Looking for the cheapest plasma cutter that will work with Mesa THCAD

rodw wrote:

Thats how it works, you can't possibly have a valid arc if you are not cutting something.

I had this issue in the past as well.

I thought it my plasma machine was faulty (had a lightning strike that destroyed my CandCNC setup) and when I built my new controller I could not get the arc OK signal to activate. I then used the synthesized signal for a while and had my plasma machine tested - it came back with no faults.

Turns out like Rod pointed out that the arc OK signal only shows then the arc is actually cutting something, not just when the torch is firing.

I have a habit of learning things the hard way.

BlueManRising wrote:

ok my apologies for using this board to vent my issues, but hopefully it just makes someone learn my mistakes so they dont do the same. I went ahead and grabbed the 5v from the board. when it goes through the plasma it dropped down to 4 volts, no biggie. then on the I/O board it saw the 4 volts, and bingo, green light on the Torch ON. The plasma is officially hooked up the the Mesa Board....

So normally, I would expect to use two power supplies on the 7i96, 5 volt logic power and a higher voltage (usually 24 volts) for field power. How have you put it together?

I just pulled 5v from the board, it has two 5v pin outputs on the board under the GPIO rail, so I just took that 5v and ran it directly through 1 of the Arc ok pins, then the other arc ok pin plugged it into GPIO 10. Then took the negative from the 5v output rail and tied it to the common. I figured why use 24v when all the GPIO pin needs 3v min I believe.

So normally, I would expect to use two power supplies on the 7i96, 5 volt logic power and a higher voltage (usually 24 volts) for field power. How have you put it together?

I'll explain just a little better,

See image

I'll probably just do a write up of how I built and wired the 55i (cheapest blowback plasma I could find on Amazon) and the 7i96 with the THC. And how I was able to configure it so maybe someone else would be able to build it, this is my 4th CNC I built so just adding the plasma was the challenge I was looking for, lasers are super easy, and spindles and 3d print head was also easy, this was a good challenge in the progression of machines I built so far.

It would be interesting to hear PCW's views about the use of 5 volt. I thought that logic power and field power were isolated from each other and it was not wise to common them. Plus 24v is much more immune to noise.

This is a very unfinished work, but this is my take on 7i96 wiring.
From left, AC terminals, 5v logic power, 24v field power, Isolated power for ohmic sensing,
Then the 7i96.
There is a Mesa Common block at the end of the 7i96 that gives 12 +24v and 12 -24V terminals for field power
A couple of DIN rail connectors one of which includes a scaling resistor for THCAD-5
Then a THCAD-10 and a THCAD-5 for my hypersensing /ohmic sensing
So I would just grab +24v field power from the common block, loop it through the Inverter's ArcOK terminals and back to an input with a pull down resistor. No relay required.

rodw wrote:

Plus 24v is much less immune to noise.

Rod, do you mean 24v is less immune to noise that 5v?

I thought that the higher the DC voltage the greater the noise immunity?
I got that from most industrial control systems running on 24VDC or higher?
Have I got that wrong?

thefabricator03 wrote:

rodw wrote:

Plus 24v is much less immune to noise.

Rod, do you mean 24v is less immune to noise that 5v?

I thought that the higher the DC voltage the greater the noise immunity?
I got that from most industrial control systems running on 24VDC or higher?
Have I got that wrong?

Yeh, sorry my writing in haste. should have been "much less affected by noise"

Can't you read my mind?

rodw wrote:

Yeh, sorry my writing in haste. should have been "much less affected by noise"

Can't you read my mind?

No worries Rod