Unless the motor is inverter duty rated, it was designed to run at the base speed on 60 hz - typically for years without much or any maintenance. Typically, I think you can get by with 2x base speed on most small motors without a very short life (less than a year of continuous operation). However their are no guarantees. Running near and beyond 2x is risking a rotor explosion on a non inverter duty rated motor, where the rotor comes apart inside the motor.
Check this out... and you will see there are other issues as well.. such a motor bearing destruction due to currents in the motors etc. http://www.industry.usa.siemens.com/drives/us/en/electric-motor/anema-motors/specification/documents/nema-application-guide.pdf Keep in mind that the Siemens guys at the Siemens Norwood plant mainly deal with above NEMA motors, so 250 hp and up. Those guys are concerned when motor life is shortened to less than 10 years! That would be an early failure. I know of some old GM spec U frame motors that ran for 50+ years continuously before they shutdown the plant in Michigan. If the lubrication guys visited the motor on schedule, they might last beyond a lifetime without other maintenance. So you need to ask yourself; How long does the motor need to last? I have installed small cheap non inverter duty 3 phase motors on industrial machinery running between 1x and 2x base speed in non-continuous operation and years later they are still going strong. We knew that overspeeding the motor would shorten its life, but the motor only cost $150. An inverter rated motor would be 3-4x the cost. One application was on an unwinder. The motor goes from 0 to 3600 rpm (base speed of 1800) depending on a PID loop in the drive itself. The speed is controlled by a dancer that turns a potentiometer that feeds the PID loop. Its a very simple application but is very effective and cheap. I think that machine is on year 6 now on a two shift per day operation. Dave On 10/22/2016 7:26 AM, Gene Heskett wrote: > Greetings all; > > Since I will be useing this vfd, as opposed to a treadmill motor with one > of Jon's excellent pwm-servo amps on this lathe, I'll have quite a > number of options to get the spindle speed I'll need as there's the > backgear to really slow it, and the 4 step pulley setup inside the door. > Quite versatile. > > I am not sure how much over speed this motor can do, but it does seem > quite happy at 120 hertz, and doesn't heat excessively at 30 hertz. A > 4/1 range. I have run it on the table as high as 200 hz, 5900+ rpms (can > the fan blades tolerate that for long?) but the current draw is under an > amp/phase (or my amprobes are lying to me as they are calibrated at 60 > hz, so I'd imagine its inductance is killing both the max currents the > vfd can push into it, but also the available torque is falling off a > cliff. > > PEBKAC being what it is around me, I think I need some sort of a set of > gladevcp or pyvcp leds to tell me if I ask for 1350 rpm and the belts > are not in a position to achieve that, or the motor will be below 40 hz, > the leds will tell me which way to move the belts in order to put the > motor "in its comfort zone". I have some working button code on the > mill I can use for the display, but might need, when I get to that > stage, some help cobbling up the near modules settings to drive > the "leds". > > ============= > > 2nd Q is only semi-related, but I can get, from gearbest, an arduino mega > r3 with a pile of 10 bit analog inputs for a tenner. See: > > <http://www.gearbest.com/development-boards/pp_18651.html> > > Which, if it can talk to linuxcnc over the usb cable, might be able to > warn me if the motor is being lugged excessively and getting too hot > since its quite well out of sight and mind where its hung. Theres a lot > more it could do, I just haven't conjured up the use scenario yet. :) > > But, mpja.com also has a $2.49 module #31588-MP, that could send an > overheat alarm bit directly to a gpio pin on a 5i25 & that looks a lot > simpler to do. Since these spindle bearings are bronze, an overtemp > alarm on each because they've not been lubed recently could also be > handy. > > Is such an effort worth it? > > Thanks guys. > > Cheers, Gene Heskett ------------------------------------------------------------------------------ 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 Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
