Stamos S-PLASMA with THCAD

Hi everybody,

I want to build a plasma table with this cutter: www.stamos-welding.com/s-plasma-125cnc . Machines from Stamos seem to be quite popular in Europe but I haven't found any info on how to connect it to the Mesa 7i96 I'm planning to use. Those have a "CNC" and "ARC OK" port so it should be relatively simple to connect but I'm not sure about the exact wiring or which THCAD to buy.

I've read about a few people on the forums here that are using a Stamos cutter but I don't think they posted any details...
Any help would be greatly appreciated!



Tom

Hi,

I found a video on youtube where the Stamos is connected to a CNC.
I also have attached a screenshot of it.
I think the Stamos has no voltage divider and is directly connected to the output from the cutting voltage. The easiest way is to connect the stamos to the plasmasensout (#2). In addition to the outputs for the height control, this also has an output for ArcOK.
For the start command, I assume that the contact of the second connection must be closed (#1). You can do this with a relay.

Most probably that plasma can be connected to any type of THC so that is the easy part. If you plan on using LinuxCNC get the Mesa THCAD, it is by far the best solution for plasma cutting and the cheapest.
Any plasma source with pilot arc will work with cnc.

This machine is no different to any other. Get the THCAD-10
If it is raw arc voltage, I wold expect there will be resistors in line.
Measure the resistance between the voltage pins and the plasma electrodes. I am guessing it will be 100k on each pin.
That is what I measured on an everlast machine and it agreed with their manual.
This resistance must be taken into account when choosing the THCAD-10 scaling resistance
Other than that it will be plain sailing.

Hi, thanks everybody for your replies!

I've measured the CNC port on the machine (marked as #2 in hermann1976's picture), the bottom pin (pin 4 on the plug) is connected directly to positive/the workpiece lead. The pin on the top (pin 2 on the plug) is connected directly to negative/the electrode.
Measuring between the pins with the COM lead on the multimeter going to positive on the plasma cutter, I got something between 210 - 290 kΩ while the cutter was on and 17 - 19 MΩ while it was off. The values were bouncing quite a bit and not stable at all, I hope that won't be a problem?

Since neither of the two THCAD suppliers (EUSurplus and Welectron) have the THCAD-300, I think I'll buy a THCAD-10 and replace the resistors according to this post by PCW .

The "ARC START" pin with the red cap is actually connected to the nozzle, I'm guessing for starting the pilot arc?
This also means that I was wrong about the machine having an "ARC OK" port. Can the THCAD somehow tell arc OK from arc voltage or does it need to get that directly from the plasma cutter (which means I'd have to take it apart and poke around...)?
I just looked at the PlasmaC user guide and it says you can wind the workpiece lead three times around a reed relay as an alternative to a port provided by the plasma cutter.
Obviously taking arc OK from the THCAD would be more elegant (less wiring to do, looks cleaner) but are there any drawbacks to it? Rather, is there any advantage to the reed relay method?



Tom

Reed relay works very good, have several of those in use for several years, and it is more reliable than the generated arcok from the voltage.
PlasmaC will work with just the voltage and has the provisions for generating the arcok, also have 2 of those in use every day, never had issues with it. Others had issues with it, but i would chalk that on the wrong settings.
Thinking of it, never had a failed arcok with the generated signal, did have some false positives with one Cebora 120A with reed relay, once every 300 to 400 starts, always when the electrode was totally worn off. Scratch the reliability thing above !
There is no need to change the resistors on the THCAD, just add a 1MOhm resistors to each of the wires from plasma to THCAD in series.

Ok, I've ordered the Mesa cards and think I'll use the 1 MΩ resistors, I'm guessing 0.1% HVR then? I'll try with the THCAD arc OK signal and maybe switch to reed relay if it doesn't work out for me.

I'm a bit worried about the fluctuating resistance on the CNC port, is that normal? Will it stabilise while the arc is established, or might it not even matter too much?

somuchforfree wrote: Ok, I've ordered the Mesa cards and think I'll use the 1 MΩ resistors, I'm guessing 0.1% HVR then? I'll try with the THCAD arc OK signal and maybe switch to reed relay if it doesn't work out for me.

I'm a bit worried about the fluctuating resistance on the CNC port, is that normal? Will it stabilise while the arc is established, or might it not even matter too much?

Just standard resistors will do one in each leg

Some people have not had good results with the synthesisesd arcOK. I believe it is because the current Plasmac algorithm does not allow for the torch voltage behaviour on piercing which I posted a plot of here.
forum.linuxcnc.org/plasma-laser/41420-arc-voltage-on-piercing

Again, i have 2 of them using generated ARCOK from Mesa THCAD voltage, one for over a year, the other some 6 months used today cutting 2mm ALU, had arc lost so i just moved the limits a bit, set to 70 and 150 now, were 80 and 140.