I did that to a spot welder I had in the lab Used my 1000 amp HP clamp
on into a HP meter.

The current was just shy of 1000 amps and the voltage was 1.5 open
circuit.

That was a 1/4" spot weld into a sheet of Al.

I think in the way back mode of this group, a home brew was made and
worked. Maybe Don made it or second sourced the design... :-)

Martin


On 9/15/2016 8:43 PM, DoN. Nichols wrote:
On 2016-09-15, Don Foreman wrote:
On Thu, 15 Sep 2016 16:08:30 -0500, Jon Elson
wrote:

Don Foreman wrote:


Sounds like a candidate for a HSM project. I wonder how much current
blade welders deliver. Don't know if a 105-amp MIG would be enough
but a re-wound microwave oven transformer surely would be.
Before I snagged a German blade welder on eBay, I had built a very bad
homebrew one. I found a transformer that had a lot of available "window"
still open, and wound a couple turns of battery cable through that, and made
up a clamp for the blade. It worked remarkably well for a total jury-rig
setup. I know if I had kept on working on it, it could have made decent
blade welds. The transformer in a Do-All welder is remarkably small, but
obviously purpose-built for the job.

Jon

Any chance you could slip a clamp-on ammeter on that puppy while
welding, and also voltage?

Which one -- the home-brew or the Do-All?

From personal experience with an import version of the welder
(came from eBay a few years ago), the weld pulse is too quick to get a
reasonable reading with a clamp-on ammeter. Add an electronic meter
which can measure the peak current very quickly and you will do better,
but that is typically lab bench equipment, not hand-held. Maybe a
storage oscilloscope, or a digital one and you could look at the
waveform out of the clamp-on probe.

Now -- if you operate it from perhaps as low as 6V or so, you
can measure the input and output voltages and calculate the turns ratio.
Then, from that, you can look at the fuse rating in series with the
primary to calculate the maximum current out of the secondary. Assume a
very low resistance load. Remember, the blade forms a complete loop as
it is being welded, so the resistance between the clamps and the ends
has to be a lot lower than the resistance though the blade the long way.

Good Luck,
DoN.