On Monday 25 January 2016 08:00:12 Marius Alksnys wrote: > 01/24/2016 11:55 PM, Gene Heskett rašė: > > On Sunday 24 January 2016 16:30:45 Marius Alksnys wrote: > >> 01/24/2016 04:37 PM, Dave Cole rašė: > >>> Is the positioning ability adequate? > >> > >> I am impressed how strong it holds in position even when fed with > >> DC current (freq = 0). I can't force it to rotate by hand, while it > >> is very easy rotating while turned off. > > > > That motors rotor has to be offcenter enough to drag under dc > > exitation, whereas it should move like it was full of cold molasses. > > Call a surveyer slow, but dead smooth. > > > > As that raises the spot heat from friction at low speeds, I'd want > > to have a spare on the shelf in case it self destructs. > > Sorry Gene, it is hard for me understand almost all of your posts > without dictionary and deeper analysis of your words.. It might be > because my mother language is Lithuanian, my English technical is ~ > ok, but your posts are full of colorful English.. :)
And despite having some Iowegian neighbors while growing up, I am in the same situation, I don't know a word of Lithuanian. I in fact, highly appreciate that you have learned English well enough to write it quite well, and I thank you for that effort. And if my posts are "entertaining" because of some of the slang phrases I might use, that I hope, is a Good Thing. > This spindle rotates at 10kRPM nicely, thus I have no doubts it is in > good balance. I think heavy magnetic field holds the magnetized rotor > almost in place when I turn 10A DC current on. If its not perfectly centered between the field poles, the magnetism will pull it farther off center, flexing anything in the assembly that can be flexed, far enough to drag on and stick to the poles. With DC applied, there is no zero crossing where the magnetic field is zero for a millisecond or so, which allows it to move. One might use a variable currant supply, put only 1 amp thru it, I'd expect it to turn & feel like any "suicide braking" setup. If the armature was perfectly centered, that 10 amps should just make the effect stronger but should not lock it up. Pole pieces touching the armature will eventually wear very smooth and the laminations can then short to each other eventually, allowing the eddy currents to flow that the laminations are there to stop. That alone will raise the current draw, and the heat in that localized are where the shorts are. Eventually the smoke gets out and the driver may fail. One could recenter the armature using a suitable thickness of brass shim stock to hold it centered while the end bells of the motor were re-assembled. But then you have no way to remove the shim stock. The ideal situation would be a much larger bearing boss in the end bells, with some set screws so the bearing carrier could be driven 5 thou or more in any direction to bring it back on center. But that would raise the price of the motor 20%, killing sales for the maker who has to deal with people that want to buy a motor that Just Works(TM), with no clue or understanding that they are also subject to the tolerances of how it was built and assembled. I think you have such a borderline motor. For you its likely an advantage, because it does lock in place, for as long as it lasts. Depending on its usage, that could well be north of a decade. If you had two of them, doing identical jobs, I suspect this one would be running a degree or so warmer than the one that was well enough centered that its not locking up with 10 amps of DC thru it. You may want to file this conversation away in a dusty corner, forgotten about, until the day when it becomes a problem when running at the lower speeds too. It will get sticky and the vfd will have to up the drive frequency before it suddenly snaps up to speed. Thanks Marius. Cheers, Gene Heskett -- "There are four boxes to be used in defense of liberty: soap, ballot, jury, and ammo. Please use in that order." -Ed Howdershelt (Author) Genes Web page <http://geneslinuxbox.net:6309/gene> ------------------------------------------------------------------------------ Site24x7 APM Insight: Get Deep Visibility into Application Performance APM + Mobile APM + RUM: Monitor 3 App instances at just $35/Month Monitor end-to-end web transactions and take corrective actions now Troubleshoot faster and improve end-user experience. Signup Now! http://pubads.g.doubleclick.net/gampad/clk?id=267308311&iu=/4140 _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
