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I would like to start by saying that I have the highest regard for Bob
Nuckolls and I agree with him on virtually every point. He uses logic
and reason ahead of habit and "conventional wisdom and practice", traits
that are fundamental to good engineering.
Regarding the article that Marv vectored me to, I agree with Bob on most
of the points he makes. In particular the one about fewer parts being,
in general, more reliable than many parts doing the same task. In theory
and practice, quality Fastons are reliable in most applications if
properly installed. The are not significantly better or worse than any
other similar connector, like ring terminal, spade terminal or crimp IDC
(insulation displacement connector). I used Fastons in my airplane,
three of them to be exact and so far one has failed. Two are installed
on the Hobbs and one on the Field lead of the B&C alternator. Engine
vibration caused the field lead Faston to fret and develop a high
impedance, disabling the primary alternator. Fortunately I have a
redundant alternator in my all electric airplane so the consequences
were minor.
The problem is that Faston terminals have become ubiquitous. Just about
every would be handyman has one of those plastic cases containing a
terminal assortment and crimper pliers with "Mad in China" printed on
the back. I am sure that our friends in the east follow strict quality
protocols regarding material properties and manufacturing tolerances as
they produce these sets that wholesale for about 28 cents. NOT! As a
result, if you put all the Fastons in the world in a big bag and
randomly selected ten, nine would likely be crap.
My point is that ALL CONNECTORS ARE BAD and should be avoided whenever
possible. Every connector you install carries with it some
un-reliability. Each connector has three critical interfaces; one
between the wire and the first pin, one between the two pins and one
between the second pin and the second wire. Soldering the two wires
directly together eliminates two of the interfaces and increases
reliability at least three fold.
Just because a device has a Faston Spade on it does not mean that you
HAVE to use a Faston shoe. I used two of the B&C 20 position fuse blocks
in my airplane. To connect wires to them I simply passed the wire
conductor through the hole in the spade and soldered it. Applying some
heat shrink produces an attractive and very reliable joint. I also
soldered all the spade connections (and silver soldered the CHT, EGT and
TIT probes) on the sensors for my VM1000 system (which has also
performed reliably).
For some reason people think of solder as "permanent" and if they think
a component may ever have to be replaced or removed it should have a
connector. In most cases a soldered joint is more reliable, lighter,
smaller, cheaper AND FASTER than a connector. Take the case (a true
story) where you have a trim servo that was neatly installed with a
connector. Five years later the servo fails and you order a replacement.
It arrives......without a connector. Oops. Order the
connector......"What do you mean you don't stock that connector
anymore?!?!". After several phone calls, 4 hours, three extra days of
down time and a $20 FedEx bill you have your mating connector.
Installing it takes ten minutes, not including the half hour you spent
looking for that damn crimper. You install the new servo and it doesn't
work. Why? Because the dumb bastard that wired the plane nicked the
conductor on one of the wires on the plane half of the connector and it
failed from the connector body vibrating. Five minutes later the servo
was working properly and all that was needed was to cut out the
connector and splice the wires directly.
Connectors are bad.
Brent Regan
Note: Just so I don't get busted, I realize that the fuses used in the
B&C fuse blocks have two Faston spades on them and that the fuse blocks
are essentially Faston shoe holders so there are, in fact at least 83
known Faston class connectors in my airplane.
LML homepage: http://www.olsusa.com/Users/Mkaye/maillist.html
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