The PCM875 is a high frequency start plasma. It is not a "spike" that is damaging your boards, likely it is the high frequency (15,000 volts, 2 megahertz) starting circuit that fires at the beginning of each cut cycle to ionize the air in the torch. Indusrial grade cnc machines are built using hardened cnc controls (not PC's or Laptops) that are designed with optical isolation on all inputs and outputs.....the drive amplifiers are built similarly with shielded, grounded cables. The torch leads on man of these machines are routed in separate power tracks an often are shielded and grounded directly to a driven earth ground.
It is extra hard to design a cnc machine using off the shelf drives and a PC or Laptop designed for office use...that will work well with a high frequency start plasma. It can be done, but requires very careful cabling , grounding and layout of components in order to minimize the effects of this electrical noise. Most of these types of cnc machines are equipped with a plasma that does not use high frequency as the torch starting method.
High frequency/high voltage travels on the outside of conductors and can easily couple (capacitively and or inductively) through insualation...hence the need for shielded, grounded motor/drive/computer cables and optical isolation for all of the low voltage cables.
tacoma747 wrote:Plasma is a ESAB PCM 875
As for grounds:
Control box is grounded (to the ground terminal)
Plasma cutter is grounded, to the chassis ground terminal
Tables is grounded, connected to the rod that goes through the grating.
All 3 have a separate ground rod. I am going to run another ground rod for the table grating.
I just don't see how feedback or voltage can be going through the motors, the plasma torch is not connected to a 'ground' in any way, the spike would have to be jumping from one insulated wire to another.
OR, I guess maybe the spike could be going through the table grating, through the drive assembly where the gantry contacts the table and back through the drive motors?
Is there anything I can do in conjunction with more ground rods to prevent this?