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Posted for Gary Casey <glcasey@adelphia.net>:
With a great deal of trepidation I'll take a slightly opposing view - maybe
more of a glancing view, as I don't actually disagree with any of the
previous posts. There appears, at least to the average builder like me, no
attempt made by the manufacturers to standardize connectors in our aircraft.
Consequently, to do an adequate job of crimping the terminals one would need
maybe thousands of $$ of crimping tools. People who do large volumes of
crimped connectors eschew even expensive manual crimpers, saying they still
allow for variability. Soldered joints can be made to be reliable, but it
takes some skill and practice; fortunately not money. I crimped those
connectors for which I had what I considered to be an adequate crimp tool,
but soldered the others, which meant most of them. The same is true of
splices.
At my day job we solder perhaps 200K joints a day and we found that the
control of heat and time is the key. Solder will wick up a stranded wire,
making it rigid and therefore prone to failure only if the wire is above the
melting point of the solder. If the wire extends through the crimp portion
of the terminal and is exposed (as is the case for Faston terminals)
soldering is fairly straightforward. With a hot iron (how hot? not sure,
but certainly above 400F) touch the iron to the terminal near the wire end.
It can touch the wire end, but that isn't necessary. It takes a tiny bit of
solder to enhance the heat transfer at this point of contact. Apply the
solder to the tip of the exposed conductor and as soon as the solder wets the
wire and terminal remove the solder and heat. Don't wait for the solder to
fully wick into the joint - the solder is only there to guarantee electrical
contact, not to provide mechanical strength. To make a nicer looking joint
and remove any solder balls that might inhibit the terminal from going into
the connector give the terminal quick flick to fling off the excess solder.
The bottom line is that the wire that goes into the terminal is never heated
above the melting point of the solder, preventing solder from wicking back
into the wire. Time is very important - the terminal should be heated above
the melting point for the shortest possible time as anything more than 1.5
seconds starts to degrade the joint and makes wicking into the wire more
likely. The same basic technique can be used for wires than aren't exposed,
such as those that go into a "solder pot" type of terminal. Heat the
terminal, NOT THE WIRE, and touch to solder to the wire/terminal interface
after the terminal is hot and then immediately remove the heat. I usually
pull the wire slightly out of the joint so there is some bare wire exposed
and then after the solder melts and fills the joint I push the wire in the
rest of the way at the same time I remove the heat. Only the tip of the
wire will then be above melting temperature, avoiding wicking.
Also, as many have said, the strain relief is the key to durability and any
terminal without one built in has to have something done to provide strain
relief. What I do for any connector exposed to vibration, even if it has a
good strain relief, is to double over the wires (make into an "S" with the
connector in the middle) and tie the wires back to the connector body. I am
willing to splice wires with solder and I do it "end-to-end" by spreading the
strands a little and then pushing the wires together. Solder is applied to
the point where the wires connect, but again very quickly so that the solder
won't wick past the actual connection. Then the spice is doubled over and
the shrink tube previously slipped over one of the wires (you did remember to
do that, didn't you?) goes over the whole thing. Finally the wire is tied to
the bundle to keep it from moving. For connectors with clamp-type strain
reliefs the trick is to slightly push the bundle into the connector before
tightening the clamp to ensure that none of the wires has any stress on it at
the terminal.
Just a suggestion,
Gary Casey
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