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nuckollsr(at)cox.net
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 Posted: Wed Aug 08, 2007 2:48 pm Post subject: Manual Battery Switch Project |
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At 09:33 AM 8/8/2007 -0400, you wrote:
| Quote: | 'lectric Bob,
What a scheme! I appreciate the work and creativity, but not too sure I am
up to it. I would have to check with my inspector about the reliability
design factors - I see him Friday night so will broach the subject.
|
Reliability should not be an issue. The classic master-switch/
battery-contactor has no published reliability statistics. I.e.,
and MTBF "calculation" would be so fraught with assumptions as
to make the exercise meaningless. Even if you purchased a manufactured
manual battery switch, there's no data to allow a quantified
comparison between the legacy switch/contactor combination versus
a manually operated substitute.
At the same time, (repeat after me) "WE craft failure tolerant
systems." I.e., we KNOW that the legacy contactors have failed
at inopportune times for thousands of airplane owners and
we've crafted a plan-B to comfortably accommodate a battery
switch failure whether it's the traditional switch/contactor
approach or a manual switch.
| Quote: | How do you find these tidbits? Having a couple of productive buddies may
prove the
answer as am 'way behind and have had to move the project up to the hangar
this week as family events will demand the 'factory' back to a bedroom.
Perhaps between us we can come up with a couple of samples.
|
I have all the materials in the shop to craft this switch
and access to the machine tools necessary to do a really "professional
looking" job. However, it would be nice if I could demonstrate a
fabrication
process that used nothing more exotic than a table or band saw,
a 1" vertical belt sander and a drill press. It would be a fun
comic book to do. Unfortunately, I've got a ton of things
on my plate right now . . . but who knows.
| Quote: | Thanks again for your diligence. It's always an eye-opener..........
Hugs to Dr. Dee
|
Thank you sir. I'll pass along your compliments.
Bob . . .
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bakerocb
Joined: 15 Jan 2006
Posts: 727
Location: FAIRFAX VA
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| Posted: Thu Aug 09, 2007 4:33 am Post subject: Manual Battery Switch Project |
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8/9/2007
Bob Nuckolls wrote:
"Reliability should not be an issue. The classic master-switch/
battery-contactor has no published reliability statistics. I.e.,
and MTBF "calculation" would be so fraught with assumptions as
to make the exercise meaningless......skip....."
and
"At the same time, (repeat after me) "WE craft failure tolerant
systems." I.e., we KNOW that the legacy contactors have failed
at inopportune times for thousands of airplane owners and
we've crafted a plan-B to comfortably accommodate a battery
switch failure whether it's the traditional switch/contactor
approach or a manual switch."
Precisely on target. I personally am aware of three contactor failures
within the last year. One nearly new, presently available, commonly used
type, and two decades older ones built by SBC. Two were battery contactors
and one was a starter contactor.
I have rewired my plane a bit accordingly.
'OC' Says: "The best investment we can make is the effort to gather and
understand knowledge."
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nuckollsr(at)cox.net
Guest
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| Posted: Thu Aug 09, 2007 6:52 am Post subject: Manual Battery Switch Project |
|
|
At 08:30 AM 8/9/2007 -0400, you wrote:
| Quote: | Precisely on target. I personally am aware of three contactor failures
within the last year. One nearly new, presently available, commonly used
type, and two decades older ones built by SBC. Two were battery contactors
and one was a starter contactor.
|
If one goes into the repair records of aircraft in
existence, there are no doubt dozens of failures
every week . . . and all of those aircraft went to
the shop for replacement from which we may infer that the
failure did not produce a "smoking-hole" event.
While your assertions concerning numbers of observed
failures are no doubt correct, we should be careful
that we do not read meaning into those assertions
that cannot be directly quantified into fleet-wide
risk.
Anecdotal data are often useful but should with
caution. For example, I could say that I'm aware
of dozens of sidewall failures in tires and then
offer a follow-on assertion as to how I reacted to
that information. Now, if I was observing the flow
of flat tires into a tire-store, and the dozens of
sidewall failures were but 1/2 percent of all failures,
then perhaps the sense of urgency to craft an
alternative philosophy for the use of tires.
| Quote: | I have rewired my plane a bit accordingly.
|
As I recall you're working with a TC aircraft.
How did you rewire your airplane?
Bob . . .
----------------------------------------
( "Physics is like sex: sure, it may )
( give some practical results, but )
( that's not why we do it." )
( )
( Richard P. Feynman )
----------------------------------------
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bakerocb
Joined: 15 Jan 2006
Posts: 727
Location: FAIRFAX VA
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| Posted: Fri Aug 10, 2007 4:07 am Post subject: Manual Battery Switch Project |
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8/10/2007
Hello Bob Nuckolls, You wrote: "As I recall you're working with a TC
aircraft.
How did you rewire your airplane?"
Thank you for your follow up interest -- amazing memory considering the many
subjects that you deal with just on this list alone.
The TC aircraft was my friend's 24 volt system Beech Sierra that suffered
first an SBC9401 (-?) black plastic case, base mounted, starter contactor
failure then within a year an SBC 9401 (-?) black plastic case, base
mounted, main battery contactor failure. (Both of these contactors had just
the number 9401 stamped on them even though the starter contactor was
supposed to be a 9401-1).
After much flailing around, false starts, wrong part ordering, and research,
the starter contactor was replaced with a metal case, side mounted, Eaton
Aerospace Controls Division, P/N 6041H190 intermittent duty contactor. The
main battery contactor was replaced with a metal case, side mounted, Eaton
Aerospace Controls Division, P/N 6041H189 continuous duty contactor.
The Beechcraft Aeroclub community and Beechcraft itself is largely ignorant
and bereft of documentation on both the fact that two different types
(intermittent versus continuous duty) of contactors are preferred / required
for these two installations and how the mounting method conversion and
wiring is to be accomplished.
To date I have not located any Beechcraft documentation on how one is
supposed to change either the physical mounting or the wiring from the base
mounted to the side mounted contactors so the local A&P is forced to just
wing it. I haven't given up entirely on trying to wring some further
information on this subject from Beech.
Also the original SBC contactors had a confusing, unmarked array of TVS
devices attached and it is unclear just how the local FBO handled the
installation of any replacement TVS devices. (I am only allowed to "help" to
a certain extent on this TC aircraft that is FBO maintained.)
My comment about rewiring my plane a bit referred to my amateur built
experimental airplane. After my hangar mate suffered a fairly new main
battery contactor failure I moved my transponder electrical power source
from the main avionics bus to the essential avionics bus so that I could
have transponder power for "get home" operation within the Washington DC
ADIZ.
'OC' Says: "The best investment we can make is the effort to gather and
understand knowledge."
PS: The few pages of Sierra wiring diagrams that you emailed to me a while
back were absolutely essential in helping to understand the aircraft's
contactor situation -- many thanks again.
----------------------------------- RESPONDING TO -----------------
Time: 07:52:11 AM PST US
From: "Robert L. Nuckolls, III" <nuckollsr(at)cox.net>
Subject: Re: Manual Battery Switch Project
At 08:30 AM 8/9/2007 -0400, you wrote:
| Quote: | Precisely on target. I personally am aware of three contactor failures
within the last year. One nearly new, presently available, commonly used
type, and two decades older ones built by SBC. Two were battery contactors
and one was a starter contactor.
|
If one goes into the repair records of aircraft in
existence, there are no doubt dozens of failures
every week . . . and all of those aircraft went to
the shop for replacement from which we may infer that the
failure did not produce a "smoking-hole" event.
While your assertions concerning numbers of observed
failures are no doubt correct, we should be careful
that we do not read meaning into those assertions
that cannot be directly quantified into fleet-wide
risk.
Anecdotal data are often useful but should with
caution. For example, I could say that I'm aware
of dozens of sidewall failures in tires and then
offer a follow-on assertion as to how I reacted to
that information. Now, if I was observing the flow
of flat tires into a tire-store, and the dozens of
sidewall failures were but 1/2 percent of all failures,
then perhaps the sense of urgency to craft an
alternative philosophy for the use of tires.
| Quote: | I have rewired my plane a bit accordingly.
|
As I recall you're working with a TC aircraft.
How did you rewire your airplane?
Bob . . .
| | - The Matronics AeroElectric-List Email Forum - | | | Use the List Feature Navigator to browse the many List utilities available such as the Email Subscriptions page, Archive Search & Download, 7-Day Browse, Chat, FAQ, Photoshare, and much more:
http://www.matronics.com/Navigator?AeroElectric-List |
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