Excessive arcing with plasma cutter

While cutting 3mm steel sheet I noticed an improvement in the arc stability of the cutting process. Unfortunately this is now combined with arcing to the work piece through the nozzle. I can burn through paint now but the thing behaves like a drunken harry potter wand.

- machine is a 40 amp Asian build
- all torch consumeables replaced
- torch checked for cracks and faulty lines
- internal circuits checked for escaped smoke (none)
- internal circuits partially reverse engineered for analysing the theory of operation
- push button start activates a relay controlled air valve only, no direct control over arc starting
- arc starts by the presence of voltage on the output terminals through an inductor and resistor network on the base
of a transistor which closes a relay on the HF transformer supply lines..(diagram attached)

any help, suggestions or open ears appreciated

sure sounds like bad tip and electrode to me, but my second place to look would be bad air- plasma requires really dry air, Thailand is hot and humid. I use the Motor Guard style "toilet paper" filters on my plasma, after regular water traps. The paper filters need to be changed out regularly, the more humid the area, the more often. The wet ones can be allowed to dry out, and reused a few times, I am generally on a two or three month rotation, but my humidity here is not very high. You might need weekly changes. Not sure, of course if a similar filter is available in thailand.

Motor Guard: Air Management

Ries said:

sure sounds like bad tip and electrode to me, but my second place to look would be bad air- plasma requires really dry air, Thailand is hot and humid. I use the Motor Guard style "toilet paper" filters on my plasma, after regular water traps. The paper filters need to be changed out regularly, the more humid the area, the more often. The wet ones can be allowed to dry out, and reused a few times, I am generally on a two or three month rotation, but my humidity here is not very high. You might need weekly changes. Not sure, of course if a similar filter is available in thailand.

Motor Guard: Air Management

Click to expand...

You are right it is humid here, in fact, everytime I get a pedicure I have to get her to trim the webs between my toes, BUT damp air just effects quality of cut and consumeable life span with this machine, it has a drag tip and unless I use water instead of air it still cuts, so although we can get or make dessicators/dryers, it has never been necessary for the use the machine gets. It actualy works better now but bringing the torch head down and aligning it to a template is like trying to jump a freight train doing 90mph.
The HF/HV runs all the time, it seems the HV is too high, perhaps there is a short in the flyback secoundary winding that has not caused total failure?.....
thanks for the thoughts