PTHC-200DC Plasma THC Problem

[Ahmedmohy]

Hello..
I have PTHC-200DC-PT works in Chinese plasma machine. It works fine, Until last month a problem happened.
When i start the program the torch go up then down to touch the metal( sheet ) then go up again to Height set value, then arc start and machine start moving. After 2 cm or less the torch drop ( fall down) and touch the sheet . And continue cutting while touching the sheet.
This lead to problem in cutting.
I noticed something up normal, after start cutting the actual arc voltage reding increase and sometimes became more than 30V higher than arc set value. Knowing that the distance between the torch and sheet is small.
Could you please help me .
Thank you in advance.

[weldguy]

This sounds simple but simple is the best place to start...

Have you checked the condition of your consumables?

Do you have clean and dry air supply to your plasma cutter?

[Ahmedmohy]

This sounds simple but simple is the best place to start...

Have you checked the condition of your consumables?

Do you have clean and dry air supply to your plasma cutter?

yes, I make sure the air is dry and change all consumable with new one (Nozzle and Electrode).

I think the main problem is the difference between the actual arc voltage and the set voltage. but i don't know why the actual voltage reading is high.

[weldguy]

Not familiar with that thc at all but if you were to alter your set voltage higher to accommodate for the higher voltage it is reading will the thc function properly at the higher set point. The voltage reading doesn't really matter, you can sort that our later, the important thing is that the thc functions correctly and can maintain a consistent cutting height.

[jimcolt]

Higher voltage equals higher cut height. Cut a simple 3" (75 mm) square out of the material with the THC off, but the torch set at the manufacturers recommended cut height (if Hypertherm it should be .06" or 1.5 mm) with a thickness gauge. Read the actual feedback voltage during the cut. Next, do the same cut with the thc on, using the feedback voltage you previously read as the cut voltage. If the thc is functioning properly....then the cut height of .06" should be maintained. If it still drags on the plate then there likely is an issue with the wiring or the divided arc voltage between the plasma and the THC.

[weldguy]

Higher voltage equals higher cut height. Cut a simple 3" (75 mm) square out of the material with the THC off, but the torch set at the manufacturers recommended cut height (if Hypertherm it should be .06" or 1.5 mm) with a thickness gauge. Read the actual feedback voltage during the cut. Next, do the same cut with the thc on, using the feedback voltage you previously read as the cut voltage. If the thc is functioning properly....then the cut height of .06" should be maintained. If it still drags on the plate then there likely is an issue with the wiring or the divided arc voltage between the plasma and the THC.

Great way to get a good voltage value to start from. Thanks Jim. I will add as well that if you do this and it drags on the plate try increasing the set point voltage by 10 volts at a time and see if it increases your cut height. Again it doesn't really matter what the voltage number is as long as it is maintaining a proper cut height.