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View Full Version : BOB\Driver crashing? on CNC Plasma table.



gr8fun
07-10-2014, 03:49 PM
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

JAZZCNC
07-10-2014, 11:43 PM
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.

irving2008
08-10-2014, 12:05 AM
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.

gr8fun
08-10-2014, 09:07 AM
Thanks Guys.
I'm more of a mechanical chap than electronics...:apologetic:

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...:distress:

EddyCurrent
08-10-2014, 09:48 AM
Have a read here maybe, there's some small diagrams showing correct and incorrect earthing.

http://www.randyray.com/tmc/rf_shielding.htm

JAZZCNC
08-10-2014, 10:37 AM
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.

gr8fun
09-10-2014, 01:50 PM
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

JAZZCNC
09-10-2014, 04:30 PM
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.!

gr8fun
11-10-2014, 09:55 AM
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

JAZZCNC
11-10-2014, 10:30 AM
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.


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.!!

gr8fun
11-10-2014, 11:44 AM
Don't go crazy on the length keep it to the minimum you need.! . . . Long wires mean longer more receptive/conductive antenna.!!

I was planning on relocating the control box and PC next to the table rather than under it. so perhaps a couple of meters difference..
Thanks for you guidance, much appreciated.

Dan

irving2008
12-10-2014, 12:27 AM
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.
Use CY cable. Never use CAT5 cable for anything that moves regularly unless it's flexible patch cable. Normal CAT5 cable will work harden and fracture.

JAZZCNC
12-10-2014, 03:13 AM
Use CY cable. Never use CAT5 cable for anything that moves regularly unless it's flexible patch cable. Normal CAT5 cable will work harden and fracture.

Irving if you read again you'll see I say use Cat5 in the control box and 1.5mm/2 and 0.75mm/2 for steppers, limits etc he knows he needs shielded so that didn't need saying.

irving2008
12-10-2014, 06:36 AM
Irving if you read again you'll see I say use Cat5 in the control box and 1.5mm/2 and 0.75mm/2 for steppers, limits etc he knows he needs shielded so that didn't need saying.
Hi Dean, sorry to be picky cos I know what you meant but I think if you read what you wrote again its somewhat ambiguous IMHO to others who may be less knowledgeable.


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

"You could also..." implies an alternative to the previous statement. If you'd said " In the control box you could also...." or " which is good to use but only in the control box" then I'd agree with you 100%. :)

JAZZCNC
12-10-2014, 10:59 AM
"You could also..." implies an alternative to the previous statement. If you'd said " In the control box you could also...." or " which is good to use but only in the control box" then I'd agree with you 100%. :)

Erm yes you are being picky and on reading again I Do and Don't agree.!! If you read it like this like it was meant.

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.
Then it's clear I meaning to be only used for signal wires which Cat5 can safely be used out side the machine as often Limits, homes and e-stop are often fixed so don't move.!. . . YES you could get more picky and say some travel but come on how far do you go wiping folks arse's they have to employ some common sense.?

I will thou agree that I should have clarified about not using on cables moving or said use CY for moving cables. SO SORRY FOLKS LET ME CLARIFY
!!! DONT USE CAT5 FOR MOVING CABLES !!!!! ALWAYS USE CY CABLE !!!