On 31 Dec 2016, at 18:50, 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. These are the worst things > on Earth.
Absolutely agree with that. Most cheap ones do not have any decent filtering. Try using a linear PSU. Much more expensive, but much less trouble. Mine is built from a couple of large toroidal transformers. No troublesome emissions. The only spurious emissions are the noise for one of the four fans, which sounds as though it has run a bearing again. Have you checked your computer for emissions? I have one computer here which sends out copious amounts of broadband noise (from the PSU). The PSU came as part of a deal with a new rack mount case. I thought it was a nice bonus at the time... Marcus > 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 > > > > -- > > Chris Albertson > Redondo Beach, California > > ------------------------------------------------------------------------------ > 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 ------------------------------------------------------------------------------ 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
