Rods "Spaceship" Scratch built Plasma Cutter build

rodw wrote:
So a question for PCW... would it be OK to power the THCAD-10 from the Plasma inverter or should it be powered by the control panel? The manual says there is 12 volts on this board so it would be pretty simple to add a 12v to 5v Buck converter to step down to 5 volts for the THCAD-10.

I would suggest not to power it from the inverter in any way shape or form. To much going on there.
Use an STP ethernet cat6 cable and send the power to the THCAD through it, it is shielded and it is enough to power it as it draws very little power.

Tommy, thanks, I suspected as such. I just realised they gave me a nice heavy duty 12 core interconnect cable so there are a few spare wires in it that could be used to power the THCAD.

In any case, its a bit of a plan B as the THCAD is already fitted in my control box but I'll give it a bit more thought. In theory, it should be more robust to send the frequency back to the control box as it should be more immune to noise then a divided arc voltage.

And if anybody has ideas for a simple DIY ohmic sensor circuit, it would be good now I have a machine that supports it.

Tommylight is exactly right, the THCADs main function is to isolate the
_very dirty_ ground of the plasma supply from the controller.

You dont want _any_ direct electrical connection from the plasma supply to the controller

Rod

My A60 doesn't have the factory divider so the I mounted my DIY voltage divider there. My THCad is mounted in a shielded box that is either on top or under my A60 and connects to the rest of my controls through a shielded Ethernet cable with Chinese circular connectors.

What I have for ohmic sensing. I have an isolated power supply (wall wart) that only powers the ohmic sensing. The power supply is protected with 1N4007 diodes so the arc voltage can't get there. I have a DPST relay to switch both sides of the circuit to disconnect it from the work and the torch shield when I am not actually measuring. I then use an Opto22 dc input module to sense when the circuit is complete. Every thing is series connected. Now with all that if you aren't going to cut sheet thinner than about 5mm you will have no need for ohmic sensing, your float switch should work fine. Look in zones 2, B & C.

Contact BrandX over on Plasmaspider, he has lots of good cut profiles for the TD torch that aren't in the book.

John

Thanks for the feedback guys. I've managed to reassemble my table with the new torch. The bigger torch lead was a bit of a squeeze in the drag chains but it worked! I also got a decent air supply to it. Tomorrow, I should be able to get the interconnect cable wired in.

and I think at this stage, I'll just replicate my wiring and see what happens.

John, Thanks, I have a small 12 volt supply I bought once with the intention of using it for ohmic sensing but I do have 24 v on the gantry I could tap into. When you spoke of relays on the Ohmic sensor, what amperage contactors did you use? Were they sized to handle the plasma current or just your signals? Also what polarity is your torch tip? Positive or Negative?