Page 1 of 2 12 LastLast
  1. #1
    Hi Everyone.
    I've had my plasma CNC table working for a few months, however today it has stopped playing ball.

    I have a driver which is the PM542 model.
    The BOB is the ZP5A-INT Breakout board from Zapp Automation

    I can boot the system fine and manually home the 3 axis, I then start the code running and notice when the plasma pierces there is a lot of interference on the CRT tube screen I'm currently using. Once the pierce has finished the screen is fine.
    However during a pierce, one axis will stop.
    The screen shows everything all fine and dandy, but the cut is a straight line.

    If I disconnect power to the power supply and therefore the drivers\BOB it seems to "reset" and be fine.... until another pierce, not all pierces, but enough to ruin the job.

    I suspect there is some sort if interference when the pierce takes place, the BOB\drivers are mounted to a board that is above the PC, but below the table and directly next to the plasma cutter.

    Does this sound plausible?
    Should move\shield the drivers\BOB from the plasma cutter\PC ?

    Any ideas how to stop this from happening?

    All advice greatly received.

    ---More info---

    I have plugged the plasma cutter into a scocket on a differnt wiring ring to the PC and things *seem* to be better. I'm loosing a few steps now instead of the whole thing crashing, which is certainly better but still not perfect.
    The losses definately happen when the arc is being struck.
    Any ideas?

    Dan


    Last edited by gr8fun; 07-10-2014 at 06:43 PM. Reason: More info

  2. #2
    Dan,

    This is clearly a noise issue so please describe your wiring and grounding setup.

    It's critical that you have shielded wires to all signal cables and steppers and that all shields go to a single earth point, as should all earth's in control box.
    Also keep any power cables away from signal cables.

  3. Since it was working ok it sounds like an earth or shield connection has come loose somewhere. Use a multimeter on a low ohms range to check resistance of all remote earth connections back to the star point.

  4. #4
    Thanks Guys.
    I'm more of a mechanical chap than electronics...

    The wiring and circuitry has always been my toughest part of this project. So, before you tell me I have deserved this...
    my earthing and shielding is, ..well lets just say.... "inadequate"

    My power lines are (more by luck than judgement) away from the signal wires but the earthing is only through what gets provided via the 3 pin plugs used - nothing more than that occurred to me - sorry.

    To improve my position, what is the proper way to earth a system like this and how best should I shield things?
    Many thanks for your help - sorry I set myself up for this, then dropped it on you...

  5. #5
    Have a read here maybe, there's some small diagrams showing correct and incorrect earthing.

    http://www.randyray.com/tmc/rf_shielding.htm
    Last edited by EddyCurrent; 08-10-2014 at 08:49 AM.
    Spelling mistakes are not intentional, I only seem to see them some time after I've posted

  6. #6
    Well I think you have been very lucky to get it working anything like stable if you haven't got sheilded wires and correct form of grounding.

    It's not difficult really and it's more attention to detail than anything with a few correct procedures.

    Earthing is all done thru the Mains earth but what you don't want is individual earth wires going to several earth points on the machine. You need ONE point which connects directly to the MAINS earth. This then acts like a STAR Earth point for all other earths Ie: shield wires to connect too. This then avoids any earth loops which flip drives etc brains out.!

    ALL Signal wires and Motor wires should use Shielded cable which the shield wire then goes to the STAR point.

    It's that simple really but makes a big difference regards noise handling.

    One more thing to note is that you shouldn't confuse DC Negative with AC Earth. All DC Negatives should be taken to the DC supply Negative and not to mains EARTH.
    Also the PC or it's case should NOT be Earthed to the STAR point. The PC will have take it's Earth from the mains directly so treat it as separate and best put on another separate Plug.

  7. #7
    Quote Originally Posted by JAZZCNC View Post
    One more thing to note is that you shouldn't confuse DC Negative with AC Earth. All DC Negatives should be taken to the DC supply Negative and not to mains EARTH.
    Thank guys.
    Grounding rod, clamp, cable and connector are ordered. Looking into shielded wires now...

    WRT the quote above JAZZCNC, I must admit, the thought had crossed my mind... but fortunately, I had taken it no further - so thank you for assuming I was a real noobie - you hit the nail on right on the head! ;-)

    ATB
    Danny
    Last edited by gr8fun; 09-10-2014 at 12:51 PM.

  8. #8
    Quote Originally Posted by gr8fun View Post
    Thank guys.
    Grounding rod, clamp, cable and connector are ordered. Looking into shielded wires now...
    You should not have to do this and I'm not sure it's a good idea even, given lightening strikes etc, in regards insurance and safety.
    Unless your mains has No Earth, which I doubt, then I'd just go with making a better job of the shielding etc.

    Regards the DC Negative AC Earth comment then wasn't meaning or thinking your a Numpty but rather it's a very common misunderstanding and cause of confussion for folks not electricly minded.!
    Last edited by JAZZCNC; 09-10-2014 at 03:31 PM.

  9. #9
    Hi JAZZCNC

    I think I should be doing something, even if it s to earth all the bits (table, water bath, garage doors etc.) to the same star earthing point as currently nothing is earthed unless it is plugged in (and I'd hazard a guess some of my kit does not have earth connected! - I inherited much of it from my grandfather)
    So I plan to link it all up and connect it to the mains earth (the rod arrived, but I've not decided on a location for it yet - if i can use the mains earth that will save me a job.)

    Moving on to the shielded cable, I've just got my head around mains wiring, but signal cables are a totally different ball game I'm sure.
    What should I be looking for? I need 4 core shielded, but how "big" or "small"? Is bigger better or detrimental?

    I'll be taking the opportunity to relocate the PC and drivers etc. further away from the table so this is all a good thing :-)
    Thanks for your help everyone.

    Dan
    Last edited by gr8fun; 11-10-2014 at 09:00 AM.

  10. #10
    Quote Originally Posted by gr8fun View Post
    What should I be looking for? I need 4 core shielded, but how "big" or "small"? Is bigger better or detrimental?
    1.5mm/2 for steppers and for signals to drives, limits etc then 0.75 or0.5mm/2 will be enough. You could also use shielded Cat5 cable which as 8 wires in twisted pairs which is good to use in the control box to cut down on wire runs.

    Quote Originally Posted by gr8fun View Post
    I'll be taking the opportunity to relocate the PC and drivers etc. further away from the table so this is all a good thing :-)
    Don't go crazy on the length keep it to the minimum you need.! . . . Long wires mean longer more receptive/conductive antenna.!!

Page 1 of 2 12 LastLast

Similar Threads

  1. 10' x 5' Plasma table design
    By Kerryfisher in forum Plasma Table Machines
    Replies: 4
    Last Post: 20-02-2013, 09:28 AM
  2. Homebuilt Plasma Table Modifications
    By Normsthename in forum DIY Plasma Build Logs
    Replies: 11
    Last Post: 27-07-2010, 12:58 AM
  3. RFQ: RFQ: Plasma Table
    By D-man in forum Projects, Jobs & Requests
    Replies: 3
    Last Post: 04-07-2010, 11:08 PM
  4. 3M x 2M Plasma table build
    By MonoNeuron in forum DIY Plasma Build Logs
    Replies: 14
    Last Post: 01-09-2009, 11:11 AM
  5. Plasma table 2m x 1m
    By Robin Hewitt in forum DIY Plasma Build Logs
    Replies: 9
    Last Post: 19-05-2009, 12:48 PM

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •