|
|
<<<<<<<<<<<<<<<<--->>>>>>>>>>>>>>>>
<< Lancair Builders' Mail List >>
<<<<<<<<<<<<<<<<--->>>>>>>>>>>>>>>>
>>
Time to add more fuel to the connector fire. I spent some years working on
MIL-SPEC electronics packages in land-sea-air applications. There you learn
that solder has NO fatigue resistance (none, nada, zero, zip) and is thus
totally unacceptable to carry loads of any type, particularly in a flexing or
vibration environment. On printed circuit boards there are standards for how
large a component can be and how long its leads can be before the component
must be supported. Fatigue failures on solder joints in printed circuit
boards were so common years ago in the days of larger components that
conformal coatings were used to seal and reinforce components to minimize
transfer of mechanical loads to the solder.
Brent is right: every connector is a failure waiting to happen. Minimize or
eliminate connectors wherever possible. However, any unsupported solder
joint that can flex or is subjected to vibration is a failure guaranteed to
happen. Soldering of connectors is not approved for aircraft. Good crimps
provide the mechanical integrity required. These can then be soldered to
provide some additional electrical pathway and to seal the copper against
possible future corrosion. But if you solder wires together, remember that
the joint should have lots of shrink tubing to help carry the loads and
reduce flexing, and the wire must be strapped down well on either side to
prevent any motion.
I also agree that Fast-on connectors do not belong in a high
vibration environment forward of the firewall although they are widely used
in automotive engine applications (which vibrate much less than aircraft).
However, their long term reliability (assuming you use top quality, dimpled
units) has been excellent in marine, truck, and automotive applications,
frequently better than ring terminations that are subject to screws coming
loose over time. In this regard, their ability to stay inplace is freauently
superior to screw/ring terminals, and the part count is reduced. They
maintain a high local spring pressure, lock in place well (if you get the
good ones with dimples from AMP, or comparable, not Radio Shack stuff), and
are used by the millions in places that are quite hostile. Good quality,
sensible application, good crimping, and use of shrink tubing as strain
relief are more important to reliability than ring versus fast on. I have
had problems with ring terminals coming loose on circuit breakers and other
areas in my C-182. I believe good fast-ons would have stayed tight and in
place. Nothing is perfect.
At the end of the day I believe that Fast-ons are just fine in the
right location (clean, low vibration environments aft of the firewall, to be
doubly safe). Your reliability will depend MUCH more on your workmanship,
crimps, application of shrink tubing, strapping of cable bundles, and good
practice than on whether you use Fast-on or ring connectors (assuming you use
all your components appropriately).
Fred Moreno
[According to Bob Nuckolls, the rocker switches in your C-182 _all_ use
FastOn terminals, and have been accepted for use in that particular
aircraft application for more than 30 years. I just received my first
little order of AMP PIDG FastOn terminals and am very impressed with
their quality. I also purchased bright brass FastOn double spades which
I'll be silver soldering to small brass panels which will provide my
various required ground busses on the back of the firewall and panel.
Needless to say, I will be taking plenty of precautions to provide for
proper support of all wires at their terminations. <Marv> ]
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
LML homepage: http://www.olsusa.com/Users/Mkaye/maillist.html
|
|