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Duty cycle of a welder (the machine)


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#1 Glenn

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Posted 27 February 2008 - 10:46 AM

A 20% duty cycle would mean welding for only 2 minutes out of every 10 minutes.

My question is what do you do the rest of the time? Let the machine run idle, turn it off, or what? How can you tell if you are exceeding the duty cycle and what happens if you do?

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#2 aametalmaster

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Posted 27 February 2008 - 11:43 AM

My Miller mig has a 60% duty cycle and i weld with it 8 hours a day when i am building my bridges. But its not a solid 8 hr weld because i have to put the parts in the welding jig so i guess the welder cools down then. I have never overheated it and i think mine has a breaker that trips, but some don't. I normally don't shut it down after i have been welding heavy because the cooling fan shuts down as well so i let it idle for a few minutes...Bob

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#3 Hillbillysmith

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Posted 27 February 2008 - 05:07 PM

You just let the welder sit and run. The time that it takes you to change electrodes, chip the weld, move the part, make another fit-up, etc is enough time for the welder to do what it needs to do to cool down. But, if you weld and do all these things too fast, then there is a great chance to overheat the machine. I have actually done this before several times. What happens is the stinger gets extremely hot and you start to smell a heavy "burning plastic/varnish" smell. That is the coating on the coils. But these machines are pretty tough, so its not THAT big of a deal as long as you don't do this too much or for too long.
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#4 Dodge

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Posted 27 February 2008 - 06:52 PM

The same is true with Mig machines. When I worked at a light pole and transmission structure manufacturer it was not unusual to weld for 5 - 10 minutes in one pass on larger work or many shorter passes with little time passing between welds. I remember that smell that Hillbilly described when the machines would really get a work out. These units were 450 amps at 38 volts DC and ran on 440v current with a 100% duty cycle, however. The most obvious affect we would see to over heating was the in the increased used of consumables such as contact tips, gas nozzles, and insulators etc.

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#5 Jose Gomez

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Posted 27 February 2008 - 07:41 PM

There is also a change in the way that the puddle acts as the temperature of the coils in the machine rise. When mig welding the puddle will tend to become noticeably stiffer and slightly more agitated, increasing the ammount of spatter. The arc will also tend to pop or sputter as the duty cycle is approached or exceeded. with stick welding the arc may tend to "soften" as the machine heats up. This is due to a slight heat associated loss of conductivity in the coils of the typical Transformer-rectifier style machines most welders are used to. Nowdays it is unusual to find a machine that does not have thermal overload protection, but they do exist. Though most machines are capable of functioning beyond their duty cycles these slight changes in performance can significantly impact the soundness of the weld, especialy with mig. MIG is already prone to cold lap, or lack of fusion, and with the additional problems caused by overheating the machine you give yourself a pretty good chance of ensuring it. Additionally, regularly overheating any machine will lead to loss of overall performance. Unfortunately, this loss typically occurs so slowly that it is difficult to measure untill the day that you realize that, "This machine just don't weld like it used ta!" or "All it does is sputter and pop" or "It'll weld good for a second but then it seems ta get a little weaker". The moral of this story is that any time you push the upper limits of any machine the overall performance is reduced and it has a measurable effect on the overall lifespan of the tool. Though it is unavoidable to exceed the duty cycle sometimes (long or large single pass welds) it should be avoided whenever possible. Your finished product will be of higher quality and your equipment will last longer. Happy Welding!

#6 irnsrgn

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Posted 27 February 2008 - 08:35 PM

you left out a critical part of duty cycle Glenn, 20% duty cycle means 2 minutes arc time out of 10 at maximum amp setting. You can usually use the machine at 50% amps or less continuous without damaging the machine.
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#7 gerald

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Posted 28 February 2008 - 08:45 AM

I don't know what happens when the duty cycle of the machine is exceeded since that duty cycle (20%, 40%, whatever) ALWAYS seems to exceed my own personal duty cycle. :)
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#8 GrandLordKhorne

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Posted 28 February 2008 - 12:47 PM

Duty cycle is why I tell most people who ask me what sort of welder to buy that they should figure out what they need and go at least one or two models better. Having said that Jose hit the nail pretty much on the head. The only thing I would add, is if you have a cheap machine without a auto-overheat-stop in it, it may catch on fire, I have personal experience with this. I will say, there is always a way to redesign or rework your project so that it can be welded in shorter sets and if you can not fined a good way to do it, rent, beg or barrow a better machine that suits the need. Even if the welder is a cheap one and you don’t care if it dose not outlast the next year, money is money and you can sell it used towards your next one if it is in good shape.

#9 covforge

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Posted 28 February 2008 - 03:46 PM

I agree with Gerald usually the welder outlast the weldor. Most welders are heavy enough that it's hard to hit the duty cycle.The little low amp ones are only desighned to do small projects. I have seen a 300 amp welder cut out but it was pushing a mig gun at 250 amps with a yung man holding the gun.
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#10 GrandLordKhorne

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Posted 28 February 2008 - 08:07 PM

^ It all depends on what your welding. A lot of the thin sheet I do runs a high % of weld time to cool time which brings it close to Duty Cycle on smaller welders or at high amps for special materials. But even on my 250DX, when I weld copper for instance, when you get up into the upper reaches of the machine it can be pretty easy to push duty cycle. The rule I always recommend if you are not sure, test your self. Get a stop watch and see what % of the time you’re welding and if you are pushing it, than puts a little to compensate. A big part of it is how well organized your welding project is as well.




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