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MM 250X voltage questions

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  • MM 250X voltage questions

    Hi, all,
    I've been a long time reader of this forum, but never had a need to sign in and post before. Tons of great info here! I am learning to weld (self-taught), and purchased a used 250X. Last night, I noticed the volt meter fluctuating, which I haven't noticed before (at least not to this extent). I was welding 1/8 steel, with the volts set to 17.3. When I released the trigger, the meter was reading 16.4, but after a few seconds reset to 17.3.
    This morning, I went back out to fool around some more with it. While welding, the voltage drops, then fluctuates (bounces!) between 16.2 and 17.3, rarely getting over 17.0. When I release the trigger, it usually stops at 16.4, then, four seconds later, bounces back to 17.3. I then thought to check the voltage without load: I turned the gas off, opened the drive wheels, and pulled the trigger. The voltage read 17.3 for 2 seconds, then dropped to 17.0 and held. When the trigger was released, four seconds later, the voltage went back up to 17.3. I pulled the cover off of my sub-panel to make sure the input voltage wasn't dropping, but it stays at 240V.
    I assume this isn't normal, that the voltage should remain fairly constant. Can someone point me in a direction to problem and cure? Thanks in advance!

  • #2
    Thats normal that they jump around a little, Maybe a question for cruizer but I'm pretty sure why it bounces around is becuse of your arc length.

    Unless your experiencing a problem dont worry about it.

    Comment


    • #3
      Thanks for the reply, Portable Welder. I wondered if that might be the case... that the bouncing voltage was normal. The thought ran through my mind as I watched it that if I had a machine without a digital readout on it, I wouldn't know that the voltage was fluctuating!

      Comment


      • #4
        Voltage will vary a little with changes in stick out length.

        I am not familiar with the 250X, I use to own a 251. Anyway, if you have the wire speed set a little to high, the power source may not be able to maintain your preset voltage.

        Comment


        • #5
          correct me if i am wrong, the mm250 was millers new welder when they retired the mm200, the 250 was millers first digital mig at that time, and they carry a slightly bad reputation for the way they weld. i would not worry at the least for the variation in voltage. line voltage changes all the time, which will show up on the dial. are you using a 6 or 8 wire with a 50 amp plug. a lite wire will increase ressistance and lower the voltage

          Comment


          • #6
            Well yes, unless your a robot, or a hudderite, the fluctuation is completely normal as the internal computer is watching your stickout and increasing or increasing the voltage to maintain the weld

            Comment


            • #7
              Thanks, everyone, for your input. To answer Kevin's question, I have a sub-panel in the shop with a 50 amp breaker, from there there is about 10 feet of #6 to the receptacle, and the welder has about 8 feet of #8. I have seen some of the old posts that indicate the 250X had some issues, so that when I noticed the voltage moving around, I thought maybe I was having some of them... issues, that is!
              Thanks, again!

              Comment


              • #8
                I'd work on trying to maintain a more consistent stick out length, and see if this helps. When I had my MM 251, the load voltage on the meter never varied more than about .2 of a volt from the preset.

                Comment


                • #9
                  And that was what seemed most odd to me,,,, with the gas off and feeding no wire (I opened the drive wheels), pulling the trigger (no welding involved) dropped the voltage from 17.3 to 17.0, then, after releasing the trigger, a four second delay before it went back to 17.3.

                  Comment


                  • #10
                    There are 2 scr rectifier banks in your machine, they have to balance themselves, there is only one in the 251 and 252. simply put not to worry about it, weld away.

                    It is best however to make sure that the bolts on them are secure as they like to blow off

                    Comment


                    • #11
                      I'll be sure to check the bolts for tightness. I wouldn't want them blowing away!

                      Comment


                      • #12
                        i remember when i had my mm250, it would weld fairly good welding .250 steel, once i jumped up in steel size, amps, volts, the quality of the weld dropped, during a hot flat weld, the puddle would change, it would mostly shrink a bit leaving a cold spot, while maintaining the same stick out. a fluctuation in voltage must of been going on,

                        Comment


                        • #13
                          A thermostat on the wall in my living room shows set temperature only briefly, then reverts to serve as a thermometer. The difference being the imprecision of the system.
                          Might this be the case with the 250? Try turning it up slightly, does your measured voltage then rise to desired levels?

                          Comment

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