plasma surge issue

[iain cant]

Hi,
I'm having problems with my cnc plasma machine.

The torch occasionally misfires and sends a pulse of electricity back to my computer, knocking out a chip on my driver board.

If i can divert the pulse to ground I think that would get me by for now.

I'm just not sure how to do this and would welcome any suggestions at all.

Iain

 

[madkayaker]

the pulse will be going to ground through the earth lead? try using a surge arrester plug on the PC and isolating the earth for the PC from the machine e.g. PC power supply not bolted to the frame of the cnc (if that make seance)

 

[Luke]

Which chip? pulse on which circuit? why isn't it opto-isolated?

 

[rtbcomp]

Opto-isolators if the pulse is going down the interface.

Add earth bonding if the earth connections between PC & machine are via the interface.

Surge protectors on the computer and the plasma cutter, consider running the PC from an online UPS.

 

[iain cant]

Which chip? pulse on which circuit? why isn't it opto-isolated?

I have a ULN2003 chip on an inverter board

The plasma switch goes through a pin on this board. Should it have an opto-isolator on the board?

 

[madkayaker]

it would remove a surge point

 

[Luke]

Are you switching the trigger signal directly with the ULN2003? it's rated at 500mA per channel.

Bearing in mind that the trigger circuitry has nothing to do with the arc circuit, I suspect you've got an earthing issue.

 

[iain cant]

Yes, the chip is switching the plasma directly.

Any ideas where to look for the earthing issue?

Could this have something to do with the intermittent firing problems?

 

[Luke]

Any circuit diagrams? Photos?