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Thread: 2 speed 3 phase motors

  1. #1
    Join Date
    Dec 2002
    Location
    Friesland, Netherlands
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    1,842

    Post 2 speed 3 phase motors

    I have a Beaver turret mill with a single speed, 3 phase motor running on 380v, 50Hz.

    As far as I know (but I may be wrong), it's delta wired. If this is so, would wiring it in star configuration reduce the motor's speed? I'd like to be able to run the spindle slower than 70 rpm, without buying a variable speed drive.

    Anyone know if this can be done? Snags?

    tia,

    Ian
    All of the gear, no idea...

  2. #2
    Join Date
    Jun 2002
    Location
    New Milford, CT
    Posts
    438

    Post

    Ian,
    Star/delta motors usually are single speed but dual voltage motors. The motor nameplate would show the voltage as 380/220 and different amp ratings for these voltages, but the motor speed would be a single value. If this is the case, then you will not be able to slow the motor by changing the voltage. There are some dual speed motors, a look at the nameplate for motor speed should tell you if you have one or not.

    Mike

  3. #3
    Join Date
    Dec 2002
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    Friesland, Netherlands
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    Post

    Mike,

    I'm sure it's not dual speed at the moment, but what started me thinking is that I have a 3 phase bandsaw that has a 2 speed motor - a rotary switch selects either speed.

    I know that single phase motors come in 2 and 4 pole varieties, giving 2800 / 1400 rpm on 50Hz, single phase; is this how 2 speed 3 phase motors work? (in which case I can forget it...)

    Thanks,

    Ian
    All of the gear, no idea...

  4. #4
    Join Date
    Jun 2002
    Location
    New Milford, CT
    Posts
    438

    Post

    yes, 3 phase motors would work the same way.

  5. #5
    Join Date
    Dec 2002
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    5,725

    Post

    Usually, two speed three phase motors have six leads for two delta circuits. Sometimes the internal leads are brought out too. A 9 wire motor is normal single speed. I remember a twelve lead motor being dual speed. Kinda foggy without my smart schematic book so don't quote me.

    Probably what you have is a dual voltage selectable motor.

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