From http://www.kevincaron.com'>http://www.kevincaron.com Artist Kevin Caron explains what "duty cycle" means when talking about welders ....

Caron takes a break from working on his latest sculpture to compare the duty cycles of three different welders and explain what duty cycle is and why it's important. The first machine is the Longevity ProMTS 200, which has three welding functions in one machine: MIG, TIG and stick (or arc). He defines "duty cycle" as how long you can run a welder over a given period of time at maximum amperage. For instance, during a 10 minute period, the ProMTS's 30 percent duty cycle means you can weld for 3 to 31/2 minutes at 200 amps (its maximum amperage), and then the machine needs to cool down the rest of the 10 minute period. Caron says that this is true for each of the functions on the welder (MIG, TIG and stick. (That doesn't mean the machine will only run for 3 minutes at a time. It will weld for much longer than that, especially if you're not running at maximum amperage, but this example helps explain what duty cycle is and how it works.) For instance, Caron had just been welding at about 80 90 amps, so he estimates he could have welded continuously for an hour before the welder shut itself off to cool down. Next he shows Longevity's MigWeld 250P. It's a MIG welder with a pulse function. It also has a duty cycle of 30%, but he's welded at 150 to 170 amps on 1/2" plate with this welder and never had it shut down on him. Then he compares the MigWeld 250P to the Millermatic 251, which is another 200 amp MIG welder, although it doesn't have pulse. The Miller is also a transformerbased machine, whereas the Longevity is an inverterbased welder. The Millermatic's duty cycle is 60% at 200 amps and 40% at 250 amps, so they're pretty close as far as duty cycle. What determines duty cycle? Caron says a lot of it boils down to the size of the electronics, how durable they are, and how readily they shed heat. These welders have temperature sensors inside that determine whether the machine is getting overheated and needs to shut down to get back to a more manageable temperature. So the Millermatic is probably a little more robust. It probably has a heavier cooling fan, bigger cooling fins, more robust electronics, etc. Next Caron shows the AHP AlphaTIG 200X, which is a TIG welder with a builtin stick welder. Its duty cycle at maximum amps is 60%. What's the difference? It has a big case, whereas the Longevity has three functions in a much smaller case. When Caron turns on the machine, he can feel the hot air coming out of the ducts 15 feet away. Why does duty cycle matter? It depends what you're going to do with the welder. Are you going to be doing short runs, like Caron does, or are you going to be in a production facility where the machine is running all day long? If you're going to be welding for a living, say, 6, 8 or 10 hours a day, you want the highest duty cycle you can find so you can keep working. See more howto videos at http://www.kevincaron.com'>http://www.kevincaron.com