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  • basic electrical question

    The breaker for a typical stick welder (nothing special) is usually 50 - 60 amps. When welding anything of thickness you're usually over 100 amps. Why doesn't the breaker trip? How does this figure in with the duty cycle, if at all? If you go to too small a breaker, will this trip before the duty cycle shuts the machine down? Is there any danger in having a too large breaker (say 70 or 80 amps)?
    TomK

  • #2
    Originally posted by Tom Kroegel View Post
    The breaker for a typical stick welder (nothing special) is usually 50 - 60 amps. When welding anything of thickness you're usually over 100 amps. Why doesn't the breaker trip?
    Simply put, because the current required to run the machine is feeding the primary side of the transformer, and the current you are welding with is coming from the secondary side of the transformer.
    Originally posted by Tom Kroegel View Post
    How does this figure in with the duty cycle, if at all?
    It doesn't.
    Originally posted by Tom Kroegel View Post
    If you go to too small a breaker, will this trip before the duty cycle shuts the machine down? Is there any danger in having a too large breaker (say 70 or 80 amps)?
    I think you're missing a fundamental concept of electrical service here: the breaker is there to protect the supply wiring. The breaker does not protect the device. If you install too small a breaker, say a 30A where the machine is actually drawing 50A, then it will trip. It has nothing to do with the duty cycle of the machine. Sometimes this concept is easier to think of if you consider the actual name of a "breaker..." The technical name is an "overcurrent protection device."

    Duty cycle, in very simple terms, is a function of temperature rise. As the machine is used, it gets hot. At some point, it has to cool back down. Duty cycle defines the ratio of heat cycling in a 10 minute period. It's definition has nothing to do with current draw, although current draw is what creates the heat.

    As far as having too large a breaker, again, the breaker has to be sized to the supply wiring. If you have a 70 breaker on a #12 wire, the wire will burn up before the overcurrent protection device trips. There are some exceptions in the National Electrical Code for devices with less than 100% duty cycle, including welders, but that's another discussion.

    Now if you're asking what happens if you install 70A rated wire and breaker when the machine only draws 50A, nothing. A machine that draws 50A only draws 50A, whether its on a 50A circuit, a 100A circuit, or a 200A circuit. The example I always use is that a 60 watt light bulb uses 0.5 amps of current. And yet it's routinely connected to a 15A circuit! If that light bulb automatically sucked 15A out of the line, every light in your house would explode like a bomb the instant you flipped a switch.
    Last edited by Zrexxer; 12-02-2008, 09:34 AM.
    Trailblazer 302 * Millermatic 212 * Syncrowave 180SD * X-Treme 12VS Feeder * Spoolmate 3035
    Thermal Dynamics Cutmaster 52 Plasma * Lincoln 175 MIG

    Victor Superrange II * Victor Journeyman

    Hobart HH 125EZ


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    • #3
      The 100+ amps of welding power is on the secondary side of the transformer. You can't look at this as amps only, you have to consider wattage.

      Say you have a 50A breaker at 230V. This allows a maximum draw of 11,000 watts (ideally.. the breaker will trip prior to this from heat buildup if it's anything more than a brief 50A draw)

      On the secondary side of the transformer you have a much lower voltage. So lets say you're welding at 100A and the output voltage is 25V. You're now producing 2,500W worth of spark (voltage x current).

      For sake of keeping it simple, lets consider the transformer in the welder 100% efficient (that is, all the power coming in also comes out of it, none gets lost by creating heat etc). This means the power output on the secondary side is equal to the power being input on the primary side.

      So even though you're welding at 100A, the power being consumed is still only 2,500W. This is roughly 11A at 230V (2,500W / 230V = 10.87A).

      The duty cycle doesn't figure in at all in this equation, really. The exception is when you're getting close to the 50A mark. If you draw lots of power for a long time the breaker will eventually trip. Keeping the duty cycle down will keep the breaker from tripping.

      Even with a smaller breaker the internal themal switch (duty cycle limiter) in the welder can trip first. The breaker will allow you to weld at 30A all day, but the welders thermal switch won't.

      There's definitely a danger to having too large a breaker. It's called fire. The breaker must be sized accoring to the wiring on that circuit. The welder itself doesn't mind being on a circuit with a large breaker, though. The welder has its own built in fuse that should protect it in case of a short circuit.

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      • #4
        Most of the small stick machines do not have their own thermal, they are just limited by the draw, 50A breakers for these with a minimum of 10 wire, better yet 8.
        http://www.facebook.com/cary.urka.urkafarms

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        • #5
          Yep. Your welder is a transformer. High voltage, low amperage going in (what the circuit breaker sees) and low voltage, high amperage going out (what the melting steel sees.)

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          • #6
            50A x 220V = 11,000W = 40V x 275A

            You can't quite get out what you put in, since some of the current going in gets converted into heat in the transformer windings, but that's the general idea.

            Just don't ask me about "power factor."

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            • #7
              Originally posted by Zrexxer View Post
              And yet it's routinely connected to a 15A circuit! If that light bulb automatically sucked 15A out of the line, every light in your house would explode like a bomb the instant you flipped a switch.
              WHAT!?!?!?

              So you're saying when I switch on my 1500W flood, I'm a mere 2.5A from being blown to bits.

              BILGEWATER!!!!!

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              • #8
                Originally posted by Pumpkinhead View Post
                WHAT!?!?!?
                Reading comprehension not your strong suit?
                Trailblazer 302 * Millermatic 212 * Syncrowave 180SD * X-Treme 12VS Feeder * Spoolmate 3035
                Thermal Dynamics Cutmaster 52 Plasma * Lincoln 175 MIG

                Victor Superrange II * Victor Journeyman

                Hobart HH 125EZ


                Comment


                • #9
                  See the part about transformers about halfway down this page. It is a pretty good explanation: http://www.allaboutcircuits.com/vol_2/chpt_1/1.html

                  Then there's this, "Hackers can turn your Home Computer into a Bomb":

                  http://unix.rulez.org/~calver/pictur...puter_bomb.jpg
                  --- RJL ----------------------------------------------

                  Ordinarily I'm insane, but I have lucid moments when I'm merely stupid.
                  -------------------------

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                  • #10
                    Originally posted by usmcpop View Post
                    Then there's this, "Hackers can turn your Home Computer into a Bomb":

                    http://unix.rulez.org/~calver/pictur...puter_bomb.jpg
                    Good thing we know how to weldify some alooominum hats and undies, just in case
                    f

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                    • #11
                      Originally posted by Zrexxer View Post
                      Reading comprehension not your strong suit?
                      My cumprenshun is fine, your understanding of lightbulbs, whether 60w or 1500w needs serious work.

                      So, till you can explain how a lightbulb equates to a bomb,
                      BILGEWATER!!!!!

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                      • #12
                        Originally posted by Pumpkinhead View Post
                        My cumprenshun is fine, your understanding of lightbulbs, whether 60w or 1500w needs serious work.

                        So, till you can explain how a lightbulb equates to a bomb,
                        BILGEWATER!!!!!
                        Time for this fruit to go in the ignore bin with the rest of the rotted turnips.
                        Trailblazer 302 * Millermatic 212 * Syncrowave 180SD * X-Treme 12VS Feeder * Spoolmate 3035
                        Thermal Dynamics Cutmaster 52 Plasma * Lincoln 175 MIG

                        Victor Superrange II * Victor Journeyman

                        Hobart HH 125EZ


                        Comment


                        • #13
                          Toss me in there too Zboy.
                          Miller 251, Lincoln PrecisionTig 275, Miller DialArc 250 AC/DC, Hypertherm 900, Bridgeport J-head, Jet 14" lathe, South Bend 9" lathe, Hossfeld bender with a collection of dies driving me to the poorhouse, Logan shaper, Ellis 3000 bandsaw, Royersford drill press and a Victor Journeyman O/A.

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                          • #14
                            Originally posted by Wyoming View Post
                            Toss me in there too Zboy.
                            I too would like to enter the "bin-o-rotted-turnips".

                            Comment


                            • #15
                              Zrexxer,

                              I've always read your posts with a modicum of respect, but what the heck is going on? Don't go funny on me, son. Sheesh! Blowed up lightbulbs and stuff...
                              --- RJL ----------------------------------------------

                              Ordinarily I'm insane, but I have lucid moments when I'm merely stupid.
                              -------------------------

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