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  1. #1
    Join Date
    Mar 2012
    Posts
    231

    More Grounding Issues

    I'm a little bit frustrated to say the least!!!

    I have a G540 build that's been working perfectly with the router for months...

    I had the brilliant idea of adding a cheapo plasma.....

    I read, and reread, everything I can find on grounding, there's a grounding rod next to the table, and star ground system on the table, I have the power supply 0V to ground, I have chokes on every comm cable, motor cables are shielded and drain to ground on the G540 side.

    This is a Lotos LTP5000D, pilot arc machine and yes I understand buy Merican, they are better machines, but I don't have $2k burning a hole in my pocket at the moment....

    Anyway, the plasma machine works fine off the table, I have relays to turn start the arc, and double relays tied to the tip for probing. Everything does what it should unless the arc is fired in the air, then the G540 craps it's pants..... No matter what I do, I've disconnected every to the G540 but the inputs and outputs, same thing. If the tip is close enough to the work piece, everything works fine, it probes, lights up and pierces, runs a cut, torch off, lights up again, etc, unless the cut goes off the plate, or over a hole....

    I bought a Proma DTC and that seems to be working OK, but trying to keep the G540 from dropping out so I can tune it a bit....

    PC Never skips a beat, always a the LED on the G540 goes red, torch goes out, gantry dead in the water...

    Is there something I'm missing? or Something else I can do?

    Thanks for any suggestions...

    CR

  2. #2
    Join Date
    Jun 2014
    Posts
    777

    Re: More Grounding Issues

    Is the g540 in a grounded metal enclosure?

  3. #3
    Join Date
    Mar 2012
    Posts
    231

    Re: More Grounding Issues

    Yes... I have an aluminum enclosure from Automation Technology, the enclosure is grounded to the star ground on the table also...

    I have the G540 48V and 0V coming from the Kelling PS, maybe I should have the 0V going directly to the star ground on the enclosure?

    CR

  4. #4
    Join Date
    Jan 2015
    Posts
    138

    Re: More Grounding Issues

    I assume table ground is the plasma torch ground. If so, can you move your star ground off of the table? Make everything come together at the star point, then run a single wire from it to the table. That should reduce the chance of plasma noise being picked up in the signal ground.

    I don't know how easy this is to do, of course, not seeing your setup.

  5. #5
    Join Date
    Mar 2012
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    231

    Re: More Grounding Issues

    By torch ground do you mean the work clamp?

    It wouldn't be too hard, I can create a buss right at the ground clamp..

  6. #6
    Join Date
    Jan 2015
    Posts
    138

    Re: More Grounding Issues

    Yes, the work clamp. What I'm worried about is that you have plasma current flowing from the arc to the clamp. There's a saying that electric current follows the shortest path--it is a lie. Current follows all available paths, according to their resistance. If just a bit of the plasma current can induce some voltage in other wiring, you have a grounding problem.

    That said, if you have a separate clamp connection for the plasma, you are already pretty close to what I suggested. Make sure the ground connection is solid. Years ago I tried to make a cnc plasma torch. I never worked out the motion problems, but forgetting to connect the clamp would shut everything down.

    On a test basis, another thing you could try is to wrap the ground clamp cable around the torch cable for however long is practical (wrap every few inches rather than just parallel). This is likely not something you could use as a permanent fix, but as a test it would reduce the amount of magnetic pickup caused by the plasma current. The worst case would be if the torch cable and the ground clamp cable form a big circle around the other electronics.

  7. #7
    Join Date
    Mar 2012
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    231

    Re: More Grounding Issues

    I understand your theory and I agree with you 100%, but if the arc is firing in the air, do you think it's sending EMI to the ground clamp?

    I have some aluminum duct work tape, I was thinking of wrapping the torch hoses in that with a drain going back to the plasma chassis that's grounded to the star... At a later date I can put a braid around the hoses with a drain...

  8. #8
    Join Date
    Jan 2015
    Posts
    138

    Re: More Grounding Issues

    If it is firing, the current is a lot less, but much more dispersed in space (more paths as RF). Any current that flows from the torch has to return to the clamp (what goes out must come in). I don't know how this goes together, I'd overlooked the bit about arcing in air.

    You said your g540's are in a grounded enclosure--all your wiring is shielded? Try a few things and see if it gets better--or worse.

  9. #9
    Join Date
    Mar 2012
    Posts
    231

    Re: More Grounding Issues

    The enclosure is grounded, the cables are shielded, I even took off all the motor cables and disco the prox limit switches... no change

    The power returns to the source? In the case of the pilot arc, the pilot arc circuit. But like you said, down the pilot arc cable/antenna which could be freaking out the G540..

    CR

  10. #10
    Join Date
    Jan 2007
    Posts
    1795

    Re: More Grounding Issues

    plasma itself should wired to a separated breaker in the breaker box..

    it shouldn't wired together with no any electronics..

    means the wall outlet should be separated at the breaker box..

    the control in metal enclosure, and all cable for motors should be shielded.. then you wont get no issue..
    of course a real ground stick for the machine table better..

  11. #11
    Join Date
    Jan 2015
    Posts
    138

    Re: More Grounding Issues

    This isn't going to help your frustration, but if everything seems to be set up right, maybe go over the setup in detail again. Make sure shields actually connect to the signal source, not the delivery end (and don't have a broken wire), make sure ground lugs aren't loose, etc.

    Another way to do this is have someone help. If you explain what you are doing and why, just the act of explaining can give you a revelation. A variant on "you don't know a topic until you teach it".

  12. #12
    Join Date
    Jun 2014
    Posts
    777

    Re: More Grounding Issues

    Continuity test all your shielding with a multimeter, consider equipotential bonding of screen wires, adding an internal grounded divider in enclosure between psu and drivers and Bob etc and mains filters to psu or toroidal are all things that can help.

    But definetely sounds like you have some eddy currents in your grounding network getting into the g540. Have you tried grounding the plasma generator and clamp only to the grounding rod? Control gear, psu, cable screens through the mains.

    v- or 0v should be going to psu v-, ground is ground and 0v is negative not to be confused.

  13. #13
    Join Date
    Mar 2012
    Posts
    231

    Re: More Grounding Issues

    I've tried to use the grounding only for the plasma and using the service panel ground for the rest, same.

    All the cabling with the exception of a short input/output are shielded. I removed all the cabling and fired the plasma, same.

    I can't tell if it's the PS in the G540 that's getting hit, or the POS G540 is just super sensitive to EMI... I leaning toward the G540 because even though the it's in an enclosure, the backplane of the unit is exposed...

    If I get a chance later today after the honey do list, I'll run over to the shop and try shielding the main plasma cable and see if that helps...

    Thanks for all your suggestions...

    CR

  14. #14
    Join Date
    Mar 2012
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    231

    Re: More Grounding Issues

    Quote Originally Posted by victorofga View Post
    plasma itself should wired to a separated breaker in the breaker box..

    it shouldn't wired together with no any electronics..

    means the wall outlet should be separated at the breaker box..

    the control in metal enclosure, and all cable for motors should be shielded.. then you wont get no issue..
    of course a real ground stick for the machine table better..
    The plasma cutter is 240V, it has it's own dedicated breaker and cabling running from the panel. I also tried removing the neutral from the 240 plug and only use the chassis ground going back to the new grounding rod, same...

    BTW
    I also tested from the new grounding rod to the hot legs and I get 125v exactly the same as from the panel neutral, so without testing for grounding resistance, I know I have a pretty close to the same reference...

  15. #15
    Join Date
    Jan 2015
    Posts
    138

    Re: More Grounding Issues

    "...the G540 because even though the it's in an enclosure, the backplane of the unit is exposed..."

    Are you saying that your enclosure has one side open? You need a box with metal on all sides, all sides connected.

  16. #16
    Join Date
    Mar 2012
    Posts
    231

    Re: More Grounding Issues

    Quote Originally Posted by sajurcaju View Post
    "...the G540 because even though the it's in an enclosure, the backplane of the unit is exposed..."

    Are you saying that your enclosure has one side open? You need a box with metal on all sides, all sides connected.
    It would be difficult with a G540 to have the entire control box in the enclosure, all the plugs are on the backplane. Attachment 307216

    Well no good with anything I tried...

    Bought a grounding buss from Home Depot, buss goes to the grounding rod, all grounds go to the buss. No Change.

    I took aluminum tape and wrapped all of the torch hose and grounded at the plasma machine end. No Change.

    Took every single cable off the G540, turn the charge pump off, fired the plasma by itself, tripped the G540.

    Remove the ground wire from the AC side of the PS, No Change

    Removed the Neutral from the AC side, ran just the ground from the new grounding rod and the hot to the PS, No Change

    I don't believe it's EMI at all, it has something to do with loosing power, or loosing the ground on the G540 that trips it, or maybe it's a setting in Mach....

    It's frustrating, but I'll get it...

  17. #17
    Join Date
    Jan 2015
    Posts
    138

    Re: More Grounding Issues

    Have you got a battery backup for a computer that you could power the g540 with temporarily?
    I see what you mean on the g540, but you could still connect it to the box shell, either with star washers between it and the case or some other method. Star washers should break through the g540 anodizing and the case oxide.

  18. #18
    Join Date
    Mar 2012
    Posts
    231

    Re: More Grounding Issues

    That was my next thought...

    Do you think an automotive inverter off a car battery would be ok on that switching PS?

    I like the star washer idea also, I'll try that too...

    CR

  19. #19
    Join Date
    Jan 2015
    Posts
    138

    Re: More Grounding Issues

    An auto inverter should work fine, maybe even better than a computer UPS (no line connection at all). Ask around, I bet you know someone who has a computer backup.

  20. #20
    Join Date
    Jan 2007
    Posts
    1795

    Re: More Grounding Issues

    nyracer


    im not sure about the idea...
    but..

    on routers , where inverter used for speedcontrol, theres a linefilter inserted..
    an rf filter..


    I can not say this is the one you need, but this type..

    Metal Shell 6 Terminal Power Line EMI Filter AC 115V 250V 30A 50 60Hz | eBay

    it will filter out the the ""backfiring"" to the powerline..

    it was discussed here on the zone.. many times.. I cant find really one topic..
    but heres a link from cnc cookbook

    CNCCookbook: Dealing with noise problems

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