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Duty cycle change with temperature

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  • Duty cycle change with temperature

    Hey everyone, I'm the new kid on the block here. I often weld outdoors in all kinds of temperatures, but I have been told duty cycles are measured at 104 ºF. Anyone know how this changes at say, 30 ºF? I have welded continuously (as in, held an arc continuously) for nearly a minute at ~170 A and never seen the temperature gauge on the machine move off of "cold".

    I've heard a rumor that the max internal temp on these machines is typically 250 ºF. So if it takes 2 min at 104 ºF ambient to reach this, it should take 2x220/146 or about 3 minutes to reach 250 ºF with 30ºF ambient temp. (This is neglecting the change in specific heat of air with temperature)

    So based on rumors and back-of-the-envelope figures, I should have a 30% duty cycle welding at 30ºF. But The temp gauge still reads cold after a minute or so of arc time, which makes me question my calculations. Do any of the Miller people here know more than I?

    Thanks

    P.S. I'm using a Multimatic 215

  • #2
    Duty cycles are also rated in ten-minute intervals. Welding for one solid minute and then taking measurements is welding at a 10% duty cycle.

    Comment


    • #3
      I'm sure there is a very good reason for your question... I'm just not sure what it is?

      As mentioned, the duty cycle is based on max out of the power source over a 10 minute period. So, if you have a 200 amp out put at 10%, you can weld for 200 amps at 1 minute, or 100 amps at 2 minutes, 50 amps at 4 minutes, staying with in the duty cycle and not over doing things.

      How about this, you have a hamster running on a wheel. Running to turn the wheel, flat out the hamster can go so fast for so long before he needs to rest.
      Slowing down, he can run further longer with out getting tired needing a rest.

      I'm sure if the weather is hot, that poor hamster will feel it, more so if no breeze is blowing...colder it is, maybe he runs further without feeling over worked and heated?

      Just remember hamsters and wheels come in different sizes. Not all hamsters get fed a good diet and not all wheels get greased.

      "
      Do any of the Miller people here know more than I?"

      Maybe? Maybe not? I'm in the maybe not group?

      Comment


      • #4
        While there is an assumed increase in duty cycle associated with a decrease in ambient temperatures, what would be interesting to see is a chart or formula showing a maybe 1% to 10% increase in duty cycle for every ten degrees decrease in temperatures, whether linear or a curve, but no, that ain't gonna happen .

        A whole lot of time consuming testing involved and data recording for something most folks ignore anyway. Duty cycle is generally an after thought. When your machine starts running like garbage and you just can't figure out why, or just plain shuts down then it's "oh yeh, duty cycle"..

        Comment


        • #5
          The duty cycle exists for a reason, almost certainly temperature given the presence of a thermal cut-off to protect the machine when the duty cycle is exceeded. The temperature inside the machine builds up due to waste heat generated in the electrical stuff: a fan blows ambient temp air through the machine to cool it off.

          It is only reasonable to assume that the duty cycle is established with the following procedure:
          1) Component X (the most fragile/prone to overheating) will have a long service life if not regularly asked to perform at temperatures above Y.
          2) Calculation and empirical testing show that, with 200 amps output continuously and some constant ambient temperature, component X takes approximately one minute to reach temperatures close to (but below) Y.
          3) Therefore we assign a rating of 200 amps at 10% duty cycle to the machine.

          OK back to my question. The Multimatic 215 has a temperature gauge, which I assume is to tell the operator how close component X is to temperature Y so that they can act accordingly (otherwise, why have it at all?). However, I have never seen mine budge even after a minute of arc time at about 170 A on mig. (The duty cycle is 20% at 200A). If all of the above were true, this should not happen. So, I'm left with several possible interpretations:

          1) The temperature gauge does not read the temperature of the heat-sensitive components (in which case, why have it at all?)
          2) The temperature gauge is actually a dummy light that will stay blank until the machine overheats and then suddenly turn red.
          3) The low ambient temperature drastically increases the time for the temperature-sensitive components to heat up and therefore the duty cycle. (My calculations above suggest this probably happens, but the change may not be large enough to account for what I am seeing)
          4) The temperature gauge is actually painted on to attract more buyers without increasing costs

          4 is far-fetched. 3 almost definitely happens but may well not be the explaination. 1 and 2 don't seem too likely either.

          Comment


          • #6
            Note that right now the temperature is in my favor. But it is necessary to understand how the machine's duty cycle changes with temperature to be able to treat it right when things get hot.

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            • #7
              Originally posted by Noel View Post
              I'm sure there is a very good reason for your question... I'm just not sure what it is?

              As mentioned, the duty cycle is based on max out of the power source over a 10 minute period. So, if you have a 200 amp out put at 10%, you can weld for 200 amps at 1 minute, or 100 amps at 2 minutes, 50 amps at 4 minutes, staying with in the duty cycle and not over doing things.
              I think the duty cycle should theoretically diminish according to the square of the output, not in direct proportionality.

              I'm sure there's some engineers from Miller around here who know all there is to know about these things... Do you guys care to explain it to us mortals?

              Comment


              • #8
                Originally posted by Lewis Hein View Post

                I think the duty cycle should theoretically diminish according to the square of the output, not in direct proportionality.

                I'm sure there's some engineers from Miller around here who know all there is to know about these things... Do you guys care to explain it to us mortals?
                Slow down partner. Think all you want about it, create your own theories, I surely do. Sometimes though, things are what they are. Take a barrel and fill it with water. Puncture a hole in the bottom and watch the water drain. If you fill it as fast as it drains 100% it will always remain full.

                I'm guessing... with out having looked, but suspect in your previous post it's a temperature contact limit switch that when heated closes to completes a circuit or three. Turn on a light, turn on a fan, and maybe energize something to shut down the power? One minute of 170 amps isn't causing the machine to sweat. Burn 4 or 5, 3/16" E7018 back to back and maybe the light will come on if that's what your hoping to see occur?

                As simple as my explanation of duty cycle was, it is to understand that it is that simple. Don't believe me, run around the block. Then after a rest, walk around a couple. Not a Miller expert here, but this friendly bunch usually corrects bad information quickly and that so far hasn't been challenged?

                Maybe your question should be, would a welding power source with 100% duty cycle be affected in it's out put characteristics with extreme's in temperature during operation? My experience suggests, not much. I've worked in cold and hot. Both suck. Small hamster and a big wheel, beats a small hamster and a small wheel for out put.

                https://www.millerwelds.com/files/ow...29038D_ENG.pdf

                Page 12 of 36. 3.2 Duty cycle and over heating. Hope it helps with a better explanation.

                Comment


                • #9
                  https://weldknowledge.com/2015/12/07...le-in-welding/

                  Comment


                  • #10
                    Thanks Helios

                    Now we need to figure out the strange behaviour of the temperature gauge on the mm215. And the relationship between duty cycle and temperature. And, while we're at it, the meaning of life, the universe and everything would be nice.

                    Comment


                    • #11
                      The last one is easy...it's 42.

                      Comment


                      • #12
                        If someone takes a few minutes to explain to me in simple terms (all my brain can handle), why do I need to know that? I'd be most grateful.
                        Raise your hand if they taught you that in school?

                        KP Bhatt posts something. I have the book. AWS 8th edition has the same blurb as the 9th edition. I checked. I have both. Don't hate the player hate the game.
                        With out a doubt, it hold a degree of value that formula...I'm not sure when I'd ever use it if I could do the math...But I'm not selling it short either.
                        Hmmm? Pgs. 16 and 17. Don't get too excited by the news, as well don't be to impressed by it either. If you read the opening blub, it would state the following:

                        INTERNAL COMPONENTS OF a welding power supply tend to heat up as welding current flows through the unit. The amount of heat tolerated is determined by (1) the break- down temperature of the electrical components, and (2) the media used to insulate the transformer windings and other components. These maximum temperatures are specified by component manufacturers and organizations involved with standards in the field of electrical insulation.

                        Fundamentally, the duty cycle is a ratio of the load-on time allowed to a specified test interval time. Observing this ratio is important in order that the internal windings and components and their electrical insulation system will not be heated above their rated temperature.. These maxi-
                        mum temperature criteria do not change with the duty cycle or current rating of the power supply. Duty cycle expresses, as a percentage, the maximum time that the power supply can deliver its rated output during each of a number of successive test. intervals with- out its temperature exceeding a predetermined limit. In the United States, NEMA duty cycles are based on a test interval of 10 minutes. Some agencies and manufacturers in other countries use shorter test intervals such as 5 minutes. Thus, a 60 percent NEMA duty cycle (a standard industrial rating) means that the power supply can deliver its rated output for 6 out of every 10 minutes without over- heating. (Note that uninterrupted operation at "rated load” for 36 minutes out of one hour does not constitute a 60 percent duty cycle but 100 percent). A 100 percent duty-cycle power supply is designed to produce its rated output continuously without exceeding the prescribed temperature limits of its components.

                        So...where does my response sit with you now? What's of value?
                        Lol...42 is a good number. Good to know someone figured it out because it wasn't me? When in doubt pick "C".

                        Comment


                        • #13
                          Thanks guys. I suppose need may be a too strong adjective... I don't need to know any of this to make a weld that sticks, so Noel has a good point. What they taught me in school contained zero about welding, but a few bits and pieces of physics and math so I tend to nerd out about things that aren't necessarily useful to others. Non-nerds are welcome to tell me if I get too nerdy and put them off, and I won't be offended

                          I still want to know about that temperature gauge, what it means, and why I have never seen it register anything. I feel like knowing this and knowing how the duty cycle on my machine changes with temperature would help me take better care of it when summer rolls around. Plus it'll satisfy that little voice in my head that never quits asking.

                          Comment


                          • #14
                            You know Lewis, what you want to know is the equivalent of asking, does a fridge cool less in the summer then it does in the winter?
                            Maybe...if you see someone in a black SUV
                            parked
                            in the hot sun with the windows rolled up, ignition off, Ac on, is he chilling?

                            You know what you need to do. Read the manual. Disconnect the power and take it apart. Have a look inside. That's the problem, you haven't had a look inside. Open it up.Careful what you touch however, your not a trained tech guy are you? Capacitors. Shock and Awh stuff. Pull out a manual, look and identify parts. Satisfy curiosity with discovery. What's the worst you can do, break it?

                            Having said that...how do you think your oven works? About the same way.
                            But I'm going out on a limb with one last kick at the cat. Rub your hands. Fast enough they catch fire. Probably not but, the faster the rub the greater the friction. Heat build up. And your wondering if they will heat up faster rubbing them in the summer time? Answer is yes. Trick is don't rub them as hard, or often. And lotion.

                            You mentioned physics and math. Not my strong areas bud. If it was I would have to think about amps through a conductor, voltage behind the flow, size of conductor and wire type in, wire size in the transformer, resistance and losses...with variance for out side ambient temperature, good luck with that. My brain says if you have a pile up on an LA express during rush hour in the middle of summer, it'll happen sooner rather then later that tempers will flare.

                            If it's to hot out, I take a break. To cold out, I take a break. That's my duty cycle. Always worked for me? Simple solutions to complicated problems.
                            The trick to those voices is sometimes to give them an answer they can live with. If you haven't got it, it could be time to call tech support?


                            Comment


                            • #15
                              Ok then, Lewis, you're getting too nerdy. Go poke yourself with something sharp, that's what I do when I need to be grounded.

                              But I think the mystery of the temp gauge might piss me off a little too.

                              Comment

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