I was welding some 3/8" aluminum, at minimum (20% EP) balance with max (200 amp) current my Everlast Super200P could deliver, with no pulse. The aluminum was cleaned pretty well - sanded, brake parts cleaner'ed repeatedly until the rag came back clean. I even scotch brite and solvent cleaned the filler rod.
I could manage about 2.5" of shiney clean weld bead, and then it would start welding nasty - oxidized, contaminated, etc. A little bit gradually at first, (just a little "pepper in the puddle",) but then the oxide skin would grow worse until it would get to thick it would prevent the puddle from wetting out.
I tried a bunch of things to fix it - changing the tungsten, changing the collet, changing the cup, checking the gas flow. The problem always kept coming back as I welded. My tank of argon was running low, about 400 psi left (which is about 20% of new fill pressure for me) so I did one last test to see if it was bad gas at the bottom of the tank. I hung things up and let it all cool off, and then came back the next day to try again. I again got a few inches of shiny weld bead and then the contamination would come back as the torch and cable heated up.
When the torch was hot, I was still able to hold it by the handle (but not up close though.) I also noticed a distinct smell which is hard to describe, but maybe was melting plastic. It seemed like the argon gas coming out of the cup has this smell. And I noticed that the power cable, draped over my shoulder, was getting noticeably hot too, especially the portion up close to the torch. (The portion of the cable back by the machine wasn't hot.)
So my end diagnosis was, running the torch/cable too hot somehow caused contaminants to be introduced into the shielding gas. Does this sound like I got it right?
I tried tightening the connector inside the handle where the power cable connects to the torch, but it didn't cure the problem. Is the torch I have (says "WP17" on the side) just inadequate for this 200 Amp machine?