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| Summer 2014 |
| ASK JIM |
 DUTY CYCLEQ. Can you talk a little about duty cycle and how Hypertherm determines duty cycle for its machines? Also, which machine is capable of cutting 1 inch thick material with a cut length of more than 40 feet? A. Duty cycle tells us how long a machine can operate within a 10 minute period. In theory, a system with a 100 percent duty cycle can run for 10 out of 10 minutes, while a system with a 50 percent duty cycle is designed to run for 5 out of 10 and so on. In reality though, duty cycle cannot simply be listed as a percentage of “on time” in a given period. This is because many factors go into determining duty cycle. These things include the output power of a system, the thickness of the metal you are cutting, ambient temperature and more. Modern plasma power supplies produce a constant current (amperage) which is set by the operator, and the load voltage or arc voltage is determined by the length of the arc. If you are cutting thicker materials, the arc length is longer. This means your arc voltage is higher so the power supply has to produce more kilowatts to maintain the arc. In other words, you system is working harder. On thin materials, the arc length is relatively short so you can often run at full output amperage when cutting gauge material without exceeding the duty cycle of a plasma system, even if the system is said to have a 50 percent duty cycle. Hypertherm rates all of our plasma systems for duty cycle based on the maximum rated thickness for each system. We are perfectly honest in our published data as we supply the rated arc voltage, arc current and ambient temperature when the rating was tested and calculated. Things to watch out for when comparing power supplies and duty cycles, and this can apply to welders as well as plasma cutters: 1. Many manufacturers do not supply the information required to determine duty cycle. They must disclose the ambient temperature, load voltage, and wattage in order to honestly portray real duty cycle. Hypertherm provides all of this data. Some manufacturers use a lower ambient temp rating, and a much lower load voltage rating as compared to Hypertherm, by doing this they can show a higher duty cycle at the given amperage. I might add it is less costly to build a lower duty cycle machine! 2. Input voltage also affects duty cycle. A power supply that operates on a wide range of input voltages is always more efficient with higher input voltage. Hypertherm shows different duty cycle ratings for their systems based on the input voltage the system is being used at. Bottom line, do not just look at amperage output for comparison. Rather, look at the true power output which is amps multiplied by load volts at a rated duty cycle. There are a lot of tricks that marketing people can play with numbers and just comparing amps to amps will not determine equality in performance! Torches are another factor that impacts the performance capability of an air plasma system but I’ll save that for another time. Now to answer the second part of your question: Which machine is capable of cutting 1 inch thick material with a cut length of more than 40 feet? In the past I would have suggested you use an oxygen plasma system like the MAXPRO200 or HySpeed HSD130. Those are still great choices; but thanks to the introduction of our Powermax125 late last year, you now have another choice. Like the MAXPRO200 and HySpeed HSD130, that system is a 100 percent duty cycle system. It’s rated to cut 1 ½ inch thick material at a speed of 18 inches per minute so it is more than capable of meeting your needs. Jim Colt Hypertherm's Jim Colt is an avid fabricator who has worked with plasma cutting systems for more than 35 years. He is the author of many articles and white papers on plasma cutting and a frequent speaker at key industry conferences. If you have a question you'd like Jim to answer please send it to askjim@hypertherm.com. Get answers to more of your metal cutting questions at the Hypertherm Cutting Institute. |
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21 Great Hollow Rd, PO Box 5010, Hanover, NH 03755 USA
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