Erik Christiansen wrote: > On Sun, Apr 20, 2008 at 10:42:31PM -0700, Kirk Wallace wrote: > >>I got the spindle VFD working on my Shizuoka and the speed varies quite >>a bit. This seems to be due to interference coming from the spindle >>motor leads. The cable has no shielding but there are six wires. One for >>each phase, and three more that seem to connect together at the motor >>end, but not to anything else. > > > That sounds an awful lot like the star point of your 3-phase motor. [1] > While it's usually within a few volts (or ten) of ground, _if_ supply > and load are reasonably balanced, it's > not_for_finger_poking_or_connecting_to_ground, I submit. (If one phase > goes open, there'll then be smoke, if not before. ;-) > The star point would be near ground with balanced 3-phase Wye power. There are also corner-grounded and center-tap grounded Delta systems where it is nowhere NEAR ground.
With a VFD, it will NEVER be near ground, and will guarantee a wild fireworks show if grounded. The VFD has a floating 400 V DC supply that is bouncing between the peaks and valleys of the input power waveform, and the motor's star point will be centered between those + and - voltages. I put a power line filter on the INPUT to my VFD, and have no shielding or other treatment on the wires between VFD and motor. I had some hash on my computer screen before I instaled that filter. Jon ------------------------------------------------------------------------- This SF.net email is sponsored by the 2008 JavaOne(SM) Conference Don't miss this year's exciting event. There's still time to save $100. Use priority code J8TL2D2. http://ad.doubleclick.net/clk;198757673;13503038;p?http://java.sun.com/javaone _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
