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nuckolls.bob(at)aeroelect
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 Posted: Sun Apr 07, 2013 8:59 am Post subject: Encapsulating connectors (Quest. for Bob) |
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At 09:59 AM 4/7/2013, you wrote:
| Quote: | Bob, reading your on-line article (URL below) reminded me of a long-standing question.
In your article you use a specialty adhesive for "potting"
or encapsulating the soldered pins on a 9-pin D-sub-miniature
connector. Unable to locate that particular connector . . . |
Did you mean to say 'connector' or 'adhesive'?
The d-sub is ubiquitous and available about everywhere
not the least of which is Radio Shack as suggested in
the article.
"RTV" has been around for many years. I think I
first encountered one variant for the first time
while working at Hughes Aircraft back about 1963.
It smelled decidedly vinegar (acetic acid). RTV,
Room Temperature Vulcanizing, is a generic term that
speaks to hundreds of similar products. If one needs
the high temperature chemical resistance of silicon
encapsulants, there are 'electronic grade' RTVs. They
do not include acetic acid in their chemistry. I'm
pretty sure there are other forms equally free of
acid. One could also consider some of the acrylic
caulking compounds used for bathtubs and window
frames. Give it a sniff and avoid anything that
smells like pickles.
Sometime during "The Great Transition" from generators
to alternators at Cessna (about 1965) the regulator
of choice was a two-relay electro-mechanical
regulator from Ford.
http://tinyurl.com/d7ln4mt
Things moved along right smartly for a time
until field reports concerning alternator
runaway events. Failure analysis of the regulators
revealed that the plastic bobbin on which the
voltage regulation wires were wound was loose
on the pole core. The bobbin 'bounced' about
on the core causing failure of the small lead
wires. Deprived of any sense of voltage, the
regulator went balls-to-the-wall.
Somebody suggested that we pull all regulators
from stock, remove covers and spot-tack the
bobbins in place with RTV. Yeah, cool idea.
I don't recall if we did a field service bulletin
for doing the same thing on delivered aircraft
or perhaps the drill called for exchanging
regulators.
Again, things smoothed out until a short time
later, brand new 'modified' regulators from
stock failed to come alive in flight test.
Seems that fumes from curing RTV put enough
corrosion on the regulator contacts to disable
it. If the modification process had only
left the covers off for a few days to allow
all the fumes to dissipate, all would have been
right with the universe.
Needless to say, this triggered the Second Great
Thrashing to remove covers and buff contacts.
Ford eventually fixed this fundamental design flaw.
| Quote: | What compound, readily available, would you recommend for sealing or encapsulating connectors?
|
The E6000 adhesive I've cited is everywhere.
Check the Walmart crafts and housewares adhesive
displays. ShoGoo sold in shoe stores is the
same stuff. Hardware and automotive parts stores
sell it under various sizes and trade names.
The common thread is water clear and smells like
dry cleaners.
Bob . . . [quote][b]
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ceengland7(at)gmail.com
Guest
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| Posted: Sun Apr 07, 2013 9:26 am Post subject: Encapsulating connectors (Quest. for Bob) |
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On 04/07/2013 11:57 AM, Robert L. Nuckolls, III wrote:
| Quote: | At 09:59 AM 4/7/2013, you wrote:
| Quote: | Bob, reading your on-line article (URL below) reminded me of a long-standing question.
In your article you use a specialty adhesive for "potting"
or encapsulating the soldered pins on a 9-pin D-sub-miniature
connector. Unable to locate that particular connector . . . |
Did you mean to say 'connector' or 'adhesive'?
The d-sub is ubiquitous and available about everywhere
not the least of which is Radio Shack as suggested in
the article.
"RTV" has been around for many years. I think I
first encountered one variant for the first time
while working at Hughes Aircraft back about 1963.
It smelled decidedly vinegar (acetic acid). RTV,
Room Temperature Vulcanizing, is a generic term that
speaks to hundreds of similar products. If one needs
the high temperature chemical resistance of silicon
encapsulants, there are 'electronic grade' RTVs. They
do not include acetic acid in their chemistry. I'm
pretty sure there are other forms equally free of
acid. One could also consider some of the acrylic
caulking compounds used for bathtubs and window
frames. Give it a sniff and avoid anything that
smells like pickles.
Sometime during "The Great Transition" from generators
to alternators at Cessna (about 1965) the regulator
of choice was a two-relay electro-mechanical
regulator from Ford.
http://tinyurl.com/d7ln4mt
Things moved along right smartly for a time
until field reports concerning alternator
runaway events. Failure analysis of the regulators
revealed that the plastic bobbin on which the
voltage regulation wires were wound was loose
on the pole core. The bobbin 'bounced' about
on the core causing failure of the small lead
wires. Deprived of any sense of voltage, the
regulator went balls-to-the-wall.
Somebody suggested that we pull all regulators
from stock, remove covers and spot-tack the
bobbins in place with RTV. Yeah, cool idea.
I don't recall if we did a field service bulletin
for doing the same thing on delivered aircraft
or perhaps the drill called for exchanging
regulators.
Again, things smoothed out until a short time
later, brand new 'modified' regulators from
stock failed to come alive in flight test.
Seems that fumes from curing RTV put enough
corrosion on the regulator contacts to disable
it. If the modification process had only
left the covers off for a few days to allow
all the fumes to dissipate, all would have been
right with the universe.
Needless to say, this triggered the Second Great
Thrashing to remove covers and buff contacts.
Ford eventually fixed this fundamental design flaw.
| Quote: | What compound, readily available, would you recommend for sealing or encapsulating connectors?
|
The E6000 adhesive I've cited is everywhere.
Check the Walmart crafts and housewares adhesive
displays. ShoGoo sold in shoe stores is the
same stuff. Hardware and automotive parts stores
sell it under various sizes and trade names.
The common thread is water clear and smells like
dry cleaners.
Bob . . .
|
If an auto supply house is more convenient, look for 'sensor safe' on the package of RTV.
[quote][b]
| | - 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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