On Monday 20 July 2020 22:14:10 Jon Elson wrote: > On 07/20/2020 07:43 PM, Gene Heskett wrote: > > Interesting. I wonder if he accidently fixed an unwanted ground, or > > made a bad one good doing it? Murphy is alive and well despite our > > reward funds. > > Yes, he had unwanted grounds (loops) all over the place. > Actually, he has NO ground, only a neutral, which is > connected to some 120 V loads. Clearly not NEC compliant. > Oh my gawd....
> Also, he had the grounds for the servo amps looped all over > the place, had the signals and grounds to the servo amps > following wildly different paths, all sorts of stuff. I had > him rewire so the signal and ground > for the servo amp inputs were bundled together, and logic > power and enable follow the shortest path. > He had to rewire the thing at least a dozen times, but it > eventually cleared up the issues. > > I just instinctively know how to wire signals in a > high-noise environment, so I didn't know how touchy > things actually were. > > One of the shortcuts I took in my servo amps was to not > isolate the power stage from the logic, and to > only have one ground, common for both the power stage and > the logic. I've had thoughts about that, but with an isolated analog supply for just that motor, its not turned out to be a problem at the end of the day. I use switchers for everything else in both cases The opto on the enable line would have made the hoops I've had to jump thru a little easier by making it controllable with normal 5 volt pulldown logic. ISTR I've got something from sparkfun switching the 12 volts into that interface in both of them, works so well I've forgotten what it is. :) With the extra toroids for spindle duty, its runs at room temps. > I SHOULD have also opto-isolated the enable pin > on the servo amp. So, if you have long wires on that common > ground, a star connection from the distant motor power > supply, large voltages will appear on the ground for the > logic as well. > That was the basic problem. I had to have him put a > terminal block as close to the servo amps as > possible, so the path from one amp's ground to the other was > as short as possible. Then, bundling the PWM, direction and > ground to the servo amps finished the fix. > > I've sold 124 of these PWM servo controllers, and NEVER run > into a problem like this. I've had a few people run into > minor noise issues, but this one really had me going in circles. > Its a great controller Jon. With suitable toroids, and a suitable current limiting resistor, mine are both set at around 17 amps, its best described as bullet-proof, you simply cannot make it hurt itself. If I have a PMDC motor to control, no discussion, you get the order. > Jon > > > _______________________________________________ > 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) If we desire respect for the law, we must first make the law respectable. - Louis D. Brandeis Genes Web page <http://geneslinuxbox.net:6309/gene> _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
