I don't have an Arc OK

My vintage Powermax 600 doesn't have and connections for machine cutting. I had to wire up a relay, voltage divider and probe. How has everyone obtained an Arc-OK signal? Is there a way of cheating and disabling the Arc-OK?

Kale Dobrohoczki wrote: My vintage Powermax 600 doesn't have and connections for machine cutting. I had to wire up a relay, voltage divider and probe. How has everyone obtained an Arc-OK signal? Is there a way of cheating and disabling the Arc-OK?

You do need an Arc OK and you have two options.
1 Set PlasmaC to Mode 0 and set Arc OK Low in the Config Panel to around half your expected arc voltage. You can play around with Arc OK High if you wish and that will create a window voltage. It is probably better to start with Arc OK High at its maximum and tune it later if you want.

2 Wire a reed relay into your work lead linuxcnc.org/docs/2.8/html/plasma/plasma...ide.html#reed-arc-ok

Will the reed relay work with all of the modes? I'm using mode 2. these are the kind of relays I have kicking around: www.amazon.ca/XCSOURCE%C2%AE-Channel-opt...l%2Caps%2C336&sr=8-4

I take it there isn't enough juice to pull it shut.

Yes, it will work for Mode 1 and Mode 2.

You need a reed relay if you want to go the relay route, otherwise try the soft ArcOK using the Arc OK Low setting.

en.wikipedia.org/wiki/Reed_relay#:~:text...d%20from%20corrosion .

I'm using a parallel port BOB. Do I have the option of using soft Arc OK? I thought that was for the THCAD and mesa hardware.

You can use a Mesa THCAD with a parallel port if you have a spare input pin on the parallel port.

If you don't already have a THCAD then you would be better of finding a reed relay as it is very reliable and you don't need to read the arc voltage as your external THC will do that for you.

Doesn't your external THC have an Arc OK output?

linuxcnc.org/docs/2.8/html/plasma/plasma...uide.html#mesa-thcad

phillc54 wrote: Doesn't your external THC have an Arc OK output?

linuxcnc.org/docs/2.8/html/plasma/plasma...uide.html#mesa-thcad

Well... I'm using an Arduino as a THC. I edited the original code and added an Arc OK output just a minute ago but I have yet to test it.

OK, now I understand.

If you can get the arduino to reliably read the arc voltage then you could output a frequency related to the voltage and feed it into a HAL software encoder and you could then use Mode 0 or Mode 1.

There is another way you might be able to work with the Arduino as it can make use of the 5 volt supply.

Grab a ferrite ring and a hall affect sensor. cut a notch in the ferrite ring and glue the sensor in the gap. Insert your ground clamp lead through the ring. You should get an ArcOK signal from the hall affect sensor output.

I would attach the output to an Arduino hardware interrupt pin and go from there...

I did make one of these but my plasma cutter died before I could test it in anger..

phillc54 wrote: OK, now I understand.

If you can get the Arduino to reliably read the arc voltage then you could output a frequency related to the voltage and feed it into a HAL software encoder and you could then use Mode 0 or Mode 1.

What frequency does the encoder use? PWM? I'm not totally sure how to ask that question. I thought there was additional hardware needed to use the encoder.

From what I read Mode 0 and Mode 1 seem to get the most out of Plasmac. If Linux CNC knows the voltage than I can adjust the THC on-screen without adjusting a set point on the THC.