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Big 40 - Idle Control Issues - What's This Thingy?

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  • Big 40 - Idle Control Issues - What's This Thingy?

    I have a new old Big 40. According to SN and Miller website, it's a 1978 model. Idle control isn't working. I can make it idle and weld using the auto idle switch, but it won't auto-excite. I have downloaded the manual from here (o450n_mil). There's no idle controller circuit board in the location shown in the manual, nor is there any place were such has been removed in that location. Number 89 in the pic is the board:
    Click image for larger version

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    There are some subtle differences in my welder and the manual, but in tracing the wires, I find no circuit board anywhere else. What I do find is this thingy (or is it a doodad, or a whatchamacallit??):
    Click image for larger version

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    This thingy connects into the wiring coming from the auto idle switch.

    Any ideas?
    Thanks in advance for your help.
    Gary

  • #2
    That's the magnetic reed switch shown as CR1 in the + weld output circuit that senses weld output and grounds the idle solenoid.
    MM200 w/spot controller and Spoolmatic 1
    Syncrowave 180 SD
    Bobcat 225G Plus LPG/NG w/14-pin*
    *Homemade Suitcase Wire Feeder
    *HF-251D-1
    *WC-1S & Spoolmatic 1
    PakMaster 100XL
    Marquette "Star Jet" 21-110
    http://www.millerwelds.com/images/sm...rolleyes.png?2

    Comment


    • #3
      Originally posted by duaneb55 View Post
      That's the magnetic reed switch shown as CR1 in the + weld output circuit that senses weld output and grounds the idle solenoid.
      Okay, I get that part now. What I don't get is that I can't find an idle control circuit board anywhere on my welder! I need to go look again, but if I remember right, this reed switch wires between the auto idle switch and the solenoid on my welder. I can't find anything that even remotely resembles a circuit board, nor can I see where one used to be mounted. My welder is a 1978 model (according to the serial number chart on this site). I'm sure there are some subtle differences in my welder and the manual I've downloaded, but this seems beyond subtle. Any ideas?
      Thanks again
      Gary

      Comment


      • #4
        Did you use your machine's SN when you searched for its manual? Manual 450N you reference is the lastest revision and likely not the correct one for your unit.

        This one http://www.millerwelds.com/om/o450_mil.pdf is the first edition and shows the circuit that includes your reed switch.
        MM200 w/spot controller and Spoolmatic 1
        Syncrowave 180 SD
        Bobcat 225G Plus LPG/NG w/14-pin*
        *Homemade Suitcase Wire Feeder
        *HF-251D-1
        *WC-1S & Spoolmatic 1
        PakMaster 100XL
        Marquette "Star Jet" 21-110
        http://www.millerwelds.com/images/sm...rolleyes.png?2

        Comment


        • #5
          Originally posted by duaneb55 View Post
          Did you use your machine's SN when you searched for its manual? Manual 450N you reference is the lastest revision and likely not the correct one for your unit.

          This one http://www.millerwelds.com/om/o450_mil.pdf is the first edition and shows the circuit that includes your reed switch.
          You are most definitely a life saver, Duane! No, I had the wrong manual... I had o450n. o450 is exactly my machine!

          Let me see if I have this straight... The idle circuit board became the brains that provided the delay before going back to idle? On my machine, there's nothing but a reed switch, a toggle switch, a rectifier and a resistor. Time to idle down is controlled by the valve in the vacuum line. So, if I get weld speed with the toggle switch, would that suggest that my problem lies in the reed switch?

          I'll test the reed switch to see if it's opening and closing with and without arc.

          Man it's great to have the right manual! Thank you so much Duane!
          Gary
          Last edited by GaryN; 08-14-2012, 08:18 AM.

          Comment


          • #6
            Originally posted by GaryN View Post
            Let me see if I have this straight... The idle circuit board became the brains that provided the delay before going back to idle?
            Correct.


            Originally posted by GaryN View Post
            On my machine, there's nothing but a reed switch, a toggle switch, a rectifier and a resistor.
            Actually, that's reed switch, toggle switch, flyback diode and solenoid valve coil.


            Originally posted by GaryN View Post
            Time to idle down is controlled by the valve in the vacuum line.
            Correct again.


            Originally posted by GaryN View Post
            So, if I get weld speed with the toggle switch, would that suggest that my problem lies in the reed switch?
            And correct again.
            MM200 w/spot controller and Spoolmatic 1
            Syncrowave 180 SD
            Bobcat 225G Plus LPG/NG w/14-pin*
            *Homemade Suitcase Wire Feeder
            *HF-251D-1
            *WC-1S & Spoolmatic 1
            PakMaster 100XL
            Marquette "Star Jet" 21-110
            http://www.millerwelds.com/images/sm...rolleyes.png?2

            Comment


            • #7
              Okay, I got some help out here today... I separated the reed switch out of the circuit, it's normally open. When my helper was running an arc, it would close. However, at idle, when he tried to start an arc, the switch didn't close. What you are calling the "flyback diode", is that what the schematic and parts lists identifies as SR4, a selenium rectifier? What's it's purpose in all this?

              What's your thoughts? Faulty reed switch, as in lacking sensitivity? I've been accused of the same, but it doesn't affect my ability to function... much. Too much ozone? Not enough ozone? Too many black holes in space? Too many birthdays (for the welder, not me)?

              Again Duane (or anyone else), I thank you in advance for your help.
              Gary

              Comment


              • #8
                That or your high and low idle rpm is out to lunch

                Comment


                • #9
                  Originally posted by cruizer View Post
                  That or your high and low idle rpm is out to lunch
                  I'm not exactly sure what you're talking about, but I can make it idle or run at weld speed using the auto idle switch. I just can't make it rev to weld speed from idle just by trying to start an arc.

                  Comment


                  • #10
                    Originally posted by GaryN View Post
                    What you are calling the "flyback diode", is that what the schematic and parts lists identifies as SR4, a selenium rectifier? What's it's purpose in all this?
                    In '73 about the time this machine was built, selenium rectifiers were still in use which have been since replaced by modern day diodes.

                    Its purpose? When the magnetic field in a coil (such as that of your idler solenoid) collapses from removing the power, the result is momentary high voltage spike out of the coil (much the same as an ignition coil). A "flyback" diode across the coil leads will sink the spike while preventing a direct short
                    when power is applied to the coil.


                    Originally posted by GaryN View Post
                    I'm not exactly sure what you're talking about, but I can make it idle or run at weld speed using the auto idle switch. I just can't make it rev to weld speed from idle just by trying to start an arc.
                    What Jeff is talking about is the machine low idle speed may be too slow which results in a low OCV (Open Circuit Voltage) that doesn't create sufficient current flow when striking an arc to close the reed switch. If so, increasing the low idle speed to specification should solve your problem.
                    MM200 w/spot controller and Spoolmatic 1
                    Syncrowave 180 SD
                    Bobcat 225G Plus LPG/NG w/14-pin*
                    *Homemade Suitcase Wire Feeder
                    *HF-251D-1
                    *WC-1S & Spoolmatic 1
                    PakMaster 100XL
                    Marquette "Star Jet" 21-110
                    http://www.millerwelds.com/images/sm...rolleyes.png?2

                    Comment


                    • #11
                      Originally posted by duaneb55 View Post
                      In '73 about the time this machine was built, selenium rectifiers were still in use which have been since replaced by modern day diodes.

                      Its purpose? When the magnetic field in a coil (such as that of your idler solenoid) collapses from removing the power, the result is momentary high voltage spike out of the coil (much the same as an ignition coil). A "flyback" diode across the coil leads will sink the spike while preventing a direct short
                      when power is applied to the coil.



                      What Jeff is talking about is the machine low idle speed may be too slow which results in a low OCV (Open Circuit Voltage) that doesn't create sufficient current flow when striking an arc to close the reed switch. If so, increasing the low idle speed to specification should solve your problem.
                      I hate to be such an idiot about all this, but I really thank all of you for educating me. So, my next question is what should the idle speed be? I find no reference to that in the manual. I recall that the manual I was trying to use (the wrong manual - before Duane put me onto the right manual) states that the weld speed should be 1800 rpm, if I remember correctly. That's not in the right manual either, nor is there anything about governor adjustment as in the wrong manual! Is that an indicator that the older machine is so dependable that it'll never need adjusting???

                      Thanks again to all for being so helpful.
                      G

                      Comment


                      • #12
                        thank's to you Garyn it's educating me too and probably a bunch of us.

                        Comment


                        • #13
                          Originally posted by GaryN View Post
                          I hate to be such an idiot about all this, but I really thank all of you for educating me. So, my next question is what should the idle speed be? I find no reference to that in the manual. I recall that the manual I was trying to use (the wrong manual - before Duane put me onto the right manual) states that the weld speed should be 1800 rpm, if I remember correctly. That's not in the right manual either, nor is there anything about governor adjustment as in the wrong manual! Is that an indicator that the older machine is so dependable that it'll never need adjusting???

                          Thanks again to all for being so helpful.
                          G
                          As long as someone else is getting some good out of it, then it's all good!
                          G

                          Comment


                          • #14
                            Originally posted by GaryN View Post
                            So, my next question is what should the idle speed be? I find no reference to that in the manual.
                            It's kinda hidden so to speak. Figure 7-2, fuel consumption chart, page 10 of the previously posted manual - 900rpm.
                            MM200 w/spot controller and Spoolmatic 1
                            Syncrowave 180 SD
                            Bobcat 225G Plus LPG/NG w/14-pin*
                            *Homemade Suitcase Wire Feeder
                            *HF-251D-1
                            *WC-1S & Spoolmatic 1
                            PakMaster 100XL
                            Marquette "Star Jet" 21-110
                            http://www.millerwelds.com/images/sm...rolleyes.png?2

                            Comment


                            • #15
                              Originally posted by duaneb55 View Post
                              It's kinda hidden so to speak. Figure 7-2, fuel consumption chart, page 10 of the previously posted manual - 900rpm.
                              Gracias... again!

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