iv'e had ground differences between a machine and a pc blow a breakout board , it transpired they were across 2 different supplies, in the building , one 3 phase , one single
On 9 September 2016 at 17:50, Gene Heskett <ghesk...@shentel.net> wrote: > On Friday 09 September 2016 12:08:27 Chris Albertson wrote: > > > It is hard to even guess the cause of this from your description. You > > are just going to have to go down the line and test each part > > independently. > > > > I remember reading here in this forum someone posting about > > "redundant" onto isolators being on both the breakout board and the > > motor drivers. Maybe this shows that even using two of them in series > > is not good enough unless you take other precautions in the design. > > > > I Think the #1 thing most amateur and many professional engineers > > forget is that all ground wires and ground traces have some finite > > amount if resistance and Ohm's Law applies to them > > > > A good why to demonstrate this is to place an AC voltmeter into an AC > > socket in a large building. Measure between Ground and Neutral and > > you might see as much as 1.5 volts. Yes the ground and neutral are > > tried together at the service entrance but the neutral is currying > > some current, the ground wire in the normal case is not. > > > > I'm guessing the root cause here is mixing up the types of grounds. > > Logic level returns (called "ground" in many circuits) are not the > > same as protective ground or AC mains return paths but many times "it > > is all just "GND" and gets connected haphazardly by those metal shells > > and screws on cables and inside power supplies and other places. This > > is almost impossible to get "right" when you are assembling a system > > from little boxes made by others. > > Amen but no other joyous shouts. Its a basic truth. > > But theres a bit of a hint there too, I have a hardwired ground from the > lathes frame to the box all the drivers EXCEPT the spindle are in. but I > am not 100% sure I tied that thru to the logic ground. If not, my bad > dog, no biscuit. > > Something to triple check. > > Everything connected to that machine is on one wall plug, with surge > absorber extensions furnishing the static ground to everything plugged > into them, 2 of them in series, one nailed to the wall the computer is > plugged into, and a second one acting as a master power switch for > everything but the computer. Perhaps I need to verify that it is indeed > connected. Something came in thru the grounds and used a very small > ground trace on the BoB's pc for a fuse. And thats all I have for clues > so far. I unboxed the motors housing so I could shine a strong light > into the brushed end of the motor, but cannot see any winding damage. > The other end of the motor is covered permanently by its fan/pulley, > which has been drilled and tapped in the threaded joint, twice, 180 > degrees separated and 4 ea 10-32 set screws installed as locks to keep > the flywheel from unscrewing itself on a violent reversal, which Pico's > PWM-servo amp can do. All sealed together with green threadlocker. (I > hope) As for the reversal brutality, I have some hal slowdowns, but they > get in the way when doing rigid tapping, so its a compromise between > demagnetizing the motor, and how many turns the spindle overshoots the > stop point, trying to get deep enough threads yet not bottom the tap and > either spin it in the chuck, or break it. So I have some more hal > trickery I can watch with a halmeter that counts the encoders overshoot. > I grab the calculator and convert that to distance, and subtract tghe > figure, obtained while tapping air, from the Z depth to program the > g33.1 with. That was enlightening, above 200 rpm is so much overshoot > its not worth cranking up the speed. 300 rpm is 3.75 turns to get to > zero speed. The chuck is heavy, but effectively ok, its that pound plus > of motor flywheel/fan/pulley that counts as the heaviest mass. > > But thats not finding the short that did all this damage. Later. > > > On Thu, Sep 8, 2016 at 2:59 PM, Gene Heskett <ghesk...@shentel.net> > wrote: > > > Greetings Peter; > > > > > > Someone made the remark a while back that it was indeed possible to > > > look at the output of a function, in this case the first pwmgen of a > > > 5i25 with the prob-rfx2 firmware in it. > > > > > > I've had a blowup, the ultimate cause of which I have not found yet, > > > but from the damages done to the cnc4pc C1G BoB that I have found so > > > far, I am inclined to think the spindle motor psu, or possibly > > > something line powered failed. The C1G damages so far found are 1 > > > blown 74ACT245N, and an almost invisible use of a ground trace on > > > the pcb as a fuse. All the opto's in my spindle encoder would appear > > > to have failed. Those I have a bag of, but that pcb makes the > > > tinfoil of a pack of smokes look like boiler plate, so I'll have > > > something I won't call fun replaceing them. > > > > > > I can run the x/z motors just fine, but the limit switches would > > > appear to be closed as those leds are at full britness when its > > > several inches from the switches. > > > > > > What happened is that I had started a short program that called for > > > a 400 rpm spindle but had neglected to engage the headstocks back > > > gear, so the motor took off and wound out to max speed before I > > > could hit the big red button. And about 1/2 second before my hand > > > hit the button, there was a pop that came from the box over the > > > spindle motor and everything coasted to a stop. The pop sounded > > > like it could have been the top of one of the hexfets on the Pico > > > Systems PWM-servo amp I am driving the motor with. But they look > > > pristine, and all the other components in that box look good and a > > > DVM says they are properly powered. Thinking the motor may have > > > thrown a winding, I've looked it over and checked for shorts and > > > come up empty so far. > > > > > > Back to the 5i25 question. So I fire up the halscope and send it to > > > gpio1.in or in_not. And try to start the spindle from axis with the > > > cable to the bob unplugged. > > > > > > I am seeing a short pulse of 1 volt p-p, which becomes inverted if I > > > look at the in_not, and trying to increase its speed has no effect. > > > So its beginning to look as if I may have blown this 5i25. And I've > > > still no clue what did it. > > > > > > Do you concur, Peter? In that event, I'll need three more, with low > > > profile brackets as I believe the one I was going to run either my > > > toy mill, or this Sheldon lathe, has a bad pin that I was using for > > > the probe, G38.2, and it got flaky. That was because the big dummy > > > I can see in the mirror here forgot to run a decent ground to the > > > frame of my G0704. And it was pretty darned noisy when I put a > > > scope on it. Fixed, but too late for that 5i25. So now I need one > > > for the little monster, one for the Sheldon, and one for my toy mill > > > that I've not found a round tuit to do yet. > > > > > > Thanks Peter, or John T. > > > > > > 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> > > > > > > ------------------------------------------------------------ > > > ------------------ > > > _______________________________________________ > > > 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> > > ------------------------------------------------------------ > ------------------ > _______________________________________________ > Emc-users mailing list > Emc-users@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/emc-users > -- The information contained in this message is confidential and is intended for the addressee only. 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