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IndustryArena Forum > CNC Electronics > Spindles / VFD > Questions about Induction motor
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  1. #1
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    Questions about Induction motor

    Hi!

    I've looked and read several posts here on the forum and elsewhere, but I'm still in doubt about what I should use in my project.


    I've had some CNC Routers, all with the famous 2.2kw water-cooled chinese spindle. But now I want to build a VMC, using epoxy granite and steel.


    My inspiration has been this project https://www.cnczone.com/forums/verti...rum-posts.html , the only problem is the cost (extremely expensive) to use the Servo spindle motor as it was used in the design of the stef110.

    I would like to be able to machine steel and aluminum, I see that Tormachs use 1.1kw induction motor and they can do this job well.

    I found some WEG W22 of 3600 rpm and 3.7kw (5hp) that are with a good price for the budget of my project. This WEG W22 is 2 poles, but I was in doubt if there is any reason for Tormach for example to use engines with lower RPM (4 poles).

    https://www.weg.net/catalog/weg/BR/e...14D/p/12219195

    What do you think?

  2. #2
    Community Moderator Al_The_Man's Avatar
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    Re: Questions about Induction motor

    If using a standard AC induction motor, I would go with a 4 pole motor, you can run these up to x2 freq, i.e. 3600rpm and being 4 pole they have higher torque at lower RPM's.
    I have always done this with no issues.
    WEG make nice motors and VFD's, BTW.
    Al.
    CNC, Mechatronics Integration and Custom Machine Design

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

  3. #3
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    Quote Originally Posted by Al_The_Man View Post
    If using a standard AC induction motor, I would go with a 4 pole motor, you can run these up to x2 freq, i.e. 3600rpm and being 4 pole they have higher torque at lower RPM's.
    I have always done this with no issues.
    WEG make nice motors and VFD's, BTW.
    Al.
    I knew it was possible to do this but I wasn't sure if it was a practice used in CNCs

    Good to know !


    I can buy one WEG AC Induction W22 with 5hp (3.7kw) with 4 poles and 1760 rpm. I intend to buy a VFD from WEG too, WEG is a best option here in my country.

    Do you know if Tormach run these up to x2 freq?

    Another thing is about encoder, my idea is to add an encoder for ATC system and tapping

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    Re: Questions about Induction motor

    Quote Originally Posted by Al_The_Man View Post
    If using a standard AC induction motor, I would go with a 4 pole motor, you can run these up to x2 freq, i.e. 3600rpm and being 4 pole they have higher torque at lower RPM's.
    I have always done this with no issues.
    WEG make nice motors and VFD's, BTW.
    Al.
    after your answer i started to research more on the subject, the vast majority of people alert to double the frequency to double the rpm, that there are several risks of damaging the engine, so I was confused about the best AC induction motor option

  5. #5
    Community Moderator Al_The_Man's Avatar
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    Re: Questions about Induction motor

    My theory is that motor manufacturers that produce 2 pole and 4 pole motors, are going to build and balance the 4 pole to the same specs as the 2 pole, so running a 4 pole at the same RPM as the 2pole is not that much of a stretch of reason!
    I have done it many times over the years. Including Very old motors.
    Al.
    CNC, Mechatronics Integration and Custom Machine Design

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

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    Quote Originally Posted by Al_The_Man View Post
    My theory is that motor manufacturers that produce 2 pole and 4 pole motors, are going to build and balance the 4 pole to the same specs as the 2 pole, so running a 4 pole at the same RPM as the 2pole is not that much of a stretch of reason!
    I have done it many times over the years. Including Very old motors.
    Al.
    Makes sense,

    And about the the torque x rpm,
    to reach 6000rpm with a 4pole motor I need to increase the frequency To 100hz (+70% rpm) and use a 2:1 pulley ratio, so my the torque will be 36% after increase the frequency and decrease half after the pulleys , resulting 0.9hp

    I saw these values in an article, I didn't find on the WEG website about the torque at higher frequencies, sorry if I did the wrong math. And I didn't use the efficiency factor (w22 of weg are above 75% according to the datasheet)

    To reach 6000rpm with a 2pole motor I just need use a 1.7:1 pulley ratio and the torque will be 2.5hp

    but as you said before, the 4-pole motor has more torque at low revs and this is good for some situations like tapping. I want to understand how much torque and average rpm I need to milling steel for example, I thinking about the 0.9hp with 4pole motor at 6000rpm is enough for aluminum milling

  7. #7
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    Re: Questions about Induction motor

    Double check Your calculations. The torque should increase much more with higher frequency.

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    Re: Questions about Induction motor

    Quote Originally Posted by Algirdas View Post
    Double check Your calculations. The torque should increase much more with higher frequency.
    really?

    I'm no expert in this on the subject, but reading this documentation https://static.weg.net/medias/downlo...nglish-web.pdf it seems that the torque will decrease when the frequency increases by more than 1.0 factor.

    I attached the chart in the post
    Attached Thumbnails Attached Thumbnails 2021-01-03 111220.png  

  9. #9
    Community Moderator Al_The_Man's Avatar
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    Re: Questions about Induction motor

    If you are using a WEG motor, and there is a WEG sales depot near you, check with their tech dept, The one close to me is very helpful and informative.
    Al.
    CNC, Mechatronics Integration and Custom Machine Design

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

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