Announcement

Collapse
No announcement yet.

VFD's; digital vs analog

Collapse
X
 
  • Filter
  • Time
  • Show
Clear All
new posts

  • #16
    Originally posted by J Tiers View Post
    The KBAC DO have a suitable motor overload function, at least in some models

    But they have little else as far as features, and "settability"is by turning a trimpot, or plugging a jumper, with limited resolution and options.

    Still, if you really need just a basic VFD, can tolerate the limitations, and can get it for an appropriately low price, it will work. KB has a decent manual, and they are still in business, and AFAIK still sell those.

    Capacitors may just need re-forming, which is not hard to do.
    Thanks for that link.

    Yeah the kbac seems more on the mechanical side when it comes to dialing in with its trimpots and jumpers, which isn't really an issue for me...I don't think anyway. Where I'm a little stumped is in the hertz and I guess it's sensitivity. The kbac offers 2 jumper positions, one at 60 Hz and the other at 120Hz while the WJ200 specs say .1 to 400 Hz.

    My guess is, and hopefully someone can confirm this, one of the WJ's parameters is a setting of max Hz which I think I'd like over the option of having just 60 or 120 to choose from. And would I be correct in thinking that the 60Hz mode (kbac) offers higher resolution when it comes to dialing in speed and that would then be halved in the 120 setting? And not that I will need 400 Hz either. Realistically, I don't see needing to go more than around 90. As you can tell, this is my first rodeo in dealing with VFD's.

    Comment


    • #17
      The Wj has "full settability". You should be able to set it at any max you want. IIRC you can set a minimum and also set several frequencies to avoid if there are resonances, etc. Any number in probably 0.1 Hz increments.

      And similar for nearly anything else you can name. But the manual has a section that is basic setup step by step, so you don't need to get too techie-wiremongery to get it running.

      As for resolution, that is a function of the control potentiometer, for either unit. But you can also keyboard-set any speed you want on the WJ with (IIRC again) 0.1 Hz resolution.
      CNC machines only go through the motions.

      Ideas expressed may be mine, or from anyone else in the universe.
      Not responsible for clerical errors. Or those made by lay people either.
      Number formats and units may be chosen at random depending on what day it is.
      I reserve the right to use a number system with any integer base without prior notice.
      Generalizations are understood to be "often" true, but not true in every case.

      Comment


      • #18
        Originally posted by Bob Engelhardt View Post
        I have my drill press, lathe, and mill VFDs all programmed for 120 Hz max & haven't had any issues.
        ...
        Originally posted by MaxHeadRoom View Post
        Are these 2 pole or 4 pole motor's?
        I tend to use 4 pole and take them up to ~120Hz.
        Max.
        Oh, yeah ... mine are 4 pole. That makes a big difference.

        Comment


        • #19
          There is essentially no difference between the rotor for a 4 pole or 2 pole. So I generally figure a 4 pole can go to 120Hz, anyway, but unless stated, I'd not go over 90Hz on a 2 pole.
          CNC machines only go through the motions.

          Ideas expressed may be mine, or from anyone else in the universe.
          Not responsible for clerical errors. Or those made by lay people either.
          Number formats and units may be chosen at random depending on what day it is.
          I reserve the right to use a number system with any integer base without prior notice.
          Generalizations are understood to be "often" true, but not true in every case.

          Comment


          • #20
            Back when I was involved with electric vehicle racing we tried to determine the burst speed for a 10hp induction rotor.

            Initially vibration at around 6,500 rpm was putting the test rig in danger, but once the rotor was re-balanced we were able to run to 14,000rpm.

            That's as fast as we could go, so we never did find the burst speed.
            Paul Compton
            www.morini-mania.co.uk
            http://www.youtube.com/user/EVguru

            Comment


            • #21
              Originally posted by lakeside53 View Post
              120hz?

              I don't like taking typcial machine 1800 rpm motors above 90hz. Remember, at 120hz your torque will be half or less.
              I regularly run motors at 200%+ for long periods without issues including 1hp 4 pole TEE (3000rpm+) and 1hp 2 pole compact frame Electro Adda (7000rpm+), reduced torque is a small price to pay to achieve required cutting speeds if you need them.
              If you plan for reduced torque at higher speeds then you use a higher rated motor in the first place to ensure you get at least what you need where you need it. You do need to ensure that gear boxes, spindle bearings and pulley bearings are rated for the speeds you plan to use but if you use decent quality new motors and not stuff saved from the junk pile it's not the issue many assume ;-)

              - Nick
              If you benefit from the Dunning-Kruger Effect you may not even know it ;-)

              Comment


              • #22
                Originally posted by RB211 View Post
                I like the Westinghouse Teco's. Cheap and feature packed!
                +1 Got two 2hp versions of these and they are really solid units, one is fitted in/to my Bridgeport and another which operates My Boxford lathe, Taylor Mill and occasionally my T&C grinder.

                Comment


                • #23
                  I run my Bridgeport pancake motor at up to 120hz now. 1800rpm motor, bringing it to 3600 rpm isn't stressing anything. Half the torque? Why would I care with a 3/8 endmill?


                  Sent from my iPhone using Tapatalk

                  Comment


                  • #24
                    My comment was "typical machine". Typical of what HSM'ers haul home. Sure, with a decent motor you can run whatever (within reason), but take care - some rotor/pulley balance really sucks. Don't just assume "you can 'cos some on the internet say you can". Check you bearings and grease also

                    I had a 2hp BP motor balanced. It was terrible at higher speeds "stock". I would have expected typical G6.3 Spec, but not even close. When finished, and joined to the pulley it was G2.5. Smooth as silk to 4000+ . If your stator is not dipped - do it.


                    IIRC imbalance forces are the square of the RPM, or something like that.
                    Last edited by lakeside53; 01-24-2017, 12:13 PM.

                    Comment

                    Working...
                    X