My small machines in my opinion are really pretenders @ 140 amp max output current since they run off of the 120v 15 amp plug house current, but for what I use them for they work just fine. At least there in Spain your standard voltage is 230 for single ph so a 150 to 170 amp machine will do just fine on the 13 or 15 amp sockets
My mid sized unit is a Miller 210 amp runs on 220v and needs at least a 40 amp breaker
I bet I've bought dozens of the Telwin machines while I lived in Kuwait Telwin is an Italian brand but made in Asia. Not really bad little machines ran on 415 v using 2 legs of 3 ph or as we called it 2 ph but for heavy production welding we could figure on replacing one after it had burned about 1500 KG of wire
My first experience with CO2 welding was back in 1971 with a huge Westinghouse machine about the size of a large refrigerator man how technology has changed over the years.
I would be interested in your write up of your version of 3 ph to 1 ph conversion especially if it is good for the heavy induction loads of the transformers in welding machines