Conductive pyrogens are also possible,obviating the need of a bridge wire.
On Wed, Jan 20, 2021 at 12:53 PM Terry McCreary <prfesser@xxxxxxxxxxx>
wrote:
Hello all, I do not solder nichrome to the leadwires and have never needed
to do so (YMMV).
One conductor of the leadwire is snipped about 3/4 inch shorter than the
other, and about 1/4 inch of each conductor is stripped. About ten turns
of nichrome (32-36 ga) is wound *tightly* around both the copper of the
shorter conductor and the insulation of the longer one. The nichrome is
spiraled up, about 2-4 turns, around the insulation of the longer
leadwire. Ten turns *tightly *around the copper of the longer conductor,
snip the nichrome. Dip.
The un-soldered connections will no doubt eventually corrode. How long
does that take? I don't know but I've used motor starters made this way
that were at least three years old with no issues. In practice it would
probably be wise to make no more than will be used within a year.
Some workers cut a bunch of pieces of nichrome of the length needed before
beginning. I've found those to be rather easy to drop on the floor, where I
usually can't find them. I prefer to start with a 2-3 foot long piece of
nichrome, snipping with scissors after winding each one.
Duplex "shooting wire" is most commonly used for leadwire, but the twisted
pairs in CAT 5 cable work nicely, and CAT5 is readily available at Home
Despot or other big-box stores. It's rather stiffer than shooting wire,
which is good; less likely to bend as nichrome is wound around it or as
it's being inserted in a long motor.
Best -- Terry "prfesser" McCreary
**These are "motor starters" or "initiators", not igniters (or ignitors,
ignitirs, whatever spelling you like 🙂). Igniters are BATFE regulated
items, while motor starters are not listed in the Orange Book (for now at
least). 🙂
Nichrome isn't readily soldered, though Rubyfluid Soldering Paste with
60/40 rosin core solder permits rapid solid connections with the
nearly-invisible 36-g wire. I've found that a bridgewire of about
0.5-inch L will swiftly heat to orange-red with the Duracell, yet not
melt or burn thru. If that bridgewire is wrapped around the PVC
insulation of one bell wire strand, it becomes less fragile yet
well-exposed for pyrogen dip.