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View Full Version : Plasma - Big Problems - HF Start !!!



jamied
20-09-2010, 11:33 PM
finaly finished my plasma table all up and running ok on Mack , but installed the plasma cutter and big problems !!! forgot about the HF start !! :redface:
tried grounding EVERYTHING bed ,torch , table control box , all on a 4ft ground spike ,tried moving plasma as far away as posable but still no good ,routed all the cable away from the plasma lead , better but still no good , any ideas guys ?? besides the obvious of changing the plasma cutter ??

thanks

Jamie

routercnc
21-09-2010, 01:43 PM
I assume the problem is false stops, and Mach3 trips out when the plasma starts up?

My mk1 router machine had a similar problem (steppers interfered with limits), and I disconnected the limit/home cables one at a time to track it down. The longest cable (z axis home) caused the problem on mine. For mk2 all cables are now shielded, the shields all run to a common earth at one end only (star pattern?), and the cable runs for motor and limits are in seperate energy chains on either LH or RH side of the machine. I've a bit more work to do before firing it all up, but hopefully this will solve my problem.

I'll also experiment with 0.1uF capacitors across the limit terminals on the control board if I still have problems.

Any of this applicable to your machine?

jamied
21-09-2010, 02:33 PM
thanks for the reply
the machine works fine no issues until I start the plasma torch and the HF sends the stepper motors shooting off !

regards

Jamie

John S
21-09-2010, 02:44 PM
Can't help but i always wondered about that.
My old AC/DC TiG with a spark gap would trash everything when running. If the show computer was running I'd come back and find about 15 windows open, many I had never seen before.

To be safe I never welded when the CNC was running, the new inverter TiG seems to behave itself but again no welding of any kind when the CNC is on.

irving2008
21-09-2010, 03:58 PM
thanks for the reply
the machine works fine no issues until I start the plasma torch and the HF sends the stepper motors shooting off !

regards

JamieAre you saying the motors spin on their own? then you have interference in the step/dir lines to the drivers. Where are the drivers in relation to the torch? You need the shortest possble cable between PC and drivers. The interference could be getting into the motor wires and thence back into the controller. Is the plasma torch on the same mains as the power supply to the drivers? You might need an RF Filter (like you'd use on a VFD) on the input to the driver PSU, AND on the input to the torch PSU.

If you disconnect the breakout -> drivers cable and start the torch do the steppers move? if not, reconnect and remove the cable from the parallel port. Does it move now?, if not, do they move with the PC on but MACH3 not running.

Need to try and isolate where the interference is getting in the system. You may need to put the motor wires through a ferrite ring to stop HF flowing back up there... and all cables should be shielded, when that plasma starts its like a mini-EMP!

jamied
21-09-2010, 04:19 PM
thanks Irving

yes the motors start moving themselves once the HF is triggered, the plasma is on a different supply to the pc/drivers , im picking up some ferrite rings today to try also havnt grounded the pc to the ground rod yet ? will test out disconecting the breakout/driver boards later to see if I can isolate where the interference is

irving2008
21-09-2010, 04:22 PM
put at least 2 or 3 turns on the rings, but no more than 5 or 6... one ring per motor

jamied
21-09-2010, 04:30 PM
where would you fit them ? as the cables come off the driver boards or at the motor end of the cable ??

irving2008
21-09-2010, 08:35 PM
as near the drivers as you can generally, but you might experiment. The other type is the clamp over ferrite... easier to move along the cable

AdCNC
22-09-2010, 12:27 AM
Just another thought ( might not apply to Jamied ), what i did to overcome limits being triggered, was to isolate the limits going to the bob with a simple relay system. so all the switching is done in the bob box!

John S
22-09-2010, 01:27 AM
In the top right hand corner of Config > General Config there is a box for debounce, this is the spacing between periods that Mach looks for any limit or estop switches, i think default is 20 bit this is micro seconds, you can safely go up to 2,000 to space the periods out so it doesn't see stray signals.

This may help anyone who machine stops for random reasons.