CIgweld Cutskill 60 - adapting to CNC use

Thanks Rod.

Found this in plasma cnc primer. So very clear now on what that means. It is referring to an HF start model but it seems the more conservative path.

If you do not have a voltage divider and you do not have room inside the plasma cutter, install a THCAD-10 in a metal case outside the plasma cutter and install 50% of the scaling resistance on each of the IN+ and IN- inside the plasma cutter case so no lethal voltages come out of the case.

I'm going go over the plasma unit looking form more data plates and will have a look inside. I might just send a question to Cigweld and see what I can find out. Is putting a volt meter on things an option? Assuming I have or can find one that will cope with up to 300V DC?

Cheers.

So because the THCAD-10 can withstand 500 volts over voltage indefinitely, sometimes we scale them to 200 volts to get a more accurate A-D conversion in the normal range. Cut volts will not exceed 130 volts and its not really necessary to see the voltage peaks on piercing. Having said that I have mine set up with a 300 volt full scale reading and I still get accurate results. (But I do have 120 amps)

This thread I mentioned shows the voltage getting to my 300 volt full scale and flatlining during piercing but we don't care about that until we get an ArcOK.

forum.linuxcnc.org/plasma-laser/41420-arc-voltage-on-piercing

I have been looking into how to deal with touching off and based on the reading I rather like the advantages of ohmic sensing and the hyper sensing system using a THCAD-5. So I have been testing my Cutskill 60 to see if the tip is always in open circuit to the work or not. Based on the schematic attached and tests done with a meter I think I might be in luck.

You should see from the attached circuit the the path between the torch tip and the work is controlled by a combo transistor and diode (Q7). When the pilot arch is not active Q7 is open so no circuit possible between Tip and Work. When it closes a pilot arch would be possible. Assuming I understand the ideas behind hyper sensing and using relays to control a 24v supply, with the +24V on the Work, the 24v-GND on the Torch Tip, then when the torch is off the only way a circuit can be achieved will be when the torch tip touches the work on a probe.

So looking better all the time for enabling this little machine to operate under a CNC setup.

Cheers - J.

Hypersensing negates the need for any relays becasue it can handle the torch voltage without any adverse affects.
When I had my Everlast I was all set to implement ohmic sensing, then it ocurred to me it would take the full brunt of the torch voltage so was worried it could jump over relay contacts if you implemented relays for ohmic sensing. I later read you need high current relays to implement it safely.

Then PCW encouraged me to develop hypersensing and there was a lot of help from him in the background. If I still had the Everlast, I would have tried it out by now.

On my machine the ohmic voltage jumps straight to full scale once cutting starts. This was expected as the full torch voltage is on the circuit.

So if you can jury up a simple probe by taking +24V from field power, attaching it to the torch tip and then connecting an input to the material and you can probe WITHOUT cutting, then you will be fine to wire in the hypersensing circuit properly per the diagrams. You don't even need any relays, just power up the isolated power supply in startup.

Thanks Rod. When I was talking relays was thinking per the THCAD-5 circuit in the plasma primer.
So was really about controling the activation of the 24V supply. Doing a simple circuit closing probe as you descrobe sounds like a good test to prove it all. Getting more enthused as I start to get the various parts together.

My next challenge is working out the best way to get the voltage feeds to a THCAD-10 with the resistors in place.
I thin: Get wires from the toruch and work lead connectors on the inside of the machine get resistors inline of those leads before they exit the case and have them terminate to say an airline plug for easy connection to leads to the THCAD in the control case.

I have seen mention of having 50% of the needed resistance on each leg of the THCAD but I'm not sure how that would work. Need to spend some more time revisiting basic electronic theory. It's been a loooong time.

If I was doing it, I would mount the THCAD inside the cutskill if it has room or in a metal jiffy box attached to it. Connect the input to the terminals internally and put half the resistance on each wire. Then I would run a 4 wire shielded cable from my mesa card with 5 volt from the encoder down to the thcad and send the frequency back. IN theory the frequency will be more noise immune. Google the weipu connectors and use them each end. 4-5 pin off aliexpress or ebay or a 4 pin gx16 microphone connector.