Overheat Miller 212

Ok... it was a over 100 degrees here when I ran into this, but still. I had make to three butt welds the other day in 3" 3/16 wall square tube. I have
welded it before and it came out ok, but I had 3 welds to make all at once. By the time I got to the third one my 212 was welding like crap. I couldn't finish the third weld before the overheat started tripping off. Then I went, "Doh! That's why it was welding like crap." If I had been using my China box flux core I wouldn't have thought twice about it, but this was the first time I ever overheated the Miller.
Anyway, I was wondering if I might have been able to weld longer and finish the job if I'ld been using lighter wire? I have copper coated .035 in it. I don't have a problem setting it aside and using smaller wire if I can weld longer.
Speaking of the Chinese welder. I used it to finish the job. LOL.
(I don't actually do much steel welding in the shop. Mostly aluminum. In the field I use the Chinese welder because I can power it off 120V, and I can carry it with one hand. Flux core also seems to work better outdoors.)
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This really bothered me, so I went out in the shop and played a little just now. Instead of trusting the settings were close I followed the old rule I follow with my two amperage setting China Box. If the wire pokes slow it down. If the wire fizzles speed it up. Over the course of fifteen minutes of free form welding on a piece of 3/16 tube I dropped the feed speed about 13 inches per minute, but it kept welding. Every time it started to poke I turned the speed down again. I had to weld slower and slower, but it kept going.
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Bob La Londe wrote:

Everything has a duty cycle. It appears the 212 is rated 210A @ 30%, 160A @ 60% and about 125A @ 100%. Operating temp range -4F to +104F.
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After my experiment the other day I think I'm going to pick up a roll of .030 and see if that helps me be able to weld longer on stuff like this.
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