On Mon, Mar 01, 2010 at 02:22:06PM -0500, Gene Heskett wrote: > > > But probably right at the motor supply terminals of the board, not 3 feet > away in the psu.
I'm with you on the "stop interference at the source" approach, but having the transorb on the board will catch fast spikes induced in that cable. > It's a pi section filter, with 75,000 uf on each side of a choke that > probably has 3 to 4 ounces of decent silicon steel in its E core but I have > not measured its true inductance. The hf noise isn't much greater at the > xylotex terminals than it is at the psu, another 50mv or so. Barring failure > of the caps, I think I am in pretty decent shape. Those 75,000 uf caps are > also beyond my ability to measure, but were top quality stuff 45 years ago, > in humungous screw terminal cans. Even I, as acutely aware of the ESR > requirements for such duty as I am, was pleasantly surprised at the seemingly > zero ESR those old caps have. Ah, I didn't realise you had a pi filter. With any decent inductance between two of those caps, and good ESR, your setup is a very serious spike killer. However, H-bridges can generate their own spikes, given the partially inductive load, and a transorb on at least the supply rail can be life-extending. > >You'd want something with tighter tolerances than the old 5Z27 devices > >floating at the bottom of my junk box, for lower headroom. > > No doubt. How are these transorbs thingies for long term stability? Only > true zeners are stable over time, and those stop at 4.7 volts, anything above > that is actually an avalanche diode, and they will drift low over time, rate > dependent on how much its average power dissipation is. Haven't seen drift in the datasheet, even for a slightly more recent device. A couple of those old 5Z27s checked out within their barn-door specs, and they've been lying about for about 30 years now. Even in-circuit, they're only conducting when there's a spike. If they are very high energy spikes, then some cooking might go on. Erik -- manual, n.: A unit of documentation. There are always three or more on a given item. One is on the shelf; someone has the others. The information you need is in the others. -- Ray Simard ------------------------------------------------------------------------------ Download Intel® Parallel Studio Eval Try the new software tools for yourself. Speed compiling, find bugs proactively, and fine-tune applications for parallel performance. See why Intel Parallel Studio got high marks during beta. http://p.sf.net/sfu/intel-sw-dev _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
