Rods "Spaceship" Scratch built Plasma Cutter build

Hi Islander,

Before i posted my comment to Rod, i have read the pfd documentation of thcad mesa card.
My worries are only about the input voltage ratio. In my opinion a save input ratio is max 400 vdc.

Tecno is right. Use a hypertherm powermax 45 xp with internal voltage divider .
Optional order one with modbuss interface. I called hypertherm too late this day. But maybe rod is
better of with a powermax to make some progress. I have sayed before i sponsor, it depends on free shipping
to australia...

Hypertherm modbus is not for THC / reading the torch voltage (it is WAY TOO slow)....

www.mesanet.com/pdf/analog/thcadman.pdf

THCAD manual,

page 8
OPERATION
ISOLATION
The analog inputs on the THCAD are full floating with a 2500V RMS test rating (1 minute). This is a common mode rating. This is also specified as a 425V continuous peak rating with 50 year life.

If you cut at 45 amps at 200 volt = 12.5 Volt (Mesa max is 10Volt in, smoke out of garage :dry: )

The THCAD10 has a maximum continuous input voltage rating of 500VDC so 12.5V or 500V will read as full scale but will
not harm the THCAD-10

The other parameter we discovered in testing is that the THCAD board has a rise time of 5 ms which in the sim equates to a lowpass of 70 Hz (I'm just quoting what Dewey told me after looking at some plots I did for him as I don't really understand that).

The THCADs rise time is less then 0.5 ms. A 5 ms risetime would be detrimental to loop tuning. Of course any post direct data
filtering will affect the loop bandwidth.

PCW wrote: The THCADs rise time is less then 0.5 ms. A 5 ms risetime would be detrimental to loop tuning. Of course any post direct data
filtering will affect the loop bandwidth.

Peter that is awesome thanks. You have no idea how long I spent trying to test this and capture a plot like that for Dewey in a very crude way. Looks like we should have just asked you!

In Dewey's simulated torch (hal file) in his HPID sim, he uses a lowpass filter with a cutoff frequency. Based on 5ms he said it should be around 70 Hz (you've already helped me with that. Now I just need to know what to change it to now to simulate the torch.
github.com/LinuxCNC/linuxcnc/blob/dgarr/...et_pid/sim_torch.hal
Any input would be appreciated.

With relation to the voltage range, the THCAD range can be scaled using an external resistor. Initially I scaled it to cover a 20 volt range, What I found is that the THCAD sees the Everlast's resistor divider network as part of this external resistance. From memory, this changes the scaling by a factor of 1.5x so it becomes a 24:1 divider (240 volts) so there is heaps of headroom so I removed the external resistor.The only time I've seen the volts go past about 130 is when I deliberately engineered a kerf crossing test off the edge of a sheet.... One more headache I had to find and deal with during this build.

I did some more test cutting yesterday but would you believe a prox sensor on the Z axis home switch failed? Should they be protected with a current limiting diode? If so what value for a 24v system?

I think I have a spare here and I've ordered some more. This is the second I've had fail.

I think the new coupling made a bit of a difference but the changed velocity means retuning. Here's a couple of plots with similar PID settings
The other day (old coupling)

Yesterday (new coupling)


I wanted to play with the eoffset scaling factor but my home switch said that was not to be!

tecno wrote: Possible to use a simple voltage divider with suitable resistors as a pre divider?

Yes, I believe so as thats what the everlast board is but I'm not sure if they do anything with the raw voltage as it comes onto the board. But if you don't have a divider already, use the THCAD-300 mounted on or in your plasma machine.