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bobcat 3 phase wont strike an arc

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  • bobcat 3 phase wont strike an arc

    hello folks this is my first post so bear with me please...machine is a lf160389 3 phase bobcat..working on this for a friend...the history:this thing sat for a few years outside with no covers in place....was super dirty...I cleaned the whole machine, went thru the kohler and got it running..(brushes were not connected until later)..f1 and f2 were bypassed...d4 was shorted ...installed the correct fuses,replaced d4..found a miller parts bag with new sr2 and sr3 rectifiers so installed those as well....I then connected the brushes and fired it up to test it. the generator makes good voltage and the machine idles up when I start my grinder...returns to idle fine..it would strike an arc on setting tig- and 50-100 amp setting..the amp selector was cooked so replaced the switch and then had all three amp outputs...still no weld exept in the tig- position...I verified the connections against the wiring diagram on the slector switch and all are correct .today it won't weld at all in any switch position...f1 is good....c1 capacitor charges up with my ohmmeter...as does the other three capacitors ...I have trouble reading the diagram as for verifiying the correct connections on those three capacitors...c2,c3,c4...there were 2 wires disconnected from the beginning from them...I believe I have those correctly hooked up since it welded once..i'm at a loss and don't know what to check now...I must be missing something so any help would be greatly appreciated...cookin down here in Arizona............one more thing....I get low (4-5)v ac at the output terminals(work and electrode)....no dc voltage anywhere on the big switches....do have dc voltage at f1 and f2
    Last edited by bdmech; 09-16-2017, 04:16 PM.

  • #2
    Dang. I wish I could help. I just have to say that's the best first post I've seen in a LONG time. You actually put the subject in the subject line and put a lot of details into the description of the problem. Someone is going to be able to give some good ideas on what to try next.

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    • #3
      haha....thanks....been getting terrible descriptions from customers for years so knew I should be specific..

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      • #4
        Welcome, bdmech. I'll add to Mac's comment--super first post! Will try to help you through this.

        Do the 120v outlets still work, or is everything dead now?

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        • #5
          yes I have aux power at the outlets...my grinder works and the machine goes full speed with that load...stop the grinder and it returns to idle....which I've set at 2200....fast speed is 3750

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          • #6
            You sound pretty capable of troubleshooting, so I assume you've checked but I just have to ask ... Brushes move completely freely in their holders? If ok, put it in AC weld mode, lowest range, and measure AC voltage between wires 12 and 11 coming right off the weld stator. Should be able to get a meter on them at connections on S3, the Range switch .

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            • #7
              thanks for the help...the brushes are free...got 27v ac @2200rpm and 45v ac @3750 between 12 and 11 at s3...ac weld mode ...50-100 amp range

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              • #8
                I'm not a welder expert, just a retired systems engineer, but that sounds low to me. That machine is rated at max of 80V AC open circuit. The troubleshooting section of the manual asks you to check C1 and plug 6. If your meter doesn't have a capacitor check function just use your ohmmeter like you did on the others. They also recommend checking SR2 and SR3. I know you just replaced them but I would check them with an ohmmeter again just to be sure.

                Need a a welder expert to join this discussion. Duane is still in flood recovery mode and Cruizer hasn't been around much lately but perhaps one of them will see this and chime in. Sure hope you don't have a bad stator but I don't know what the readings should be for it. You might try calling Miller tech support. They can tell you if that voltage is OK or not, and probably give you resistance values for the stator. They will help troubleshoot over the phone. Good luck!

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                • #9
                  ok thanks....I was thinking that the stator must be ok if the machine runs the outlets..hmmmm........so it (weld stator) is separate?....machine has 2 systems?...weld and aux power?...wish I knew more about this type of stuff....gimme a spankin new truck with 30 different computers on board and I can fix that....haha....i'll try calling miller when they are there next week and see what they got for me....thanks again and to anyone else that reads this it will be active until I post that its fixed

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                  • #10
                    Don't know if this makes a difference or not, but the grinder will run on DC, so while you have power at the aux receptacles, it could be DC, not the AC it should be. Now, I don't know the possibility of that being a symptom, and your receptacles are probably working just fine. But just thought I'd mention that the grinder isn't the perfect test for it.

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                    • #11
                      Yes-there are separate stators for weld and power. It appears from your initial post that someone was desparately trying to fix this thing in days long past. That always worries me because you don't know if they'd moved any wires around.

                      Looking at at the diagram again tonight, please check voltage between 10 & 12 -- that's the full stator as opposed to just part of it.

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                      • #12
                        thanks i'll check 10 to 12 in the morning...and also have concerns about previous "monkeys" moving wires around. I was able to clean up enough of the crud on the large wires to read the numbers and verified they were in the right places on the mode and range switches. anything else I removed to build the engine I put my own markings with paint markers before anything came apart. all the small gauge wires(white) are legible and look ok....will post results of the next test tomorrow.(10 to 12 voltage)

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                        • #13
                          and to mac702...I will check ac or dc at the recepticles . definitely help to know which it is....thanks

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                          • #14
                            Has to be AC. there are no rectifiers between the power stator and the plug on the panel. That was a fair question, though. Some welders have DC outlets.

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                            • #15
                              Originally posted by Aeronca41 View Post
                              Has to be AC. there are no rectifiers between the power stator and the plug on the panel. That was a fair question, though. Some welders have DC outlets.
                              I didn't think it was a possibility with that machine, but I didn't know. I just knew the grinder would work on DC. I ASSUMED the power was generated as AC on that machine, but I've been wrong once, so figured I'd bring it up and make sure for myself. Thanks for the confirmation.

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