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Ground Loop Problem on CNC

I have discovered a ground loop potential of 3.0VAC between a CNC
lathe and common ground of seperate 120v plug. The make of the CNC
are the same as the other 10 CNC's, same control, no problems there.
1) When machine is off, there is about 1.9VAC potential. Same reading
when main breaker at the panel is off for this machine.
2) When CNC is powered on, and not in E-Stop condition, the ground
loop potential is about 3.0VAC. When in E-Stop, is goes down to about
2.5VAC.
3) Checked identical machine right beside it, and there is about
0.3VAC ground potential of that machine and any other ground.
This is causing random RS232 characters on sending from the CNC, but
it is able to receive a CNC program no problem. The cable is shielded
and grounded at the computer. Ground potential readings of the cable
and the same ground near the CNC are 0.3VAC, but then measure the
cable shielded ground to the CNC, upto 3.0VAC.
Any suggestions on curing the random garbage over RS232 or fixing the
ground potential? I think fixing the ground potoential would fix the
RS232 problem.
Thanks,
samurai.
Reply to
samurai
Loading thread data ...
how long is your cable?
Reply to
vinny
Sigh...
Reply to
Black Dragon
lol
Im scared to use the altopia account. It's just too easy to abuse? Im only human man!!!
Reply to
vinny
I had the same trouble except it would blow the com ports in my computer. After replacing 4 com boards someone here told me to cut the ground wire on the rs232 cable end at my computer. That was 5 years ago & have not had any trouble since.
Reply to
Why
Cut it at one end or the other....and remeasure
it should be noted that a long run will act as a 'linear transformer' if close to AC lines and pick up a goodly voltage just laying there.
gunner
Reply to
Gunner Asch
Afraid of a little temptation are you? Meheh. I better not invite you over to my house then. Weather was crappy yesterday so was stuck indoors for most of it and finally got around to adding wireless access to my network. Then found out I've got idiots for neighbors. There no less than a half dozen wireless access points nearby and only two, including my own, are secured...
Reply to
Black Dragon
=========== Not to be obtuse, but why not simply just run a direct low resistance common ground wire between the machines?
Unka' George [George McDuffee] ------------------------------------------- He that will not apply new remedies, must expect new evils: for Time is the greatest innovator: and if Time, of course, alter things to the worse, and wisdom and counsel shall not alter them to the better, what shall be the end?
Francis Bacon (1561-1626), English philosopher, essayist, statesman. Essays, "Of Innovations" (1597-1625).
Reply to
F. George McDuffee
I suspect the air line could be the culprit. You did not say what the DC reading was. (dc being galvanic, AC being inductance ) In my opinion for you to track the problem down could take a long time and the only long term problem( unless you CPU is glowing) will be electrolysis. So for that reason alone I would fix it with a bonding wire.
Reply to
cncfixxer1
nooooooooooooo!!!!!!!!!!!!!!!!!!
Reply to
Gunner Asch
What gunner said. If you have to cross an ac line, make it at right angles. Parallel runs are evil.
Reply to
Jon
Would that work, grounding the troubled CNC to another CNC that isn't having a ground issue? The cable is low capicatance, about 150t running at 4800bps. Speed changes made no effects. The cable also runs underground, in plastic conduit(so I'm told), under the concrete. I can't tell if there are AC lines running parallel. But the AC lines also run underground.
Why would the ground potential increase once the servos kick in?
The cable has the frame ground cut at the CNC, testing the ground at the compter and the cable is near zero.
What else can be done to get rid of the ground loop?
samurai.
Reply to
samurai
Black Dragon wrote in news:g333en$hmp$ snipped-for-privacy@bdhi.local:
Or the other secure WAPs aren't broadcasting their SSID's.
It's more fun to broadcast it with something vile.
Reply to
D Murphy
I piggyback all the time. Im careful not to use too much bandwidth, or to leave any security holes for a 3rd party to take advantage of.
shrug...my laptop wifi ID is 'Harmless Piggybacker"
several people know who I am, because I located them and asked them..and they have no problem with it. In fact..the majority have told me they dont use wep, so their neighbors can use wifi, providing security on their own computers to keep the rest from peeking in.
Gunner
Reply to
Gunner Asch
If you can't solve the problem at the source you can always try one of these -
formatting link
Reply to
paul
Our techs seem mystified by phase to ground voltages on our 480V delta distribution. They seem to think that ground is ALWAYS a reference. I keep trying to tell them it is likely do to capacitance effect between conductors and conduit.
Wes
Reply to
clutch
I Looked at those, and thought of setting up this machine wireless to see if that makes a difference. Someone came in and fixed the ground loop problem, not sure what they did. First I'm run a new cable on the floor to test it out, then maybe try the optical isolator and then the wireless.
Why there be an effect sending from the CNC, but not receiving at CNC?
samurai.
Reply to
samurai
an opto-isolated RS-232 converter would solve this. But, it seems like there may be a bad ground connection somewhere between the machine and the breaker panel. There really isn't a magic bullet, you need to go into the junction boxes and look for where this voltage drop occurs and then fix the connection. Of course, you need to do this carefully!
Jon
Reply to
Jon Elson

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