Today's Message Index:
----------------------
1. 07:49 AM - Re: Alternator Warranty Data Point - Rebuilt vs. New (Hinde, Frank George (Corvallis))
2. 07:50 AM - Re: Alternator Warranty Data Point - Rebuilt vs. New (Robert L. Nuckolls, III)
3. 08:57 AM - Re: Alternator Warranty Data Point - Rebuilt vs. New (Robert Feldtman)
4. 09:13 AM - Re: Alternator Warranty Data Point - Rebuilt vs. New (BobsV35B@aol.com)
5. 10:42 AM - Z-20 and 504-1 OV Kit (ianwilson2)
6. 10:55 AM - Re: Slow make/break contacts (Eric M. Jones)
7. 12:21 PM - Re: Z-20 and 504-1 OV Kit (Dick Fisher)
8. 01:20 PM - Re: Z-20 and 504-1 OV Kit (Robert L. Nuckolls, III)
9. 01:34 PM - test (Paul)
10. 02:38 PM - Re: Lead-Free Solders (Paul)
11. 04:04 PM - Re: Contactor Diodes (Dave VanLanen)
12. 06:42 PM - Re: Re: Contactor Diodes (Robert L. Nuckolls, III)
13. 06:44 PM - Re: Lead-Free Solders (Robert L. Nuckolls, III)
14. 07:51 PM - Re: Slow make/break contacts (Robert L. Nuckolls, III)
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| Subject: | Alternator Warranty Data Point - Rebuilt vs. |
New
Or indeed what the Plane Power folks are seeing.
I must admit I have personally not heard of a single warranty failure on ei
ther of these units..
Frank 7a flying 300 hours
________________________________
From: owner-aeroelectric-list-server@matronics.com [mailto:owner-aeroelectr
ic-list-server@matronics.com] On Behalf Of Bill Schlatterer
Sent: Wednesday, June 18, 2008 8:07 PM
Subject: AeroElectric-List: Alternator Warranty Data Point - Rebuilt vs. Ne
w
Just a data point I thought might be interesting. I recently had the oppo
rtunity to review warranty rates on several of the major rotating electrica
l rebuilders for alternator warranty returns through autopart stores. Low
number was 9.6% and high was 18%. This includes wholesale as well as retai
l sales with no data as to specific cause. The manufacturers all report "t
rue" warranty rates at 5%- 8% on product tested after it was returned. Wa
rranty on New Alternators was running 5.6% so they were substantially bette
r. No numbers on the "true" rates for New product but I would think it abo
ut 3%. These numbers are very much in line with historical rates we saw se
veral years ago. Also should note that warranty rates do vary considerably
by specific application and these numbers apply to the category and not a
particular unit.
It is interesting that while the technology involved in the rebuilding and
testing processes has improved over the past few years, the actual return r
ates have not reflected the benefits of better processes. ( I attribute t
hat to "trial and error" troubleshooting on the retail side.)
I would interpret this to say that if you are using an automotive alternato
r, the odds of a failure in the first few hours of operation are about doub
le for rebuilt versus new and 1 bad rebuilt unit out of every 10-15 should
be a normal expectation. For our purposes,..... buy new if you can.
It would be very interesting to know what the return rate and actual failur
e rate is on B&C units after they have done all the extra tuning, balancing
, etc. Maybe Bob could get that number for comparison?
Bill S
7a Finishing
Z13 P-mag B&C
Message 2
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| Subject: | Re: Alternator Warranty Data Point - Rebuilt vs. |
New
At 10:07 PM 6/18/2008 -0500, you wrote:
>Just a data point I thought might be interesting. I recently had the
>opportunity to review warranty rates on several of the major rotating
>electrical rebuilders for alternator warranty returns through autopart
>stores. Low number was 9.6% and high was 18%. This includes wholesale as
>well as retail sales with no data as to specific cause. The manufacturers
>all report "true" warranty rates at 5%- 8% on product tested after it was
>returned. Warranty on New Alternators was running 5.6% so they were
>substantially better. No numbers on the "true" rates for New product but
>I would think it about 3%. These numbers are very much in line with
>historical rates we saw several years ago. Also should note that warranty
>rates do vary considerably by specific application and these numbers apply
>to the category and not a particular unit.
>
>It is interesting that while the technology involved in the rebuilding and
>testing processes has improved over the past few years, the actual return
>rates have not reflected the benefits of better processes. ( I attribute
>that to "trial and error" troubleshooting on the retail side.)
>
>I would interpret this to say that if you are using an automotive
>alternator, the odds of a failure in the first few hours of operation are
>about double for rebuilt versus new and 1 bad rebuilt unit out of every
>10-15 should be a normal expectation. For our purposes,&.. buy new if you can.
>
>It would be very interesting to know what the return rate and actual
>failure rate is on B&C units after they have done all the extra tuning,
>balancing, etc. Maybe Bob could get that number for comparison?
I don't know that B&C keeps detailed records on such things
and I'm not personally cognizant of their field experience
over the last 6-8 years. But while I was working directly
with and for B&C (during the production of first 2000
or so alternators) I can say that I witnessed an exceedingly
low return rate. Probably on the order of 1% per year for
the FLEET of fielded product. I can also state that the
majority if not all returns were for installation or maintenance
induced damage. We replaced a number of b-lead studs
that were burned off due to loosened nuts. I recall one
alternator that needed new bearings . . . seems the guy
liked to wash his engine often with high-pressure, soap
laden water.
I never saw a brush failure or rectifier failure or
an opening of a joint either electrical or mechanical.
Of course this begs the question of just what warranty
is either implied or stated in writing. If one does
a Google search on the B&C website for the word "warranty"
you get one hit at:
http://www.bandc.biz/SYSTEM_DIAGRAMS.html
An this use of the word speaks only to reader's
options to adopt the design goals of any of the
electrical system architectures posted.
I worked 12 years running in the OSH booth for
B&C. A common question I fielded from attendees
was "what's the warranty on this stuff?". I could
confidently answer, "Our warranty is no unhappy
customers. If you have an issue with a B&C
product, you call this guy over here (pointing
to Bill). If he doesn't take care of your
needs, you call me and I'll drive up to Newton
and find out what his problem is!"
The answer to your question does not stand simply
on consideration of "rebuilt" versus "new". It
cannot be divined from the study of published
warranty return numbers. The return on investment
for the user of any product starts with efficient
and robust satisfaction of design goals supported
by a sense of craftsmanship and customer service
from the time the first parts are assembled until
the customer is finished with the product and is
satisfied with the demonstrated service life.
In B&C's case, they start with a robust component
with a exemplary, demonstrated service life in
the field. They do only that which is necessary to
make that product fit the legacy design goals for
aircraft electrical system performance and control.
Finally, they stand behind their stated warranty
policy.
This isn't a numbers game, it's a say what you do,
do what you say game. In B&C's case up until 2000
or so, they said "no unhappy customers" and I believed
that because it was my job to help deliver to that
statement. I have no reason to believe that either
statement or policy has changed since that time.
I've worked in this industry for virtually all of
my professional career . . . and even in 'retirement'
my major cash flow comes from aviation. If I had
a major disappointment to share with you, it was
the huge shift from a satisfied, loyal customer
game to a numbers game. Our highest institutions
of learning have discovered ways to analyze the
hell out of any constellation of processes and
to chart the results in living color. Other
departments in those same institutions have neglected
to teach their students that those analysis techniques
are useful tools to help you fine tune performance
but must be applied and interpreted carefully so
as to avoid obscuring facts.
I have seen a warranty returns investigation that
was ultimately "resolved" by cutting the warranty
period from two down to one year. The bleeding fell by
90%. The change of one word on a piece of paper
saved the company about a quarter million a year!
An the warranty return numbers for that device
jumped dramatically . . . and some bureaucrat
got to take credit for it.
This same industry drives design decisions based on
so-called reliability studies. We get out the
holy-watered documents that tell us how to predict
the failure rates of components used in electronics.
We enter all the components into this big computer
model and crunch the numbers to see what number
falls out for predicted mean time between failure
(MTBF). My customers live and die on MTBF numbers.
Sitting in a conference room last year I had to
struggle to keep a straight face when our customer's
purchase specification called for a 20,000 hour
MTBF on our proposed product. The byproduct of these
numbers games is almost total BS. After ten years
of production on the finished product, it is
axiomatic that we will have made numerous repairs
to fielded systems for a combination of reasons
not limited to design error, manufacturing error,
installation error, maintenance error, operating
error or conditions that were never anticipated
in the original design . . . and NONE of those
systems will have been in service for 20,000
hours!
Nonetheless, somebody will massage and tweak the
so-called MTBF "study" until the computer model
coughs out the desired number whereupon our customer
smiles and signs the check that purchases a few
million dollars worth of this "golden product".
The global warming cult has applied computer
modeling tools to their particular social engineering
goals with great success.
As consumers, our faith in such numbers needs to
be tempered with understanding of how they were
generated. The warranty return rate for brand
X may appear a whole lot better than brand Y simply
because brand X has a 90 day warranty and brand
Y has a 1 year warranty.
Further, their numbers may or may not reflect
returns based on careful analysis of manufacturer's
culpability. I can say that all the returns on
B&C alternators I witnessed were for installation
or maintenance induced failures but we fixed them
under warranty anyhow . . . not because the product
failed to meet performance expectations but because
the warranty was "no unhappy customers".
The true answer to your question comes from the
search for an unhappy B&C customer. I've heard
many a tale from guys who heard that a second
cousin of their friend thought B&C and or
AeroElectric Connection stuff was junk. But even
after offering cash rewards for these unhappy
customers to step forward and at least get their
money back, silence from the field was noteworthy.
Bob . . .
Message 3
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| Subject: | Re: Alternator Warranty Data Point - Rebuilt vs. New |
Bob - you bring up an interesting point - what is the best way (from an
aicraft electrical standpoint) to "wash" an engine. Different A&Ps recommend
different soaps, detergents, ways etc. I once lost a GM alternator on a
truck when it was "Steam cleaned" - and the alternator did go out at an
inopportune time. Obviously don't squirt anything into the alternator, but
what about for all the other wires etc? I've never seen that addressed on
the forum as to the best and safest way to clean up under the cowl!
thanks
bobf
125GS LOM powered Glastar
On 6/19/08, Robert L. Nuckolls, III <nuckolls.bob@cox.net> wrote:
>
> nuckolls.bob@cox.net>
>
> At 10:07 PM 6/18/2008 -0500, you wrote:
>
> Just a data point I thought might be interesting. I recently had the
>> opportunity to review warranty rates on several of the major rotating
>> electrical rebuilders for alternator warranty returns through autopart
>> stores. Low number was 9.6% and high was 18%. This includes wholesale as
>> well as retail sales with no data as to specific cause. The manufacturers
>> all report "true" warranty rates at 5%- 8% on product tested after it was
>> returned. Warranty on New Alternators was running 5.6% so they were
>> substantially better. No numbers on the "true" rates for New product but I
>> would think it about 3%. These numbers are very much in line with
>> historical rates we saw several years ago. Also should note that warranty
>> rates do vary considerably by specific application and these numbers apply
>> to the category and not a particular unit.
>>
>> It is interesting that while the technology involved in the rebuilding and
>> testing processes has improved over the past few years, the actual return
>> rates have not reflected the benefits of better processes. ( I attribute
>> that to "trial and error" troubleshooting on the retail side.)
>>
>> I would interpret this to say that if you are using an automotive
>> alternator, the odds of a failure in the first few hours of operation are
>> about double for rebuilt versus new and 1 bad rebuilt unit out of every
>> 10-15 should be a normal expectation. For our purposes,&.. buy new if you
>> can.
>>
>> It would be very interesting to know what the return rate and actual
>> failure rate is on B&C units after they have done all the extra tuning,
>> balancing, etc. Maybe Bob could get that number for comparison?
>>
>
> I don't know that B&C keeps detailed records on such things
> and I'm not personally cognizant of their field experience
> over the last 6-8 years. But while I was working directly
> with and for B&C (during the production of first 2000
> or so alternators) I can say that I witnessed an exceedingly
> low return rate. Probably on the order of 1% per year for
> the FLEET of fielded product. I can also state that the
> majority if not all returns were for installation or maintenance
> induced damage. We replaced a number of b-lead studs
> that were burned off due to loosened nuts. I recall one
> alternator that needed new bearings . . . seems the guy
> liked to wash his engine often with high-pressure, soap
> laden water.
>
> I never saw a brush failure or rectifier failure or
> an opening of a joint either electrical or mechanical.
> Of course this begs the question of just what warranty
> is either implied or stated in writing. If one does
> a Google search on the B&C website for the word "warranty"
> you get one hit at:
>
> http://www.bandc.biz/SYSTEM_DIAGRAMS.html
>
> An this use of the word speaks only to reader's
> options to adopt the design goals of any of the
> electrical system architectures posted.
>
> I worked 12 years running in the OSH booth for
> B&C. A common question I fielded from attendees
> was "what's the warranty on this stuff?". I could
> confidently answer, "Our warranty is no unhappy
> customers. If you have an issue with a B&C
> product, you call this guy over here (pointing
> to Bill). If he doesn't take care of your
> needs, you call me and I'll drive up to Newton
> and find out what his problem is!"
>
> The answer to your question does not stand simply
> on consideration of "rebuilt" versus "new". It
> cannot be divined from the study of published
> warranty return numbers. The return on investment
> for the user of any product starts with efficient
> and robust satisfaction of design goals supported
> by a sense of craftsmanship and customer service
> from the time the first parts are assembled until
> the customer is finished with the product and is
> satisfied with the demonstrated service life.
>
> In B&C's case, they start with a robust component
> with a exemplary, demonstrated service life in
> the field. They do only that which is necessary to
> make that product fit the legacy design goals for
> aircraft electrical system performance and control.
> Finally, they stand behind their stated warranty
> policy.
>
> This isn't a numbers game, it's a say what you do,
> do what you say game. In B&C's case up until 2000
> or so, they said "no unhappy customers" and I believed
> that because it was my job to help deliver to that
> statement. I have no reason to believe that either
> statement or policy has changed since that time.
>
> I've worked in this industry for virtually all of
> my professional career . . . and even in 'retirement'
> my major cash flow comes from aviation. If I had
> a major disappointment to share with you, it was
> the huge shift from a satisfied, loyal customer
> game to a numbers game. Our highest institutions
> of learning have discovered ways to analyze the
> hell out of any constellation of processes and
> to chart the results in living color. Other
> departments in those same institutions have neglected
> to teach their students that those analysis techniques
> are useful tools to help you fine tune performance
> but must be applied and interpreted carefully so
> as to avoid obscuring facts.
>
> I have seen a warranty returns investigation that
> was ultimately "resolved" by cutting the warranty
> period from two down to one year. The bleeding fell by
> 90%. The change of one word on a piece of paper
> saved the company about a quarter million a year!
> An the warranty return numbers for that device
> jumped dramatically . . . and some bureaucrat
> got to take credit for it.
>
> This same industry drives design decisions based on
> so-called reliability studies. We get out the
> holy-watered documents that tell us how to predict
> the failure rates of components used in electronics.
> We enter all the components into this big computer
> model and crunch the numbers to see what number
> falls out for predicted mean time between failure
> (MTBF). My customers live and die on MTBF numbers.
>
> Sitting in a conference room last year I had to
> struggle to keep a straight face when our customer's
> purchase specification called for a 20,000 hour
> MTBF on our proposed product. The byproduct of these
> numbers games is almost total BS. After ten years
> of production on the finished product, it is
> axiomatic that we will have made numerous repairs
> to fielded systems for a combination of reasons
> not limited to design error, manufacturing error,
> installation error, maintenance error, operating
> error or conditions that were never anticipated
> in the original design . . . and NONE of those
> systems will have been in service for 20,000
> hours!
>
> Nonetheless, somebody will massage and tweak the
> so-called MTBF "study" until the computer model
> coughs out the desired number whereupon our customer
> smiles and signs the check that purchases a few
> million dollars worth of this "golden product".
> The global warming cult has applied computer
> modeling tools to their particular social engineering
> goals with great success.
>
> As consumers, our faith in such numbers needs to
> be tempered with understanding of how they were
> generated. The warranty return rate for brand
> X may appear a whole lot better than brand Y simply
> because brand X has a 90 day warranty and brand
> Y has a 1 year warranty.
>
> Further, their numbers may or may not reflect
> returns based on careful analysis of manufacturer's
> culpability. I can say that all the returns on
> B&C alternators I witnessed were for installation
> or maintenance induced failures but we fixed them
> under warranty anyhow . . . not because the product
> failed to meet performance expectations but because
> the warranty was "no unhappy customers".
>
> The true answer to your question comes from the
> search for an unhappy B&C customer. I've heard
> many a tale from guys who heard that a second
> cousin of their friend thought B&C and or
> AeroElectric Connection stuff was junk. But even
> after offering cash rewards for these unhappy
> customers to step forward and at least get their
> money back, silence from the field was noteworthy.
>
> Bob . . .
>
>
Message 4
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| Subject: | Re: Alternator Warranty Data Point - Rebuilt vs. New |
Good Morning Bob,
Different Bob here, but I never do any cleaning within my cowl other than
wiping with a rag. On the very rare and unlikely occasion when a small bit of
grime gets in a difficult corner, I will use a small paint brush moistened with
mineral spirits to loosen things up.
Other than that, it is a rag only.
That rag may or may not be moistened with mineral spirits or another
appropriate cleaner.
Works for me!
Happy Skies,
Old Bob
AKA
Bob Siegfried
Ancient Aviator
628 West 86th Street
Downers Grove, IL 60516
630 985-8502
Stearman N3977A
Brookeridge Air Park LL22
In a message dated 6/19/2008 11:00:00 A.M. Central Daylight Time,
bobf@feldtman.com writes:
Bob - you bring up an interesting point - what is the best way (from an
aicraft electrical standpoint) to "wash" an engine. Different A&Ps recommend
different soaps, detergents, ways etc. I once lost a GM alternator on a truck
when it was "Steam cleaned" - and the alternator did go out at an inopportune
time. Obviously don't squirt anything into the alternator, but what about for
all the other wires etc? I've never seen that addressed on the forum as to the
best and safest way to clean up under the cowl!
thanks
bobf
125GS LOM powered Glastar
**************Gas prices getting you down? Search AOL Autos for
fuel-efficient used cars. (http://autos.aol.com/used?ncid=aolaut00050000000007)
Message 5
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| Subject: | Z-20 and 504-1 OV Kit |
Hi All,
As part of the materials for my Z-20 based X-Air, I purchased a 504-1 OV kit from
B&C as it was cheaper than the individual bits. In the kit is a yellow warning
lamp that isn't used in the Z-20 architecture. Can I make use of the lamp
to give me an 'alt off' type of indication, or maybe some other indicator or
am I just being daft?? I already have the OV warn module, also from B&C, that
gives me a low/high warning lamp.
Thanks in advance.
Ian
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=188628#188628
Message 6
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| Subject: | Re: Slow make/break contacts |
I'm going out on a limb here, because all this stuff is older than the Internet....but
I vaguely recall that there is a perfectly good reason for these Series-F
switches--
Cogging and trim applications where you want minimum ON time, and you want to tease
a motor to move a crane or even aircraft elevator trim.
I don't think this is anyone's ripoff marketing idea at all.
"A witty saying proves nothing."
--Voltaire
--------
Eric M. Jones
www.PerihelionDesign.com
113 Brentwood Drive
Southbridge, MA 01550
(508) 764-2072
emjones@charter.net
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=188633#188633
Message 7
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| Subject: | Re: Z-20 and 504-1 OV Kit |
Yes you can. I did just that with my Jab 3300 powered Sonex using a three
position master Switch.
Dick Fisher
sonex76@velocity.net
Message 8
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| Subject: | Re: Z-20 and 504-1 OV Kit |
At 10:38 AM 6/19/2008 -0700, you wrote:
>
>Hi All,
>
>As part of the materials for my Z-20 based X-Air, I purchased a 504-1 OV
>kit from B&C as it was cheaper than the individual bits. In the kit is a
>yellow warning lamp that isn't used in the Z-20 architecture. Can I make
>use of the lamp to give me an 'alt off' type of indication, or maybe some
>other indicator or am I just being daft?? I already have the OV warn
>module, also from B&C, that gives me a low/high warning lamp.
Sure, if B&C is still shipping the same lamp holder
I remember, it's a generic incandescent holder
and lense:
http://aeroelectric.com/Pictures/Lighting/T-1-3slash4_domed_holder.jpg
Put the right voltage bulb in it an you can use it
for any purpose well served with an incandescent
lamp.
Bob . . .
----------------------------------------)
( . . . a long habit of not thinking )
( a thing wrong, gives it a superficial )
( appearance of being right . . . )
( )
( -Thomas Paine 1776- )
----------------------------------------
Message 9
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do not archive
Message 10
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| Subject: | Re: Lead-Free Solders |
One additional point. The tin-whisker problem is a major concern in
aerospace etc. where the life of the circuitry is important. Your statement
about external coating can prevent (external to the device) whisker growth
is correct. The concern in the industry is internal whisker growth with
expected lifetimes of only a few years (before lead removal the life was
several decades). Consumer electronics have an average useful life of only a
few years (due to technology etc. improvements) and it is not a large issue
there. It is a large issue in aerospace where the needed lifetime is
typically tens of years. This is a major reason for the exemption of RoHS
requirement in aerospace among other long life systems.
Paul
----- Original Message -----
From: "Robert L. Nuckolls, III" <nuckolls.bob@cox.net>
Sent: Tuesday, June 17, 2008 8:53 AM
Subject: Re: AeroElectric-List: Lead-Free Solders
> <nuckolls.bob@cox.net>
>
> At 08:53 AM 6/17/2008 -0400, you wrote:
>><jmcburney@pobox.com>
>>
>>I agree with you, Bob, that lead-free isn't the best way to go. However,
>>it's getting harder and harder to get past the "tree-huggers". Notice how
>>often you see "RoHS" in the catalogs anymore.
>>
>>Do not archive
>>
>>Blue skies and tailwinds
>
> Yes, but the RoHS components solder down very nicely
> with good ol' 63/37. I probably have a lifetime supply
> of the "good stuff" on my shelves.
>
> Now, this DOES raise the specter of tin-whiskers on
> components that are built to RoHS standards even when
> they're assembled to the product with 63/37.
>
> Fortunately, these experiences are rare. We've had
> hot tin dipped, closely spaced relay terminals on our
> GA aircraft for decades. 99.9% of the time, any whisker
> that might have offered a potential for system malfunction
> simply gets burned away.
>
> Of course, not the case with micro-electronics. In this
> case, it appears that conformal coatings have held the
> Whisker Dragon at bay.
>
> Bob . . .
>
Message 11
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| Subject: | Re: Contactor Diodes |
I am still confused, but I think my reading of the second document might
help me clarify my questions. This document states that the spike is
negative-going, which I assume means that it is flowing toward ground (?)
If this is true, then it leads me to two related questions: 1) If the spike
is travelling toward ground, why would it hurt the switch, which is
installed in the positive wire?, and 2) Why would the spike be stopped by
the diode when it could more easily travel through the coil wire directly to
ground? This last question may be a lack of understanding of how a diode
works - does it "block" the spike from travelling against the arrowhead in
the diagram, or does it actually "absorb" the spike?
Thanks,
Dave
From: "Robert L. Nuckolls, III" <nuckolls.bob(at)cox.net>
Subject: Re: Contactor Diodes
<http://www.matronics.com/searching/getmsg_script.cgi?INDEX=73419981?KEYS=co
ntactor_diodes?LISTNAME=AeroElectric?HITNUMBER=1?SERIAL=0858017710?SHOWBUTTO
NS=NO>
I am reading Chapter 11 of the AeroElectric manual, pp. 11-20 and 11-21
>regarding battery and starter contactors, and I am having trouble
>understanding the use of diodes for spike protection.
>
>In figure 11-20 for a battery contactor, the diode is connected between
>the coil terminal and the large battery terminal. When the contactor
>switch is opened, and the magnetic field of the coil collapses, what
>prevents an electrical spike from traveling directly out of the coil back
>through the 22AWG wire to the master switch, bypassing the diode, which is
>shown as being wired in parallel to the coil?
>
>In figure 11-21 for a starter contactor, the direction of the diode
>appears to prevent a flow to ground, where there are no electrical
>components to protect. Again, what would prevent the spike from traveling
>back through the 20AWG wire to the starter switch, bypassing the diode?
>
>I m sure these are dumb questions, but I m not very quick at picking up
>some of these things as some folks are. I would appreciate help in
>understanding it.
No problem Dave,
See:
http://www.aeroelectric.com/articles/spike.pdf
http://www.aeroelectric.com/articles/spikecatcher.pdf
If these don't answer or satisfactorily explain
then get back with us here on the List.
Bob . . .
Message 12
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| Subject: | Re: Contactor Diodes |
At 05:58 PM 6/19/2008 -0500, you wrote:
>I am still confused, but I think my reading of the second document might
>help me clarify my questions. This document states that the spike is
>negative-going, which I assume means that it is flowing toward ground
>(?) If this is true, then it leads me to two related questions: 1) If
>the spike is travelling toward ground, why would it hurt the switch, which
>is installed in the positive wire?
Polarity isn't the risk . . . it's VOLTAGE. The dielectric
strength of air (insulation quality) is on the order of 700
volts per mil. Okay, how far apart are the contacts of a switch
when they first open. Microinches? Nanoinches? Naw . . . damned
SMALL inches. How many volts does it take to jump across
damned small inches? damned small volts.
So, this says that any time you break the contacts of any circuit
there is a tiny little fire that strikes up in the gap. Now,
depending on the energy stored (no much but enough to certainly
feel if you put your finger on it), how fast the rate of rise
for votlage (pretty quick, see graphs), spreading velocity of
contacts (the faster they open the more likely they are to break
the arc) and their mass (the heavier, the more heat they take
out of the arc and promote quenching), there is some erosion
of contact surface.
We largely ignored it during the first 4 decades of aviation
mostly out of lack of technical imperative combined with
some ignorance. The cost of replacing a switch from time to
time was quite small in the overall cost of owning an airplane.
But about 10-12 years ago, the first of the two-stage
starter solenoids started showing up on both OBAM and
TC aircraft. The energy stored on the coils for these
devices took a big jump and we saw a rash of contact
failures in the legacy OFF-L-R-BOTH-START style keyswitches.
This prompted the AD against ACS and similar switches
for replacement of starter solenoid control contacts
in the switch and ADDING the spike catcher diode. Problem
was, as described in the article, the diode was originally
installed across the switch in a manner that did not
perform as needed. It was ultimately corrected and
re-published to put the diode across the contactor coil.
>, and 2) Why would the spike be stopped by the diode when it could more easily
> travel through the coil wire directly to ground?
Don't understand this . . . since the induced voltage
caused by coil collapse is negative going at switch
when the switch opens, and the diode (a check valve for
electron flow) is positioned to conduct for any voltage
that attempts to go more negative than ground, the
spike current presented at the switch end is indeed
shunted to ground and returns to the coil through
ground. Virtually ALL the energy stored in the coil's
magnetic field is dissipated in THE RESISTANCE OF
THE COIL over tens of milliseconds.
Review the write up on Kettering ignition system
in chapter on OV relays. Kettering's points/coil/
distributor exploited this effect to generate a
multi-kilovolt spike from a 6v car battery. Here
he WANTED the spike to live long and prosper. In
our case, the same kind of spike has deleterious
effects on the contacts of the controlling switch.
Kettering used 'condenser' to mitigate deleterious
effects on points.
> This last question may be a lack of understanding of how a diode works
> - does it block the spike from travelling against the arrowhead in the
> diagram, or does it actually absorb the spike?
It's a check valve for electrons. Electrons flow
through the device only in direction opposite the
arrowhead. See description in Chapter 1.
Oh yeah, sorry about that first article. Noticed
later it didn't have the information I was thinking
about. I'm not sure where the right one got off too.
I've been reorganizing the website indexes. I'll find
it evenually.
Bob . . .
Message 13
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| Subject: | Re: Lead-Free Solders |
At 02:36 PM 6/19/2008 -0700, you wrote:
>
>One additional point. The tin-whisker problem is a major concern in
>aerospace etc. where the life of the circuitry is important. Your
>statement about external coating can prevent (external to the device)
>whisker growth is correct. The concern in the industry is internal whisker
>growth with expected lifetimes of only a few years (before lead removal
>the life was several decades). Consumer electronics have an average useful
>life of only a few years (due to technology etc. improvements) and it is
>not a large issue there. It is a large issue in aerospace where the
>needed lifetime is typically tens of years. This is a major reason for the
>exemption of RoHS requirement in aerospace among other long life systems.
Yeah, that and the lack of toughness in lead-free joints. Seems
that re-flowed joints of lead-free products don't get the
wetting or structural integrity that we've enjoyed in 63/37
all these years. One of my clients has tried several lead-free
solder systems and decided he wasn't going to change over soon . . .
not at least with his present warranty policy!
Bob . . .
Message 14
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| Subject: | Re: Slow make/break contacts |
At 08:03 AM 6/18/2008 -0500, you wrote:
><david.nelson@pobox.com>
>
>
>Very well, then. Boy, those marketing folks can sell anything! Thank you, Bob.
>
>Take care,
Not sure it's a marketing issue so much . . . just a factual statement
of performance. Probably 99.99+ percent of all switches operated by
the fingers are slow make/break devices. This included those things
on the walls of your houses. It's a rare instance that potential
stresses on a switch warrant the added cost of crafting a fast
operating switch.
I was in M.L. last week and needed to rip a long hunk of
2 x 10. Dug out "Old Shagnasty". A 10" table saw
grandpa bought before I was born . . . I remember seeing it
on the job sites when I was 6 or 7. That was the first time I'd
seen both ends of a Bowden cable. Grandpa or one of the
sons had rigged this choke cable to a fat switch built into
the base of the Big Kahuna motor sitting a platform beneath the
saw such that pushing and pulling on knob at the operator
end would toggle the switch down below. Pretty cool gizmo
even in the eyes of a first grader.
When I pulled on that knob, it moved with considerable
resistance at first. Thought it was just stiff for not
having been used for 10+ years. But as I pulled the switch
handle past the point-of-no-return, it literally jumped
in my fingers and raced to complete the stroke faster than
I could pull it. The saw came to life and I made a
satisfyingly expeditious cut through that match stick
with a REAL saw.
Later when sucking up the sawdust with a sweeper, I took
a close look at the switch and recalled having disassembled
one just like it many moons ago. This was a Cutler-Hammer
product with 10-32 screw terminals on the back. I recalled
that not only was it a very robust spring loaded, non-teasing,
over-center mechanism, the contacts were little KNIFE switches
http://aeroelectric.com/Pictures/Switches/knife_switch_1.jpg
This kind of switch doesn't arc badly on closure because
you're not slamming masses together and hoping that they'll
quit bouncing eventually . . . This incorporation of the
knife switch also arcs less on opening because the design
was double-make, double-break . . . you had two sets of
contacts WIPING in series for twice the spreading velocity
augmented by the benefits of a non-teasing transfer mechanism.
That explains in part why that switch has performed for
decades from before I was born and is still working
today. If you really want that level of performance
for your airplane (or any other application) they're
still made. But the suckers are about 2 x 2 x 2"
behind the panel and wire with really big terminals.
Guarantee they'll last the lifetime of your airplane
but probably not a good return on investment. They
probably make smaller versions.
I just found a nice switch training manual from one of
the pillars of the switching industry. I've posted it
at:
http://www.aeroelectric.com/Reference_Docs/Switches/CH_Switch_Training_Manual.pdf
I think that 10" saw sits on it's original base and
getting wobbly. The rubber power cord jacket is craking
too. Zach and I are planning to build a new base on
retractable casters and replace the power cord with stuff that
isn't cracked. If all goes well, that saw will cut wood for
5 generations of workers in the Nuckolls family woodshop
. . . with what I believe is the original switch.
Bob . . .
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