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Bobcat 225NT - Possible bad stator or windings

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  • Bobcat 225NT - Possible bad stator or windings

    Hello, I'm new to this forum. I am looking for a little help. I have a Bobcat 225NT that does not make AC or DC power. With the adjustment knob at 10 and a volt meter in the 120 volt receptacle there is about 8 volts at the plug when the motor is started. Leave the motor running for about 20-30 seconds and the voltage will make its way up to about 15 volts and then smoke/ a popping sound comes from the generator inside of the windings. I double checked the fuses and connections nothing appears to be bad. This unit has been sitting outside for a few years because my cousins irrigation company had a issue with it and decided to replace it with a new unit. I was told I can have it so I am trying to fix the electrical issues. The Onan motor runs like a dream. I thought the light amount of smoke might have been from the dirt, spider webs, and leaves that were inside of the generator from being stored outside. Hoping that was the issue, and that the smoke was not from a burned electrical component, I pulled the generator and separated the outside case from the inner stator, cleaned everything and inspected it. I do not see any signs of a burned spot or broken wires so I reassembled the generator and still get the same thing. Low voltage that slowly builds and smoke shortly after. I am thinking it is the windings but i'm not sure. I do not have access to a technical manual to help me perform any tests to better diagnose the issues yet. Any help would be greatly appreciated.

  • #2
    First thing I would do is clean/polish the slip rings and make sure the brushes are not stuck or seized in their holders.
    Does it have an hour meter on it?
    Lincoln Idealarc 250
    Miller Bobcat 250
    Thermal Arc Hefty 2 feeder
    Thermal Dynamics Cutmaster 52
    Torchmate CNC table

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    • #3
      I did try cleaning the slip ring and the brushes are free. The brushes appear to have been changed recently. There is a little over 1,400 hours.

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      • #4
        There are some resistance checks you can do to check the windings. Duaneb55 has posted some of the numbers before but I can't remember what specific welders they were for. Do a search on his postings and you may find some help. Or maybe he or one of the Miller techs will see this thread and respond. You could also call Miller tech support for help in checking the windings. 920-734-9821

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        • #5
          Farm-mechanic Welcome to the Forums! We recommend calling our tech support team to walk through this. As Aeronca41 already kindly mentioned, the number is 920-734-9821. Please let us know if you have any questions.

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          • #6
            Thank you. I will call Miller for some help and see what I can figure out.

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            • #7
              Update - I spoke with the miller technician support and was told the following. Test the wires coming out of the generator winding after unhooking all of them. I was looking for 1ohm resistant between any two wires and no continuity to ground. I was also looking for 3-4 ohms between the slip rings and no continuity from either slip ring to shaft or between both slip rings.

              Findings - After testing I have found that there is continuity between the slip rings but the ohms are in spec. The large wires that go to the welder output have continuity and so do two of the four small wires leading to the 120 volt plugs. This leads me to believe that the windings on both halves are bad.

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              • #8
                They should have continuity. 1 ohms is almost a dead short. 3.2 on the slip rings is normal. Have you checked every other possibility? Rectifier, capacitor main bridge, etc. Shorted stators are very rare. if you have a dead short in a bridge you might boil smoke from the stator. Where are you located?

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                • #9
                  I am just going off what the tech told me from Miller over the phone. I was going to call back when I get a few free minutes during business hours. I have not checked anything else. I would like to know what caused the problem. I'm located in California. Having the service manual would be helpful, I do not work with electrical components too often. Most of my time is spent working on large equipment. Any help is appreciated.

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                  • #10
                    It's a little hard to help you without having some knowledge of electrical equipment. You need to do a diode check on the main bridge. It's the aluminum looking item right in front on the bottom. If you can't do that check locate the big cables going to it. Clean them a bit and you will see cables 70 and 77. Disconnect those and see if that stops the smoke. Turn the process switch to CV and you may have power, not sure, but if the smoke stops it may be a shorted main bridge- rectifier.

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                    • #11
                      Thanks 1997CST! I will check that out and see. I would love to get my hands on the service manual for this welder. I assume it would give step by step testing procedures for the whole unit?

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                      • #12
                        I think paper copies are available? Don't quote me but they used to be available for $30? You can call tech support and ask.

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