The inverter output voltage have very fast flanks to get low switching losses and the circuit is closed by the capacitance in motor to protective earth. There are usually also a capacitance between internal transistors and cooling fin connected to protective earth. The capacitances charge/discharge with the switching frequency and usually cause severe problem with digital communication unless not mitigated. I have also read there may be current thru the bearings and EDM is known method for material removal.
A common mode filter rise the impedance in the loop from the power cables to the protective earth. I have also seen articles with active filters but not tried them myself yet. Nicklas Karlsson On Fri, 6 Mar 2015 14:43:00 -0500 (EST) "Todd Zuercher" <[email protected]> wrote: > What sort of screen? and where is it in relation to the VFD? We have a > router with 2 VFDs mounted on the outside of a wooden cabinet, and they wreak > havoc on the CRT display inside the cabinet when they accelerate/decelerate > (about 6 inches away). It is fine while its running, just when stopping and > starting. I was thinking I should make some sort of metal shield to mount > between them, but its been that way for more than 15 years without any thing > more than this aesthetic problem so it hasn't been real high on my to do > list. > > ----- Original Message ----- > From: "Bruce Layne" <[email protected]> > To: "Enhanced Machine Controller (EMC)" <[email protected]> > Sent: Friday, March 6, 2015 1:58:09 PM > Subject: Re: [Emc-users] VFD causing limits to trip. Huh? > > > My 2'X4' CNC router has a 2.2 KW water cooled spindle and VFD - the > typical Chinese kit off eBay. > > http://www.ebay.com/itm/221354796303 > > I'm getting noise on the video signal that usually causes annoying > screen jitter but sometimes blanks out the screen entirely, which can be > a bit disconcerting when running a CNC machine. That sounds like RFI, > but I used good shielded cable between the VFD and spindle motor. The > shield is grounded at the VFD, and I think I upgraded to a better > quality shielded video cable, so I then assumed the noise was leaking > out as conducted (as opposed to radiated) interference on the VFD's > power leads, although I haven't verified that with the digital storage > oscilloscope. I installed some toroids as RF chokes on the incoming VFD > power leads and it seemed to help a tiny bit. I almost never use that > machine, so this problem wasn't high on my To Do list, but I'm building > a 2'X2' CNC router for me (the larger machine was mostly for my > brother), and I'd like to avoid replicating the problem on the second > CNC router build. > > I just ordered a 14A Rasmi power line input filter on eBay for the VFD. > It cost US$16 delivered. > > http://www.ebay.com/itm/290958532530 > > Hat tip to Andy for the recommendation. > > > > > On 03/06/2015 12:43 PM, Andy Pugh wrote: > > Almost certainly EMI. An input filter for the VFD can help. Check eBay > > for "Rasmi" they are not expensive. > > > ------------------------------------------------------------------------------ > Dive into the World of Parallel Programming The Go Parallel Website, sponsored > by Intel and developed in partnership with Slashdot Media, is your hub for all > things parallel software development, from weekly thought leadership blogs to > news, videos, case studies, tutorials and more. Take a look and join the > conversation now. http://goparallel.sourceforge.net/ > _______________________________________________ > Emc-users mailing list > [email protected] > https://lists.sourceforge.net/lists/listinfo/emc-users > > ------------------------------------------------------------------------------ > Dive into the World of Parallel Programming The Go Parallel Website, sponsored > by Intel and developed in partnership with Slashdot Media, is your hub for all > things parallel software development, from weekly thought leadership blogs to > news, videos, case studies, tutorials and more. Take a look and join the > conversation now. http://goparallel.sourceforge.net/ > _______________________________________________ > Emc-users mailing list > [email protected] > https://lists.sourceforge.net/lists/listinfo/emc-users ------------------------------------------------------------------------------ Dive into the World of Parallel Programming The Go Parallel Website, sponsored by Intel and developed in partnership with Slashdot Media, is your hub for all things parallel software development, from weekly thought leadership blogs to news, videos, case studies, tutorials and more. Take a look and join the conversation now. http://goparallel.sourceforge.net/ _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
