EDIT: I typoed and made the subject line "100v extension cord". Obviously, I meant 110v.
In response to Mark's request for shots of customers using Everlast products, I staged some shots today of me "welding on my trailer" (actually a piece of scrap that I clamped to the trailer, but I thought it would look better than just welding up a piece of scrap). In order to get power over to where the welder was, I ran a 110v extension cord--14 gauge, probably. Maybe 12 gauge. 50 feet. No, it's not rated for the 20+ amps that the welder is going to pull, but for a few seconds at a time of arc just to take a shot, I figured no big deal.
Man, it was no good. The arc was incredibly erratic and sputtered and died within a second or two of being struck. I normally run 3/32" E6011 around 75 amps at most, but I had to turn the welder all the way up to its 110v max of 96 amps just to get the arc to stay lit that long. I could tell things weren't right when I could hear the welder's fan slow down about a half-second after the arc started up. We managed to get a few shots taken within that half-second, and there was a total of maybe 10-15 arc strikes, so I doubt any real damage was done, but it was no good. No good at all. It goes without saying that the "welds" were total garbage.
Most likely, the long, thin-gauge extension cord was causing voltage drop when the amperage kicked up. Take it as a lesson, folks: if you're going to run your welder on an extension cord, feed it with a big fat one! Don't pussyfoot around!
Interestingly, I never popped my breaker, even with the welder maxed out. It's a 20 amp breaker at most, so I'm frankly a little surprised. But oh well... there you go.