Douglas...
AS I was reading I thought...OK this guy is giving a fairly
good description of soldering to the masses.
BUT! you've made one MAJOR ERROR in your description
(and apparently in your technique.)
Solder itself is only designed to maintain the
mechanical connection. IT IS NOT designed to BE the connection
nor is good at handling current. The chemical/molecular
junction where solder meets metal is resistive. Current
passing through this junction creates heat.
This is why all high power joints are crimped.
(then some are also soldered but to maintain
mechanical joint integrity.)
The proper connection is to first produce a good
mechanical bond, then use the solder to hold it in place.
Clean the wires, (splay the stands and lightly sand them)
wrap them together tightly, then solder them as you described.
The IEEE Institute has extensive documentation on this
subject. Years back, I had to spend quite of bit of time studying this,
what seems to be, simple subject. At that time I was working
on and designing automated test facilities for Hybrid micro-circuits
in a clean room environment and our studies were related
to the metallurgy of the solder connections and wire bonds on the dies.
Do a simple test yourself. Use a crimped, un-molested
battery to starter cable.....
then use a battery cable as connected like you described, simply joined
with solder. You've got yourself one heck of a heater. :-)
Sure this is an extreme case but it will verify
without a doubt, the need for a good, clean, mechanical connection
first, regardless of power levels.
Paul Tegler ptegler@gouldfo.com www.teglerizer.com
----- Original Message -----
From: "Douglas" <mup1dm@surrey.ac.uk>
To: "mgs" <mgs@autox.team.net>
Sent: Monday, March 05, 2001 8:42 AM
Subject: RE: Wiring basics
It has been written:>That's what I do when I need to join a couple of
wires....solder.
Since most of us on the list are beginners in SOME aspect of working
on our MG's, I'll chip in where I have some expertise:
The Basics of Soldering:
When you solder wiring you are joining two bits of metal with some
other metal. When done right it will be the best sort of connection
that can be made. It isn't even difficult to do.
Equipment:
Soldering iron: For sensitive electronics you want a low wattage iron,
but for general purpose joining wires, 20-30 watts should do. The ones
that are 100 watts and over are more intended for plumbing, but will
do in a pinch. I've started buying irons in "closeout" type stores for
$3 and under, because I do audio work in so many places that it helps
to have basic tools in each location rather than dragging everything
with me all of the time. I haven't found much practical difference
between the cheapies and the major brands.
Solder: You get choice of alloy, size, and flux. Biggest element is
flux -- for electrical work you want rosin core and NOT acid core
solder. Alloy will be listed as 60/40 or 70/30 etc. and it doesn't
make much difference in practice. Size is a matter of taste and what
you are working with -- if find that I always have problems getting
too much solder in a joint and never too little, so I always go with
the thinnest solder available. Bottom-line -- if it is on the same
store display as the 20 watt irons it is highly likely to be tthe
right stuff.
Clamps to hold wires. You can buy those little alligator-clip
many-jointed weighted-base "extra hands" tools, but I usually just
wrap a rubber-band around the handles of a pair of pliers and use
that as a clamp to hold one of the pair of wires in a fixed position.
Technique:
You need bright shiny metal on both pieces to be joined. Strip back
until you find it. Better to splice in extra wire if you end up too
short than to have a bad connection.
You might want to burnish the tip of the soldering iron before heating
it. Heat the iron, then clean off the tip with a damp sponge, then
'tin' the clean portion of the soldering iron tip by pressing the end
of the new solder against it. If it 'flows' on everything is good, if
it 'beads' then either your iron isn't clean (of oxidation) or it
isn't hot enough yet.
Many people like to make a linesman's or western-union splice, so that
there is strength against pulling in the joint. My view is that the
wire ought to be secured on both sides of the joint to cable clamps or
similar, so I am more interested in electrical than mechanical 'good-
ness' in the joint. Here is my technique:
Slide on "heat-shrink" tubing (long enough to cover joint and a bit
either side.
'Tin' each bare end of wire. This means coat it with solder. You do
this by heating the WIRE until it is hot enough to melt the solder.
To do that you need good heat conduction between the wire and the
iron, so your clean iron should have a little bit of bright new solder
on it (a tinned iron). Heat the end of the wire until it starts to
'draw' the solder off of the iron, then press the new solder against
the wire (but not against the tip of the iron) and let the wire
draw up solder until it reaches the insulation. Do this on all of
the bare ends that you are joining.
Hold all of the tinned wire ends securely together (this is where
you need three or four hands) and heat them with the soldering iron
until solder flows between them. Remove the iron and let them cool
naturally.
Now weatherproof with heat-shrink tubing or tape, and attach wire-
clamps or other strain relief. And you are done!
Douglas McKinnie
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