View Full Version : EMI Filters, any purpose in a diy control circuit?

13-03-2014, 11:17 AM
Do EMI power line filters serve any purpose in a DIY control circuit, or should I ask is it worth including one at the mains inlet. I'm getting mixed responses.

13-03-2014, 09:06 PM
Hi Jim,

I included one between the mains and VFD unit (plus a ferrite coil around the spindle cable) and have had absolutely no problem with interference from the spindle over several years of operation, the radio reception is crystal clear (digital if that make a difference), and there are no complaints of electrical noise issues inside the house when it is running.

Unfortunately I have never run it without so don't know if it is definitely required - but I don't remember paying much for it and would do it again just to ensure no issues.

14-03-2014, 12:15 AM
Yes is the short answer...

Without it I had real issues with noise on the mains affecting answerphones, tv (admittedly analogue tv) and Ethernet.

14-03-2014, 05:54 AM
Thanks for your responses, but what is a ferrite coil. I'll google it but you may be able to explain in simple terms that I will understand.

14-03-2014, 08:47 AM
Basically a ring of ferrite. You wind a few turns of your cable onto it and it acts as a high frequency choke. For smaller cables you can also use a ferrite bead which you slip over the cable or a ferrite clamp which is like a large split bead for thicker cables. All of these can help but a good EMI filter is best.

14-03-2014, 08:51 PM

As Irving has described I clipped one of these types of ferrites on each end of the spindle cable just in case:

12 5mm Clip ON Ferrite Core Data Cable Ferrous Ring Bead Choke Filter EMI RFI | eBay (http://www.ebay.ca/itm/12-5mm-CLIP-ON-FERRITE-CORE-DATA-CABLE-FERROUS-RING-BEAD-CHOKE-FILTER-EMI-RFI-/330856274467?pt=UK_Computing_Sound_Vision_Video_Ca bles_Adapters&hash=item4d08921a23#ht_2250wt_867)

Here's my VFD (top right), mains filter (bottom right), and brake resistor (middle) which was a waste of money (50) as I never used it since the spindle stops pretty quickly without it.

14-03-2014, 10:38 PM
Thanks for your responses, but what is a ferrite coil
Jim, I
t's not a coil, it's a Ferrite Core,