need to know more about what goes on inside
some of the internally regulated alternators that are out there. In the
meantime the solution using the White_Rodgers_Emerson_Stancor Type 70
contactor is probably not a good plan to isolate the internally regulated
alternator because it won't kill the arc (If you poke a hole in the
contactor top and fill it with oil--then it will work as planned). I have
some technical types looking at the Type 70--but it reminds me of
technological archeology. So far my sources say "no way", but can't seem to
get the bottom file drawer open to show me the old data....
I think the option of using an external regulator complicates the design and
introduces problems that many do not recognize. I'll bet I could find ten
failed-in-flight alternators from people on this list and not a single
internally regulated runaway. It's all those wires and connections and parts
that cause failures--not the field FETs or transistors.
I confess---the concept of single-point failure just seems to me---vague and
even illusory---the kind of safety pronunciamento a committee might make.
Sure, I see that the concept has merit, but I try not to examine it closely
because I am certain that I will find it bogus.
We tend to defend against monsters from our past. I put dual batteries and
dual alternators into that category. The contactor, switch and related
wiring is probably less reliable than one good battery and one good
alternator bolted tight. And two of something tends not get get
inspected....because we have a backup anyway.
Bob was right that a press-to-test-switch is unnecessary with LEDs. Lots of
things are just like that and they are hard to see.
Regards,
Eric M. Jones
www.PerihelionDesign.com
113 Brentwood Drive
Southbridge MA 01550-2705
Phone (508) 764-2072
Email: emjones@charter.net
"The man who carries a cat by the tail
learns something that can be learned
in no other way."
--Mark Twain
---
---
Message 14
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| Subject: | off-topic - thick cessna windshield |
--> AeroElectric-List message posted by: rd2@evenlink.com
Sorry, off-topic, couldn't resist asking the list:
Does anyone know of a source for 0.25" thick windshield for a C-172 made 1981?
Or a heated one .25" ? (to make it somewhat more on topic :)
(The OEM product is 1/2 that and there is only one STC for .25" for C-172 I
know of, but for a different year.)
Rumen
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