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bakerocb
Joined: 15 Jan 2006
Posts: 727
Location: FAIRFAX VA
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 Posted: Sat Jul 07, 2007 3:59 am Post subject: Electrical Risk |
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7/7/2007
Hello Bob Nuckolls and Fellow Listers, I recently became aware of an
aircraft electrical event that I'd like your opinions on:
1) Situation: Type certificated aircraft. Day VFR, shut down for refueling
at a field a short flying distance from home field (fuel is cheaper).
Maintenance with significant delay until following week (this was Friday
afternoon) was possible. Retrieval of pilots by third party driving
automobile very awkward.
2) Upon starting attempt starter gave a brief bump to prop and then all
electrical feed from the battery to the aircraft ceased.
3) Borrowed voltmeter and some poking around revealed that the battery had
24.8 volts available.
4) The main battery contactor ("Battery Relay" P/N 6041H189) would click
once each time when the master battery switch was turned on, but no voltage
would appear on the output terminal of the contactor.
5) Conclusion was reached that the main battery contactor had failed
internally.
6) Solution applied was to use a battery jumper cable to bypass the main
battery contactor.
7) The aircraft was then started with the key switch in a normal fashion.
 Once the alternator started functioning, after the engine started
running, electricity was available in a normal fashion.
9) The aircraft was flown to home base with normal electrical functioning,
but with no battery available to either buffer / cushion the alternator
output or provide electricity in case of alternator failure or opening of
the 50 amp alternator feed line circuit breaker.
10) Flight risk was considered acceptable because a no electrical supply VFR
landing could be made at either of two non towered airports in the vicinity.
Questions are:
A) Was any part of the electrical system put at risk of damage by operating
the aircraft in this manner for the short flight to home field? If so, why?
B) Where is the best source to buy this rather obsolete "Battery Relay" P/N
6041H189; NSN 5945-00-588-8555, or a currently manufactured acceptable
substitute part?
Thanks.
'OC' Says: "The best investment we can make is the effort to gather and
understand knowledge."
PS: Could you please respond direct as well as to the list -- I only get the
list digest so have a 24 hour delay.
PPS: This is the second main battery contactor failure that I am aware of
within the last year. Other failure was with a garden variety contactor (P/N
111-226) when the very small coil wire fractured. I have rewired my amateur
built experimental a bit with this failure in mind.
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nuckollsr(at)cox.net
Guest
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| Posted: Sat Jul 07, 2007 9:09 am Post subject: Electrical Risk |
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At 07:55 AM 7/7/2007 -0400, you wrote:
7/7/2007
Hello Bob Nuckolls and Fellow Listers, I recently became aware of an
aircraft electrical event that I'd like your opinions on:
1) Situation: Type certificated aircraft. Day VFR, shut down for refueling
at a field a short flying distance from home field (fuel is cheaper).
Maintenance with significant delay until following week (this was Friday
afternoon) was possible. Retrieval of pilots by third party driving
automobile very awkward.
2) Upon starting attempt starter gave a brief bump to prop and then all
electrical feed from the battery to the aircraft ceased.
3) Borrowed voltmeter and some poking around revealed that the battery had
24.8 volts available.
4) The main battery contactor ("Battery Relay" P/N 6041H189) would click
once each time when the master battery switch was turned on, but no voltage
would appear on the output terminal of the contactor.
5) Conclusion was reached that the main battery contactor had failed
internally.
6) Solution applied was to use a battery jumper cable to bypass the main
battery contactor.
7) The aircraft was then started with the key switch in a normal fashion.
Once the alternator started functioning, after the engine started
running, electricity was available in a normal fashion.
9) The aircraft was flown to home base with normal electrical functioning,
but with no battery available to either buffer / cushion the alternator
output or provide electricity in case of alternator failure or opening of
the 50 amp alternator feed line circuit breaker.
10) Flight risk was considered acceptable because a no electrical supply
VFR landing could be made at either of two non towered airports in the
vicinity.
Questions are:
A) Was any part of the electrical system put at risk of damage by operating
the aircraft in this manner for the short flight to home field? If so, why?
Slightly. The alternator was running without benefit of a battery on
line. If I were
going to ferry a similarly afflicted aircraft, I would make a solid
connection of battery
relay, fat wires to bypass the battery relay. Without the battery,
there is slight risk
that a large, transient event (lowering the gear) could trigger an
overshoot in the
alternator's output response or stall the alternator and cause it to
shut down. However,
modern panel mounted electronics (DO-160 qualified) are 99+ percent
okay with this . . . and
the landing gear can be extended by hand. The totally risk-free ferry
philosophy would be
to start the engine, leave the electrical system cold. Leave the gear
down and don't use
flaps. It'a all a trade-off of options that should be left up to the
knowledgeable pilot
tasked with planning and executing the mission.
B) Where is the best source to buy this rather obsolete "Battery Relay" P/N
6041H189; NSN 5945-00-588-8555, or a currently manufactured acceptable
substitute part?
The 6041 series contactors are very much in production and still used
both for spares and for new design. Like all such devices, they continue
to fill a niche market where the designer realizes, "Sometimes the best
way to drive the nail is with a hammer."
Having said that, it's also true that the niche for these devices is
narrowed compared to breadth of the DC power controls market and
they're not as easily acquired. I did a google search on "6041H"
and "contactor" and got only 17 hits . . . a few of which were
suppliers. The catalog of variations on the theme for this part can
be downloaded from
http://www.aeroelectric.com/Mfgr_Data/Contactors/Eaton_CH/
But let's noodle through the simple-ideas behind the notion that
the el-cheeso relay is worthy of relegation to the scrap heap
in favor of its more expensive and much rarer cousin . . .
The el-cheeso contactor (RPM Controls, White-Rogers, Stancore)
has been flying aboard light aircraft for about 70 years and in
proportionately huge volumes compared to the "mil quality"
device. If you ask any FBO mechanic how often they need to replace
one of these things, you'll get, "Oh yeah, I've replaced a boat-load
of those things!" But ask too how often he/she has replaced tires,
batteries, spark plugs, etc and you'll no doubt hear, "I've replaced
a boat load of those too."
The point being that ALL things have a service life limit. Further,
those limits are profoundly influenced by environment, operational
stresses and out-of-the-ordinary abuse by technique and perhaps
lack of preventative maintenance on the part of the owner/operator.
Things like tires and plugs are replaced based on physical
observation and/or periodic maintenance intervals. But somehow,
things like batteries, contactors, switches and other components
vulnerable to service-stresses are not so blessed with the mechanic's
attention.
This happens because there is (1) a lack of understanding as
to how life limit on these parts is influenced, (2) determination
of condition that goes beyond ordinary visual inspection (read labor
and thought-intensive) and (3) an insanely aggravated cost-of-
ownership generated from over-regulation by individuals demonstrably
short on understanding.
Yet we are loath to treat these components like spark plugs and
put service life limits on them. At the same time we get
our shorts in a bunch worrying about some failure to perform
that generates a maintenance inconvenience (as cited above)
or becomes the opening bars of the prelude for one's personal
dark-n-stormy-night story.
What's the first practical increment for elevating the comfort
levels of ownership of the aircraft cited above? The writer cites
multiple replacements of the battery contactor. Is this hard
evidence of and inability of the contactor to perform? Hmmmm . . .
there are hundreds of thousands of these same devices flying.
While replacement RATES (Failures per flight hour) are probably
higher than that of the high-dollar cousin, there's nothing
to that indicates these parts don't yield an acceptable
cost-of-ownership value. Two short-coupled failures of the
contactor? Hmmmm . . . is it possible that there's an underlying
operating stress that's shortening the life of the contactor?
Maybe . . . probably not. These parts have a calculable and probably
demonstrable mean time between failure. But when considering
some cited MTBF number reveals an average service life.
A small number of parts will go twice that value, a small number
of parts will crap 10 hours out of the box.
To make an upgrade decision without benefit of a detailed
study of the physics and field experience is intellectually
comforting . . . but the high-dollar part WILL also fail
at some point in time. If all you seek is to push the
inevitable out in time, then an upgrade is a perfectly
rational thing to do. If you're REALLY more interested
in reduced cost of ownership and/or canceling the show
on your personal dark-n-stormy-night drama, then an alternate
approach is indicated.
First, how about treating this contactor like a spark plug?
If you're willing to put $20 to $70 PER PLUG into an engine
every so often, is it also reasonable to plan for $25 for
a battery relay every so often as well?
I had a conversation with a reader some years ago worried
about getting stuck on a remote lake with his float plane.
We decided it was a good thing to carry spare contactors
and tools necessary for replacement.
If it were my airplane, in addition to periodic preventative
maintenance, the Avionics Master would become an e-bus
alternate feed switch and a normal feed diode would be
installed. Then I would be inoculated from both the
in-flight failure scenario as well as the conundrum of
"how to best ferry this airplane".
Thanks.
'OC' Says: "The best investment we can make is the effort to gather and
understand knowledge."
Yup. There is no single "solution" that best fits the needs
for all owner/operators and a host of options.
PS: Could you please respond direct as well as to the list -- I only get
the list digest so have a 24 hour delay.
Done.
PPS: This is the second main battery contactor failure that I am aware of
within the last year. Other failure was with a garden variety contactor
(P/N 111-226) when the very small coil wire fractured. I have rewired my
amateur built experimental a bit with this failure in mind.
Depending on how many hoops you're willing/forced to jump, there
are other "upgrade" options. Consider:
http://www.aeroelectric.com/Mfgr_Data/Contactors/Tyco_Kilovac/ev200.pdf
There are a lot of opportunities (but widely spaced and
take $time$ to locate) for purchases. Some options to
explore are . . .
http://www.aeroelectric.com/Mfgr_Data/Contactors/Tyco_Kilovac/ev200.pdf
http://tinyurl.com/2usy58
http://tinyurl.com/3847kw
http://www.warbirdrelics.com/Electrical.htm
http://www.silindustries.com/_RefFiles/Capabilities%20List(19apr07).swf
http://www.electrospec.com/electronic/components-parts/index599.html
http://www.marineairsupply.com/index.html
http://www.clarkreiss.com/Inventory/relays/rl-speci
Of course, the one place guaranteed willing and able to supply
such a part is the service-parts department of your local FBO.
This presupposes that $time$ is no object. I think the lowest
cost-of-ownership solution is to carry a spare contactor and
tools necessary for replacement optionally combined with a
shift of duties for the avionics master switch.
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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bakerocb
Joined: 15 Jan 2006
Posts: 727
Location: FAIRFAX VA
|
| Posted: Sat Jul 07, 2007 7:40 pm Post subject: Electrical Risk |
|
|
7/7/2007
Hello Bob, Thanks for your detailed and prompt response to my request for
help. I'll follow up with a few comments put in [brackets].
Skipping most of OC's original email -- it is available in the archives if
needed.
At 07:55 AM 7/7/2007 -0400, Bob Nuckolls wrote:
| Quote: | Questions (from OC) are:
A) Was any part of the electrical system put at risk of damage by
operating the aircraft in this manner for the short flight to home field?
If so, why?
Slightly. The alternator was running without benefit of a battery on
line. If I were
going to ferry a similarly afflicted aircraft, I would make a solid
connection of battery
relay, fat wires to bypass the battery relay. Without the battery,
there is slight risk
that a large, transient event (lowering the gear) could trigger an
overshoot in the
alternator's output response or stall the alternator and cause it to
shut down. However,
modern panel mounted electronics (DO-160 qualified) are 99+ percent
okay with this . . . and
the landing gear can be extended by hand. The totally risk-free ferry
philosophy would be
to start the engine, leave the electrical system cold. Leave the gear
down and don't use
flaps. It'a all a trade-off of options that should be left up to the
knowledgeable pilot
tasked with planning and executing the mission.
|
[Unfortunately, reentering the Washington DC ADIZ required electrical power
for VHF comm and transponder.]
| Quote: | B) Where is the best source to buy this rather obsolete "Battery Relay"
P/N 6041H189; NSN 5945-00-588-8555, or a currently manufactured acceptable
substitute part?
The 6041 series contactors are very much in production and still used
both for spares and for new design. Like all such devices, they continue
to fill a niche market where the designer realizes, "Sometimes the best
way to drive the nail is with a hammer."
Having said that, it's also true that the niche for these devices is
narrowed compared to breadth of the DC power controls market and
they're not as easily acquired. I did a google search on "6041H"
and "contactor" and got only 17 hits . . . a few of which were
suppliers. The catalog of variations on the theme for this part can
be downloaded from
http://www.aeroelectric.com/Mfgr_Data/Contactors/Eaton_CH/
|
[Yes, the current Eaton catalog has many 6041 series contactors, but none of
them are the 6041H189. We attempted to obtain a 6041H189 for this very same
Beech airplane a while back in order to replace the failed, but not
available, Starter Relay, P/N SBC 9401-1. The word from the Beech community
was that the 6041H189 would be an acceptable starter relay subtitute so we
attempted to obtain one. We never did get one, but that fact became moot
when the A&P doing the install insisted on documentation from Beechcraft
saying that a 6041H189 would be acceptable. Beech said "no it would not" and
a different starter relay (I don't have the P/N here) was obtained and
installed.]
[So now with the failure of the Battery Relay P/N 6041H189 we really need
that exact part or one that Beech says is an acceptable substitute. I can
find indications that there are some 6041H189 relays in existence on
shelves, but just not readily available.]
| Quote: | But let's noodle through the simple-ideas behind the notion that
the el-cheeso relay is worthy of relegation to the scrap heap
in favor of its more expensive and much rarer cousin . . .
The el-cheeso contactor (RPM Controls, White-Rogers, Stancore)
has been flying aboard light aircraft for about 70 years and in
proportionately huge volumes compared to the "mil quality"
device. If you ask any FBO mechanic how often they need to replace
one of these things, you'll get, "Oh yeah, I've replaced a boat-load
of those things!" But ask too how often he/she has replaced tires,
batteries, spark plugs, etc and you'll no doubt hear, "I've replaced
a boat load of those too."
|
[In this instance of a type certificated airplane with the manufacturer's
IPC (Illustrated Parts Catalog) calling for a specific relay P/N and an
installing A&P mechanic insisting on documentation from the manufacturer to
cover his ass before he will install a different part, the el-cheeso
contactor is not an option.]
| Quote: |
The point being that ALL things have a service life limit. Further,
those limits are profoundly influenced by environment, operational
stresses and out-of-the-ordinary abuse by technique and perhaps
lack of preventative maintenance on the part of the owner/operator.
Things like tires and plugs are replaced based on physical
observation and/or periodic maintenance intervals. But somehow,
things like batteries, contactors, switches and other components
vulnerable to service-stresses are not so blessed with the mechanic's
attention.
This happens because there is (1) a lack of understanding as
to how life limit on these parts is influenced, (2) determination
of condition that goes beyond ordinary visual inspection (read labor
and thought-intensive) and (3) an insanely aggravated cost-of-
ownership generated from over-regulation by individuals demonstrably
short on understanding.
Yet we are loath to treat these components like spark plugs and
put service life limits on them. At the same time we get
our shorts in a bunch worrying about some failure to perform
that generates a maintenance inconvenience (as cited above)
or becomes the opening bars of the prelude for one's personal
dark-n-stormy-night story.
What's the first practical increment for elevating the comfort
levels of ownership of the aircraft cited above? The writer cites
multiple replacements of the battery contactor. Is this hard
evidence of and inability of the contactor to perform? Hmmmm . . .
there are hundreds of thousands of these same devices flying.
While replacement RATES (Failures per flight hour) are probably
higher than that of the high-dollar cousin, there's nothing
to that indicates these parts don't yield an acceptable
cost-of-ownership value. Two short-coupled failures of the
contactor? Hmmmm . . . is it possible that there's an underlying
operating stress that's shortening the life of the contactor?
Maybe . . . probably not. These parts have a calculable and probably
demonstrable mean time between failure. But when considering
some cited MTBF number reveals an average service life.
A small number of parts will go twice that value, a small number
of parts will crap 10 hours out of the box.
|
[The three contactor failures that I am aware of during the last year are:
1) The Starter Relay, P/N SBC 9401-1 in the Beech aircraft; 2) A garden
variety master battery contactor (P/N 111-138D or similar) failure in a
fairly new RV-8; and 3) Now the master battery contactor failure P/N
6041H189, in the same Beech aircraft as failure 1.]
[My reaction to failure number 2 was to rewire my own amateur built
experimental aircraft so that I could supply electrical power to my
transponder from my essential bus if my master battery contactor failed. A
transponder is required for operating in the Washington DC ADIZ where my
home field is located.]
| Quote: | To make an upgrade decision without benefit of a detailed
study of the physics and field experience is intellectually
comforting . . . but the high-dollar part WILL also fail
at some point in time. If all you seek is to push the
inevitable out in time, then an upgrade is a perfectly
rational thing to do. If you're REALLY more interested
in reduced cost of ownership and/or canceling the show
on your personal dark-n-stormy-night drama, then an alternate
approach is indicated.
First, how about treating this contactor like a spark plug?
If you're willing to put $20 to $70 PER PLUG into an engine
every so often, is it also reasonable to plan for $25 for
a battery relay every so often as well?
I had a conversation with a reader some years ago worried
about getting stuck on a remote lake with his float plane.
We decided it was a good thing to carry spare contactors
and tools necessary for replacement.
If it were my airplane, in addition to periodic preventative
maintenance, the Avionics Master would become an e-bus
alternate feed switch and a normal feed diode would be
installed. Then I would be inoculated from both the
in-flight failure scenario as well as the conundrum of
"how to best ferry this airplane".
|
[Probably not a feasible course of action for the type certificated Beech
aircraft. It may be possible to push such a 337 change through our local
FSDO, but I doubt the owner would pay the tab for it.]
| Quote: | Yup. There is no single "solution" that best fits the needs
for all owner/operators and a host of options.
|
| | - 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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