"jim rozen" wrote in message
...
| In article s.com, Karl
| Townsend says...
|
| I have a multi conductor cable with very small wires. I guess 22 or 24
| gauge.
|
| Those are huge wires. :^)
|
| My suggestion would be *not* terminate those under screws.
|
| If it's a standard, double screw terminal board barrier strip,
| take out one of the screws and solder the wires directly to
| the terminal.
|
| To strip those I use a standard el-cheapo stripper made of
| what looks like strap iron. Those typically have a limit
| screw that allows them to only close so far, so the V-shaped
| notches only cut the insulation. I find that the simple
| ones work better, overall, than the fancy ones.
|
| I suggest you do like I do, and throw away the limit screw,
| and do it by feel.
|
| Strip only 0.1 inch or so of insulation, and tin the wires
| without melting much of the insulation if you can. If
| you can get the solder to flow up under the insulation
| a bit, that's OK even if it cooks up the plastic a teeny
| bit. Gives it extra strength at the stress point.
|
| Then tin the barrier strip, and then tack the wires onto
| the region where you tinned them.
|
| The key to this approach is you need to mechanically strain
| relieve the cable jacket near the strip so the wires *never*
| see any stress. Unless you have a strain relief set up
| somehow, I would suggest you drill a couple of holes in
| whatever is supporting the barrier strip. Drill two pairs
| of holes, with each pair separated by about the diameter
| of the cable jacket. Then pass a nylon zip tie through the
| holes from underneath and cinch them down across the cable
| jacket, immobilizing it.
|
| The trouble with crimp or solder lugs on conductors of this
| size, is that eventually the wire will flex near the termination
| and fail at that point. Also it's tough to get crimp lugs
| that work really reliably on 24 gage conductors.
|
| A microscope is actually pretty handy for stuff like this.
|
| Jim
|

I handle wires in the 24 gauge range all the time, and while Jim is
right on about the issues, I'll add a few more.

Soldering wires this size (or any size of stranded wire, for that
matter) creates a stress point at the spot where the solder stops. One side
flexes, the other doesn't, so fatigue breaks the wire. It isn't enough to
just support the wire near the joint, you really need to stick the whole
thing down. I like silicone RTV for jobs like this. Just slather the joint
and wires to about half an inch back (gotta go about 1/4" beyond the solder
wick point) so that no part of the joint sees any sort of vibration.
There are terminals and lugs made for this size wire. Amp is the common
one I use, in aerospace grade, but there are others. This size usually
takes special luggers, though. The terminals work best because they crimp
the strands of wire (without solder) but most importantly have an insulation
grip. Wires that size we also have to add shrink sleeving over the whole
thing for more support.

At home, if I have to so something like this, I cut the end of the
ribbon cable straight, and do not separate the wires yet. Mark the strip
lengths on the end wires on both sides. Go get a brand new razor blade, and
with the lightest touch, just nick the insulation on both sides with a
single pressing motion, rather than a cutting motion, and not deep enough to
get near the conductor. Fold the "tab" until you see strands on both sides,
indicating that the insulation has "ripped" clean through. Now, gently
separate the conductors without removing the insulated part of the wire.
Only at the very last moment when you are ready to make the connection will
you gently pull the piece of insulation off. You will find it is perfect,
stranded neatly still, and nick free. If you have to tin it, put a _wiped
off_ iron tip on the wire in the middle of the exposed strands. Touch your
65/35 (not 60/40!) solder to the end of the wire and you will see the solder
wick to just beyond the iron tip. As son as the wire starts to wick up the
solder, pull the iron and solder away. You'll get more wicking when you do
the next solder operation, so you need a small dollop of solder at the joint
already in place. Melt the dollop, insert the wire, and pull the iron away
quickly. If you use 65/35, you will not get a cold joint and the wicking
will be at a very minimum. If you prefer, Rat Shack used to/still sells
flat tipped alligator clips that you could use for anti wicking tweezers,
but they always took up too much open space on the strands for my taste.