ok
I get some of this stuff,but what is duty cycle??
Duty-cycle - The minutes out of a 10-minute period an arc welder can be operated at maximum rated output. For example, a 60% duty cycle @ 300 Amps means that the welding machine can be used for 6 minutes (at 300 Amps) and then must be allowed to cool with the fan running for 4 minutes. This reduces the chance of heat damage to the system.
so the Hobart Handler 140 Welderhas a Duty Cycle : 20% @ 90 A,
so whats that mean??
The term is pretty well defined above, so I'm guessing that you want to know the practical impact to you.
Most home/hobby machines have a low duty cycle when run near their max capacity. There just isn't enough metal in the chassis nor a big enough fan/heat sink to allow the lighter duty machines to actually deliver that "140 amps" implied by the model number..
The Hobart Handler is only rated to weld at 90 amps for 2 minutes out of 10. This can be one continuous 2 minute bead, or 8 separate 15 second beads. If you exceed this you risk damaging the machine. If you cranked it all the way up to 140 amps the duty cycle probably falls to 5 percent, or even less. Figure a 30 second bead, then stop welding for 10 minutes to let it cool. It's a little bit like those supposed "5 horsepower" air compressors running on 115 volts.
Many welders have some sort of thermal protection built in, and will shut the welder off if you push the duty cycle too hard, but you shouldn't rely on this.
As you turn the output down from the max, duty cycle rises rapidly until it is no longer a factor. At 50 amps or so, the Hobart can probably run all day (100 percent duty cycle). For sheet metal and light duty fab work you'd never run into the duty cycle limits.
Another factor is that as an individual doing hobby work, it takes you time to set up the pieces to be welded, and to position yourself and the weld nozzle before you pull the trigger. Often you are running only short beads and the trigger is held for only 10 seconds or so. The machine can cool off anytime you are not holding the trigger down, which is a lot of the time. You usually don't need the kind of high duty cycle that would be required in an industrial environment, where the owner expects the welders to be actively welding, not farting around.
I have a Lincoln 175 amp Mig machine, and only tripped the thermal cutout once. I was running a 5 foot long fillet bead between two pieces of structural steel, with the machine turned up fairly high.