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Does stalling a motor cause any damage?

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  • Does stalling a motor cause any damage?

    Sometimes while drilling large holes on the mill, or hogging too fast on the lathe, the motors will stall.
    I quickly retreat, and the motor returns to full speed.
    I'm wondering, do repeated stalls cause any damage to electric motors?
    Usually 3-4 stalls per day.
    (I know, I know.... "Quit feeding it so hard!!!")
    Mill motor is 1 horse, 240v. Single phase, Baldor
    Lathe motor is 2 horse, 240v. 3 phase, Baldor, with VFD

  • #2
    Good Question!!

    I'm just geuessing but over time repeated stalls would have some negative effect?

    Comment


    • #3
      Once you let the smoke out there won't be any more worries, at least about that..........

      Comment


      • #4
        Yes. It causes rapid rises in heat that will take its toll on the insulation.

        The lathe VFD (if it's programmed correctly) will protect that motor. The mill is another story.

        Comment


        • #5
          Your stalling a 2hp 3 phase motor? What depth and feed of cut does that?
          Andy

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          • #6
            When you stall the motor, the current draw goes up to the "locked rotor" current, which is essentially the same as the "starting surge" , only it is continuous, not just for a short time at start.

            That can be 6x normal current. You can find out what the power draw is by decoding the letter code often found on motors.

            If you "un-stall" it right away, that isn't "good for it" but likely causes no damage past some heating, and stress on the start capacitor if it is single phase.

            Stalling it and "letting it cook" will usually "burn something in the pan" in anywhere from 10 seconds to a minute.
            1601

            Keep eye on ball.
            Hashim Khan

            Comment


            • #7
              Originally posted by vpt
              Your stalling a 2hp 3 phase motor? What depth and feed of cut does that?
              Would not take much to stall such a small motor...
              Precision takes time.

              Comment


              • #8
                Your stalling a 2hp 3 phase motor? What depth and feed of cut does that?
                R.C.'s right. It doesn't take much.
                Usually it happens when I'm manually cranking it, and 'hogging' off metal by hand.... not using the auto feed. (Thanks to my biceps of steel.. )
                1018 or 4140 steel, .030 depth, but cranking the pi$$ outta it, trying to remove alot of metal as quickly as possible.

                Comment


                • #9
                  A motor with no controller has only the protection of the overloads or fuses, with a VFD the current limit should kick in and normally would turn off and go into fault?
                  Max.

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                  • #10
                    As has been said, stalling a motor makes is draw a lot of current, and the heat produced will have to be dissipated somewhere- in the windings and the start cap for the most part. Heat = expansion, cooling = contraction- a lot of that and there will be wear on the insulation. Heat in the start cap will dry it out eventually, and in a bad case can make it explode. Best to avoid this stalling in the first place.

                    Having said that, I am reminded again of a device I built to protect another tool- in this case a die grinder. Basically it was a centrifugal clutch, but in reverse. You could hold the output shaft with your fingers and turn the motor on, no problem. The output would not turn, but if you let it begin to turn, the weights would force outwards, engaging the motor shaft. With the output shaft up to speed, the full motor torque could be had on the output- but if you stalled the output, the clutch would instantly disengage and the motor would not be stalled.

                    I realize that in many if not most cases, there won't be room to add such a device to a machine. The idea is good, though.
                    I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

                    Comment


                    • #11
                      Originally posted by KiddZimaHater
                      R.C.'s right. It doesn't take much.
                      Usually it happens when I'm manually cranking it, and 'hogging' off metal by hand.... not using the auto feed. (Thanks to my biceps of steel.. )
                      1018 or 4140 steel, .030 depth, but cranking the pi$$ outta it, trying to remove alot of metal as quickly as possible.

                      Never knew it was that easy. I don't hand feed much but I have taken off .020" chromoly before in my little atlas with a 1/2hp single phase motor without a problem. From what i remember in school working on the 3 phase machines I don't remember anyone ever stalling a machine. I did see lots of broken tooling though. lol
                      Andy

                      Comment


                      • #12
                        I have stalled my B'port a couple of times. Power feeding a 2 or 3 inch face mill in annealed 4140 a little too fast. It is also REALLY HARD on inserts.

                        Now that I know the limits, I try not to exceed them. If I see or hear the spindle slow down at all, I slow the feed down. I sense that stalling the motor is not good.

                        Brian
                        OPEN EYES, OPEN EARS, OPEN MIND

                        THINK HARDER

                        BETTER TO HAVE TOOLS YOU DON'T NEED THAN TO NEED TOOLS YOU DON'T HAVE

                        MY NAME IS BRIAN AND I AM A TOOLOHOLIC

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                        • #13
                          Yep, stallinig a motor is bad ju ju. After a few seconds smoke escapes as mentioned. Try not to stall the machine. I don't need a new 3 hp, 3 ph motor for my Webb mill but when I was refurbishing the mill a couple of years ago, I checked the price - $900. LOL. We've got to be careful.


                          .

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                          • #14
                            Heres a calc for a 2 hp cut.



                            The calculator is here, interestingly it also gives an estimate of the tangential force:

                            http://mpwr.iscar.com/machiningpwr/M...m&InsertType=1

                            Phil

                            Comment


                            • #15
                              Originally posted by philbur
                              Heres a calc for a 2 hp cut.

                              The calculator is here, interestingly it also gives an estimate of the tangential force:


                              Phil
                              Nifty, however i'll note you used 3 degree lead angle, From the diagram I would suspect that involves one that is almost parallel to the work (I think you wanted 87 degrees?)
                              Also, theres transmission losses, and power used to drive the feed. So you can assume a 2HP motor is only gonna be good for 1.5HP or so at the spindle.
                              Play Brutal Nature, Black Moons free to play highly realistic voxel sandbox game.

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