nuckolls.bob(at)aeroelect
Guest
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 Posted: Fri Sep 21, 2012 1:39 am Post subject: Why did this AMP crimp on connection get singed and fail? |
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Everything about the crimp appears fine to me. I used a band saw to
cut half way thru it but it looks solid.
Any thoughts about what would cause the singeing and the variable
voltage? I'd like to understand what went wrong with this crimp.
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The rubber hits the road for crimped terminals inside the
wire grip area. The terminal's wire grip barrel must
be closed down over the wire strands such that no voids
exist within the stranding.
Here's a microscopic photo of how the gas-tight
crimp looks when cross-sectioned.
http://www.aeroelectric.com/articles/CrimpTools/GR.jpg
I wish I had the polishing jig we used at HBC to
smooth these cuts. When really smooth, you can
see the squashed wires because each strand is 'ringed'
by its tin coating.
When the crimp height is too tall, moisture laden air
can get between the strands and a corrosion cycle
starts with subsequent increases in resistance for
the joint. The small voltage drop x load current is
a few milliwatts to begin with but as the corrosion
(aggravated by rising temperatures) advances, the
rate of joint degradation accelerates.
Time to operational failure can be long . . .
as some have noted, hundreds of flight hours over
years of calendar time.
Strobe supplies are the most likely to manifest
this failure due to their 100% duty cycle, significant
current draw in most airplanes. Unless the current
is high enough to start the corrosion acceleration,
poorly crimped terminals may never manifest failure.
See:
http://tinyurl.com/93yweyd
http://tinyurl.com/bqznffp
The inline splice of spade terminals in this photo
http://rv6aproject.ckhand.com/panelAndElectrical/electrical/electricalPg6.htm#photo3
would best be replaced with PIDG butt splices or
lap-solder/shrink joints. Ideally, the ship's harness
would have been extended on down to pins in the
connector that mates with power supply.
Bob . . .
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