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Re: Minimum /maximum speed with a VFD

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  • Bill Pace
    Before the change to VFD, first on my 12x36 lathe and then on a new Bridgestone clone , I had DC on the lathe, a 6x26 mill, a 9x20 lathe, a chi-con floor
    Message 1 of 21 , Apr 3, 2007
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      Before the change to VFD, first on my 12x36 lathe and then on a new
      'Bridgestone clone', I had DC on the lathe, a 6x26 mill, a 9x20 lathe,
      a chi-con floor drill press, and was trying out DC on a belt sander
      (that was disappointing!) A 1hp shunt wound on the lathe and a 3/4hp
      Grainger PM on the mill, the others were a mixed bag of treadmill
      motors. The shunt wound didnt work out very well at all, really noisy,
      and laddering/moire/striping was REAL bad, -- just couldnt get a
      smooth finish...replaced that with a big 2hp treadmill from Surplus
      center and the power/torque just wasnt compatable with that size
      lathe. The mill actually did pretty well on a lowly 3/4hp, and the
      other apps perform quite acceptably,.....But!... since Ive got these
      VFDs, there just really isnt any comparison, sooo quiet! and torque
      out the gazoo!!

      I had always hesitated on 3ph, --- going with the converters & RPCs,
      but with the VFD prices falling the way they have in the last couple
      yrs and the availability of industrial quality motors at bargain
      prices (I got the lathe 2hp at the scrap yard for $17.50) theres a lot
      more incentive to go 3ph now.

      --- In mill_drill@yahoogroups.com, "larry_zigler" <larry_zigler@...>
      wrote:
      >
      > > I went from DC variable speed to the VFDs and while I did like that
      > > setup, the VFD blows it out of the water!
      >
      > Bill, I am thinking about modifying my HF mill/drill, and trying to
      > decide between DC drive and VFD. Why do you think VFD is much better?
      > What is your reasoning?
      > Thanks, Larry
      >
    • leasingham_connelly
      ... run this motor from 6 to 60 ... damage. It can also be ... love mine. ... on a ... have a ... think ... is pretty ... I ve got to ... 2000/2400rpm ...
      Message 2 of 21 , Apr 4, 2007
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        --- In mill_drill@yahoogroups.com, "bilinghm" <bilinghm@...> wrote:
        >
        > I just got off the phone with Leeson and they say it is safe to
        run this motor from 6 to 60
        > hertz under normal conditions with no danger of overheating or
        damage. It can also be
        > overspeeded to a max of 75 hertz. They say it a 3 pole motor.
        >
        > --- In mill_drill@yahoogroups.com, "bilinghm" <bilinghm@> wrote:
        > >
        > > How low down do you turn the cycles when running at 30-50 RPMs?
        > >
        > > --- In mill_drill@yahoogroups.com, "Bill Pace" <pace8@> wrote:
        > > >
        > > > Well, for sure you are in for a treat using that VFD!! I Do
        love mine.
        > > > You'll probably have to do a bit of experimenting to settle in
        on a
        > > > pulley setting,-- should be somewhere in the mid range. I dont
        have a
        > > > 3600rpm motor so my experiences dont completely match, but I
        think
        > > > your playing around with it will still be necessary. The VFD
        is pretty
        > > > amazing in the range of speeds/torque that it will handle.
        I've got to
        > > > where I do threading with mine, cranking it up to about
        2000/2400rpm
        > > > to drill for tapping 4-40 and then backing off to 30-50rpm and
        running
        > > > the tap with it.
        > > > I probably do 95-98% of my work without changing belt setting,
        but
        > > > occasionally a situation will arise that will put to much
        strain on it
        > > > and I;ll kick it down to a lower setting, --- like using a BIG
        drill,
        > > > .. up in the 1" range
        > > > My lathe also has VFD and I've had it running for periods of 1
        or more
        > > > hrs with out stopping and can barely feel warmth off it.
        > > > I went from DC variable speed to the VFDs and while I did like
        that
        > > > setup, the VFD blows it out of the water!
        > > >
        > > >
        > > >
        > > > --- In mill_drill@yahoogroups.com, "bilinghm" <bilinghm@>
        wrote:
        > > > >
        > > > > With my new motor & VFD in place I need advice on the
        appropriate
        > > > speed range that is
        > > > > practical with such a set up. The motors' 60 cycle speed is
        3500
        > > > rpm, and I would like to
        > > > > achieve the goal of seemless variable speed control from
        maybe a low
        > > > of 100 rpm all the way
        > > > > to 2500 os so without touching a belt. I have a full array
        of belt
        > > > ratios available with the
        > > > > original 12 speed pulley arrangement, but I want to "set it
        and
        > > > forget it". Does anyone have
        > > > > experiences with this that they will share? What speed ratio
        did you
        > > > set the machine at? How
        > > > > slow can you go by just turning down the cycles? Does the
        machine
        > > > work properly at all
        > > > > speeds? Does the motor get hot when running slow?
        > > > >
        > > > > Thanks,
        > > > >
        > > > > Bill
        > > > >
        > > >

        I do not know what belt setting I have on mine, it's been so long
        since I opened the cover. I think it is somewhere in the middle of
        the available range. Last night I was gashing an alumium blank prior
        to hobbing. I was plunging the slitting saw into the edge (1/2" wide
        blank) about 1/8" deep. About 80 seconds per slot, 63 to do. After
        about 50 there was a smell of hot metal so I stopped the motor and
        did a quick check of the VFD and motor. Not even warm. The blank,
        however, was hot enough to feel the glow from an inch away. I was
        cutting dry and there was a small buid up of aluminum on the saw
        teeth. Knocked this off the blade and carried on. This is using a
        basic, not a VFD special, off the shelf, 3 phase motor. I run the
        spindle down to less than 60 rpm for tapping (with a tapping box)
        and at 0.5hz on the motor can use it as a spindle lock to allow easy
        tightening and loosening of the drawbar.
        At this setting it is low enough power to hold the spindle against
        turning with a wrench on the drawbar nut. I only do this when the
        drawbar does not loosen off when the wrench is given a smack with a
        mallet. Normally inertia of the spindle is enough to allow loosening
        this way.

        Martin
      • bilinghm
        ... Martin, So I read you right, you are getting usable power at slow speed low hertz settings? Is your motor a 3600 or 1800 RPM model? Does your belt setting
        Message 3 of 21 , Apr 4, 2007
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          >
          > I do not know what belt setting I have on mine, it's been so long
          > since I opened the cover. I think it is somewhere in the middle of
          > the available range. Last night I was gashing an alumium blank prior
          > to hobbing. I was plunging the slitting saw into the edge (1/2" wide
          > blank) about 1/8" deep. About 80 seconds per slot, 63 to do. After
          > about 50 there was a smell of hot metal so I stopped the motor and
          > did a quick check of the VFD and motor. Not even warm. The blank,
          > however, was hot enough to feel the glow from an inch away. I was
          > cutting dry and there was a small buid up of aluminum on the saw
          > teeth. Knocked this off the blade and carried on. This is using a
          > basic, not a VFD special, off the shelf, 3 phase motor. I run the
          > spindle down to less than 60 rpm for tapping (with a tapping box)
          > and at 0.5hz on the motor can use it as a spindle lock to allow easy
          > tightening and loosening of the drawbar.
          > At this setting it is low enough power to hold the spindle against
          > turning with a wrench on the drawbar nut. I only do this when the
          > drawbar does not loosen off when the wrench is given a smack with a
          > mallet. Normally inertia of the spindle is enough to allow loosening
          > this way.
          >
          > Martin
          >

          Martin, So I read you right, you are getting usable power at slow speed low hertz settings?
          Is your motor a 3600 or 1800 RPM model? Does your belt setting reduce the spindle
          speed in half at 60 cycles?
        • larry_zigler
          ... satisfactory results with good quality dc. So, it means that with high quality (and expensive) DC motor and PWM controller I can only get close to the
          Message 4 of 21 , Apr 4, 2007
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            > While not equal to the VFD 3 phase setups, I think you can get very
            satisfactory results with good quality dc.


            So, it means that with high quality (and expensive) DC motor and PWM
            controller I can only get close to the performance of a cheap VFD
            setup? Why to bother than?
            I have heard many times that VFD plus 3 phase motor is better than DC
            motor, but what exactly is better?
            On the other hand I read about excessive vibration of 3 phase motor
            driven by VFD, 16 KHz noise some other VFD issues.
            On yet another hand I read that high end precision machines (lathes
            and mills) are built with DC motorsÂ…
            Well at this point I guess I am completely lost.

            Larry
          • SupportOurTroops - Skip
            There is a very broad range of dc motors and controllers from very cheap to expensive. The range in VFDs and 3 phase motors is not that broad. I submit that
            Message 5 of 21 , Apr 4, 2007
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              There is a very broad range of dc motors and controllers from very
              cheap to expensive. The range in VFDs and 3 phase motors is not
              that broad. I submit that when comparing the performance of the two
              that quality dc motors and controllers should be considered. A good
              commercial TEFC dc motor and a good quality PWM dc controller
              are as much superior to the cheap versions as VFDs are. I have
              a KBWT-112 controller on my GE 1 1/4 HP TEFC dc motor on my
              mill/drill and it is awesome. The KBWT models are what KB calls their
              "whisper drives" and the only noise is from the fan on the motor at
              higher speeds. The PWM controllers also give much better torque
              at low speeds than SCR type dc controllers. While not equal to the
              VFD 3 phase setups, I think you can get very satisfactory results with
              good quality dc.

              Skip Campbell
              mkctools.com



              larry_zigler wrote:

              > > I went from DC variable speed to the VFDs and while I did like that
              > > setup, the VFD blows it out of the water!
              >
              > Bill, I am thinking about modifying my HF mill/drill, and trying to
              > decide between DC drive and VFD. Why do you think VFD is much better?
              > What is your reasoning?
              > Thanks, Larry
              >
            • Roy L. Pope
              Larry, DC drives are old technology that is still used in some special applications. IMHO VFD s are superior to DC due to no brushes, reliability,
              Message 6 of 21 , Apr 4, 2007
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                Larry,

                DC drives are old technology that is still used in some special applications.
                IMHO VFD's are superior to DC due to no brushes, reliability, adaptability,
                adjustibility, etc., etc.  Electrically speaking  a 3 phase drive offers more power and
                less current draw. Drives, DC or VFD, are like anything else. They are available from
                lowest cost to how much would you like to spend for features, filters, programming
                controls etc. The advent of low cost VFD's which work fine in most applications
                has made them popular. As a design, project, and plant e
                ngineer
                for 30 years I would choose a VFD over DC every time.

                My experience,
                Roy

                Oh, brush less DC drives are advantageous in some cases.


                larry_zigler wrote:


                > While not equal to the VFD 3 phase setups, I think you can get very
                satisfactory results with good quality dc.

                So, it means that with high quality (and expensive) DC motor and PWM
                controller I can only get close to the performance of a cheap VFD
                setup? Why to bother than?
                I have heard many times that VFD plus 3 phase motor is better than DC
                motor, but what exactly is better?
                On the other hand I read about excessive vibration of 3 phase motor
                driven by VFD, 16 KHz noise some other VFD issues.
                On yet another hand I read that high end precision machines (lathes
                and mills) are built with DC motors…
                Well at this point I guess I am completely lost.

                Larry

              • SupportOurTroops - Skip
                Brand new KBWT-PWM controller are 150.00 or less. Like new TEFC motors off ebay for under 100.00 shipped. Sometimes cheaper than that. Not every day but they
                Message 7 of 21 , Apr 5, 2007
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                  Brand new KBWT-PWM controller are 150.00 or less.
                  Like new TEFC motors off ebay for under 100.00 shipped.
                  Sometimes cheaper than that. Not every day but they can
                  be had.

                  Skip Campbell

                  larry_zigler wrote:

                  > > While not equal to the VFD 3 phase setups, I think you can get very
                  > satisfactory results with good quality dc.
                  >
                  > So, it means that with high quality (and expensive) DC motor and PWM
                  > controller I can only get close to the performance of a cheap VFD
                  > setup? Why to bother than?
                  > I have heard many times that VFD plus 3 phase motor is better than DC
                  > motor, but what exactly is better?
                  > On the other hand I read about excessive vibration of 3 phase motor
                  > driven by VFD, 16 KHz noise some other VFD issues.
                  > On yet another hand I read that high end precision machines (lathes
                  > and mills) are built with DC motorsÂ…
                  > Well at this point I guess I am completely lost.
                  >
                  > Larry
                • larry_zigler
                  DC Motors The brushed DC motor is one of the earliest motor designs. Today, it is the motor of choice in the majority of variable speed and torque control
                  Message 8 of 21 , Apr 6, 2007
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                    DC Motors
                    The brushed DC motor is one of the earliest motor designs. Today, it
                    is the motor of choice in the majority of variable speed and torque
                    control applications.
                    Advantages
                    Easy to understand design
                    Easy to control speed
                    Easy to control torque
                    Simple, cheap drive design

                    Controlling the speed of a brushed DC motor is simple. The higher the
                    armature voltage, the faster the rotation. This relationship is
                    linear to the motor's maximum speed.
                    The maximum armature voltage which corresponds to a motor's rated
                    speed (these motors are usually given a rated speed and a maximum
                    speed, such as 1750/2000 rpm) are available in certain standard
                    voltages, which roughly increase in conjuntion with horsepower. Thus,
                    the smallest industrial motors are rated 90 VDC and 180 VDC. Larger
                    units are rated at 250 VDC and sometimes higher.

                    Most industrial DC motors will operate reliably over a speed range of
                    about 20:1 -- down to about 5-7% of base speed. This is much better
                    performance than the comparible AC motor. This is partly due to the
                    simplicity of control, but is also partly due to the fact that most
                    industrial DC motors are designed with variable speed operation in
                    mind, and have added heat dissipation features which allow lower
                    operating speeds.

                    Simple, cheap drive design
                    The result of this design is that variable speed or variable torque
                    electronics are easy to design and manufacture. Varying the speed of
                    a brushed DC motor requires little more than a large enough
                    potentiometer. In practice, these have been replaced for all but sub-
                    fractional horsepower applications by the SCR and PWM drives, which
                    offer relatively precisely control voltage and current. Common DC
                    drives are available at the low end (up to 2 horsepower) for under
                    US$100 -- and sometimes under US$50 if precision is not important.
                    Large DC drives are available up to hundreds of horsepower. However,
                    over about 10 horsepower careful consideration should be given to the
                    price/performance tradeoffs with AC inverter systems, since the AC
                    systems show a price advantage in the larger systems. (But they may
                    not be capable of the application's performance requirments).

                    These quotations are from Automation Consulting & Supply web site.

                    Larry
                  • bilinghm
                    I finally got everything hooked up, adjusted and ready to run. The pulley selection I fitted provides 2,500 RPM at the spindle when the motor is turning 3550,
                    Message 9 of 21 , Apr 9, 2007
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                      I finally got everything hooked up, adjusted and ready to run. The pulley selection I fitted
                      provides 2,500 RPM at the spindle when the motor is turning 3550, the full 60 cycle
                      speed. So I have been experimenting with this arrangement and the results are very
                      positive. I put a 3/4" endmill in the collet and took some cuts on a big bar of mild steel at
                      10 cycles. The cuts were fine and the machine performed without protest, plenty of
                      power. It seems that the goal of no belt changes and sufficient power for all operations,
                      low to high speed, has been achieved. On a side note, I eliminated all of the additional
                      pulleys and belts, I run just two pulleys and one belt instead of the previous set up of four
                      pulleys and three belts. The difference in smoothness is exceptional.

                      Bill

                      --- In mill_drill@yahoogroups.com, Art Eckstein <a_eckstein@...> wrote:
                      >
                      >
                      > >Hi,
                      >
                      > I know I am jumping into this conversation fairly late in the game,
                      > but I have spent a couple of hours mapping what my VFD/Motor setup will do.
                      > Background:
                      > A few years ago, I purchased a combination motor/VFD from Dealers
                      > Electric to put on my RF31 mill/drill (2 HP 1800rpm)
                      > At that time, I did quite of bit of googling and reading of many of
                      > the sources on the net. In my case, I finally figured that I could
                      > safely run this motor to 120 HZ (3600 rpm nominal). Even though the
                      > same sources seemed to indicate a minimum of 10 Hz, in practice I
                      > found that even with the torque boost on the VFD, there was
                      > insufficient torque to handle a big mill. It would stall and pretty
                      > quickly thereafter, the VFD tripped out anyhow. Sometimes at 10 or
                      > below, the VFD would trip out on its own anyhow (remember, the motor
                      > is TEFC and there is little cooling at that point) Again based on
                      > experience, I find 20 Hz to be the minimum reliable to do any positive work.
                      >
                      > Shortly after getting it installed, I found the small pot used for
                      > the speed setting was pretty course, so I dug in my junk box and
                      > found a 10 turn pot that wasn't the proper size, but added resistors
                      > to make it work. My VFD was set to max 120 Hz, but with this pot
                      > (till I get round-tu-it), the max is 116 Hz and the min is 12 Hz.
                      >
                      > Now, having mapped my system by having the VFD readout in Hz and
                      > using an optical Tach, I find that one particular belt combination
                      > will give a range of 370 to 3596 RPM. This covers 90% of what I do
                      > and for the other 10%, another belt combination will give 44-435
                      > RPM. I really don't want to push the quill any higher as I am not
                      > sure the bearings could stand it. The nose gets quite warm after a
                      > period of time at ~3000 rpm.
                      >
                      > The next thing to do is to change the display setting back to read
                      > RPM directly (for the major belt setting) and then use a multiplier
                      > to figure the actual rpm when I do have to change belts.
                      >
                      > I know this is a long post, but thought some might find the
                      > information useful in making their own determinations.
                      >
                      > Bubba
                      >
                      >
                      >
                      >
                      > > > > > --- In mill_drill@yahoogroups.com, "bilinghm" <bilinghm@> wrote:
                      > > > > > >
                      > > > > > > With my new motor & VFD in place I need advice on the appropriate
                      > > > > > speed range that is
                      > > > > > > practical with such a set up. The motors' 60 cycle speed is 3500
                      > > > > > rpm, and I would like to
                      > > > > > > achieve the goal of seemless variable speed control from maybe a low
                      > > > > > of 100 rpm all the way
                      > > > > > > to 2500 os so without touching a belt. I have a full array of belt
                      > > > > > ratios available with the
                      > > > > > > original 12 speed pulley arrangement, but I want to "set it and
                      > > > > > forget it". Does anyone have
                      > > > > > > experiences with this that they will share? What speed ratio did you
                      > > > > > set the machine at? How
                      > > > > > > slow can you go by just turning down the cycles? Does the machine
                      > > > > > work properly at all
                      > > > > > > speeds? Does the motor get hot when running slow?
                      > > > > > >
                      > > > > > > Thanks,
                      > > > > > >
                      > > > > > > Bill
                      > > > > > >
                      > > > > >
                      > > > >
                      > > >
                      >
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