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machinedude wrote:

my understanding so far was the THCAD-2 can be used but you have to add the HV resistor for ir to work and the THCAD-300 does not need the external resistor in my application;

That is correct.

my understanding so far was the THCAD-2 can be used but you have to add the HV resistor for ir to work and the THCAD-300 does not need the external resistor in my application;

Means not for use with HF/HV pilot arcs.
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NOT advice:
The thing is it can be used but requires open the plasma source and wiring it at the rectifier output. Any place else risks letting out the magic smoke. I have THCAD 10 and 300 wired to HF start, probably over 10 or 15 of them.

"The 300V version of the THCAD has all input divider resistor on board and can connect directly to the plasma voltage of touch start type torches only."

this was the section of the description on the Mesa site that confused me.

machinedude wrote:

the only thing i noticed was that the THCAD-300 seems to be for only scratch start HF machines?

Scratch start has no HF nor HV pilot arc, it needs to be dragged on material to fire.
THCAD 300 would work fine for your plasma (i use them on HF/HV start despite warning all not to do that, it just needs to be wired in the right spot), and so will any THCAD, just get 2 of 1MOhm resistors rated at 2W or 5W and wire one on each arc voltage wire.

Rod  i did some digging and found out that this Machine has been done with THCAD before. the person that did this has some YouTube videos and i found this image on here. this is basically the exact same setup i was going to do minus the THCAD since i was not sure on that part; I watched the videos and in the video he said the THCAD-300 would have been a better choice with this machine. the only thing i noticed was that the THCAD-300 seems to be for only scratch start HF machines? this machine has a 1:1 ratio but has the blow back start so which would be better the THCAD-2 or the HTCAD-300 ?
 

Also, don't forget spikes on piercing will be much higher than cutting. Even at 40 amps, it is enough to exceed 300 volts when cut volts is around 120 volts. Not sure how much higher because that was the max voltage my thcad was calibrated to. Also when crossing a void, when a slug drops when cutting a hole, running off a sheet when severing all cause huge peaks. A thcad used for ohmic sensing Is exposed to the full torch voltageeven if calibrated fro 24volt full scale.

It has been done before. Ethercat is really just a way of controlling your motors and I/O so it does not change anything or prevent you from building a plasma table.
Choose a plasma cutter with a proper CNC interface and voltage divider that does 20:1 or 30:1 division
You will need an Ethercat I/O module for inputs and outputs.
Torch voltage sensing is something the 7i76e/thcad combo does well. the THCAD has a 0-10 volt range with 500volt overvoltage protection
In an Ethercat environment, I would look for a 0-10 volt Ethercat analog input module that has overvoltage protection to 500 volts.(not hard to find)
To give QTplasmac the voltage output, you should be able to scale the voltage using the QTplasmac voltage scale settings.

Another probably more costly way would be to buy an Ethercat encoder input and attach a thcad to it.

Advanced options would be to home using the drive internals and implement torque mode homing to eliminate the need to wire home switches. This would require a custom homing module in linuxcnc. I am not sure if gantry homing would be supported.

Unfortunately my Herocut plasma gives full arc voltage. I also have a THCAD 300 card to interface with.
It's a possibility what you say. Anyone wishing to give it a go have all the schematics and pcb layouts
as a starter, and all software needed to deliver values over EtherCAT on github.

You know the path isn't always that straight when I develop things. I started with the LAN9252 and it is more or less coincidental that I went with the Ax58100. And you are right, they are used as gateways. In the setup with a MCU I don't really see a difference, can go with any of the two. They are both available on aliexpress and cost about the same. I have gone back to the LAN9252.

For the plasma build, my initial thoughts with EaserCAT-3000 card and the Ax58100 was to use existing stepper motor drivers and have the card do pulse/dir. While that now works, I have skipped that path and are now going to use ECT60 Ethercat stepper motor drives. My own cards will be used for Digital IO (limit switches, float switch, break-away switch, torch on), and for reading the THCAD-300.

Here is the reader for THCAD. A stripped version of the EaserCAT-3000, with LAN9252. The MCU reads PWM frequency on one pin. Could definitely use a smaller MCU, but it is also easy to reuse what I know works.


Digital IO. This card does use the DIO of the LAN9252 directly, no MCU.


I find that the documentation for the Ax58100 is lacking for the special functions, like stepper motor driver. There is a reference application supplied that uses TwinCAT to drive a stepper motor. I guess one could try to understand how all that works, but I haven't. And that is all info I know of.
 

I have never used EtherCAT as in doing a full setup, although i have fixed industrial machines using it i never had to mess with the EtherCAT part, so no idea.
I have used and use a lot of Mesa boards, they are worth every cent/penny/dime as they are extremely reliable and come with the best support on planet earth in the shape of PCW (an active member here), so i will not be switching to EtherCAT ever, especially since i learned it lacks some important stuff for me.
BTW, whatever the price for Mesa is, i have to pay at least double to get them here (black hole named Kosovo), still, i pay it gladly.
Reminds me, have to order some THCAD, installed the last one today.

The other part I always mess up is after installing.

so I’m going to config a machine with 7i76eu + thcad-2 (I think, whatever model the currently have). So I need to configure the system with plasmac

i alway alway forget how to set plasmac on the system.

Yes that one was the default. I just switched to the one Phil provided. Was able to run the materials in QTPlasmac but I seem to have an issue in Height control or maybe it was the consumable guess ill check that real quick...
Ok those look good but I'm getting intermittent raised cuts probably a settings issue in my HC but I've seen some PP create issues there as well. Im using the MESA THCad2 so its more than likely I haven't dialed that in correctly yet.

Thank you guys, I connected before the choke coil, there are 3kV capacitors so the voltage can't be higher than that. I used HV resistors.

Now I'm stucked with the arc voltage.
I placed a 9V battery on the input with a potmeter to test it. I set and calibrrated everything, encoder.0.velocity net to arc-voltage-in, the value changes with the pot but the arc voltage on the GUI and arc-voltage-out signal does not change, stays zero. Tried different scale settings, no result.
How to get that voltage?

Not sure about the analog input of your MESA hardware but it might be possible to use a MESA THCAD board which converts DC voltage to frequency and connects to an encoder input. But you would need to check if it is suitable for 3.3V

'M52 Pn' is Gcode so it would have to go into the Gcode program or be issued as an MDI command.

once you have the voltage (or frequency ) in HAL you can do all kinds of things including a PID loop to control the feedrate also a GUI panel should be trivial then.

forum.linuxcnc.org/plasma-laser/54413-th...-will-kill-it#314239