Ferrite Donuts (Toroids) to suppress noise, or not?

[HayTay]

Should we be using ferrite donuts (toroids) on our stepper motor wiring to suppress electrical noise/interference (RFI, EMI, TVI, xxI)? If so, which end should it be placed on, the driver end, stepper motor end, or both? If not, should we be using them on other wiring like the AC or DC power leads? I've taken apart a lot of equipment and invariably there is at least one ferrite donut (or split bead) in there somewhere (see attached picture).

There must be some rule of thumb to figure out if we need one and where it should be placed. If we have one already, how do we know whether or not it is performing as expected.

Inquiring minds and all,

HayTay

[High Seas]

HayTay - I'll preface this with this is my HAM experience I'm basing on and not my ancient E/EE in uni.
I'm sure someone like PMinMO is a bit more "switched on" and might have a better answer for you - but for your consideration I offer...

Toroids and ferrite chokes; What and Why -- These are use to reduce the possibility of the wire(s) they are attached to, from being effective antennas. NOTE - That is reduce - not elminate. These wires pick up a variety of electromagnetic energy - it can be line (shop power) orginated or something as close to the work efffort as the PC itself. If you're using converted pc power supplies - you might be generating more rf there too.

If you look at some old modem/com/crt cables you may see these "chokes" attached each end. Here's a look at how stuff works:
http://computer.howstuffworks.com/question352.htm

You can source these little guys at your local salvation army/op shop--usually in the cables bin and they shouldn't cost too much. Might even check your "spares locker." "Radio snack" has 'em too and they can be ordered from a variety of sources.

How do you know they're working? On an HF radio - your signal improves and someone tells you. Or follow the approach at this site:
http://www.emcesd.com/tt2005/tt090105.htm
this site is focused on comparing single vs multiple wraps and the difference in effectiveness - but ought to be able to get a correlation to "with/without ferrites" I'd think too.

I tend to use these rules of thumb - on suspect areas:
1. use twisted/shielded and grounded wires where possible. Grounding the shield to the pc case and the controller case.
2. If unable - add a ferrite choke at the end(s) you'd be concerned about most:
A. close to the driver on wires leading from the pc, and
B. near the motors coming from the driver.

Hope that is helpful.
Jim

[HayTay]

So, according to How Stuff Works the interfering signals are converted to heat by the ferrite bead which it then safely dissipates.

But, I thought what the ferrite bead did was evenly distribute the RFI/EMI/xxI over the number of conductors in the cable looping through it proportionate to the size of the conductor(s). Which, in the case of data cables, should be shielded. Thus, the shielding, being the largest conductor having the least resistance (if properly grounded) closest to the interfering signal would induct the largest portion of the interference and pass it to ground, theoretically.

Am I way off? Have I lost it? Logically, my theory, to me, makes more sense. But, then, I'm me!

While disconnecting/connecting a lot of computers and peripherals I've never happened upon a ferrite bead that was warm, let alone hot, unless it happened to be in the direct path of the units exhaust fan. Does this mean there's no RFI/EMI/TVI/xxi present or that they don't work by dissipating heat?

Confused,

HayTay

[Al_The_Man]

Some Manufacturers like Aerotech recommend that Ferrite Chokes be placed in all motor leads using their drives, this essentially is a toroidal ferrite choke which has all three motor leads wound with about three turns on the common choke close to the motor.
This acts as a high impedance to high frequency signals which effectively reduce the EMI and follows the same laws of any inductance in an AC circuit.
If this energy were high enough it would produce heat, but we are talking relatively low energy, too low to have heating effect.
Al.

[erase42]

the amount of heat that would be created would be so small, that it would easily be radiated into the air faster than a buildup of heat could happen. keep in mind that the amount of energy in that stray emi/rfi extremely small.