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Thread: duty cycle

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    duty cycle

    Hi, new to welding and have a question about duty cycle specific to TIG welding. I understand that it is a period of time out of 10 minutes that you can continuously weld. What if you start and stop again within a very short time, how does this factor? Also does anyone here run into duty cycle forcing them to stop welding but you know that you can continue to weld if it were not for the machine overheating?

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    Re: duty cycle

    Starting and stopping is considered "tacking". I've never heard of anyone overheating a machine while tacking.

    I've had a few occasions with a Lincoln Cracker Box (AC) machine where I stopped due to the overheating odor.

    Most of my welding has been done in the Heavy Industrial construction field. There are few
    duty cycle issues in that arena. Hit the reset button and continue on.

    Thanks,

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    Re: duty cycle

    A good part of this question could be answered knowing the machine and it's intended use. If you have a very small machine, then duty cycle issues are more likely to be a problem than with say a larger machines, since chances are you will be running closer to the "edge" with the smaller machine.

    If you have a very small Dc tig ( 95 amp max for example), there is a very good possibility that you will exceed the duty cycle on the machine if you are pushing it pretty hard.

    For the home hobbyist with a 175-200 amp tig, chances are you will exceed the duty cycle on the torch before you exceed the duty cycle on the machine, assuming you are using the stock air cooled torch that comes with most machines. If you are running a water cooled torch, especially if trying to do high amp tig on alum, then chances are you can easily exceed the duty cycle on the machine if you are not careful.
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    Re: duty cycle

    Quote Originally Posted by an75 View Post
    Hi, new to welding and have a question about duty cycle specific to TIG welding. I understand that it is a period of time out of 10 minutes that you can continuously weld. What if you start and stop again within a very short time, how does this factor? Also does anyone here run into duty cycle forcing them to stop welding but you know that you can continue to weld if it were not for the machine overheating?
    For most hobby/home welding you'll not hit the duty cycle because, as you mentioned, you rarely weld continuously even if the machine has a low duty cycle of 20%. That is 2 minutes of straight non stop welding.

    Now watch a clock for 2 mins starting now
    .
    .
    .
    .
    get the the idea?


    You'll weld a bead,stop, move to another section, weld a bead, stop, weld another bead.. so on and so on.

    * Note- it is possible to hit the duty cycle so if you do then you just need to adjust your sequence.. if you hit it a lot, time to buy a new machine
    Last edited by Broccoli1; 08-30-2012 at 11:40 PM.
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    Re: duty cycle

    Quote Originally Posted by Broccoli1 View Post
    get the the idea?


    You'll weld a bead,stop, move to another section, weld a bead, stop, weld another bead.. so on and so on.
    And thats assuming you prepped everything right and your welds go fine, if not its weld, stop, grind, And all of that takes more time than one would know.

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    Re: duty cycle

    most of the newer big name machines have a thermal shut down built in that will kill the welding output if the machine gets too hot. I have rarely seen them hit this in hobby use.

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    Re: duty cycle

    I have a Lincoln squarewave 175, and had to use it to finish a project for which one would otherwise not use tig. I welded 17 of the 100 brackets with my 175 mig, before I broke the trigger (fixed that later). The material was 1/4 x 1 1/2 HRS FB, welded to 1 1/2 x 1 1/2 x 1/4 HRS angle. Three 1.5" welds on each piece, and the part had to be moved 90 or 180 degrees for each piece (turned the parts into counter top supports).

    I had three parts on the table at one time. I'd do one weld, rotate all three pieces, do another weld, rotate three pieces, and so on and so on. 5 hours or so of welding, once all of the parts were tacked up, and ready for finish welding. Averaged out to 3.15 minutes a piece of welding, including material handling time. The second 50 took a lot less time to weld up. At first, I could only run the machine at 150 amps, since I only had a 20 amp breaker in the wall, and could only do about 7-9 brackets, taking my time, before the breaker blew.

    A few brackets into each run of 25 or so, and the torch was definitely getting warm. Had to hold it at the end of the plastic insulation, furthest away from the torch. After the first batch of 50 (again,17 were mig welded), I purchased a $7.98 cent 30 amp breaker, stuffed it into the panel, cranked the machine up to its max of 175, and went to town. No issues at all with the machine, or the breaker. Welded up 25 brackets, wiped (acetone) the other 25 brackets down, and tack welded them together, then welded those up.

    Just writing this to give some input into duty cycle on the Lincoln 175, and to support what DSW said about the air cooled torch getting WARM with continued use.

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    Re: duty cycle

    Quote Originally Posted by Broccoli1 View Post
    For most hobby/home welding you'll not hit the duty cycle because, as you mentioned, you rarely weld continuously even if the machine has a low duty cycle of 20%. That is 2 minutes of straight non stop welding.

    Now watch a clock for 2 mins starting now
    .
    .
    .
    .
    get the the idea?


    You'll weld a bead,stop, move to another section, weld a bead, stop, weld another bead.. so on and so on.

    * Note- it is possible to hit the duty cycle so if you do then you just need to adjust your sequence.. if you hit it a lot, time to buy a new machine
    Ok so doesn't starting, stopping moving and starting again have an effect on the machine overheating as it doesn't have an adequate time to cool off? My understanding is a 20% duty cycle means that you weld for 2 minutes cool for 8 to get another 2 minutes of welding.Now if you cool for 4 that gives you 1 minute of welding when you restart as the machine is still hot, am I correct in this assumption (I understand that the numbers are estimates as well thus theoretically speaking)? Also, since I've never laid a bead, is it normal to weld continuously for 2 4 or 6 minutes?

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    Re: duty cycle

    Most or some duty cycles are rated/tested at 40 c (104 f ).

    So if your ambient temp is below 40 c, then your duty cycle would be extended.



    Some manufactures/resellers bolster their duty cycles by testing at a lower ambient temp.

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    Re: duty cycle

    Quote Originally Posted by an75 View Post
    Ok so doesn't starting, stopping moving and starting again have an effect on the machine overheating as it doesn't have an adequate time to cool off? My understanding is a 20% duty cycle means that you weld for 2 minutes cool for 8 to get another 2 minutes of welding.Now if you cool for 4 that gives you 1 minute of welding when you restart as the machine is still hot, am I correct in this assumption
    Well, to get back to the "zero" or "break even" point after welding 2 minutes at 20% DC, you would need to cool, with the fan on, for 8 minutes. If you only allowed 4 minutes cooling time, that would mean you were still in the "red" on your cooling time if you started welding again. IMHO, you should probably stick to the "10 minute" DC rule/schedule.

    Quote Originally Posted by an75 View Post
    Also, since I've never laid a bead, is it normal to weld continuously for 2 4 or 6 minutes?
    For a hobbyist, it would probably be very rare and in any event probably not anything to worry about.
    Last edited by Kelvin; 08-31-2012 at 06:51 PM.

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    Re: duty cycle

    15 years ago, i had a 130amp MIG that i hit the duty cycle a few times. Never welded the same after. Sent it in for repair and burnt it a short time agail later.

    I then went out and brought a 210amp unit and never had problems again.

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    Re: duty cycle

    Quote Originally Posted by LarryO View Post
    Most or some duty cycles are rated/tested at 40 c (104 f ).

    So if your ambient temp is below 40 c, then your duty cycle would be extended.



    Some manufactures/resellers bolster their duty cycles by testing at a lower ambient temp.
    Ya, I understand that duty cycle ratings should be taken with a grain of salt and that they are simple estimates.






    Quote Originally Posted by Kelvin View Post
    Well, to get back to the "zero" or "break even" point after welding 2 minutes at 20% DC, you would need to cool, with the fan on, for 8 minutes. If you only allowed 4 minutes cooling time, that would mean you were still in the "red" on your cooling time if you started welding again. IMHO, you should probably stick to the "10 minute" DC rule/schedule.



    For a hobbyist, it would probably be very rare and in any event probably not anything to worry about.
    Hmm. So I assume that large pipe welders and such have this issue then (maxing duty cycle I mean)? Also it seems that the machines they use are the same as the ones sold to the hobbyist/home welder and they dont have any improved cooling.

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    Re: duty cycle

    Quote Originally Posted by an75 View Post
    Hmm. So I assume that large pipe welders and such have this issue then (maxing duty cycle I mean)? Also it seems that the machines they use are the same as the ones sold to the hobbyist/home welder and they dont have any improved cooling.
    It sounds like you already know the answers to your own questions, so I'm not going to argue with you. Good luck.

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    Re: duty cycle

    I just sold a 130A, 120V MIG to a guy. I think he burned it up from overheating after a day and a half.
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    Re: duty cycle

    Quote Originally Posted by rabidchimp View Post
    ...At first, I could only run the machine at 150 amps, since I only had a 20 amp breaker in the wall, and could only do about 7-9 brackets, taking my time, before the breaker blew.

    I purchased a $7.98 cent 30 amp breaker, stuffed it into the panel, cranked the machine up to its max of 175, and went to town. No issues at all with the machine, or the breaker.

    -Aaron
    Hmmm.. not wise. In fact this is a dangerous thing to do.

    I'd be willing to bet that your home / shop wiring between the circuit breaker and the wall outlet was 12 gauge. The general code rating for most locations with that gauge wiring in the US is 20 Amps. The circuit breaker is there to protect your wiring, inside the walls of your home / shop, so it will never get too hot (and start a fire.) And yes, with those electrical / building codes, there may be a slight safety margin build in.. you might have beat the odds this time, but why do you think those codes are in place, anyway?

    Please, put the original 20 Amp circuit breaker back in the box. If you need more capacity, have an electrician quote you for a wiring upgrade.. You can go to a 50 amp circuit (6 gauge wire...) Play it safe for you, your property and the ones you love. (and if I've got my assumptions incorrect, apologies up front...)

    Zip...

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    Re: duty cycle

    Depending on machine, Ive witnessed erratic arc from a tombstone I was working, my cute 120v MIG cut-out on thermal O/L and my shops Maxstar 150 will quit welding until she cools again. Maxstar has never quit when wired to 208/230 though...

    I prefer engine drives for everything, while not always practical I know I have 100% duty cycle. Pipe welding can take a toll on an inferior machine.

    For the home hobbyist, get setup with 230/240V machine and start burning. You'll likely never hit Duty Cycle, and have a much more enjoyable experience, not to mention the extra options with real machines...
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    Re: duty cycle

    Quote Originally Posted by an75 View Post
    Hi, new to welding and have a question about duty cycle specific to TIG welding. I understand that it is a period of time out of 10 minutes that you can continuously weld. What if you start and stop again within a very short time, how does this factor? Also does anyone here run into duty cycle forcing them to stop welding but you know that you can continue to weld if it were not for the machine overheating?
    First, keep in mind that 'duty cycle' over a 10 minute period is not a 'standard' per se. Each manufacturer is free to pick any standard they want. The better ones actually tell you under what conditions you can expect say 30% duty cycle. Its one thing to run your machine at the artic circle, its another thing to run it in Phoenix Arizona during the summer.

    Again, the better machines also have thermal limiting systems that will typically cut-off the power if you exceed some threshold.

    That being said. If you running your MIG wide open on 110V, it really doesn't take much to overheat it. Do you have to wait 10 minutes to let it cool down? No, it would be best, but if you have an inch of bead to run, wait a minute, then finish it off.

    The better machines out there carefully analyze air flow through the cases. Make sure your fan is unobstructed and clean. Place your welder in a cooler place and maybe point a big fan at it. On the cheaper units (say Harbor Freight) pump a squirrel cage fan straight into it and see what happens. I don't remember the brand but one of those cheap Chinese welders had a 90Amp and a 110Amp version and we could tell the only difference was the fan. Friend bought the 90Amp and install BFF (Big Fine Fan) - actually ran it with the cover off and a fan pointing right at it. Definitely gave it a bit more life.

    Oh and tacking a large panel can lead to overheating... at least with the aforementioned 90Amp Mig. A rough guess, we had about 16 ft of tacks on automotive sheet metal.
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    Re: duty cycle

    Thanks guys. Seems that this discussion has gotten me thinking a bit. Would there be a market for improving cooling on a machine, or a better cooled machine? Seems that the oil and gas sector would have lots of welding as well as large manufacturing or do they all use engine powered welders (madmax31 mentioned that they are 100% duty cycle)?

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    Re: duty cycle

    Industrial welding bussineses will choose a welder that will meet their duty cycly requirements rather than buying a small machine and try to cool it.

    For instance, my Kemppi does 430amps at 70%@40c and 400amps at 100%@40c, so i could weld at 400amps all day without hitting the duty cycle limits.
    On a 20c day, i could probably/nearly weld at 420 all day without hitting duty cycle.



    You can get non-engine drive machines that do 100% duty, but not all that common.

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    Re: duty cycle

    I spent six straight hours once off the duty cycle reservation doing a emergency front end loader cutting edge replacement. He was having his 1/8th mile driveway paved and was prepping it the day before and broke the cutting edge. The new edge was standing in the corner for over a year when it broke. Anyway we both had the exact same welder which was to small for the application in the first place but sometimes you gotta do what you gotta do. So the deal was I'd do it for him but use his welder. Five hours later the magic smoke poured out. The transformer actually melted down. Did the last hour with mine and a half dozen beer breaks

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    Re: duty cycle

    Even if a unit is rated at 20% duty cycle, that doesn't mean it is inferior.
    Yes, my Ranger 9 had a 100% duty cycle. I did enjoy that.

    But if you never need to weld over 250amps, and your unit is a 350amp unit, depending on the manufacturer, 250amps may very well run at 100% duty cycle and only 350amps at 20%. I just made up those numbers. Not actual numbers. But you can see how selecting a machine based solely on a duty cycle higher than 20% could be misleading.
    I only welded with my Precision Tig at Max amps for 20 seconds just to see what that was like. I have never actually needed that.
    I did weld at 250amps for a while on aluminum though.
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    Re: duty cycle

    Quote Originally Posted by an75 View Post
    Thanks guys. Seems that this discussion has gotten me thinking a bit. Would there be a market for improving cooling on a machine, or a better cooled machine? Seems that the oil and gas sector would have lots of welding as well as large manufacturing or do they all use engine powered welders (madmax31 mentioned that they are 100% duty cycle)?
    they already exist- but if you want to go in to engineering ...You'll probably need Electrical and mechanical .. for creating an even more efficient machine there's nothing wrong with that. Welding Manufacturers are always looking for ways to improve their products- just look at the history of welding machines.

    I think you need to to do some research on Welding machines so that you understand them a wee bit more.

    You can get 600amp Water Cooled Mig Guns so that you don't burn up the Gun when welding at high amperages
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    Re: duty cycle

    Quote Originally Posted by Joker11 View Post
    Even if a unit is rated at 20% duty cycle, that doesn't mean it is inferior.
    Yes, my Ranger 9 had a 100% duty cycle. I did enjoy that.

    But if you never need to weld over 250amps, and your unit is a 350amp unit, depending on the manufacturer, 250amps may very well run at 100% duty cycle and only 350amps at 20%. I just made up those numbers. Not actual numbers. But you can see how selecting a machine based solely on a duty cycle higher than 20% could be misleading.
    I only welded with my Precision Tig at Max amps for 20 seconds just to see what that was like. I have never actually needed that.
    I did weld at 250amps for a while on aluminum though.
    I see what your getting at. If you know your going to weld at 200amps max for a period of time you will buy a machine that will to 100% duty at 200amps. This means that it may be rated at 350 max, but duty cycle at this max range (which you know you will rarely weld at) may be 20 or 40 percent.

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    Re: duty cycle

    Quote Originally Posted by zipzit View Post
    Hmmm.. not wise. In fact this is a dangerous thing to do.

    I'd be willing to bet that your home / shop wiring between the circuit breaker and the wall outlet was 12 gauge. The general code rating for most locations with that gauge wiring in the US is 20 Amps. The circuit breaker is there to protect your wiring, inside the walls of your home / shop, so it will never get too hot (and start a fire.) And yes, with those electrical / building codes, there may be a slight safety margin build in.. you might have beat the odds this time, but why do you think those codes are in place, anyway?

    Please, put the original 20 Amp circuit breaker back in the box. If you need more capacity, have an electrician quote you for a wiring upgrade.. You can go to a 50 amp circuit (6 gauge wire...) Play it safe for you, your property and the ones you love. (and if I've got my assumptions incorrect, apologies up front...)

    Zip...
    Not completely disagreeing with you but the wire sizing for a "dedicated" recep for welder isn't the same as what would commonly be used for other appliances. This is because of the duty cycle of the welder. The literature supplied with my Miller Maxstar stated 14 ga. wire for 30 amp circuit. Got my attention, but check NEC wrt welders.

    The thing to remember is that a dedicated recep should be labled and only used for said machine. The danger of somebody using it for something it was not intended for should be obvious. A commercial/industrial setting with strict guidelines/safety program is quite different than someone's garage...

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