Valid Arc Lost, Thcad 300 config & Plasmac override

A note about your picture with the probes: If you connect a non-current limited voltage
where you show the probes, you _will_ destroy the THCAD input circuitry

Rodw, YES now I see , I understood that I will see the 0V frequency.

....I had a burn out some time ago and since that time I don't get things right the first time(or quick)....it's embarrassing, but no excuse

I fixed the card as well put a filter capacitor on and established the connections to the connector again ...

On the plasma:
I am trying to find the right spot to get the voltage where the pilot arc voltage is not applied.
thank you!!

PCW, YES I understand, all testing is over anyway

Is there a possibility to use the thcad 300 on my plasma cutter?
How can I bypass the ignition voltage?
Thank you

Finally found it....

@Tommylight.. Did you do the Video?
forum.linuxcnc.org/27-driver-boards/36814-mesa-thcad#136977

That is a video i did 6 years ago on how to wire a THC to a plasma cutter, everything is valid for inverter type plasma's but it is much harder to find the right place.
Do some pictures of the inside of the plasma, maybe that can help figure out where to wire it.

I don't know if the feedback of voltage is taken from a resistor.for loop regulation.
I added some labels which I think I identified.












It could be that the connection point is under the igbt rectifier console.

Thx!

Looks easy enough, at least from here, but please do double check:
The IGBT section:
The upper parts are IGBT or Mosfets, i can not read from the picture
The lover parts are diodes as i am pretty certain from the picture, i can barely make a diode sign on all 4 of them,
I can also see some heavy copper wire going from that board, lover part, to the board with the big inductors
My best guess is those are the 2 main wires from the rectifier, so if that is the case, that would be the place to wire the THC, just check the polarity, easily dome with a DVM as both of them will give you a short to the output terminals. That way you know that the one going to the torch in negative and the one going to the clamp is positive.
Do use double insulated wire for that, yank a cable from an old radio or something. Also make sure they do not get crimped when closing the cover.
Buy a 5$ DVM, set it at maximum DC voltage, wire it to those wires from the plasma and fire the torch. If it survives all is good and you can wire the THC.

I can't wait to see Fred's next smoke signal experiment!

rodw wrote: I can't wait to see Fred's next smoke signal experiment!

I could write a book (quite a big one at that) about how many times i tried to smoke stuff on purpose but failed !
Quite often companies, local and foreign, send me stuff to test to the limits, but aside for some badly designed power supplies i had never the pleasure of seeing the "magic smoke".
I did ask for permission from Proma Elektronika to test their THC150 and they agreed and sent another 2 pieces just in case, it would not die, even when inverting the polarity of the power supply or the plasma source, nothing. Fix wiring, continue working.
Last batch i did for a local company on some imported power supplies from 5 different manufacturers, it is pitiful what they are selling as none of them passed their rating, 2 of them made it to about 65% and the rest got to the breaking point at 30 to 40% load. Most of them use a single transistor on the output stage, no filtering chokes, very bad capacitors so the ripple is terrible.
Remember those badly designed power supplies from above? They were made by "Horoz" and they would fail by burning the output choke to a crisp! The output choke is wound with 1.5mm thick wire. Badly miss calculated chopping frequency.
This got long winded, but the main thing is: Fred, do record the "smoky" events, please!