Carl Ijames wrote:

I (probably among others) suggested discharging a capacitor into the
primary of a soldering gun to get a high current pulse out the secondary
as a spot welder, but I've never tried it myself. However, for blade
welding you need continuous current to do resistance welding, not a
pulse of current for a spot weld. Maybe this is what to do with all
those old low duty cycle ac stick welders now that everyone has moved up
to MIG? :-)


That won't work. The transformers have a HUGE leakage inductance, and run
right at the edge of saturation as it is. You really can't get much
more out of them
than they already produce. Also, the primary wire is much too thin for high
current pulses. If you made a somewhat larger transformer, with just a few
turns of primary, and a one-turn secondary, and interwound the pri and sec
windings to get the leakage inductance down as far as possible, and then
dumped
energy storage caps into the primary, that could very well work, sort of.
But, you'd get a VERY narrow weld zone, which might lead to a weak joint.
The commercial welders take about 1/4 second or so to make the joint,
providing time for the metal to fuse and upset (push together) a bit.
I don't know if this is necessary, but I suspect it really is for this type
of weld, a butt weld. The strength comes from the merging of metals on both
sides of the joint, and a millisecond pulse weld probably is not the correct
way to butt weld thin strips. (It does work fine in spot welding thin
sheets.)

Jon