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Thread: Brush shifting motor

  1. #1
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    Brush shifting motor

    Some folks have been using this motor on a printing press and in all my old books, I can't find much about them. From what I could get, it's a repulsion motor and that the brushes short across the armature, moving them changes the pole position(?) thus varying the speed. The owner tells me than if you move the lever from one end to the other while it's running, it'll spark something fierce when it reverses.... I wouldn't recommend doing that.

    Any pointers to better info? (No photos of the brushes at the moment, I'll be back there later next week and get some.)
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    190210-1947 EST

    zbang:

    See https://en.wikipedia.org/wiki/Repulsion_motor .

    .

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    Quote Originally Posted by gar View Post
    Yes, read that, it didn't tell me much I didn't already have.

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    Quote Originally Posted by zbang View Post
    Some folks have been using this motor on a printing press and in all my old books, I can't find much about them. From what I could get, it's a repulsion motor and that the brushes short across the armature, moving them changes the pole position(?) thus varying the speed. The owner tells me than if you move the lever from one end to the other while it's running, it'll spark something fierce when it reverses.... I wouldn't recommend doing that.

    Any pointers to better info? (No photos of the brushes at the moment, I'll be back there later next week and get some.)
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    What kind of pointers are you looking for?

    Stop the motor first before trying to change it's direction would be my number one pointer. It has sleeve bearings that need oil. Brushes are still available from the web, you'll likely need a caliper to get the dimensions to order them. It has already run longer than the people that built it have lived, with the right care it will keep running.
    If you don't think too good, don't think too much.

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    Says to read the instructions right on the label.
    Code references based on 2005 NEC
    Larry B. Fine
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    Looks like a Schrage motor, my avatar is a drawing of one.

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    The reports of my death are greatly exaggerated.

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    190211-1119 EST

    zbang:

    See Chapter 18 of "Alternating-Current Machinery", Bailey and Gault, McGraw-Hill, 1951.

    https://archive.org/details/inductio...iliala/page/n6 link seems to not work.
    http://ece.umich.edu/bicentennial/chairs/bailey.html
    https://www.lib.umich.edu/faculty-hi...ssroom-profile Gault worked on the development of the capacitor motor and electro;ytic capacitors. This link also seemed to not work.

    .

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    Quote Originally Posted by gar View Post
    See Chapter 18 of "Alternating-Current Machinery", Bailey and Gault, McGraw-Hill, 1951
    Thanks, that's the kind of pointer I was looking for. I don't have Bailey & Gault and neither does the SF public library (they do have Lawrence, 1953; that's worth a check) (none of my various Croft volumes cover these motors much).

    Mechanically, it's an old motor- lube the bearings, make sure the brushes fit and the commutator doesn't have any raised mica, etc. And don't reverse under power. Since it's using a flat belt to the press, overloading will not be an issue. Anything else useful to know?

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    Need to find "Electric Motor Rebuilding" by Robert Rosenburg.

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    Quote Originally Posted by zbang View Post
    Thanks, that's the kind of pointer I was looking for. I don't have Bailey & Gault and neither does the SF public library (they do have Lawrence, 1953; that's worth a check) (none of my various Croft volumes cover these motors much).

    Mechanically, it's an old motor- lube the bearings, make sure the brushes fit and the commutator doesn't have any raised mica, etc. And don't reverse under power. Since it's using a flat belt to the press, overloading will not be an issue. Anything else useful to know?
    Nowhere in the nameplate states that it is a REPULSION MOTOR.
    It is usually and clearly stated because these motors have different characteristics.

    Therefore, it would be safe to say that it is not a repulsion motor. You could possibly be looking at a series wound induction motor.

    The field winding of a repulsion motor is not connected to the power source.
    You are correct to infer that speed can be changed by positioning the brushes as well as changing the rotation.
    The arcing you mentioned indicates that it is series wound motor. The above speed adjustment principle can be applied to both series wound and repulsion-induction run motors as well as regular series wound-- pure induction motors.

    Repulsion motors of this size (3HP) at 110/220 volts AC don't usually generate arc. This is the “beauty” of this type motor.
    (you probably know this already through your venerable Wikipedia arsenal)

    Higher voltages above 1500 volts can cause arcing-- that's why they don't make repulsion motors with this high a voltage.

    The armature (rotor) winding of a repulsion motor terminates and shorted at the “slip disc”. Shorting is done after the motor arrives or close to the rated speed . At this stage the motor would be acting like a regular induction motor.
    This is in addition to the “segmented” commutator that you see in DC motors.

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