THC questions

I am wiring up my THC at the moment and have a few questions. I have seen where some folks put the THCAD in a metal enclosure near the torch power supply, other put it in the cabinet... any reason for this?

Does anyone have an agreed upon schematic showing the wiring between a 7i76e, HT PowerMax85 (or similiar), using a THCAD5 or THCAD10? I have the CPC cable to connect my HT/voltage divider to the THCAD and Mesa 7i76e, as well as a 24vdc -> 5vdc step down transformer. I have been using fabricators diagram to wade through this. I found the thread where fabricator was in the process of making the diagram (and building his setup) ... it's one of the better schematics out there IMO... but I am a bit confused about the resistor he added, then mysteriously removed, by the final drawing.

I would recommend putting the THCAD in your control box. Be sure to power it from 5 volt from the mesa card.

Stefan (thefabricator) had issues with his setup in hot weather and there was a school of thought that noise was being induced because he used an independent power supply.

One of his circuit diagrams for arc OK can be found in the plasma primer.

If you change the divider to be 20:1 than the THCAD-10 full scale is 200 volts without any scaling resistors. That works well.

rodw wrote:

I would recommend putting the THCAD in your control box. Be sure to power it from 5 volt from the mesa card.

Stefan (thefabricator) had issues with his setup in hot weather and there was a school of thought that noise was being induced because he used an independent power supply.

One of his circuit diagrams for arc OK can be found in the plasma primer.

If you change the divider to be 20:1 than the THCAD-10 full scale is 200 volts without any scaling resistors. That works well.

The diagram for ArcOk in the primer does not involve a THCAD board at all. The schematic that is in there was from an earlier version of Fabricator's schematic.... perhaps I am looking in the wrong place.

txtrone wrote:

but I am a bit confused about the resistor he added, then mysteriously removed, by the final drawing.

I need to think back to early 2019 when I built my initial controller, I was having issue with something - I think it was the arc OK circuit, and I removed the resistor to simplify the wiring.

I ended up getting the system to work and I never put it back in. Now I have been running the system for two years since and only had the issue with the THCAD fluctuating during hot weather, which Rod worked out must be a ground loop somewhere in my workshop.

thefabricator03 wrote:

txtrone wrote:

but I am a bit confused about the resistor he added, then mysteriously removed, by the final drawing.

I need to think back to early 2019 when I built my initial controller, I was having issue with something - I think it was the arc OK circuit, and I removed the resistor to simplify the wiring.

I ended up getting the system to work and I never put it back in. Now I have been running the system for two years since and only had the issue with the THCAD fluctuating during hot weather, which Rod worked out must be a ground loop somewhere in my workshop.

Can you send me the latest/greatest schematic of your system? Thanks! I would send you a PM, but there is no option for that on here. Do you use another forum/board?

txtrone wrote:

The diagram for ArcOk in the primer does not involve a THCAD board at all. The schematic that is in there was from an earlier version of Fabricator's schematic.... perhaps I am looking in the wrong place.

I might have a old diagram posted somewhere that might be causing confusion, the latest version is available here, www.forum.linuxcnc.org/plasma-laser/3629...anel?start=40#148670

The Arc OK circuit is a 24V input circuit on the 7i76e with output pins 14 and 12 on the Hypertherm CPC connector, it does not use the THCAD.

The THCAD is used for pins 5 and 6 and takes the voltage reading from the unit voltage divider and sends it to the THCAD to convert to a frequency.

Pins 3 and 4 are an output on the 7i76e for the torch on circuit. The output connects to a relay that will close the Hypertherm circuit and start the torch.

I am on Plasma Spider, if you look in the PlasmaC section I have a thread there where you can find my details.

thefabricator03 wrote:

I might have a old diagram posted somewhere that might be causing confusion, the latest version is available here, www.forum.linuxcnc.org/plasma-laser/3629...anel?start=40#148670

Thank you sir! This schematic is the one I have been working from, studying, cursing, then working from some more. I wasted too many brain cycles on that resistor...

Also I meant to post this, its the CPC page of the Hypertherm Manual, It might come in handy.

thefabricator03 wrote:

I might have a old diagram posted somewhere that might be causing confusion, the latest version is available here, www.forum.linuxcnc.org/plasma-laser/3629...anel?start=40#148670

Just for a sanity check, is the wire coming from pin 14 supposed to continue on to the Mesa and connect to 0v? It could be my PC rendering the PDF incorrectly, but it almost looks like it is tied to the 24v+.

rodw wrote:

I would recommend putting the THCAD in your control box. Be sure to power it from 5 volt from the mesa card.

Could I use a step down power supply (similiar to fabricator's 24v to 5v) connected to the same power supply that the Mesa is connected to? Or must the 5v come directly from the Mesa card?