EMI reduction with X2Y caps (Brushed DC Motor)

[wraper]

Wraper,

No one's trying to debate here. I had a problem, I tried a potential solution, and posted my before and after results. If you think my result is incorrect, fine, but post facts, not cartoons.

I had an excellent result and will keep using the X2Y solution for my brushed motors despite the stupid high cost.

I have nothing against them, actually I use them myself. That pic is from Freescale document as you can see.

[LabSpokane]

Wraper,

No one's trying to debate here. I had a problem, I tried a potential solution, and posted my before and after results. If you think my result is incorrect, fine, but post facts, not cartoons.

I had an excellent result and will keep using the X2Y solution for my brushed motors despite the stupid high cost.

I have nothing against them, actually I use them myself. That pic is from Freescale document as you can see.

Understood. Apologies.

[Circlotron]

As you can see from the spike and the ringing, the 1N400x diode is pretty slow for that more or less 100ns rise time.  If you spend a couple pennies on an ultrafast diode like a UF4002 instead of a straight 1N4002 you should see considerable improvement.

Steve

Indeed. And seeing it is a low voltage motor a Schottky diode may be even better. No reverse recovery spike to twang your stray inductances like a guitar string.

[RayeR]

I had an excellent result and will keep using the X2Y solution for my brushed motors despite the stupid high cost.

And did you already measured radiated RF spectrum? Did you passed an EMC test? It's more important than measuring waveforms on a scope...

[LabSpokane]

I had an excellent result and will keep using the X2Y solution for my brushed motors despite the stupid high cost.

And did you already measured radiated RF spectrum? Did you passed an EMC test? It's more important than measuring waveforms on a scope...

Not yet. I'm still shopping for a spectrum analyzer. And I don't really have to submit for EMC because my stuff is covered under the industrial use only exemption, but the huge amount of noise going into my power bus and elsewhere was going to be a problem sooner or later.

[Zero999]

I would have expected the vast majority of brush noise to be below a Mhz or two, if that. I find it difficult to believe that it extends up to 40Mhz.
Have you actually measured the high frequency noise?

Brushes by definition are arcing radio transmitters with unlimited bandwidth. It extends up to UV light and beyond, or hundreds of THz.

With brushed motors, you do what you can to filter the noise, and accept the rest. Very much depends on the actual brush design. Some motors are surprisingly "quiet" and some cheap-ass ones cannot be fixed to acceptable EMI with any filtration.

Have you measured the noise spectrum?

No I haven't measured the spectrum myself but I see no reason why arcs in motors or anything else can't radiate at EHF and above. Some of the earliest research in to millimetre waves was conducted using spark gap transmitters.

I created a thread about this awhile ago:
https://www.eevblog.com/forum/chat/the-work-of-jagadis-chandra-bose/msg546705/#msg546705
https://www.cv.nrao.edu/~demerson/bose/bose.html
http://articles.adsabs.harvard.edu/cgi-bin/nph-iarticle_query?bibcode=1925ApJ....61...17N&db_key=AST&page_ind=1&plate_select=NO&data_type=GIF&type=SCREEN_GIF&classic=YES

In the case of the motor of course there will be strong emissions at the resonant frequency of the armature coils and their harmonics but that'll only be at the lower end of the spectrum. There will also be numerous resonances dependant on the physical dimensions of the brushes and commutator, including the gaps between the contacts and the physical thickness of the wire. There will be various emissions resonances all over the RF spectrum from kHz to THz.