My Newb Plasma Table Attempted Build

PCW wrote:

If the yellow LED CR2 does not blink, and you have 5V power on the THCAD
the THCAD is faulty or damaged.

It turns out I wasn't mistaken about the yellow LED. It just stays on without ever blinking. I'm pretty sure I've never seen it blinking either, although that little light hasn't been my focus until this morning. It's been powered via the encoder pins on the 7i96 (which has always seemed to be running flawlessly, btw), and I have that on it's own dedicated Meanwell 5v power supply.

Pat

Annnnd.....I turned everything off for about 10 mins, went in the house to use the restroom and grab more coffee, came back out and turned everything back on...and now the little yellow light on the THCAD-10 doesn't come on at all. Everything else seems to be working fine. I guess it decided to fully give up the ghost now.

Pat

You could get a not blinking condition if you have the plasma voltage inputs reversed
(and enough voltage at all times) so as a last check you might disconnect the
voltage input and see if you get a blink. If not , the THCAD is definitely broken.

(The LED state is not guaranteed but it must blink)

This morning's testing I didn't have the plasma powered on at all, so there was no voltage going there.

Pat

So...I just wanted to be 100% sure about the THCAD-10 being the issue or not, or at least as sure as I can get to be. I took my multi-meter out and tested voltage coming from the 5v power supply that is dedicated for the 7i96. It was fluctuating from 3 to 4.8v, and not in a discernible pattern either. I then went a few towns over (I'm not located near any businesses that would have something like a DC power supply). There I purchased a new power supply and brought it home. I terminated it to the 7i96 (after testing with the meter), and viola! The THCAD-10 now has BOTH the CR2 LED light (slowly flashing) and the CR5 LED steady yellow. The CR5 LED had never came on before this. So, apparently although this power supply I originally used is new, it isn't worth a damn.

I just need to put all of my electronics back together and then I can resume testing. Thanks for all of the help leading up to this.

Pat

Don't you hate that! Anyway, its good you did not give up and hopefully, we helped you think through the issue.

I wouldn't have made it very far at all without help from you guys! Much appreciated!

I had my doubts about it being the THCAD-10...they've obviously been doing this for a good while now and I don't recall anybody bringing up quality issues during my research.

Pat

I have everything back together. Just did a pulse test on the plasma, and the arc voltage reading goes to about 200v on the control panel. I have no idea if this is correct or not, but at least now the THCAD-10 is grabbing something.

When I did the pulsing yesterday and hooked up my meter, I read about 30v less. I take this to mean my resistors aren't working right?

Any insight is much appreciated.

Pat

If you really doubt Mesa's ability to calibrate the THCAD, you could put a 9v battery on the inputs and you should get 90% of your full scale reading. And you can bypass the voltage converison if you observe the encoder velocity output as we showed you. But I just put my faith in PCW!

I have faith in PCW too. I think I didn't state my concern clearly. I'm not confident in my use of the resistors, as I've never used them like this before. It's actually showing about 210v on a pulse, which honestly seems like it would be in the ballpark for blowback. I have yet to try to run a gcode cut file so I don't know what it'll be showing on a regular stable cutting arc.

My concern is that I may have gotten the right Ohm resistors, but they're only 1/2 watt. If you guys think that should be fine, then I'm fine with it too.

Pat