Are Ferrite Cores On Wires Useful At All?

I often find ferrite cores on things like USB cables or power adapters. Since I have never been able to see any difference between cables with and without cores, I typically take the cores apart (by unclipping them when they're removable or by using a fine adjuster when they aren't) and get rid of them, becase uncored cables are easier to bundle up and store. I have yet to see adverse effects from un-cored cables, so I wonder why do they put them there at all.

I mean, I can understand ferrite cores on data cables in critical situations, but on 5V power adapters for household electronics?

I forgot to re-install the ferrite bead on an optical mouse that needed it's cord fixed. The mouse worked for about 2 seconds after each time i plugged it in then locked up. Reinstalling the ferrite bead fixed it. So yeah I would say anything that's susceptible to noise or is high speed might need its ferrite bead.

They are there to try to stop some of the HF switching noise left over from the SMPS.

the cores keep rfi/emi down ... going out and coming in .
this is something not many people appreciate as they do not have to deal with rfi/emi in an environment where it rears it's ugly head in a big way :
equipment used around/with broadcast (business and commercial) transmitter sites/areas .

Well, these days how many companies do you know that want to put that extra component in the mix if they don't need to be there?

Some are placed of course to filter out HF noise that finds it`s way into your gear, and some to stop your gear from putting the noise elsewhere, so in the case of your one bit of gear functioning correctly - in the latter case you might conclude they`re not `needed. However, if everyone removed the ones that weren`t critical for their `selfish`operation, then will your bit still function selfishly with all that added noise.

On topic - We had an issue a few years back with our FK-503`s not working correctly. The core was shipped (not installed) and the road guys thought perhaps they were simply for decoration and tossed them. Although environment had a lot to do with it, about an even half of the units wouldn`t function properly - blowing comm codes and errors.

Just the other day we had a motor drive which was malfunctioning in the presence of an induction heater. I suggested putting a few turns of the power cord through a large ferrite toroid. Problem averted.

When you're working with power systems, noise of course is magnified by scale, to the point where normally robust systems can fail. This is far in excess of the reason ferrite beads are added to consumer equipment: to keep radio emissions down.

Too much noise and many important bands disappear: AM broadcast, shortwave, maritime and Coast Guard, TV (I believe digital TV channels are in the same bands as analog was, except you can't tell if a signal is weak with static, it just drops out altogether), all the way up to FM radio and civil and military aircraft.

It used to be relatively easy to do around-the-world QRP. About the only reason it's still possible is due to highly directional antennas and sensitive Fourier analysis. The airwaves are clogged with the debris of everyday life.

Tim

I am having some noise issues with my CNC switches. I have some of my control wires running somewhat close to my motor wires. Every once in a while I get will get false E-stop trigger. I have considered getting a couple of these to see if they help.

5 or so years ago I read the full USB spec. It specifically says that there's no point in putting ferrite beads on USB cables, but I can't remember the reason.

Ferrite suppression cores are necessary under adverse conditions, even though you may not notice any difference when conditions are good.
That's the bottom line.

USB in and of itself is supposed to be fully shielded, so no signals from the interface get to see the light of day. Induced fields from other sources (especially the many switching supplies inside a computer or peripheral) can do much worse, however.

Tim

Hmm. Well, I guess I'll be keeping the cores from now on. Thanks

Keep them on the cables!

A few years back I was having a headache with some kind of peripheral...I can't remember what it was now though? I think it might have been a cordless IR mouse/remote control thing.

Anyways,the cable didn't come with a ferrite,and I couldn't get it to work,and couldn't figure out why. For kicks I clipped a ferrite on each end of the cable. POOF! Worked like a champ after that.

Plus,it helps keep some of the radiated noise down. If you've ever tried to use a scanner radio or something next to a PC,you'll know what I mean. Lots of whistles and 'ghost' carriers.

Some time ago I bought a card reader from a Chinese store. It never worked right, stalling on both writes and reads. I blamed it on poor quality and tossed it in the parts bin.
About an hour ago I remembered this thread, so I dug it out, grabbed a USB extension cord, put a ferrite core on it, plugged it in, and it's been happily copying gigabytes of data to and from a microSD card for the past half hour.
Funny thing is, this reader isn't even designed to work on a wire - its plug is soldered directly to its board.

So the standard goes.

I wonder if cores - and beads - somehow don't get the same respect as 'components' due to their lack solderable leads, standard value markings, and schematic ambiguity. Components with a complex.

Meh. So much for that - the reader failed again, even with the core on. I'm going back to crappy quality.

Nice coincidence. Broke one of the cores (fragile bugger, fell on the floor as I was threading the cable) from the flat foil cable that sends the CCD data to the image processing board. Buttoned 'er up and crossed my fingers, but nope. Recognizable images, but about the same results you get opening a jpeg image in HxD and randomly altering data with girl parts cusswords - uh, er so I assume that is.

Yup, they're useful double confirmed. now lets see if they still work - or will at least eek by - reassembled with super glue and short a few pie shaped bits .

Won't superglue prevent conductivity and stop them from working?

In general, performance will be reduced perhaps 10-50%. Impossible to say if that "stops them from working", of course.

The extra airgap will have a detrimental effect on high permeability (low frequency) cores, not as much on high frequency materials. It depends.

Tim