Valid arc lost & top limit is reached while THC moving up

tommylight wrote:

For some strange reason i can not quote last post from Snowwy, but i can all the others, even mine !

Same here, it must be another forum feature.

Mode 0 is not without issues due to the simplistic ArcOK algorithm using thresholds when the torch voltage is quite erratic in piercing and not a smooth transition but thats another story. Its not something I would trust.

What I do see is in the original post the OP said he was using a THCAD-300. That makes no sense on a machine that has a voltage divider and a CPC port. The THCAD-300 designed to consume raw arc voltage.

So how is the THCAD connected to the machine and what voltage divider is used? Where is the THCAD located?
Where is it drawing 5v power from?

rodw wrote:

Mode 0 is not without issues due to the simplistic ArcOK algorithm using thresholds when the torch voltage is quite erratic in piercing and not a smooth transition but thats another story. Its not something I would trust.

Well it is more than just thresholds, it does require a number of valid samples within the thresholds.
I have never had any issues with it.

tommylight wrote:

Mode 0 works perfectly well with most plasma sources, but it will not work with some older ones as they do not have capacitors on the output rails.
Works perfectly with an old Iskra and Cebora, both 50A, does not work with Thermal Dynamics 90A -fails about twice every 10 fires, works perfectly with a new Stamos 70A, etc etc.

Exactly my point, not to be trusted. If I did not have an ArcOK I would use your reed relay solution Tommy, I would never try and synthesise it.

I think I have fixed the issue. Checked everything from point to point and came to conclusion that the air tube is too long and can't give the needed flow to the plasma cutter when cutting. The momentary air loss generates the error/warning only when cutting, i never saw error in plasma source because i was monitoring controller (linuxcnc).
A faulty air pressure supply, which the plasma cutter lost the ArcOK due to less than minimum air pressure needed to cut, which indicates in LinuxCNC (and well indicated) a "Valid Arc Lost". The fact that cuts time to time it's when the air compressor supply  is working. I've managed to supply the right air pressure to the cutter and it's working. Now just need a few adjusts in THC movement.

I want to thank everyone that was able to help, I apreciate that! Now I understand better the works of plasmac and what to chek if anything isn't ok.
Sorry for the trouble.

THANK YOU 

Great news. I know Jim Colt from Hypertherm always recommended to add a pressure gauge right at the plasma cutters inlet but air flow  at the design pressure is the most critical thing.

Just curious. Were there any errors reported on the plasma cutter's front panel? my Thermal Dynamics does report  low air pressure and I've seen it a few times if a breaker on the compressor pops. 

rodw wrote:

Just curious. Were there any errors reported on the plasma cutter's front panel? my Thermal Dynamics does report  low air pressure and I've seen it a few times if a breaker on the compressor pops. 
 

Sorry for the delay.
I think it's very common the alert 0-12  low gas pressure alert when the cut ends
And the 0-20 low gas pressure.