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Table Motor - Help!

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  • Table Motor - Help!

    Our center recently got some new AMF table/sweep motors. They're rated at 1450 RPMs and are spinning almost twice as fast as our Westinghouse table/sweep motors that are rated at 1750 RPMs. Any ideas? I swapped the gearbox with a different one and it seems to be way better, but I'm super confused as to why this would be. Thanks!
    Experience: We currently maintain 12 AMF 82-70's

  • #2
    The motor speed is determined by the frequency of the power grid it is attached to and the number of poles in the motor. So in the U.S. where we use 60 Hz motors the speed for a 4 pole motor would be 1800 rpm (1750 or 1725 is likely the rpm accounting for slip) whereas across the pond or down under they use 50 Hz power grids and so you get 1500 rpm or the 1450 you show when accounting for slip. (frequency * 2 * 60sec/min divided by # of poles)

    Your profile shows that you are in the US so you are either reading the nameplate incorrectly in which case you should have the two rpm's listed and the motor should be rated for dual frequency i.e. 50/60 Hz or you purchased motors designed to run on 50 Hz systems. A 50 Hz motor will run on a 60 Hz system although depending on the motor it may not run properly. (the opposite is not true) Because the motor speed is dependent on system frequency it doesn't care what the nameplate says the motor will run at the higher speed. You need to make sure your motor is rated for 60 Hz. None the less it shouldn't run any faster than the previous motor did because once again, it is dependent on the supply frequency and number of poles in the motor and nothing else. Your rpm's listed indicate these are both 4 pole motors and so the only other dependent is the frequency and it is determine at the power company by government regulation unless you are using a variable frequency drive which isn't likely in your case.

    The other thing to consider would be mechanical components such as gear ratio but I would think you would have alignment issues if that was the case. Simple enough to check though simply look at the gears on the old motor shafts and compare to the gears on the new.

    Hope this helps.

    Edit: Post a picture of your nameplates if you want us to look at this.

    2nd edit: If they truly are running at twice the speed then they would have to be wired as 2 pole motors which I'm not even sure you can do in the field. Did these come factory wired or did you have to do any wiring.

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    • #3
      We did not modify wiring. The gearboxes were modified by a previous owner and were geared up to run faster. The motors say they're rated for 50/60Hz. They weren't literally running at twice the speed, they were just running significantly faster. Thanks.
      Experience: We currently maintain 12 AMF 82-70's

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      • #4
        AMF had two different gear ratios in the combo motors. If you run the fast gear boxes I recommend you only use them on the sweeps. If you put them on tables you are looking to get interlocks big time.

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        • #5
          Yes, I agree it has to be mechanical related and not the motors themselves. None the less they shouldn't run faster than those they replace. Are you seeing issues related to these motor gearboxes. It seems slower is generally better.

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          • #6
            Yep. Slower is better. They can be converted though by changing the brass drive gear and the rotor worm.

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