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.


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