On Saturday 22 October 2016 10:59:25 Dave Cole wrote: > 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 > Interesting reading, I saved a copy. Looks like a grounding brush, running against the shaft end center might make the bearings last longer. In some cases. This inverter is 240v single phase powered. Motor frame wasn't grounded other than by metallic corrugated conduit, but is now a wired ground and flexible plastic conduit.
> 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. Broadcast motors for air moving or water pumps will typically run forever given an occasional bearing refresh. I've done that several times, particularly in the Ingersol-Rand water pumps in the 10 to 20 hp range. > So you need to ask yourself; How long does the motor need to last? I bought 2 of them for a 50 dollar bill. They came off of some air compressors that were out in the weather for about 25 years at the local hospital. One was in rather dire need of fresh bearings, which I installed. I cleaned out a collection of paper wasp nests while I did the bearings. So I'll put one in the lathe, and the other, and a set of bearings for it, on the shelf. As for lasting? Long enough for the estate sale, or one of my boys to rent a cargo van & take it to his place in Nebraska. Since I am now 82 yo, statistically the inverter will die before the motor does, and maybe even on my remaining watch. So given that, I am not concerned about the motors life since even if one should have an insulation failure, there's still one on the shelf. There's also the 2nd reference I've seen to that type of bearing failure. Admittedly, my age changes the outlook in that the 2 of them only have to outlive me. :) > 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 And barring a potentiometer failure, with good periodic bearing maintenance, likely to be running fine when the plant is obsoleted and shut down in another 40 years. [...] Thanks Dave. 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 Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
