On Thursday 26 January 2017 10:11:05 Stephen Dubovsky wrote: > Eric, Did you lock the rotor? If you don't and just apply a field the > motor will align to a stable N-S. Even at VERY high temps & fields > you will not damage the magnets (you are actually trying to magnetize > them even more - its how magnets are made afterall.) You need to lock > the rotor (or use active field/orientation control) if using opposing > forces just sitting still N-N & S-S as this is a highly unstable > condition. Any tiny offset will generate Q axis forces and the rotor > will *RAPIDLY* move to the stable N-S state. We never ruined a motor > but were instructed by the motor designers that it can happen. No > idea what the coercivity of a modern neodymium magnet is at typical > motor operating temp. > In useing Jon's pwm-servo amp to run 1 hp spindle motors, that concern has allways entered into my thinking when setting the current limit of that amplifier. Those motors have an FLA of about 9.5 amps, so the amps were setup to hold to 15 max. I ran an ER32 nut down onto a clamp and stalled it for 3 or 4 seconds 2 days ago, but when it had moved off the clamp, everything fired right back up. I can hear the motor iron singing at about 14 kilohertz as it limits. But I don't believe I have damaged the magnets. Bearings in the mills headstock, now those we won't discuss. They were crap from the gitgo and I have got to replace them with quality bearings by spring if not sooner.
> On Thu, Jan 26, 2017 at 7:09 AM, Eric Keller <[email protected]> wrote: > > On Wed, Jan 25, 2017 at 11:22 PM, Stephen Dubovsky > > <[email protected]> > > > > wrote: > > > On Wed, Jan 25, 2017 at 10:25 PM, Jon Elson > > > <[email protected]> > > > > wrote: > > >> Field weakening is not possible on permanent magnet > > >> brushless motors. > > > > > > It actually is. Apply current in the D axis will oppose and > > > reduce the > > > > net > > > > > flux in the gap. Move a coil in between two N poles permanent > > > magnets facing each other and you will get no voltage as the field > > > is zero at the center. You risk demagnetizing the magnets at high > > > temp. > > > > We tried to do this for some fault detection research. We set the > > winding currents so that the motor didn't move, but just heated > > itself. No failures. There is enough change in the magnets with > > heat that we could detect the changes, but they went right back to > > normal when the temperature went back down. We were hoping to get > > some degradation in the magnets over time, but it never happened. It > > was disappointing and reassuring at the same time. I suppose we > > should have gone higher with the current, because we never had any > > winding failures either. The drive was made for a lot more current > > than the motors could take. > > > > ------------------------------------------------------------ > > ------------------ > > Check out the vibrant tech community on one of the world's most > > engaging tech sites, SlashDot.org! http://sdm.link/slashdot > > _______________________________________________ > > Emc-users mailing list > > [email protected] > > https://lists.sourceforge.net/lists/listinfo/emc-users > > ---------------------------------------------------------------------- >-------- Check out the vibrant tech community on one of the world's > most engaging tech sites, SlashDot.org! http://sdm.link/slashdot > _______________________________________________ > Emc-users mailing list > [email protected] > https://lists.sourceforge.net/lists/listinfo/emc-users 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> ------------------------------------------------------------------------------ Check out the vibrant tech community on one of the world's most engaging tech sites, SlashDot.org! http://sdm.link/slashdot _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
