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  • Electric motor overheats at speed

    I have a speed problem on my Motor VFD on my Vertical mill head.
    When I use the highest speed on the belts (for 3600 rpm at 50hz) the motor will not drive the speed but instead runs quite slowly and overheats. The motor is a 900W (1.2HP) Brooke Compton wired in delta/Mesh 1450 rpm wired to a ABB ACS101-4K1 VFD using all default settings.
    The original motor was a 3/4HP 1450rpm 415V Elliot.
    The motor drives it fine at lower belt ratios.

    Any Ideas
    Last edited by derekm; 08-11-2008, 12:03 PM.

  • #2
    If it is an option with your model allowing the VFD to auto detect the motor without any belts installed, this is what I needed to do with my Myford lathe, 1HP motor & Siemens VFD, it would "hunt" for the correct rpm in some speed ranges before detecting the motor on it's own with no drive train connected,
    Regards,
    Nick

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    • #3
      I would resheave it to a very low speed, your VFD should have tons of top end, I find if they run for extended periods below 30hz (1/2 speed) both the drive and the motor don't last long, IMHO.
      Opportunity knocks once, temptation leans on the doorbell.....

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      • #4
        I tried turning it by hand on the high speed belt setting- it wasnt that easy to turn. The spindle with no belts turns smoothly but if you try to spin it stops after a turn . I thought this is normal because of the pre load needed for accuracy on the "light angular bearings" but is it? ... I have no set up manual for the spindle But from the exploded diagram in the ops manual there is a preload setting collar in there somewhere.

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        • #5
          Originally posted by hardtail
          I would resheave it to a very low speed, your VFD should have tons of top end, I find if they run for extended periods below 30hz (1/2 speed) both the drive and the motor don't last long, IMHO.
          This would be an option if I had the control panel for the VFD but I dont so for the moment I'm stuck to 50Hz max. This VFD tops out at 1000Hz but 100HZ on the 2000 rpm belt speed would do me nicely.

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          • #6
            A bit more data

            After running for 15min at 2100 rpm on the next to highest belt ratio the motor case temp (measured with a contact thermocouple) was 48C. (118F) and the spindle bearing was 64C (147F) despite being filled to overflowing with grease. My experience from along time ago on larger fan bearings would say these bearings are a bit on the warm side but still safe. What do you think.

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            • #7
              Every ridden a ten speed bike and put it in tenth gear and then decided to pedal up a hill...still in tenth gear?

              That's what its like to put the drive train in its highest gear and then effectively "underpower" the motor by reducing the frequency of the power coming in. VFD's are great, but I always figured you need to use good judgement with regard to just how much you rely on varying the frequency vs. changing ranges at the belts, gears, or whatever.

              Paul
              Paul Carpenter
              Mapleton, IL

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              • #8
                You might also check to see if your VFD is set for constant speed or constant torque.
                I just need one more tool,just one!

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                • #9
                  Originally posted by pcarpenter
                  Every ridden a ten speed bike and put it in tenth gear and then decided to pedal up a hill...still in tenth gear?

                  That's what its like to put the drive train in its highest gear and then effectively "underpower" the motor by reducing the frequency of the power coming in. VFD's are great, but I always figured you need to use good judgement with regard to just how much you rely on varying the frequency vs. changing ranges at the belts, gears, or whatever.

                  Paul
                  I understand and and agree with you. However,
                  I still have the problem starting with the pot set to 50hz. This surfaced trying to run at the full line frequency (which is 50hz here and is the rated frequency on the motor) going for the 3600 rpm that the tool says it can do in the book at 50hz with a motor that is bigger than the standard motor. (900w as opposed to 560w)
                  .
                  Last edited by derekm; 08-11-2008, 02:20 PM.

                  Comment


                  • #10
                    Originally posted by wierdscience
                    You might also check to see if your VFD is set for constant speed or constant torque.
                    I think its set up for a constant torque application
                    from the manual

                    U/f Ratio
                    U/f below weakening point.
                    1 = Linear (curves A and
                    C)
                    2 = Square (curves B and
                    D)
                    Linear is preferred for
                    constant torque
                    applications and Square
                    for centrifugal pump and
                    fan applications. Default is 1

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                    • #11
                      You say the spindle bearing is "filled to overflowing with grease." That may be part of your problem; too much drag because of too much grease.
                      ----------
                      Try to make a living, not a killing. -- Utah Phillips
                      Don't believe everything you know. -- Bumper sticker
                      Everybody is ignorant, only on different subjects. -- Will Rogers
                      There are lots of people who mistake their imagination for their memory. - Josh Billings
                      Law of Logical Argument - Anything is possible if you don't know what you are talking about.
                      Don't own anything you have to feed or paint. - Hood River Blackie

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                      • #12
                        Originally posted by SGW
                        You say the spindle bearing is "filled to overflowing with grease." That may be part of your problem; too much drag because of too much grease.
                        I had the problem before I filled it today. But I dont think you are wrong... This mill has a history of lubrication issues e.g. the wrong lubricants and not enough and then being left to stand.

                        So I thought if its resistance then maybe its the old hard grease. Paticularly since it was only doing 2030 rpm when it ought to be doing 2240. So to push the old grease out so I put as much in of the recommended grease as I could through the grease nipples until the old stuff started to come out through the vents. To help things along I also removed the bearing covers to let some more come out. Btw this has taken over 500g of grease to do this. I then ran it at the 2240 belt ratio and took the temperatures in the previous post.

                        As it warmed up the grease came out and came out as the quill was exercised up and down. I then went back later after it had all cooled down and then ran it up. I got 2130 which then rose to 2150... Something had improved.

                        I thought maybe its improved enough to run the top ratio. So I tried the top ratio which previously fried the motor and run at 200 rpm and it ran ok its only 3060 rpm not the 3600 it ought to be but its a move in the right direction.

                        Comment


                        • #13
                          Bearings should be filled with about 1/3 grease. Anything more and they will overheat. And it should be a good spindle grease like Kluber Isoflex NBU15.

                          Comment


                          • #14
                            I seem to recall motors should run up to 40 deg greater than ambient, that said I've encountered some extremely hot ones that lived and some quite cool so I take it as a general guide, sudden changes tell more. The full grease will definately increase your drag although I can see your goal.......they do have some purge products that will flush out a bearing in ~8 hrs. I think your gonna have to try and get some interface to ramp up speed, seems like your trying to start in high gear.

                            We have some drives at work that have the drive on half the enclosure and a bypass on the other all in the same enclosure, the bypass side has way beefier electrical components than the drive side due to the heavy full load start requirements.
                            Opportunity knocks once, temptation leans on the doorbell.....

                            Comment


                            • #15
                              I'm sure not saying that overfilling the bearings is not an issue...it is. However, the description that it was difficult to turn (by hand) in high range with the belts attached but not so difficult with the belts removed tends *not* to suggest binding at the spindle, but rather high work load due to the established belt ratios. The possible exception could be after longer running times if binding occured due to heating (from a grease overfill).

                              A related question, but not one that should be the source of your problem....are the bearings supposed to be greased (as opposed to drip oiled)? What is the recommended grease? Most sealed bearings, as already stated, get partial fill...and usually with a grease with a light thickener...maybe an NLGI 1 or 1.5 as opposed to the all-too-common NLGI 2 chassis grease. The Kluber product already recommended is great. I used Mobilgrease 28 (another synthetic designed for the purpose) on my sealed mill spindle bearings. Its an NLGI 1.5 and I don't recall the viscosity of the base oils.

                              I guess I misread (or misinterpreted) what you were saying....not thinking that 50 Hz was rated line frequency rather than a reduction from 60Hz we are used to in the US. I should know better than to not pay attention to where a guy is from when replying.

                              Paul
                              Paul Carpenter
                              Mapleton, IL

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