The blacksmith's plasma table

tommylight wrote:

polskleforgeron wrote:

Also when you say you plugged the cheap china plasma through 2 resistors (both 1MO 2W) with a capacitor (0.1uF and what power rating ?) shorting the two, would it look like that :
 

Exactly !
Capacitors have no power rating, just capacity and voltage, sometimes temperature range in a form of a single letter. Anything from 300-500V will do just fine.
 
 

Is it better to add the resistors and capacitors closer to the THCAD-2 or the connexion in the plasma cutter ? I feel like it would be better at the source, inside the frame of the plasma.
Also dumb question, I can easily fin some 300V AC 0.1uF capacitors. But we're talking DC here right ? Is it still OK or should I find a specific DC one ? I remember something about electrolytic capacitors that can only be use in DC..

Some pictures of the project !

 

Would this capacitor do the job ?

composant-electronique.fr/condensateur-1uf-400v-ccap1uf400v-b

I've read polypropylen ones are more stable in HF environment.

tommylight wrote:

Nope, that is 1uF, you need 0.1uF or 100nF
It does not mater much where, but i would still place the capacitor at the THCAD input, resistors inside the plasma.
Not a DC capacitor nor electrolytic one, metal film have no polarity and are good ad reducing interference.
 

While I greatly appreciate all your advice, it bother me to not understand why I'm adding a capacitor. Would you have some ressources where I can learn what this capacitor does in this case ? I tried to look it up but I dont even know where to start, there is so much information.

Does the capacitor act as some kind of "electronic spring" to absorb a HV surge ? And how did you know which capacity and voltage it should have ?
 

tommylight wrote:

In this case, it acts as a dead short for the AC interference while the HV start/pilot is on, it does not affect the DC voltage that THCAD needs to measure.
 

 

I found this paper which seems to explaina little bit the subject : www.vishay.com/docs/28153/acfilmconnectionmains.pdf
Does it ?

Hi Tommy,

I've received everything I needed to finish the build, 0.1uf capacitors, 1M 2W resistors and wired everything. My base machine was working fine, following 2D gcode comand etc.

I started to follow the step in the plasmac configuration page and got an error message on the first one --'

When I try to run the command :
python /usr/share/doc/linuxcnc/examples/sample-configs/by_machine/plasmac/configurator.py

It tells me no such file exist. I dont have a "plasmac" repertory at this path. I've tried to find elsewhere "configurator.py" or a "plasmac" repertory with no luck.

I thought maybe my linuxcnc installation was incomplete so I tried with the debian iso found on the linuxcnc installation guide but there was no plasmac repertory at this path either.

I have no idea what I'm doing wrong. The second time I litteraly followed the step on the "getting linuxcnc" page. Do you have any idea ?