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IndustryArena Forum > Machine Controllers Software and Solutions > Fanuc > Question about AC servo motor type Alpha C
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  1. #1
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    Question about AC servo motor type Alpha C

    Hello gentlemen,

    Quick question to the group, I was about to install a new servo amplifier since the old one was faulty, but I wanted to make sure there was no problem witht the motor, so I checked the resistance with the ohmmeter, of all three motors in order to compare since I didn´t hava a nominal value to be used as reference. The motors from axis X and Y read 2.6 ohms in all cable combinations. but the motor from axis Z read 0.08 ohms. To me that reading is close to a short. but I am not a 100% sure, since I don´t know the nominal value.

    Does anyone know what should be the reading for this motor that would like to share please? please see attached picture for motor details. Thank you!




  2. #2
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    Re: Question about AC servo motor type Alpha C

    your motor is short circuit.

  3. #3
    Community Moderator Al_The_Man's Avatar
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    Re: Question about AC servo motor type Alpha C

    Is that between all three? UVW ?
    Back feed-rotate it with other means and read the generated voltage between phases.
    Al.
    CNC, Mechatronics Integration and Custom Machine Design

    “Logic will get you from A to B. Imagination will take you everywhere.”
    Albert E.

  4. #4
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    Re: Question about AC servo motor type Alpha C

    Shorted windings on an AC servo usually makes the shaft hard to turn by hand or feel lumpy. Dave

  5. #5
    Community Moderator Al_The_Man's Avatar
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    Re: Question about AC servo motor type Alpha C

    I have a Fanuc S5/300 here that is around the same size, it measures 0.75 ohms between winding's.
    Are you sure that is not reading 0.8?
    Al.
    CNC, Mechatronics Integration and Custom Machine Design

    “Logic will get you from A to B. Imagination will take you everywhere.”
    Albert E.

  6. #6
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    Re: Question about AC servo motor type Alpha C

    I had an almost identical motor fail that way, it was full of water. The resistance readings returned to normal once I had dried it out, but it was rusty as hell inside so I swapped it anyway.

  7. #7
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    Re: Question about AC servo motor type Alpha C

    If you have a megger or a multimeter that can check up to 60 Megaohms, check resistance from a phase to ground. A megger is better for this, but a multimeter will detect and obvious problem with insulation leakage.

    From my experience even 20 Megaohms gave me trouble and damaged a servo amp, but luckily for me that was in the cables and the motor windings were still well insulated.

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