From: Fredmoreno@aol.com
Message-ID: <412b2854.24914f60@aol.com>
Date: Thu, 10 Jun 1999 13:26:56 EDT
Subject: Connectors and solder
To: lancair.list@olsusa.com
Mime-Version: 1.0

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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>    ]

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