On Saturday 31 December 2016 13:50:38 Chris Albertson wrote: > Gene, > > I think you know all this but I wonder if you implemented it..... > > I wonder if the issue is not with grounding. If a signal moves > relative to ground maybe it is the ground that moves? The only way > to avoid a moving ground is tomato absolutely certain that it is > impossible for current to flow through a ground line. The ground > moves because volts is current times reactance (Ohms law) Yes > "reactance" not resistance because we are dealing with AC. > > Every positive power supply line needs a dedicated return line and > keep them inside the same cable assembly or even twisted. The fields > cancel that way, no common ground return paths > > The only way I know to prove there is not current in a ground line is > to remember Kirkoff: Current flows in a loop. Make the ground such > that there are no loops. This is VERY hard to do an requires things > like lifting the connect to a shielded cable on one end and > > I think the most serious problems are common ground current returns > > My experience with this is mostly with professional level audio where > we try and keep noise at the -100 dB level. It can be done even with > switching mode power supplies > Noise can also readout but never through a grounded metal box > > A good thing to invest in is a lab grade bend power supply. Even the > cheap $100 units are decent. When you are building your prototype > systems use that known-good power supply. I think you said you were > using a re-cycled computer power supply.
Heavens no Chris, what I said was that I had cut the entrance filters out of a couple of them, one was on a separate PCB, but the other I had to drive the mill around the corners to cut it out of the main PCB. But see my post of a few minutes ago, this could be the ultimate solution since its the SPI bus that is being mucked with. > These are the worst things > on Earth. I use one to power my Lithium battery charger > > If the grounding is done well and you've fixed radiated EMI by maybe > using all balanced power cables and metal boxes then LC filters really > work as designed. A large iron core choke will seriously attenuate > noise > > > All that said, most of my motion control work is robots and I use > battery power. The battery powers a set of switching mode DC/DC > converters and these power the electonics these switch at the MHz > level and are easy to filter the other trick is not using one central > power supply but placing smaller DC/DC units near their loads > > On Sat, Dec 31, 2016 at 8:54 AM, Gene Heskett <ghesk...@shentel.net> wrote: > > Greetings all; > > > > While I like the SPI interface as its faster that even a parport, I > > am finding it quite susceptible to mistakes cause by emi from a > > switching psu's typical of stepper motor psu's. These things it > > seems can radiate back out the line input connections, while > > switching at 17 kilohertz, is making the whole system bounce around > > with high frequency switching noises of 5 or more volts with rise > > times in the sub 5ns range, 2 feet of ground braid away from the > > common bolt, totally tearing up the data integrity of the spi bus. > > > > With the z motor psu unplugged, the system runs fine although the > > noise from the 5 v 4a computer and interface supply is still in the > > 1.5 volt range, measured from the common ground bolt to a grounded > > pin on the 7i90's center i/o connector. A filter of sorts, with too > > long (about a foot) interconnection leads from that 5v supply to the > > filter reduces that noise to about 400 millivolts, so its definitely > > helpfull. So I have bought 2 of corcoms 20 amp rated brick wall's, > > should be here the end of next week. $24/copy. > > > > So my question is: > > > > If I mount one adjacent to the psu's for the motors, and feed both > > psu's from that filter with lead wires in the 2 or 3 inch range, is > > this going to cause the crap from one supply to be rejected into the > > other supply, possibly damaging it? > > > > Both supplies carry universal, up to 250 volt input ratings. In fact > > I'd feed them 254 from the wall plug, except the inputs are labeled > > L & N, not L & L. Being a std residential hookup here, my 254 is > > centertapped, balanced to ground. 127 vac to dirt ground from either > > leg. > > > > The 2nd, I will strip room for it on the inside of the lid, so that > > the little supply also has very short leads to the filter. > > > > I quit adding a third one for the 2nd supply because I an running > > out of mounting space for it in this box. So I almost have to make > > one filter do for both supplies. > > > > Cheers, Gene Heskett > > -- > > "There are four boxes to be used in defense of liberty: > > soap, ballot, jury, and ammo. Please use in that order." > > -Ed Howdershelt (Author) > > Genes Web page <http://geneslinuxbox.net:6309/gene> > > > > -------------------------------------------------------------------- > >---------- Check out the vibrant tech community on one of the world's > > most engaging tech sites, SlashDot.org! http://sdm.link/slashdot > > _______________________________________________ > > Emc-users mailing list > > Emc-users@lists.sourceforge.net > > https://lists.sourceforge.net/lists/listinfo/emc-users Cheers, Gene Heskett -- "There are four boxes to be used in defense of liberty: soap, ballot, jury, and ammo. Please use in that order." -Ed Howdershelt (Author) Genes Web page <http://geneslinuxbox.net:6309/gene> ------------------------------------------------------------------------------ Check out the vibrant tech community on one of the world's most engaging tech sites, SlashDot.org! http://sdm.link/slashdot _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
