Here's a better VFD/motor matching overview, with a pretty picture of what's going on (scroll down until you get to the schematic showing the three output PWM waves):
http://www.franklin-controls.com/pump/blog/motors/ On Thu, Jan 7, 2016 at 5:29 PM, Steve Traugott <stev...@t7a.org> wrote: > On Thu, Jan 7, 2016 at 5:14 PM, Brian Morel <brianmore...@gmail.com> > wrote: > >> As far as the current issue, you need to be careful using old motors with >> a vfd. The insulation ratings of the older motors were not designed to >> handle the voltage spikes that can occur with running motors fairly >> deviated from their original hz designs. >> > > This sounds to me like a likely culprit. The high-frequency, > high-amperage switching on the output side of a VFD causes high voltage > transients which, if the motor isn't rated for VFD duty, can pierce the > winding insulation and cause internal arcing and carbon tracks. You may be > seeing higher current simply because the windings are now shorting together > in a few spots. > > I remember spending some time searching for a good 5 HP motor with the > right insulation rating to run on a VFD -- they cost a bit more, and are > harder to find. I don't now remember what the magic designation is, but a > quick google search just now tells me it may have been "class H" > insulation. In several subsequent years of running said motor and VFD, > I've never had any issues. > > This looks like a pretty good overview: > http://energy.gov/sites/prod/files/2014/04/f15/motor_tip_sheet14.pdf > > Steve > ------------------------------------------------------------------------------ _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
