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Miller Bobcat 225NT assistance

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  • #16
    Oh-my-god..... I have been looking absolutely everywhere for this info!!! Thank you so very much!

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    • #17
      I knew I sniffed out a problem I could help with.

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      • #18
        Well I can not perform any ovc till I receive the replacement diode block... however I do have 5.6 ohms on the revolving coil measured at the connector just outside of the generating unit. I measured the rings only and discovered 3.6 ohms there... looks like I might need to revisit the brush ***

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        • #19
          The other resistances all fall within. Where is R8? I can not locate it on your drawing anywhere? Also... do you have a schematic of the stabilizer connections so I could verify correctness? Thank you all for assistance thus far

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          • #20
            I didn't show R8 as it was not on topic for this issue, I try my very very best to stay 100% on task, lol.... but sometimes....


            *OFF TOPIC WOLVERINE PICTURE*
            Click image for larger version

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            Now... where was I?

            In regards to the extra ohms you saw, having some extra resistance in that Revolving circuit sure can effect things, but once you are back online I'd be more curious on the Voltage readings. Also, a really good way to clean-up that slip-ring surface is the pads of scotch brite, a ruler/foot long paint stick and some electrical tape. Cut a slighty over-sized swath and fold it over/tape it to end of ruler/paint stick. While engine is running, use that to clean surfaces of slip-ring to a nice shiny-new texture, if they are bad enough you may need a Re-surfacing stone, they can dig the grooves out, then allow you to fully polish it up to a fine, even surface with the scotch brite. Just try to have the stick being pulled rather than pushed (if that makes any sense) a few trial's and I am sure you will get it.

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            • #21
              I have polished the rings and the brush contact surfaces.... I suspect an issue in the Connection to the brush *** or poor wire conditions.

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              • #22
                Okay Good, I'll wait till she is back up and running to see the voltage readings for V7, and V6, as well as exact O.C.V.'s in the separate polarity's and modes. I have seen the excitation voltage off more than not, so that the DC voltage that feeds the revolving field is low and thus in turn the magnetic field's actual strength, is low; resulting in a low output condition. That, to me, is #1 priority in terms of what to check-off the list of possible causes.

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                • #23
                  Ok, I have some voltage info for you guys....

                  V6
                  @ idle 7vdc
                  @high idle 17.5vdc

                  V7
                  @ high idle 47.5vac

                  V1
                  @ min 57vac
                  @ max 73vac

                  V2
                  @ min 50vdc
                  @ max 64vdc

                  V3
                  @ min 21.3vdc
                  @ max 27.7vdc

                  globally the ocv readings are down and I could assume that is also the reason for my low welding output? I re leaned the brushes and repaired a ton of connections. There is a new bridge and diode block installed. As of this message I have not attempted to weld with it... I want to give the brush assembly time to "run in" again.

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                  • #24
                    Have you checked field voltage filter capacitor C1 yet?
                    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

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                    • #25
                      Originally posted by duaneb55 View Post
                      Have you checked field voltage filter capacitor C1 yet?
                      Yes I did.... however like a dope I did not scribble it down. I did not see wild fluctuations and I did recall the voltage was smooth but I also was alone and unable to run welding current while taking measurements. I have another cap on order and will replace it once it arrives.

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                      • #26
                        I notice you did not have a range for V 6, as in, there should be a min to max for both Idle, and Wide open RPM.

                        Idle should have been 6.5-10.5
                        Wide open: 13 - 29

                        I had a feeling it was excitation being low, which in turn would result in a low output across the board. Also, are you 100% sure R1 (the fine amperage control on front of machine) is in good working order, you also could jump the leads to R1 to rule it out as a point of voltage drop.

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                        • #27
                          Originally posted by LoganpClayton View Post
                          I notice you did not have a range for V 6, as in, there should be a min to max for both Idle, and Wide open RPM.

                          Idle should have been 6.5-10.5
                          Wide open: 13 - 29

                          I had a feeling it was excitation being low, which in turn would result in a low output across the board. Also, are you 100% sure R1 (the fine amperage control on front of machine) is in good working order, you also could jump the leads to R1 to rule it out as a point of voltage drop.
                          The listed measurements for V6 are from max setting only. Yes I have measured the rheostat several times now to verify resistance. The parts listing shows 11 ohms needed and the info you provided claims 10 ohms... I am right in the middle at 10.5 ohms. It is nice and smooth response from one pin to the other pin. I am waiting on the cap to arrive.

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                          • #28
                            Originally posted by duaneb55 View Post
                            Have you checked field voltage filter capacitor C1 yet?

                            I measure 40.6vdc across the cap, this is also the same measurement I get at the rheostat and the diode block. I did verify that I am still reading 10.5 ohm resistance on the rheostat when set to min, almost a dead short 0.6 ohm at max. It is worth mention that I see 0.5 ohm noise on my meter alone.

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                            • #29
                              Originally posted by LoganpClayton View Post
                              I notice you did not have a range for V 6, as in, there should be a min to max for both Idle, and Wide open RPM.

                              Idle should have been 6.5-10.5
                              Wide open: 13 - 29

                              I had a feeling it was excitation being low, which in turn would result in a low output across the board. Also, are you 100% sure R1 (the fine amperage control on front of machine) is in good working order, you also could jump the leads to R1 to rule it out as a point of voltage drop.

                              Ok... V6 voltage....
                              Min 7.2vdc
                              Max 18.3vdc measured at the R2 output going to the brush assembly

                              measuring input put voltage into R2
                              min 15.8vdc
                              max 39.9vdc

                              i did jumper the R1 with the same high reading.
                              Last edited by J-Mo; 02-06-2017, 02:09 PM.

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                              • #30
                                I am not sure if this matters or not in the grand scheme of things but I just remeasured R2 to show 7 ohms instead of the 5 ohms listed in the parts book... when I reduce the resistance to under 1 ohm at idle my voltage readings globally go just above where we want them... should I suspect a failed ballast resistor?

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