From what i have read an emi filter can help with vfd interference issues. I just bought one of these: https://www.amazon.it/dp/B08GPBZQRX/ref=pe_3310731_185740161_TE_item Question is where do i put it? I was planning to put in on the input of the vfd, which i remember seeing suggested. But, are they bidirectional? As in, connected like that will it stop noise coming out of the vfd into the mains? Would it maybe be better to put it on the input of the 24v psu which runs everything else, to keep the nasties from the vfd out? Advice appreciated. I also note it does not filter the earth.. Since i read a lot of vfd noise comes through the earth/shield connections, is there some kind of filter i could put there to keep the noise from propagating into the other earth and shield connections? I guess you dont want to filter /block anything on the earthing circuit? Thanks!
They are meant to filter the power coming IN to the device (plug in the wall > EMI filter > Load) - but most of them do a pretty good job of filtering out some of the Load's noise from making it back into the circuit too. Most VFDs actually have that side built in though, so you may want to use this between the wall and your other accesories instead VFD noise MOSTLY comes from the high frequency output stage (400hz) - in the form of switching of the IGBTs, motor windows and eddy currents. Fascinating read over on Problems VFDs cause and cable types that help solve them Problems VFDs cause and cable types that help solve them covers that too, and no, you want to EARTH it, not filter it.
Thaks for the reply, yeah ive read that guide a few times, definitely interesting! I wonder how much real difference the double shield and symmetric ground makes? Ive been speaking to Igus for cables, and the one their guy recommended was single shield and single non-symmetric earth.. When i suggested a "fancier" cable might be better he seemed a bit offended i was questioning his advice!
Shielded cables are not all made the same, but at the same time, it's kinda hard to screw up. Double shielding is a combination of foil and a braided mesh. Single shielded cables are usually just mesh, but as long as its a decent mesh and not the nonsense single strand wrapped around, you'll be fine. Shielded cables that only use foil tend to be on the cheaper side. By that, I mean low strand count (poor flexibility and durability) and inferior sleeve material.
