Understanding Duty Cycles

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Well, this seems to be one of those helpful little things that one might make the assumption that it'd be taught in any welding class, but, not so in my case....I'm looking to buy a DC stick welder. The one that I'm looking at has a 20% duty cycle, running flat out at 160 amps (full capacity). Its duty cycle hits 100% at 60 DC amps.What I'm trying to find out, is what the duty cycle would be at about 100-120 amps, where I do most of my welding. Is there any sort of an equation, or a graph one could make to find this out?? I've searched the Hobart website and can't find anything too useful. Or, is this something that varies from machine to machine, and isn't predictable... Its something I've kind of been wondering about, thanks guys...[Account Abandoned 8/8/16 Please Do Not Attempt Contact Or Expect A Reply]. See you on YouTube! -ChuckE2009
Reply:Lanse,Look in the manual (if one is available) and you should find a duty cycle graph that answers your question.
Reply:If you can't find the manual for what you have, a Hobart Stickmate is about that size welder.:http://www.northerntool.com/download...als/164679.pdf
Reply:Lanse, I'd expect to see the duty cycle at about 70% for that level of welding. Believe it or not, the units tend to do very well regarding duty cycle and it matters most on ample amperage available, with clean power fed to the unit. Stick is a very simple operation, and so the machine does not have a lot of bells and whistles to muck up the works. Be sure the unit is clean on the inside, blow it out with forced air if it is used, and you will be in decent shape.And then, after so much work...... you have it in your hand, and you look over to your side...... and the runner has run off. Leaving you holding the prize, wondering when the runner will return.
Reply:The duty cycle curves are usually linear, if you look at them, so you can draw a graph with the two points and then draw a line between them.In this case, if we have 100% duty cycle at 60 amps, and 20% duty cycle at 160 amps, you can split the difference.  Halfway between 60 and 160 is 110 amps.   Halfway between 100% and 20% is 60%.   So I would estimate a 60% duty cycle at 110 amps.  You would have to be burning rod pretty hard to get over 60% duty cycle, although it could be done.  By the time you change rods, chip off slag, and wire brush the weld, I think that you will be down to 60% duty cycle or less.  Another reason to sit back and look at your work, and consider what you need to do next, and let your welder cool down.By the way most industrial welders have a nominal rated power at the 60% duty cycle, even though they can put out more power than that at a lower duty cycle.  Look at the millermatic 252, rated at 60% duty cycle at 200 amps.   The Millermatic 180 is rated at 30% duty cycle at 135 amps.  Hobby or light duty welders, like a Millermatic 180, are usually rated at low duty cycles, so a 60% duty cycle at the power levels you expect to use is pretty good.As others have said, the owner's manual often has a duty cycle chart or graph, but if you don't have that, you can make the assumption of a linear relationship between amps and duty cycle.RichardSculptures in copper and other metalshttp://www.fergusonsculpture.comSyncrowave 200 Millermatic 211Readywelder spoolgunHypertherm 600 plasma cutterThermal Arc GMS300 Victor OA torchHomemade Blacksmith propane forge
Reply:yes it is fairly hard to exceed 60% unless you have a helper or your slamming one rod after the other and going back later to chip and wire brush. when i do that i don't chip and wire brush anyway. i grab the needle gun...much faster and easier.225NT bobcatAEAD200LEScott 125mm175, mm252 w 30A, PT225mm211, TA 181iHyper Therm 380, cut master 529100X & XX, Digital Elite6 Victor setssmith little torch, meco midget kalamazoo band sawsteel max saw evoulution circular saw
Reply:My Miller T-bolt manual shows duty cycle for 100 amps dc as being about 45 %. I assume you'relooking at the Stick-mate which appears to be the same or similar to the Thunderbolt xl.(looks the same, weighs the same,same part #'s,20% duty cycle,but rated slightly differently)The only time I've ever been concerned with duty cycle has been when I was practicing with 1/8" 7018.Otherwise set-up,changing electrodes,chipping,etc takes enough time that the machine always has a chance  to cool.If I was repairing excavator buckets etc. it would be a differant storyMiller a/c-d/c Thunderbolt XLMillermatic 180 Purox O/ASmith Littletorch O/AHobart Champion Elite
Reply:Hobart and Miller sites show manuals with duty cycle graphs.Miller a/c-d/c Thunderbolt XLMillermatic 180 Purox O/ASmith Littletorch O/AHobart Champion Elite