Today's Message Index:
----------------------
1. 04:44 AM - Re: Autozone alternators (Stewart, Michael (ISS Atlanta))
2. 05:28 AM - Re: Internally regulated alternator OVP (marknlisa@hometel.com)
3. 06:03 AM - A 380 first flight (Gilles Thesee)
4. 08:04 AM - Re: Re: Internally regulated alternator OVP protection (Ken)
5. 08:58 AM - Re: Re: Contact Arc Suppression (Robert L. Nuckolls, III)
6. 09:13 AM - Re: Autozone alternators (Hinde, Frank George (Corvallis))
7. 10:59 AM - Re: Re: Contact Arc Suppression (rv-9a-online)
8. 12:36 PM - Intercom wiring (Ken Simmons)
9. 01:56 PM - Master/Starter Contactor connection (Matthew Brandes)
10. 02:36 PM - Re: Re: Contact Arc Suppression (Gilles Thesee)
11. 03:47 PM - Re: Re: Contact Arc Suppression (Robert L. Nuckolls, III)
12. 04:05 PM - Re: Re: Contact Arc Suppression (Robert L. Nuckolls, III)
13. 04:05 PM - Re: Re: Contact Arc Suppression (BobsV35B@aol.com)
14. 04:32 PM - SD-8 and No Battery (rwtalbot@purephotos.com.au.by.themail.purephotos.com.au.with.HTTP;Thu; (SquirrelMail authenticated user rwtalbot);,)
15. 04:33 PM - Re: Re: Contact Arc Suppression (Gilles Thesee)
16. 05:39 PM - Re: Re: Rebuilt versus Original (Charlie Kuss)
17. 05:39 PM - Re: Master/Starter Contactor connection (Robert L. Nuckolls, III)
18. 06:27 PM - OT- Lebelle Caravelle (BobsV35B@aol.com)
19. 06:42 PM - Re: Master/Starter Contactor connection (BobsV35B@aol.com)
20. 08:17 PM - Re: Master/Starter Contactor connection (Robert L. Nuckolls, III)
21. 08:43 PM - Re: Internally regulated alternator OVP protection ()
Message 1
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| Subject: | Autozone alternators |
--> AeroElectric-List message posted by: "Stewart, Michael (ISS Atlanta)" <mstewart@iss.net>
Wow great post Bill!
Thanks
Mike
Do not archive
-----Original Message-----
From: owner-aeroelectric-list-server@matronics.com
[mailto:owner-aeroelectric-list-server@matronics.com] On Behalf Of Bill
Schlatterer
Subject: RE: AeroElectric-List: Autozone alternators
--> AeroElectric-List message posted by: "Bill Schlatterer"
<billschlatterer@sbcglobal.net>
Geez, something I actually know about! Parts business guy! You didn't
ask
the right question. AutoZone, just like NAPA, Advance, O'Reilly and
even
the good ole Bumper to Bumper guys all sell several alternators at
various
price points remanufactured by one of several folks. Yup, you guessed
it.
Pay more get more. Not only that, but occasionally you actually get a
"new"
product for rebuilt.
It used to be that there was a distinction between rebuilt and
remanufactured. Not so any more, all marketing hype. There are only a
handful of national manufacturers who can produce the volume for
national
chains. These would be folks like DelcoRemy, Worldwide, AMP, Unit
Parts,
etc. They produce and package it in a AZ box. The next run off the
same
line goes in a NAPA box, CarQuest box, etc. No surprise, who fills the
box
is a price quality trade-off. Also noted are many smaller regional
manufacturers who all produce at various levels of quality under not one
but
usually 5 or 6 different brand names.
In most electrical reman facilities, they test everything that comes off
the
line. Normal defective rates BEFORE they go out the door will run about
5%.
These are returned to the line and repaired again. Normal defective
rates
on rebuilt/remain electrical will run 10-18% at the local parts store
(these
are normal defective return rates, TRUE defective rates run 6% - 9%)
What goes in them? Some good stuff and some not so good. A new
regulator
can cost from cents to a couple of bucks on the line but there is a huge
variance in where they come from. Stuff from the Pacific Rim is much
cheaper and usually but not necessarily inferior. Who knows at the
local
level what goes in them,.... nobody!
Next question is what is in the box? The reason AutoZone brands their
product is kinda obvious for "marketing" but not so obvious is that they
can
switch brands, quality, manufacturers, etc at will and you will never
know
it. This is not unique to AZ, it's the way all private branded parts
packaging works. It's that way on purpose.
Next questions is "where" is what is in the box? Because of the problem
with handling cores (two ways) and the weight of the products which
results
in high freight costs, you have no guarantee that what is in the AZ or
NAPA
or CarQuest(choose any)box is the same in California as it would be in
Florida. This is just the business and nothing wrong with it! EXCEPT
if
you want to really know what is in the box and I promise that the
average
guy on the parts counter can't tell you any more than is written on the
box.
This means "new regulator" but does not mean "quality regulator". Maybe
or
maybe not!
The ONLY way you know about the quality of a reman alternator is to know
the
guy that built it and know what he is using, or rely on the price point
as
an assurance of "quality". Just remember that there are various levels
of
"good".
What do you get with B&C? Who knows, BUT, they know where the buy
parts,
they know they check the balance, they field test the unit AGAIN,
remember
5% defects right off the line, and they know the specs on their
regulators.
If you don't have a local rebuilder who knows what he is doing rebuild
the
unit, you really just don't know what is in the box. B&C is the
rebuilder
and we all trust them to put out a better than "good" product in every
box.
Good news! Virtually any good parts store has a "best" quality line
that
will have "good" quality parts but don't delude yourself into thinking
that
a cheap one is as good as a more costly version just because both are
"tested" and use "new" replacement parts. They will all give good
service
in average conditions with a good battery.
From my perspective, B&C is the quality inspection guy! They do know
what
is in the box because they put it there.
YMMV
Bill S
7a Ark
-----Original Message-----
From: owner-aeroelectric-list-server@matronics.com
[mailto:owner-aeroelectric-list-server@matronics.com]On Behalf Of Hinde,
Frank George (Corvallis)
Subject: AeroElectric-List: Autozone alternators
--> AeroElectric-List message posted by: "Hinde, Frank George
(Corvallis)"
<frank.hinde@hp.com>
So does anyone have any input specifically on Autozone rebuilt
alternators?
I don't have enough data to say whether I should go get a refun on my
Camry ND unit.
Thanks
Frank
Message 2
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| Subject: | Re: Internally regulated alternator OVP |
--> AeroElectric-List message posted by: marknlisa@hometel.com
--> AeroElectric-List message posted by: Speedy11@aol.com
> I learned everything I need to know about Mr. Messinger when he
acted on
> his need to share all his wonderful industry awards. Those to whom
> awards mean the most learn humility in their acceptance. Those who
> deserve awards the most rarely need to display them to earn other's
> respect.
> Mark & Lisa Sletten
> Malarky!
> There's nothing wrong with Paul (Mr. Messinger) defining his
expertise by
> mentioning awards or honors received. On the internet, it is
helpful for
> one to explain his background and experience so that we have tools
with
> which to judge his remarks.
Stan,
Mr. Messinger failed to answer to simple requests to provide data to back
his claims. Without other merit for his argument he chose to plaster us
with his awards. Why? Do industry accolades mean more to you than data?
As a 20-year veteran of Gov't service (US Military) I had many occasion to
deal with an Awards and Decorations (A&D) program, as both recommender and
recipient. I'm not saying his awards were bestowed by the same program,
but my guess it that any endeavor where one human judges another will
result in many of the same problems. I saw folks that deserved awards
ignored and vice versa. It ain't a perfect process...
That being said, it isn't my intention to dispute Mr. Messinger's claim to
his awards, I only say that I've learned to give these kinds of
"credentials" their (in my opinion) proper due.
In direct response to your comment above, if in the course of a discussion
my credentials are questioned regarding a subject where I consider myself
an "expert" I might feel the need to share them. I don't remember anyone
questioning Mr. Messinger's credentials, only his methods and motives.
Mark
DO NOT ARCHIVE
Message 3
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| Subject: | A 380 first flight |
--> AeroElectric-List message posted by: Gilles Thesee <Gilles.Thesee@ac-grenoble.fr>
Hi all,
Now live at
http://www.airbus.com/A380/Seeing/live/video/live.asx
Regards,
Gilles Thesee
Grenoble, France
Message 4
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| Subject: | Re: Internally regulated alternator OVP protection |
--> AeroElectric-List message posted by: Ken <klehman@albedo.net>
Chris & Kellie Hand wrote:
>--> AeroElectric-List message posted by: "Chris & Kellie Hand" <ckhand@earthlink.net>
>
>Ken & Bob,
>Thanks for the education...and at the risk of sound a little EE-ignorant, I
>hope you don't mind a few follow up questions:
>
>When you say you've replaced a few similar shorted transistors, are you
>talking about replacing ICs due to short type faults (how could you tell?),
>or are you talking about a failed stand-alone single transistor in a ckt?
>
>
I don't do a lot of electronics repair but I was referring to discrete
power transistors with similar part numbers to the ones shown in the
diagrams you referenced. They are often the hottest component in
circuitry and depend on good assembly to heat sinks etc. The last one
that I replaced was in a $1500. amplifier that the high school was going
to scrap. It was one of eight similar transistors and it failed shorted
and blew the power fuse because the factory had overtightened and
stripped the screw fastening it to a heat sink seven years previously.
The manufacturer was happy because it survived the warranty and they
would make a new sale. My point is merely that such components do at
least sometimes fail shorted or fail such that they could cause the
alternator to run at maximum output.
>Do you consider transistors in an IC ckt (such as those used in an I-VR) to
>be any more or less likely to short than single device transistors in a
>standard built up ckt? Or is there any way to know/quantify the difference
>in reliability?
>
>
For several reasons my limited experience suggests that IC's are
generally more reliable, especially if they are installed by automated
machinery. I don't think it matters to us though.
>Are you saying it's not possible to design ICs for I-VRs without having a
>single point failure mode, or is your position based on assuming that most
>are designed with a single point failure mode (or you can't tell)?
>
It can certainly be done but it raises all kinds of related issues and
it raises the price. In the case of our alternators it is difficult to
tell but the circuitry that is normally published would suggest that
most do have a single point of possible failure. When you design and
build an IC it may cost very very little to incorporate additional ov
protection or to provide better input and output protection on a single
piece of silicon (It is still on one piece of silicon but lets ignore
that). But if the IC controls one power transistor then you still have a
one point failure mode. Does it matter - I don't know. Add another power
transistor and you can fix that but again system reliability probably
goes down and costs go up. So I'd expect to see only one power
transistor but perhaps a few extra cents spent to raise its quality
such that it almost never fails, and I think that is the common state of
the art... This is speculation though.
More pertinent and as has been pointed out by others, it is not in the
manufacturers best interest to make alternators that never fail. It is
in their interest to make alternators that fail passively by ceasing to
produce power rather than going overvoltage and killing other expensive
computers and such. I think that is the main point that proponents of
using a NEW MODERN IR alternator are making and I think it has merit.
But to have some fun, it's not totally inconceivable that some
automotive ecu's could shutdown the engine to protect itself if it
detects an extended overvoltage! Overspeed protection is pretty common
in ecu's. As is reduced power limp home modes. Why not protection from
extended overvoltage ? ;) Years of watching automotive conversions have
taught me to be cautious about applying automotive reliability to
aircraft. Many things such as that battery master, different types and
sizes of batteries, alternator location, or one off wiring, may make it
irrelevant to us. Failures of automotive conversions are given little
publicity and electrical issues are not uncommon. I am doing a
conversion myself - but someone saying that this or that component never
fails in a car means little to me. I like Bob's philosophy of making
failures a non-event!
Ken
Message 5
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| Subject: | Re: Contact Arc Suppression |
--> AeroElectric-List message posted by: "Robert L. Nuckolls, III" <b.nuckolls@cox.net>
At 05:39 PM 4/11/2005 -0400, you wrote:
>--> AeroElectric-List message posted by: "Eric M. Jones" <emjones@charter.net>
>
>The automotive industry has been moving gung-ho towards 42 volt systems. The
>gung-ho slowed considerably when it was generally appreciated that there was
>no way to make a contact arc extinguish reliably. This could lead to
>horrendous consequences where switches or relays were opened and the current
>just continued in a bright arc until something melted into a puddle. The
>progress towards 42 volt is now more tentative.
Hadn't heard about this "stumbling block" . . . I just assumed that
part of the 42v development goals would be to eliminate mechanical
switches . . . solid state devices don't arc (they've got other
vulnerabilities to the same stresses however).
>A standard B+ contactor for disconnecting the alternator in the case of an
>alternator runaway may not work if the contactor is suddenly presented with
>a voltage much above 13-16 VDC, because the arc may not extinguish.
The territory just above 16v isn't the edge of the earth . . . the
dielectric strength of air is about 1000v/mil . . . but how far apart
are contacts of a switch when they first open? Micro-inches, nano-inches,
pico-inches? How much voltage does it take to jump damned few inches?
Damned few volts. So every set of contacts that open under any
circumstances
for current flow and system voltage WILL arc.
Contact mass, spreading velocity, arc source rise time and ultimate limits
to open circuit amplitude in both voltage and energy are key players and
tightly interlinked.
One can mitigate an arcing situation with any combination of adjustments
to these effects. For the past few months, transorbs have been under
discussion
as means by which ultimate voltage and total energy available to feed
an arc
can be brought to heel. Contactors and switches can be selected or modified
to improve on resistance to arcing under conditions presented by the
system.
Of particular interest to me right now is the capability of a
Stancore/White-Rogers/
RBM Controls generic contactor to disconnect an internally regulated
alternator
after it's well into the self destructive cycle of a regulator failure.
Here
we know that transorbs won't help . . . they're for transient,
relatively low
energy events. The runaway alternator is not transient. It goes on
until something
shuts it down (difficult from the outside on an internally regulated
alternator),
or it destroys itself. The best we can hope for with incorporation of a
b-lead
contactor is that we can effectively disconnect it from the rest of the
airplane.
Here, the event isn't "just above 16" or even 32 volts (general rating for
contacts in this product) but well over 100 volts.
>Arcing of contacts is typical of DC systems with voltages much higher than
>standard automotive voltages.
I'd caution the use of "standard" in this context. Boats, railroads,
wind driven generators on farms have used 18-cell (36v battery/42 volt)
systems for nearly 80 years and they all had to learn to live with
the task of making and breaking circuits.
>A huge amount of engineering has gone into
>making contacts survive. Many engineers have spent their entire career on
>the subject.
Absolutely! The volumes of data available on contact science is
staggering. Just consider this alternator regulator from Ford
circa 1960.
http://www.aeroelectric.com/Pictures/Ford_EM_Reg.jpg
http://www.aeroelectric.com/Pictures/Ford_EM_Reg_Volage_Relay.jpg
http://www.aeroelectric.com/Pictures/Ford_EM_Reg_Field_Relay.jpg
Here's a set of contacts that had to switch the most inductive
load in a vehicle (alternator field) hundreds of times per
second for thousands of miles of operation of the vehicle.
No transorbs were available at the time. However, both regulation
dynamics and contact life were enhanced by putting some constant
ON bias to the alternator field with a resistor visible here:
http://www.aeroelectric.com/Pictures/ALTREG6.JPG
While this helped, designers still had to depend on VERY hard
contact material common to distributor points and copper-n-steel
regulators that dated back to the 1920s.
> A couple years ago Tyco engineers looked at the problem and
>someone decided that this was a perfect application for their Polyswitch.
>
>The Tyco refs are:
>http://www.circuitprotection.com/appnotes/AppNote_42V_PR.pdf
>
>Remarkably, if you choose the right polyswitch there is NO CONTACT ARC AT
>ALL.
Interesting application for this device. Pretty slick.
>To explain how this can be
>http://www.periheliondesign.com/downloads/Polyswitch.pdf --imagine a
>Polyswitch across the contacts, in parallel with the contact gap. I have
>used a relay to illustrate this, but it works the same in switches and
>connectors. Everything is OFF. The Polyswitch in its OFF condition has a
>very low resistance, thus for an instant the Polyswitch actually conducts
>before going into its high resistance mode. (This is not optimal in all
>circumstances but we can examine it later).
>
>When the relay is energized, the contacts close. As a general rule, this
>does not cause arcing below 330 volts or so. The Polyswitch is now shorted
>or bypassed by the path through the relay contacts. As a consequence, the
>Polyswitch goes cold and reverts to its Low Resistance state.
Hmmm . . . I've worked dozens of contact life issues on the airplanes'
over the years and virtually ALL of them had issues based on contact
closure (bounce) and downstream loads (lamp loads, reactive loads due
to combined effects of shielded wire and radio filter capacitors, etc).
None had issues with respect to arcing on contact opening.
>When the relay is turned off, the Polyswitch is still shorted across the
>contact gap, and as a result, prevents any contact arcing. In an instant the
>Polyswitch heats up and goes into its high resistance state--thus turning
>off the circuit.
>
>There will be more on this as time allows, but the key point here is that
>the B+ contactor should probably be equipped with such a scheme to ensure
>that the B+ line is really cut off. Contactors, relays, connectors, and
>switches will last about forever with such a scheme.
Don't know about forever but it will indeed be a quantum jump in
service life.
>Caveat: Nobody said it was easy. Some selection of the proper part is
>required. Perhaps some experimenting needs doing.
>
>If you are not convinced that this is a good idea I suggest some reading
>about the micro-details of how contacts open. Terrifying reading!
>http://relays.tycoelectronics.com/app_pdfs/13c3203.pdf
>
>Finally please note the bi-directional transorbs across the coils.
I read this article. It's generally factual but contains
a lot of non-quantified conditions. Further, it's got some
fundamental problems with their description of contact physics.
For example, the authors allude to a 'breakover voltage' depending
on contact material to wit:
Different contact materials have different arc voltage ratings. For fine
silver, the arc voltage is 12 volts. For cadmium, it is 10 volts; and for gold
and palladium it is 15 volts. Let's assume the contacts are fine silver.
Within nanoseconds after the molten bridge explodes, if the material is
silver and if circuit voltage is 12 volts or more, voltage breakover occurs.
If circuit voltage is less than 12 volts, breakover cannot occur and there
will be no arc.
Hmmmm . . . . the dielectric strength of air is about 1000v/mil.
What is the gap between contacts when they FIRST open? Nano
inches? Picoinches? Damned small inches. This suggests the
the potential for establishing an arc across spreading
contacts with damned small volts as well. Quoting from some
Honeywell-Microswitch documents on contact and switch physics . . .
During contact bounce on closure, molten metal splashes. As the contacts
separate to open the
circuit, arcing occurs again. Meanwhile, things are happening on the atomic
scale. As the
contacts begin to separate, a bridge of molten metal is drawn between them.
As it ruptures, it may
leave more metal on one contact than on the other. This is called bridge
transfer and opinions
differ as to exactly how it occurs. A short arc is drawn as the bridge
breaks. Electrons emitted
from the negative terminal (cathode) cross the gap without interference
(the gap at this time is
too short to contain many gas atoms) and bombard the positive terminal
(anode). Their high
energy causes ionization of some of the surface atoms of the anode
terminal. The resulting
positive ions of negative contact material are repelled by the anode and
attracted to the cathode.
Thus, metal is moved from anode to cathode. As the contacts continue to
separate, a phenomenon
occurs which moves material in the opposite direction in the form of vapor
and continues until
the contacts are about 4 microns apart (assuming silver contacts in air).
As the contacts continue to separate, a significant amount of electron
avalanching begins and a
plasma of ionized gas develops. The gap becomes wide enough to contain an
appreciable amount
of ambient gas. Electrons emitted by the cathode strike gas atoms, losing
some of their energy in
the process, ionizing some of the gas atoms and thus releasing more
electrons. The electrons
reaching the anode have such low energy that ionization of the anode
practically stops. Pressure
of the metal vapor in front of the cathode is higher than that in front of
the anode, and the
pressure differential draws a jet of metal vapor from the cathode. The jet
strikes the anode and
the vapor condenses there. This is called plasma arc transfer and causes
migration of metal from
cathode to anode.
Wow! Things are starting to happen at 4 microinches of separation.
If your interested in having these documents they can be
acquired from the reference docs page on my website at:
http://aeroelectric.com/Reference_Docs
Go to the Microswitch folder and download the two .pdf files.
The most striking feature of the article is lack of depth with
respect to contact life issues. For example.
Here's a 5A relay that has been qual tested to over 100,000 cycles
at full load.
http://www.aeroelectric.com/Pictures/MaintRelay_D.jpg
Looks pretty bad . . . but it STILL met requirements for normal
operations.
Now look at this relay:
http://www.aeroelectric.com/Pictures/1_B30K3_stick.jpg
This relay was sticking at less than 30,000 cycles and was
a player in a trim runaway scenario. Part of what drove the
sticking phenomenon was contact bounce and downstream
conditions in the system which was documented here:
http://www.aeroelectric.com/Pictures/4_bounce500Knocap1.gif
EVERY time the high failure rate relay closes, it takes
4-8 hits. Another brand of relay qualified to the same
spec only bounces 2-3 times and had less than 1/10th the
failure rate. This has nothing to do with presence
or lack of arc suppression across the coil and little to
to with textbook loading conditions.
The article isn't "wrong" but it's very textbookish in
and simply regurgitates a lot of standard stuff on contact life,
most of which doesn't apply to light aircraft that fly an
average of 50 hours a year. When I encounter relay and switch
problems on airplanes, these are generally machines that fly
hundreds of hours per year . . . and the root cause is almost
never based on poor switch selection or failure to observe
ratings.
I'd advise caution before one reacts to this article as
a basis for making design decisions . . . I've not researched
the article in detail but it has some serious holes in the
facts and logic.
Bob . . .
Message 6
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| Subject: | Autozone alternators |
--> AeroElectric-List message posted by: "Hinde, Frank George (Corvallis)" <frank.hinde@hp.com>
Wow...So I guess I'll fit the alternator and see if it dies?....Would
you guys add the OVP as an external protection device just to be safe?
What do you all think?
-----Original Message-----
From: owner-aeroelectric-list-server@matronics.com
[mailto:owner-aeroelectric-list-server@matronics.com] On Behalf Of Bill
Schlatterer
Subject: RE: AeroElectric-List: Autozone alternators
--> AeroElectric-List message posted by: "Bill Schlatterer"
--> <billschlatterer@sbcglobal.net>
Geez, something I actually know about! Parts business guy! You didn't
ask the right question. AutoZone, just like NAPA, Advance, O'Reilly and
even the good ole Bumper to Bumper guys all sell several alternators at
various price points remanufactured by one of several folks. Yup, you
guessed it.
Pay more get more. Not only that, but occasionally you actually get a
"new"
product for rebuilt.
Message 7
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| Subject: | Re: Contact Arc Suppression |
--> AeroElectric-List message posted by: rv-9a-online <rv-9a-online@telus.net>
Hmmm. Back when I was blowing up power transistors for a living :-) , I
had to quickly learn about SOA (Safe Operating Area) of semiconductor
devices.
Switching off any load, especially inductive loads, can overstress
electronic devices unless explicit steps are taken to prevent it. It
appears that the exact analogy exists for mechanical contacts. A
particular contact (switch, relay, contactor) will have a manufacturer's
specified SOA... a combination of dynamic voltage and current conditions.
The 'fix' I used for transistors was called a snubber circuit: a
resistor and capacitor in series connected from the collector to
emitter. In a switching power supply, this get's very warm so component
selection was important. In an aircraft, a snubber circuit would only
have to handle instantaneous power, but the average power would be very
low.
The Polyswitches are fancy snubbers, and my opinion is that they are not
foolproof.
My question to Bob is: do you have any experience with prevention of
contact welding by using R-C snubbers?
Vern Little RV-9A
Robert L. Nuckolls, III wrote:
>--> AeroElectric-List message posted by: "Robert L. Nuckolls, III" <b.nuckolls@cox.net>
>
>At 05:39 PM 4/11/2005 -0400, you wrote:
>
>
>
>>--> AeroElectric-List message posted by: "Eric M. Jones" <emjones@charter.net>
>>
>>The automotive industry has been moving gung-ho towards 42 volt systems. The
>>gung-ho slowed considerably when it was generally appreciated that there was
>>no way to make a contact arc extinguish reliably. This could lead to
>>horrendous consequences where switches or relays were opened and the current
>>just continued in a bright arc until something melted into a puddle. The
>>progress towards 42 volt is now more tentative.
>>
>>
>
> Hadn't heard about this "stumbling block" . . . I just assumed that
> part of the 42v development goals would be to eliminate mechanical
> switches . . . solid state devices don't arc (they've got other
> vulnerabilities to the same stresses however).
>
>
>
>
>>A standard B+ contactor for disconnecting the alternator in the case of an
>>alternator runaway may not work if the contactor is suddenly presented with
>>a voltage much above 13-16 VDC, because the arc may not extinguish.
>>
>>
>
> The territory just above 16v isn't the edge of the earth . . . the
> dielectric strength of air is about 1000v/mil . . . but how far apart
> are contacts of a switch when they first open? Micro-inches, nano-inches,
> pico-inches? How much voltage does it take to jump damned few inches?
> Damned few volts. So every set of contacts that open under any
>circumstances
> for current flow and system voltage WILL arc.
>
> Contact mass, spreading velocity, arc source rise time and ultimate limits
> to open circuit amplitude in both voltage and energy are key players and
> tightly interlinked.
>
> One can mitigate an arcing situation with any combination of adjustments
> to these effects. For the past few months, transorbs have been under
>discussion
> as means by which ultimate voltage and total energy available to feed
>an arc
> can be brought to heel. Contactors and switches can be selected or modified
> to improve on resistance to arcing under conditions presented by the
>system.
>
> Of particular interest to me right now is the capability of a
>Stancore/White-Rogers/
> RBM Controls generic contactor to disconnect an internally regulated
>alternator
> after it's well into the self destructive cycle of a regulator failure.
>Here
> we know that transorbs won't help . . . they're for transient,
>relatively low
> energy events. The runaway alternator is not transient. It goes on
>until something
> shuts it down (difficult from the outside on an internally regulated
>alternator),
> or it destroys itself. The best we can hope for with incorporation of a
>b-lead
> contactor is that we can effectively disconnect it from the rest of the
>airplane.
>
> Here, the event isn't "just above 16" or even 32 volts (general rating for
> contacts in this product) but well over 100 volts.
>
>
>
>
>>Arcing of contacts is typical of DC systems with voltages much higher than
>>standard automotive voltages.
>>
>>
>
> I'd caution the use of "standard" in this context. Boats, railroads,
> wind driven generators on farms have used 18-cell (36v battery/42 volt)
> systems for nearly 80 years and they all had to learn to live with
> the task of making and breaking circuits.
>
>
>
>>A huge amount of engineering has gone into
>>making contacts survive. Many engineers have spent their entire career on
>>the subject.
>>
>>
>
> Absolutely! The volumes of data available on contact science is
> staggering. Just consider this alternator regulator from Ford
> circa 1960.
>
>http://www.aeroelectric.com/Pictures/Ford_EM_Reg.jpg
>http://www.aeroelectric.com/Pictures/Ford_EM_Reg_Volage_Relay.jpg
>http://www.aeroelectric.com/Pictures/Ford_EM_Reg_Field_Relay.jpg
>
> Here's a set of contacts that had to switch the most inductive
> load in a vehicle (alternator field) hundreds of times per
> second for thousands of miles of operation of the vehicle.
> No transorbs were available at the time. However, both regulation
> dynamics and contact life were enhanced by putting some constant
> ON bias to the alternator field with a resistor visible here:
>
>http://www.aeroelectric.com/Pictures/ALTREG6.JPG
>
> While this helped, designers still had to depend on VERY hard
> contact material common to distributor points and copper-n-steel
> regulators that dated back to the 1920s.
>
>
>
>> A couple years ago Tyco engineers looked at the problem and
>>someone decided that this was a perfect application for their Polyswitch.
>>
>>The Tyco refs are:
>>http://www.circuitprotection.com/appnotes/AppNote_42V_PR.pdf
>>
>>Remarkably, if you choose the right polyswitch there is NO CONTACT ARC AT
>>ALL.
>>
>>
>
> Interesting application for this device. Pretty slick.
>
>
>
>
>>To explain how this can be
>>http://www.periheliondesign.com/downloads/Polyswitch.pdf --imagine a
>>Polyswitch across the contacts, in parallel with the contact gap. I have
>>used a relay to illustrate this, but it works the same in switches and
>>connectors. Everything is OFF. The Polyswitch in its OFF condition has a
>>very low resistance, thus for an instant the Polyswitch actually conducts
>>before going into its high resistance mode. (This is not optimal in all
>>circumstances but we can examine it later).
>>
>>When the relay is energized, the contacts close. As a general rule, this
>>does not cause arcing below 330 volts or so. The Polyswitch is now shorted
>>or bypassed by the path through the relay contacts. As a consequence, the
>>Polyswitch goes cold and reverts to its Low Resistance state.
>>
>>
>
> Hmmm . . . I've worked dozens of contact life issues on the airplanes'
> over the years and virtually ALL of them had issues based on contact
> closure (bounce) and downstream loads (lamp loads, reactive loads due
> to combined effects of shielded wire and radio filter capacitors, etc).
> None had issues with respect to arcing on contact opening.
>
>
>
>
>>When the relay is turned off, the Polyswitch is still shorted across the
>>contact gap, and as a result, prevents any contact arcing. In an instant the
>>Polyswitch heats up and goes into its high resistance state--thus turning
>>off the circuit.
>>
>>There will be more on this as time allows, but the key point here is that
>>the B+ contactor should probably be equipped with such a scheme to ensure
>>that the B+ line is really cut off. Contactors, relays, connectors, and
>>switches will last about forever with such a scheme.
>>
>>
>
> Don't know about forever but it will indeed be a quantum jump in
> service life.
>
>
>
>
>>Caveat: Nobody said it was easy. Some selection of the proper part is
>>required. Perhaps some experimenting needs doing.
>>
>>If you are not convinced that this is a good idea I suggest some reading
>>about the micro-details of how contacts open. Terrifying reading!
>>http://relays.tycoelectronics.com/app_pdfs/13c3203.pdf
>>
>>Finally please note the bi-directional transorbs across the coils.
>>
>>
>
> I read this article. It's generally factual but contains
> a lot of non-quantified conditions. Further, it's got some
> fundamental problems with their description of contact physics.
> For example, the authors allude to a 'breakover voltage' depending
> on contact material to wit:
>
>
>Different contact materials have different arc voltage ratings. For fine
>silver, the arc voltage is 12 volts. For cadmium, it is 10 volts; and for gold
>and palladium it is 15 volts. Let's assume the contacts are fine silver.
>Within nanoseconds after the molten bridge explodes, if the material is
>silver and if circuit voltage is 12 volts or more, voltage breakover occurs.
>If circuit voltage is less than 12 volts, breakover cannot occur and there
>will be no arc.
>
> Hmmmm . . . . the dielectric strength of air is about 1000v/mil.
> What is the gap between contacts when they FIRST open? Nano
> inches? Picoinches? Damned small inches. This suggests the
> the potential for establishing an arc across spreading
> contacts with damned small volts as well. Quoting from some
> Honeywell-Microswitch documents on contact and switch physics . . .
>
>
>During contact bounce on closure, molten metal splashes. As the contacts
>separate to open the
>circuit, arcing occurs again. Meanwhile, things are happening on the atomic
>scale. As the
>contacts begin to separate, a bridge of molten metal is drawn between them.
>As it ruptures, it may
>leave more metal on one contact than on the other. This is called bridge
>transfer and opinions
>differ as to exactly how it occurs. A short arc is drawn as the bridge
>breaks. Electrons emitted
>from the negative terminal (cathode) cross the gap without interference
>(the gap at this time is
>too short to contain many gas atoms) and bombard the positive terminal
>(anode). Their high
>energy causes ionization of some of the surface atoms of the anode
>terminal. The resulting
>positive ions of negative contact material are repelled by the anode and
>attracted to the cathode.
>
>Thus, metal is moved from anode to cathode. As the contacts continue to
>separate, a phenomenon
>occurs which moves material in the opposite direction in the form of vapor
>and continues until
>the contacts are about 4 microns apart (assuming silver contacts in air).
>
>As the contacts continue to separate, a significant amount of electron
>avalanching begins and a
>plasma of ionized gas develops. The gap becomes wide enough to contain an
>appreciable amount
>of ambient gas. Electrons emitted by the cathode strike gas atoms, losing
>some of their energy in
>the process, ionizing some of the gas atoms and thus releasing more
>electrons. The electrons
>reaching the anode have such low energy that ionization of the anode
>practically stops. Pressure
>of the metal vapor in front of the cathode is higher than that in front of
>the anode, and the
>pressure differential draws a jet of metal vapor from the cathode. The jet
>strikes the anode and
>the vapor condenses there. This is called plasma arc transfer and causes
>migration of metal from
>cathode to anode.
>
> Wow! Things are starting to happen at 4 microinches of separation.
> If your interested in having these documents they can be
> acquired from the reference docs page on my website at:
>
>http://aeroelectric.com/Reference_Docs
>
> Go to the Microswitch folder and download the two .pdf files.
>
> The most striking feature of the article is lack of depth with
> respect to contact life issues. For example.
>
> Here's a 5A relay that has been qual tested to over 100,000 cycles
> at full load.
>
>http://www.aeroelectric.com/Pictures/MaintRelay_D.jpg
>
>
> Looks pretty bad . . . but it STILL met requirements for normal
> operations.
>
> Now look at this relay:
>
>http://www.aeroelectric.com/Pictures/1_B30K3_stick.jpg
>
> This relay was sticking at less than 30,000 cycles and was
> a player in a trim runaway scenario. Part of what drove the
> sticking phenomenon was contact bounce and downstream
> conditions in the system which was documented here:
>
>http://www.aeroelectric.com/Pictures/4_bounce500Knocap1.gif
>
> EVERY time the high failure rate relay closes, it takes
> 4-8 hits. Another brand of relay qualified to the same
> spec only bounces 2-3 times and had less than 1/10th the
> failure rate. This has nothing to do with presence
> or lack of arc suppression across the coil and little to
> to with textbook loading conditions.
>
> The article isn't "wrong" but it's very textbookish in
> and simply regurgitates a lot of standard stuff on contact life,
> most of which doesn't apply to light aircraft that fly an
> average of 50 hours a year. When I encounter relay and switch
> problems on airplanes, these are generally machines that fly
> hundreds of hours per year . . . and the root cause is almost
> never based on poor switch selection or failure to observe
> ratings.
>
> I'd advise caution before one reacts to this article as
> a basis for making design decisions . . . I've not researched
> the article in detail but it has some serious holes in the
> facts and logic.
>
> Bob . . .
>
>
>
>
Message 8
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--> AeroElectric-List message posted by: "Ken Simmons" <ken@truckstop.com>
I'm still dinking around with upgrading my intercom to a PM3000. I asked the question
about connecting the multiple grounds/shields and appreciate the answers
on that. Hopefully this will be the last post before I get this done.
After digging deeper into the existing wiring on my plane I believe I understand
it now and the configuration may actually be a benefit. The original builder
used a terminal strip to wire up the avionics. This allowed him to wire the radio
power, headset/mic jacks, etc. and then deliver the plane to an avionics
shop to install the radios.
The terminal strip has the power, grounds and audio signals routed through it.
The odd thing, at least in my opinion, is how the grounds are done. The dsub connector
on the intercom, a PM501, uses the daisy chain ground/shield setup that
Bob recommends, all originating from the ground pin on the intercom. The ground
wires for these cables are tied to a common point on the terminal strip along
with the ground wires from the radio. The headset and mike jacks are grounded
to the central ground on the terminal strip that is not tied directly to
the common ground point for the radio/intercom. To me this is a potential for
a ground loop at worst, and at best, not a very logical way to wire the thing.
It seems to me, here comes the question, that if the terminal strip was used as
a central ground for the audio circuits the ground for each cable from the intercom
(headset/mic/music) wouldn't have to be routed back to the terminal strip.
This would eliminate the ground loop potential and simplfy the wiring. For
example, on a headset cable, use a two wire with shield. The two wires would
be used for the left and right channels and the shield would be grounded only
at the terminal strip. The intercom cable is about two feet long if that makes
a difference. Does that seem reasonable?
I wonder how Approach Systems deals with multiple grounds since they have the central
hub setup.
I hope I've described this well enough that it makes sense.
Thanks.
Ken
DO NOT ARCHIVE
Message 9
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| Subject: | Master/Starter Contactor connection |
--> AeroElectric-List message posted by: "Matthew Brandes" <matthew@n523rv.com>
Connected my starter and master contactor with a single piece of bus bar...
should I use two pieces?
Matthew Brandes,
Van's RV-9A (Finish Kit)
#90569
<http://www.n523rv.com/> http://www.n523rv.com
EAA Chapter 1329 President
EAA Chapter 868 Web Editor
Message 10
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| Subject: | Re: Contact Arc Suppression |
--> AeroElectric-List message posted by: Gilles Thesee <Gilles.Thesee@ac-grenoble.fr>
Hi Bob and all,
> The territory just above 16v isn't the edge of the earth . . .
>
>
This discussion is most interesting. But why should 16 V be deemed too
high, while airplanes and helicopters have been running on 28 V DC for
more than half a century ?
Voltages in the 12/16 V range are not that high after all.
Or am I missing something ?
Regards,
Gilles Thesee
Grenoble, France
Message 11
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| Subject: | Re: Contact Arc Suppression |
--> AeroElectric-List message posted by: "Robert L. Nuckolls, III" <b.nuckolls@cox.net>
At 11:35 PM 4/27/2005 +0200, you wrote:
>--> AeroElectric-List message posted by: Gilles Thesee
><Gilles.Thesee@ac-grenoble.fr>
>
>Hi Bob and all,
>
> > The territory just above 16v isn't the edge of the earth . . .
> >
> >
>This discussion is most interesting. But why should 16 V be deemed too
>high, while airplanes and helicopters have been running on 28 V DC for
>more than half a century ?
>Voltages in the 12/16 V range are not that high after all.
>Or am I missing something ?
Excellent question . . . and I think the authors stubbed
their toe on that on. The notion that something evil happens
in that range is not supported by others. I didn't do an
extensive literature search but I was unable to find a
single reference to the relatively high striking voltage
for arcs in opening contacts. The Microswitch papers
clearly argued with their premise.
Higher voltage DC systems have been around longer than
6v or even 12v cars. Large boats got electrical systems
before cars did . . . and they recognized the value of higher voltage
devices (mostly lighting and ventilation fans) being
wired with smaller wire if the current could be kept low.
32V wasn't 'easy' to control but they managed. Railroads
had 32v lighting systems driven from the same class of
generators used for wind-charging of batteries in rural
households. The generators are visible on the running gear
of antique passenger cars of the early 1900s. Each car
had its own generator/battery combination.
32 volt lamps are still made to support marine applications.
My dad served on a wooden hulled mine sweeper in the "1000-mile
War" in Alaskan waters. It had a 32v system . . . twisted pair
to reduce generation of stray magnetic fields.
http://www.atlantalightbulbs.com/ecart/nw012104/6S6.30V.htm
http://www.go2marine.com/g2m/action/GoBPage/id/16170F/medium_screw_standard_base_lamp_bulbs_ancor.html
Chas. Kettering's first starter was a 24 volt machine.
But for some reason, 6V generators were the hardware
of choice. This means that he had to charge 4 batteries
in parallel and discharge them into the 24 volt motor
with an elaborate switching arrangement. It would be
interesting to see the "starter control" on this vehicle.
I imagine a rather large lever with considerable throw . . .
but still preferable to the arm wrenching crank. See
"1911 Application for car self-starter patent" at:
http://www.safran-arts.com/42day/history/h4apr/h4apr17.html
The folks anticipating higher voltage cars are having
to re-invent the wheel. Higher voltage DC equipment for
the railroad/marine markets is fairly hefty and largely
tolerant of the special needs for switchgear. Now they
need to miniaturize it. I suspect we'll see a LOT more
solid state switching just to get rid of the classic
moving contact switches and relays.
But the 12 volt breakover voltage doesn't make sense.
Just for grins, I just went the bench and loaded a 1.2
volt NiMh battery with a 1 ohm resistor (1.2 amp current
draw). Looking at the "contact" area under a microscope
in a darkened room, both a closing and opening arc
were clearly visible. If the 12 volt breakover threshold
were operating, I shouldn't have been able to see
anything.
Bob . . .
Message 12
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| Subject: | Re: Contact Arc Suppression |
--> AeroElectric-List message posted by: "Robert L. Nuckolls, III" <b.nuckolls@cox.net>
At 10:58 AM 4/27/2005 -0700, you wrote:
>--> AeroElectric-List message posted by: rv-9a-online <rv-9a-online@telus.net>
>
>Hmmm. Back when I was blowing up power transistors for a living :-) , I
>had to quickly learn about SOA (Safe Operating Area) of semiconductor
>devices.
>Switching off any load, especially inductive loads, can overstress
>electronic devices unless explicit steps are taken to prevent it. It
>appears that the exact analogy exists for mechanical contacts. A
>particular contact (switch, relay, contactor) will have a manufacturer's
>specified SOA... a combination of dynamic voltage and current conditions.
>
>The 'fix' I used for transistors was called a snubber circuit: a
>resistor and capacitor in series connected from the collector to
>emitter. In a switching power supply, this get's very warm so component
>selection was important. In an aircraft, a snubber circuit would only
>have to handle instantaneous power, but the average power would be very
>low.
>
>The Polyswitches are fancy snubbers, and my opinion is that they are not
>foolproof.
>
>My question to Bob is: do you have any experience with prevention of
>contact welding by using R-C snubbers?
Absolutely. See Figure 6-2 in the 'Connection. R-C arc suppression
was the technology of choice in the design and fabrication of
OV RELAYS in 1975. Problem was that the capacitor, resistor and
contact spreading characteristics were tuned to the inductive
characteristics of the alternator for best life. Fortunately,
one life-time then was 50 cycles as far as Beech and Cessna
were concerned.
The OV relay I was replacing was this big hog:
http://www.aeroelectric.com/Pictures/RBM138-1_B.jpg
The boss said a design goal was to make it 1/10th the weight
an volume. This is the same kind of challenge the 42 volt
car guys are facing. 32v equipment for boats and railroads
was honky stuff with enough size and mass to shrug off
arcing. Now, the task is to handle the same switching
job in a miniature, hermetically sealed relay that is
indeed small . . . but vulnerable to arcing.
So a new paradigm was born with R-C snubbers that the
original product got along without. The paradigm shifted
again when the crowbar system came along with a design
goal to force all contact closure into solid state device
(SCR) for no contact bounce. Contact opening was
moved to a circuit breaker being asked to handle exactly
the task it was designed for: clear a resistive hard fault.
All the issues driven by the inductive nature of
alternator fields simply evaporated.
From the energy management perspective, it was a marriage
made in heaven. For the first time, meeting the service
life requirement of 50 consecutive faults was easy . . .
the new system would readily handle hundreds if not thousands
of repeated OV events.
Bob . . .
>Vern Little RV-9A
>
>Robert L. Nuckolls, III wrote:
>
> >--> AeroElectric-List message posted by: "Robert L. Nuckolls, III"
> <b.nuckolls@cox.net>
> >
> >At 05:39 PM 4/11/2005 -0400, you wrote:
> >
> >
> >
> >>--> AeroElectric-List message posted by: "Eric M. Jones"
> <emjones@charter.net>
> >>
> >>The automotive industry has been moving gung-ho towards 42 volt
> systems. The
> >>gung-ho slowed considerably when it was generally appreciated that
> there was
> >>no way to make a contact arc extinguish reliably. This could lead to
> >>horrendous consequences where switches or relays were opened and the
> current
> >>just continued in a bright arc until something melted into a puddle. The
> >>progress towards 42 volt is now more tentative.
> >>
> >>
> >
> > Hadn't heard about this "stumbling block" . . . I just assumed that
> > part of the 42v development goals would be to eliminate mechanical
> > switches . . . solid state devices don't arc (they've got other
> > vulnerabilities to the same stresses however).
> >
> >
> >
> >
> >>A standard B+ contactor for disconnecting the alternator in the case of an
> >>alternator runaway may not work if the contactor is suddenly presented with
> >>a voltage much above 13-16 VDC, because the arc may not extinguish.
> >>
> >>
> >
> > The territory just above 16v isn't the edge of the earth . . . the
> > dielectric strength of air is about 1000v/mil . . . but how far apart
> > are contacts of a switch when they first open? Micro-inches,
> nano-inches,
> > pico-inches? How much voltage does it take to jump damned few inches?
> > Damned few volts. So every set of contacts that open under any
> >circumstances
> > for current flow and system voltage WILL arc.
> >
> > Contact mass, spreading velocity, arc source rise time and ultimate
> limits
> > to open circuit amplitude in both voltage and energy are key players and
> > tightly interlinked.
> >
> > One can mitigate an arcing situation with any combination of adjustments
> > to these effects. For the past few months, transorbs have been under
> >discussion
> > as means by which ultimate voltage and total energy available to feed
> >an arc
> > can be brought to heel. Contactors and switches can be selected or
> modified
> > to improve on resistance to arcing under conditions presented by the
> >system.
> >
> > Of particular interest to me right now is the capability of a
> >Stancore/White-Rogers/
> > RBM Controls generic contactor to disconnect an internally regulated
> >alternator
> > after it's well into the self destructive cycle of a regulator failure.
> >Here
> > we know that transorbs won't help . . . they're for transient,
> >relatively low
> > energy events. The runaway alternator is not transient. It goes on
> >until something
> > shuts it down (difficult from the outside on an internally regulated
> >alternator),
> > or it destroys itself. The best we can hope for with incorporation of a
> >b-lead
> > contactor is that we can effectively disconnect it from the rest of the
> >airplane.
> >
> > Here, the event isn't "just above 16" or even 32 volts (general
> rating for
> > contacts in this product) but well over 100 volts.
> >
> >
> >
> >
> >>Arcing of contacts is typical of DC systems with voltages much higher than
> >>standard automotive voltages.
> >>
> >>
> >
> > I'd caution the use of "standard" in this context. Boats, railroads,
> > wind driven generators on farms have used 18-cell (36v battery/42 volt)
> > systems for nearly 80 years and they all had to learn to live with
> > the task of making and breaking circuits.
> >
> >
> >
> >>A huge amount of engineering has gone into
> >>making contacts survive. Many engineers have spent their entire career on
> >>the subject.
> >>
> >>
> >
> > Absolutely! The volumes of data available on contact science is
> > staggering. Just consider this alternator regulator from Ford
> > circa 1960.
> >
> >http://www.aeroelectric.com/Pictures/Ford_EM_Reg.jpg
> >http://www.aeroelectric.com/Pictures/Ford_EM_Reg_Volage_Relay.jpg
> >http://www.aeroelectric.com/Pictures/Ford_EM_Reg_Field_Relay.jpg
> >
> > Here's a set of contacts that had to switch the most inductive
> > load in a vehicle (alternator field) hundreds of times per
> > second for thousands of miles of operation of the vehicle.
> > No transorbs were available at the time. However, both regulation
> > dynamics and contact life were enhanced by putting some constant
> > ON bias to the alternator field with a resistor visible here:
> >
> >http://www.aeroelectric.com/Pictures/ALTREG6.JPG
> >
> > While this helped, designers still had to depend on VERY hard
> > contact material common to distributor points and copper-n-steel
> > regulators that dated back to the 1920s.
> >
> >
> >
> >> A couple years ago Tyco engineers looked at the problem and
> >>someone decided that this was a perfect application for their Polyswitch.
> >>
> >>The Tyco refs are:
> >>http://www.circuitprotection.com/appnotes/AppNote_42V_PR.pdf
> >>
> >>Remarkably, if you choose the right polyswitch there is NO CONTACT ARC AT
> >>ALL.
> >>
> >>
> >
> > Interesting application for this device. Pretty slick.
> >
> >
> >
> >
> >>To explain how this can be
> >>http://www.periheliondesign.com/downloads/Polyswitch.pdf --imagine a
> >>Polyswitch across the contacts, in parallel with the contact gap. I have
> >>used a relay to illustrate this, but it works the same in switches and
> >>connectors. Everything is OFF. The Polyswitch in its OFF condition has a
> >>very low resistance, thus for an instant the Polyswitch actually conducts
> >>before going into its high resistance mode. (This is not optimal in all
> >>circumstances but we can examine it later).
> >>
> >>When the relay is energized, the contacts close. As a general rule, this
> >>does not cause arcing below 330 volts or so. The Polyswitch is now shorted
> >>or bypassed by the path through the relay contacts. As a consequence, the
> >>Polyswitch goes cold and reverts to its Low Resistance state.
> >>
> >>
> >
> > Hmmm . . . I've worked dozens of contact life issues on the airplanes'
> > over the years and virtually ALL of them had issues based on contact
> > closure (bounce) and downstream loads (lamp loads, reactive loads due
> > to combined effects of shielded wire and radio filter capacitors, etc).
> > None had issues with respect to arcing on contact opening.
> >
> >
> >
> >
> >>When the relay is turned off, the Polyswitch is still shorted across the
> >>contact gap, and as a result, prevents any contact arcing. In an
> instant the
> >>Polyswitch heats up and goes into its high resistance state--thus turning
> >>off the circuit.
> >>
> >>There will be more on this as time allows, but the key point here is that
> >>the B+ contactor should probably be equipped with such a scheme to ensure
> >>that the B+ line is really cut off. Contactors, relays, connectors, and
> >>switches will last about forever with such a scheme.
> >>
> >>
> >
> > Don't know about forever but it will indeed be a quantum jump in
> > service life.
> >
> >
> >
> >
> >>Caveat: Nobody said it was easy. Some selection of the proper part is
> >>required. Perhaps some experimenting needs doing.
> >>
> >>If you are not convinced that this is a good idea I suggest some reading
> >>about the micro-details of how contacts open. Terrifying reading!
> >>http://relays.tycoelectronics.com/app_pdfs/13c3203.pdf
> >>
> >>Finally please note the bi-directional transorbs across the coils.
> >>
> >>
> >
> > I read this article. It's generally factual but contains
> > a lot of non-quantified conditions. Further, it's got some
> > fundamental problems with their description of contact physics.
> > For example, the authors allude to a 'breakover voltage' depending
> > on contact material to wit:
> >
> >
> >Different contact materials have different arc voltage ratings. For fine
> >silver, the arc voltage is 12 volts. For cadmium, it is 10 volts; and
> for gold
> >and palladium it is 15 volts. Let's assume the contacts are fine silver.
> >Within nanoseconds after the molten bridge explodes, if the material is
> >silver and if circuit voltage is 12 volts or more, voltage breakover occurs.
> >If circuit voltage is less than 12 volts, breakover cannot occur and there
> >will be no arc.
> >
> > Hmmmm . . . . the dielectric strength of air is about 1000v/mil.
> > What is the gap between contacts when they FIRST open? Nano
> > inches? Picoinches? Damned small inches. This suggests the
> > the potential for establishing an arc across spreading
> > contacts with damned small volts as well. Quoting from some
> > Honeywell-Microswitch documents on contact and switch physics . . .
> >
> >
> >During contact bounce on closure, molten metal splashes. As the contacts
> >separate to open the
> >circuit, arcing occurs again. Meanwhile, things are happening on the atomic
> >scale. As the
> >contacts begin to separate, a bridge of molten metal is drawn between them.
> >As it ruptures, it may
> >leave more metal on one contact than on the other. This is called bridge
> >transfer and opinions
> >differ as to exactly how it occurs. A short arc is drawn as the bridge
> >breaks. Electrons emitted
> >from the negative terminal (cathode) cross the gap without interference
> >(the gap at this time is
> >too short to contain many gas atoms) and bombard the positive terminal
> >(anode). Their high
> >energy causes ionization of some of the surface atoms of the anode
> >terminal. The resulting
> >positive ions of negative contact material are repelled by the anode and
> >attracted to the cathode.
> >
> >Thus, metal is moved from anode to cathode. As the contacts continue to
> >separate, a phenomenon
> >occurs which moves material in the opposite direction in the form of vapor
> >and continues until
> >the contacts are about 4 microns apart (assuming silver contacts in air).
> >
> >As the contacts continue to separate, a significant amount of electron
> >avalanching begins and a
> >plasma of ionized gas develops. The gap becomes wide enough to contain an
> >appreciable amount
> >of ambient gas. Electrons emitted by the cathode strike gas atoms, losing
> >some of their energy in
> >the process, ionizing some of the gas atoms and thus releasing more
> >electrons. The electrons
> >reaching the anode have such low energy that ionization of the anode
> >practically stops. Pressure
> >of the metal vapor in front of the cathode is higher than that in front of
> >the anode, and the
> >pressure differential draws a jet of metal vapor from the cathode. The jet
> >strikes the anode and
> >the vapor condenses there. This is called plasma arc transfer and causes
> >migration of metal from
> >cathode to anode.
> >
> > Wow! Things are starting to happen at 4 microinches of separation.
> > If your interested in having these documents they can be
> > acquired from the reference docs page on my website at:
> >
> >http://aeroelectric.com/Reference_Docs
> >
> > Go to the Microswitch folder and download the two .pdf files.
> >
> > The most striking feature of the article is lack of depth with
> > respect to contact life issues. For example.
> >
> > Here's a 5A relay that has been qual tested to over 100,000 cycles
> > at full load.
> >
> >http://www.aeroelectric.com/Pictures/MaintRelay_D.jpg
> >
> >
> > Looks pretty bad . . . but it STILL met requirements for normal
> > operations.
> >
> > Now look at this relay:
> >
> >http://www.aeroelectric.com/Pictures/1_B30K3_stick.jpg
> >
> > This relay was sticking at less than 30,000 cycles and was
> > a player in a trim runaway scenario. Part of what drove the
> > sticking phenomenon was contact bounce and downstream
> > conditions in the system which was documented here:
> >
> >http://www.aeroelectric.com/Pictures/4_bounce500Knocap1.gif
> >
> > EVERY time the high failure rate relay closes, it takes
> > 4-8 hits. Another brand of relay qualified to the same
> > spec only bounces 2-3 times and had less than 1/10th the
> > failure rate. This has nothing to do with presence
> > or lack of arc suppression across the coil and little to
> > to with textbook loading conditions.
> >
> > The article isn't "wrong" but it's very textbookish in
> > and simply regurgitates a lot of standard stuff on contact life,
> > most of which doesn't apply to light aircraft that fly an
> > average of 50 hours a year. When I encounter relay and switch
> > problems on airplanes, these are generally machines that fly
> > hundreds of hours per year . . . and the root cause is almost
> > never based on poor switch selection or failure to observe
> > ratings.
> >
> > I'd advise caution before one reacts to this article as
> > a basis for making design decisions . . . I've not researched
> > the article in detail but it has some serious holes in the
> > facts and logic.
> >
> > Bob . . .
> >
> >
> >
> >
>
>
>--
>
>
>-- incoming mail is certified Virus Free.
Bob . . .
--------------------------------------------------------
< Throughout history, poverty is the normal condition >
< of man. Advances which permit this norm to be >
< exceeded -- here and there, now and then -- are the >
< work of an extremely small minority, frequently >
< despised, often condemned, and almost always opposed >
< by all right-thinking people. Whenever this tiny >
< minority is kept from creating, or (as sometimes >
< happens) is driven out of a society, the people >
< then slip back into abject poverty. >
< >
< This is known as "bad luck". >
< -Lazarus Long- >
<------------------------------------------------------>
http://www.aeroelectric.com
Message 13
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| Subject: | Re: Contact Arc Suppression |
--> AeroElectric-List message posted by: BobsV35B@aol.com
Good Afternoon Bob,
For What It Is Worth!
The Caravelle Sud Est 210 had a lever just to the left of the
captain. It was used to manually switch the battery system
from parallel to series for use in starting the engines. My
recollection is that we had about one hundred and twenty
volts DC to hit the starter with. The voltage would drop
down to somewhere in the 80 volt range during the cranking
cycle. As I said, I don't remember the precise number.
I kinda think that we were supposed to stop the cranking
cycle if the voltage fell below 80 volts. After both engines
were started, we would move the lever to put the batteries
back in their parallel mode for charging. The Caravelle was
pretty much a twenty four volt DC airplane. Unlike more
modern jet transports, we had no AC alternators on the
engines. We had inverters for those few items that used
115 volt, 400 cycle AC. The electrical system was much
more akin to the DC-6 than it was to any Boeing or Douglas
turbine powered airplane.
I had no idea Sud Est had stolen the idea from Kettering.
There is truly nothing new under the sun!
Do Not Archive.
Happy Skies,
Old Bob
AKA
Bob Siegfried
Ancient Aviator
Stearman N3977A
Brookeridge Airpark LL22
Downers Grove, IL 60516
630 985-8502
In a message dated 4/27/2005 5:49:04 P.M. Central Standard Time,
b.nuckolls@cox.net writes:
Chas. Kettering's first starter was a 24 volt machine.
But for some reason, 6V generators were the hardware
of choice. This means that he had to charge 4 batteries
in parallel and discharge them into the 24 volt motor
with an elaborate switching arrangement. It would be
interesting to see the "starter control" on this vehicle.
I imagine a rather large lever with considerable throw . . .
but still preferable to the arm wrenching crank. See
"1911 Application for car self-starter patent" at:
Message 14
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|
authenticated user rwtalbot);,
28 Apr 2005 09:31:18+1000@roxy.matronics.com (EST)
| Subject: | SD-8 and No Battery |
Just to clear up my mind.... Will the SD-8 installed as per Bob's
recommendations function acceptably in the event that it is disconnected
from the battery?
Is the battery needed to get the SD-8 "started"?
Richard
Message 15
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| Subject: | Re: Contact Arc Suppression |
--> AeroElectric-List message posted by: Gilles Thesee <Gilles.Thesee@ac-grenoble.fr>
BobsV35B@aol.com a crit :
>--> AeroElectric-List message posted by: BobsV35B@aol.com
>
>
>Good Afternoon Bob,
>
>For What It Is Worth!
>
>The Caravelle Sud Est 210
>
Hi Bob S,
Funny you mention the Caravelle. I believed it was essentially to be
found in Europe and Mediterranean countries. Or did you have some in the
USA ?
I may have some schematics in the attic.
Regards,
Gilles Thesee
Grenoble, France
Message 16
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| Subject: | Re: Rebuilt versus Original |
--> AeroElectric-List message posted by: Charlie Kuss <chaztuna@adelphia.net>
At 06:36 PM 4/26/2005, you wrote:
>--> AeroElectric-List message posted by: "Eric M. Jones" <emjones@charter.net>
>
>There has been some disparagement of rebuilt equipment recently--so I think
>we should set the record straight.
>
>Is original stuff better than rebuilt?
>
>Original equipment is "good enough" for the task, and task is mainly to
>satisfy the customer until the warranty expires. I'm not being cynical here.
>Since the huge production volumes are sensitive to costs, nothing that is
>better than what-is-needed-to-satisfy-the-task is required. In fact to do
>anything else would be throwing money away. My Dad showed me how American
>machine tools made in 1941 would have the sharp edges INSIDE castings
>smoothed down while the same machine made a few months later would not. The
>task had changed.
>
>It is also true in some assembly operations that a part which goes into an
>assembly may have inspections and tests done on it which a part destined for
>the new original stock (but not used in an assembly) never has to undergo. A
>part that comes out of a box may indeed be inferior to a part out of a
>junkyard in these instances. Selling slightly not-so-good parts in the
>aftermarket is common.
>
>But let's look at original and rebuilt alternators.
>
>Mythical rebuilding operation: Starting with a "core", the alternator is
>disassembled. All the fasteners and bearings are thrown away and new ones
>are used. The bearings can be of better quality than original. The case,
>rotor and stator are inspected and cleaned up. Often new, higher
>voltage-withstand diodes are retrofitted, new brushes are added. Often a new
>regulator assembly (incorporating the newest electronics) is fitted.
>Everything is inspected, torqued, fitted, and sometimes, YES (per B&C,
>thanks Bill...) even dynamically balanced.
>
>Is this better than new? Probably so....In many cases it certainly is. Offer
>to take the rebuild shop owner up in your airplane. Watch his reaction.
>
>Regards,
>Eric M. Jones
Eric,
What you say may be true in some instances. My experience as a
professional auto mechanic, is "you get what you pay for". Cheapo
remanufactures "usually" have poor quality rectifier diodes, bearings and
voltage regulators. If you want a good unit, you usually have to pay for
it. Ask the vendor whose parts (brand) do you use in your units. If they
don't know, generally, the parts are "crap".
Charlie Kuss
Message 17
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| Subject: | Re: Master/Starter Contactor connection |
--> AeroElectric-List message posted by: "Robert L. Nuckolls, III" <b.nuckolls@cox.net>
At 03:54 PM 4/27/2005 -0500, you wrote:
>--> AeroElectric-List message posted by: "Matthew Brandes"
><matthew@n523rv.com>
>
>Connected my starter and master contactor with a single piece of bus bar...
>should I use two pieces?
Don't know why you would need to. What are your concerns?
We often "bus" multiple devices that would normally accept
terminals for fat-wires.
If I understand your question, the pictures below
are illustrative of copper (or brass) straps used
to connect adjacent terminals of high current
carrying devices.
http://www.aeroelectric.com/Pictures/DISKA09F.JPG
http://www.aeroelectric.com/Pictures/DISKA11F.JPG
http://www.aeroelectric.com/Pictures/DISKA12F.JPG
Bob . . .
Message 18
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| Subject: | OT- Lebelle Caravelle |
--> AeroElectric-List message posted by: BobsV35B@aol.com
In a message dated 4/27/2005 6:34:34 P.M. Central Standard Time,
Gilles.Thesee@ac-grenoble.fr writes:
Funny you mention the Caravelle. I believed it was essentially to be
found in Europe and Mediterranean countries. Or did you have some in the
USA ?
I may have some schematics in the attic.
Regards,
Gilles Thesee
Grenoble, France
Good Evening Gilles,
United Air Lines Operated twenty of them, mostly in the
eastern portion of the USA.
It was an extremely inefficient airplane. Small, carried
very few people and it burned a lot of fuel. It's efficiency
and general technology level was about the same as a
De Havilland Comet. However, it was a start. The first
jet we operated was the Douglas DC-8. The second was
the Caravelle. We needed something smaller for low volume
markets. The Caravelle filled the bill for us until the
Boeing 727 became available.
Because of it's lack of efficiency, it wasn't around very
long. It was a superb airplane to fly. No unusual
characteristics. Just a pleasure to fly.
It was the first Jet airplane I ever flew.
One very nice thing about the Caravelle. We sold every
one we bought. That and the 720 were the only two types
we could say that about until the 747.
Do Not Archive
Happy Skies,
Old Bob
AKA
Bob Siegfried
Ancient Aviator
Stearman N3977A
Brookeridge Airpark LL22
Downers Grove, IL 60516
630 985-8502
Message 19
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| Subject: | Re: Master/Starter Contactor connection |
--> AeroElectric-List message posted by: BobsV35B@aol.com
In a message dated 4/27/2005 7:41:02 P.M. Central Standard Time,
b.nuckolls@cox.net writes:
If I understand your question, the pictures below
are illustrative of copper (or brass) straps used
to connect adjacent terminals of high current
carrying devices.
http://www.aeroelectric.com/Pictures/DISKA09F.JPG
http://www.aeroelectric.com/Pictures/DISKA11F.JPG
http://www.aeroelectric.com/Pictures/DISKA12F.JPG
Bob . . .
Good Evening bob,
My goodness, what were you adding to that Bonanza?
Do Not Archive
Happy Skies,
Old Bob
AKA
Bob Siegfried
Ancient Aviator
Stearman N3977A
Brookeridge Airpark LL22
Downers Grove, IL 60516
630 985-8502
Message 20
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| Subject: | Re: Master/Starter Contactor connection |
--> AeroElectric-List message posted by: "Robert L. Nuckolls, III" <b.nuckolls@cox.net>
>
>Bob . . .
>
>
>Good Evening bob,
>
>My goodness, what were you adding to that Bonanza?
You don't REALLY wanna know . . .
Bob . . .
do not archive
Message 21
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| Subject: | Re: Internally regulated alternator OVP protection |
--> AeroElectric-List message posted by: <gmcjetpilot@yahoo.com>
Thanks Larry and Doug:
Larry and Doug pointed out to me off list, I should not respond to personal
comments. I totally agree. I made a mistake and apologize to all if I offended.
Thanks Larry and Doug. Regards George.
Some want to know some background. It is free advice and worth every
penny. If you really care write me off line. The short story is I am a former
aerospace engineer for Boeing and consultant, now fly for a living. I have a
CFI-(I)-MEI, ATP 737/57/67,CE500. My degree is ME engineering and
went to grad school at UW. I was not smart enough to be an EE but they force
dumb ME students to take some EE courses anyway. Also I am an amateur
electronic hobbyist (since age 10 with my radio shack science-fair 160 in 1
electronics project kit) and now work with complex aircraft electrical systems.
Im now building a RV-7 and have had my hand building a RV-6 and finishing a
RV-4, which I flew for many years until selling it. I am concerned not paranoid
about internet fraud and privacy of info. No apologize, just the way it is. If
you
want to pick my brain off list great, but pretty slim pick-ins. Regards George
============================================
>"Chris & Kellie Hand" <ckhand@earthlink.net> Subject:
>Re: Internally regulated alternator OVP protection Date: Apr 26, 2005
>
>Ken & Bob,
>Thanks for the education...and at the risk of sound a little EE-ignorant, I
>hope you don't mind a few follow up questions:
>
>When you say you've replaced a few similar shorted transistors, are you
>talking about replacing ICs due to short type faults (how could you tell?),
>or are you talking about a failed stand-alone single transistor in a ckt?
Good question Chris
============================================
>From: "Robert L. Nuckolls, III" <b.nuckolls@cox.net> protection Subject:
>Re: Internally regulated alternator OVP protection protection
>
>Hi Chris
>
>>"If the field driver shorts (part MTB20N20E in your first reference or
>>part 2N6284 in your second reference) then there is no way that I can
>>see for the referenced devices to stop an over voltage. How likely is
>>that - I don't know but I have replaced a few similar 'transistors' that
>>were indeed shorted in other equipment over the years.
>
>Hear hear! This is exactly the simple-idea upon which
>the notion of additional OV protection and/or external
>control by means of switch on panel is based. Every alternator
>has some sort of solid state device in series with the field
>with a responsibility to modulate field current in response
>to regulator commands for voltage control. If that puppy
>fails shorted -OR- gets an uncontrolled ON-command from
>failed circuitry elsewhere, the alternator's voltage is
>officially out of the gate and racing for the moon.
>
Gents that went over the head of 99% of the audience, including me.
What I got from this is "If driver shorts", "how likely, I don't know", "I replaced
transistors....shorted...in other (?) equip..."
That is all good, but.what kind of short? What equip? what kind of transistor are
we talking about?
We are talking about a catastrophic transistor failure. Right? Also it must fail
in a
very specific way. The transistor drives how much current flows to the field. The
IC controls this transistor. The more current to the field, the higher the alternators
output. So far so good. Normally the IC senses voltage and if there is over voltage
it tells the drive transistor to shut down, but in this scenario the transistor
fails in
such a way the IC is not in control of it. In this scenario there is no fuse/current
limiting device also in the picture in the event this happens.
The IC is watching the transistor and sensing currents thru out the alternator.
The
logic should detect an impending transistor melt down (short). Do transistors just
melt down to a dead short between the drain and source? I have not plowed thru
the whole 20 page document yet but page one has a good diagram and page 14,
par: Field Coil Drive Device Protection, Drive Device = transistor.
http://www.freescale.com/files/analog/doc/data_sheet/MC33099.pdf
The proposed scenarios is a catastrophic instantaneous failure of the transistor
resulting in a loop where the alternator drives it self right up to the rails.
The
transistor (FET) must not only fail it must fail in a mode where the (drain) and
(source) short. Transistor control (gate) provided by the IC is not effective.
We
have a real melt down. Also we are going to assume there is no other internal
current limiting or fuse backup in the loop to protect from this runaway loop,
if
the transistor melts-down in this very specific way. The ND diagram I have does
show a fuse or current limiter in the loop. How it exactly works I cant tell you?
The IC normally will shut the current off to the transistor (gate) if it senses
a
pending overload or shorted output transistor by comparing the response of the
transistor to control input. In the above failure the IC short/overload protection
control of the transistors has no affect, full melt down is already in effect.
This
sudden catastrophic melt down might be very rare. I am thinking a common
failure would be just an open failure, not a short. Also many transistors short
to
the (gate), meaning it will stop current from running thru it (drain to source).
So what is Bob and Chris saying? What I get out of it is a rare transistor
failure will fail dead short, not open. The IC's controls the alternator (field),
thru
that transistor will not catch it in time and all control lost. That is a lot
of bad things
to one component, but possible? Dont know. I am not saying can't happen, just
that it sounds unlikely with the reliability of transistors and the smarts of IC
protection are pretty good.
(WARNING: EE types dont read the following, your head will explode. )
I think some basics are in order. I promise its not too technical, because I dont
know that much.
Transistors are real reliable. The kind in the new alternators, field effect
transistors, (FET or MOSFET), are very reliable. Also the way the VR controls the
FET produces much less heat than older designs. What the industry says about
these transistors is what you already know from the reliability of your TV, they
rarely fail in short. The topic of how transistors fail is a subject for a PHD.
The
field-effect transistor is a very important type of transistor developed after
the
junction transistor. It draws virtually no power from an input signal, overcoming
a
major disadvantage of the junction transistor. You have much less heat with a FET
than older designs using junction transistors. They are faster acting which allows
them to be controlled with pulse width modulation, PWM. This means the controlling
current is turned on/off very fast, and the width of the pulses is varied to control
the transistors output. Way more efficient and cooler.
Keeping the transistor cool is important; that is why they have heat sinks attached.
Even though the FET runs real cool, a heat sink gets rid of heat and adds reliability.
(Look at a ND alternator, you will see the cooling fins. Not all internal VR have
this.)
=================================================
>>If a separate external OVP device fails to work when it should then we
>>have two separate devices failing simultaneously which is pretty rare.
>>We can't test the functionality of an OVP internal to an alternator but
>>we can test the separate OVP device if we so desire.
>
>Dead-on . . .
Agree, multi failures are rare, and that applies to internal regulators also. The
trans melt I understand and I guess you could have a IC failure but still think
this is in the rare range. The IC has its own fault protection, in other words
the
"chip" in the chip is watching the shop. The specific transistor failure that the
IC voltage regulator cant control or "predict" is also got to be rare. What about
the secondary fuse in some internal VR alternators.
CERTIFICATION ANYONE?
A company called Plane-Power in Texas is in the process of certifying PMA
replacement alternators based on Nippondenso alternators. They will offer internal
and external voltage regulated versions. The certified versions will replace existing
systems with external regulators, therefore they will also do the same. For the
experimental market, in the next 2 months, they will have kits for $400, with
brackets, both internal and external regulated. If you buy the external regulated
model it will not come with a regulator. What about the internal VR version. As
I
understood it from Steve at plane-power said they modify the stock VR and add an
internal crow-bar on the condition wire. I confirmed the condition wire was
not a field wire and was the IGN wire (also known as: sense wire or on/off
wire). I know that this approach is not advocated by Bob N. If that is a good
approach than we could we just add the OV crow-bar on the breaker of an internal
regulated alternator just like an external regulator? It would not help if your
field
driver transistor was dead short, as described above? However I am sticking to
my guns, and will not be adding any extra OV protection to my ND alternator at
this time. Yea for me.
=================================================
>>FWIW my feeling is that yes external OV protection is a good thing on an
>>IR alternator but not essential for most of us. I suspect that it will
>>indeed decrease overall system reliability and I doubt very much whether
>>that is going to be quantified on this forum. However I also believe it
>>reduces risk to my brand new icomm A-200 transceiver that still warns
>>that over 16 volts will kill it and that it must be turned off during
>>engine starting... (%$#%) I did add the transorbs to the alternator
>>side of the my ov contactor to increase the likelihood of the contactor
>>working as desired. And I'm still happy with my decision to not route
>>the alternator B-lead through a battery master.
>
>Which goes to another post of mine that speaks to design goals. There
>are no REQUIREMENTS that any of us can levy upon the wishes
>and goals of any other builder. Lots of folk are tightly
>wrapped around an axle assuming that what I write has
>come manner of social design goal to control or set requirements
>on other people's actions.
>Ken is demonstrating a high level of understanding that
>would assuage any concerns I might have should I have
>an opportunity to ride with him in his airplane.
>
>This kind of conversation is what makes the AeroElectric-List
>an arena of ideas as opposed to a barroom brawl over who
>is trying to control whom.
>
>Bob . . .
The fastest way to turn off an over voltage exist inside a modern alternator. Not
with standing the melted shorted transistor scenario above, the internal OV
protection will react very fast. So fast the buss may never see the OV. The crow
bar method does have to wait for the buss to see the OV first (along with radios)
and than wait to pop the CB, which may take a fraction of a second. How much
abuse your radio can take.
The auto industry cant stand over voltage or transient voltage any better than
your
avionics, may be even less (air bag, engine, transmission, anti-lock computers,
gps,
stereos). Bob N. says we need not bother with a master switch and turning off
radios for start, which I understand. This is because modern radios have their
own
protection, but I have a master switch I am ashamed to say. Sorry Bob. It makes
me
feel better. Unless you really know how resilient your avionics are (like the icom
A200, which I have) its prudent to take precautions as you see fit, as Bob says.
The
same with OV protection on top of internal regulated alternators. If you feel you
must add the OV protection, do it. Chances are it will never be needed, you hope.
Worst case scenario is it accidentally trips and causes your alternator some grief,
but your radios should be safe.
Bottom line you have to have a transistor fail. It must not only fail, but fail
in a
specific way. In this mode how much current can flow thru it with out just opening
and basically acting as a fuse? Is the IC capable of proactively preventing it
failing
in the first place, thru good control and logic? What about other internal fuses?
Cheers George
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