THC Problem - Linux/THCAD10/SheetCam

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11 May 2021 21:57 #208588 by tommylight
60 PSI is to low for plasma, it should be between 75 and 90 for normal ones, 105 to 120 for industrial ones.

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12 May 2021 12:30 - 12 May 2021 12:30 #208618 by RNJFAB
Thanks guys, UPDATE

Yesterday - The mesa output led seams dim compared to the other lights (input led's), but it still comes on and off like it should, replace relay and all wiring to plasma, still nothing.

Tonight - Back at it trying to get it going. redo all the wiring again, change to output 2, change relay, double check everything from pictures of setup that worked, double check all MESA manual setup, etc.

NOTHING...........

Thinking there may be something wrong with he outputs I go all the way to output 5. change settings in the HAL. check to ensure the right output is firing, connect everything, test, BAM it's all working, torch fires as requested. SWEET.

Start to cut, first holes cut, second hole cut, third hole - torch doesn't fire. FFS. check in the control panel to find that the LED for output 5 doesn't light up when I activate the torch. BUGGER. upon closer inspection output 4 and 3 led's are glowing.

Just a random guess, but, I think the outputs may be fried, another MESA board gone. actually lost for words right now.

any suggestions?

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Last edit: 12 May 2021 12:30 by RNJFAB.

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12 May 2021 12:44 #208620 by phillc54
Are you switching a relay from the Mesa card? If so do you have a flyback diode across the relay coil.

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12 May 2021 14:24 #208623 by RNJFAB
Hey Phil,

From all the reading I did ( forum.linuxcnc.org/27-driver-boards/3845...tput-wiring?start=20 ) and the optically isolated relays I’m using, no fly back diode was required. I have used the extra relay to seperate everything. Using a cheap cut 50 plasma.

With this setup I have done hundreds of meters of cutting with no issues, nothing has changed for this problem to start. Hence the confusion.

Cheers

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12 May 2021 23:53 #208674 by phillc54
I didn't see the other thread, it seems that they don't need flybacks.

It is weird that #3 and #4 leds are on, maybe a power supply issue??? sorry but I really don't know... :(

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13 May 2021 01:23 #208682 by PCW
Isolated output LEDs illuminated when not commanded 'On'
Likely means one or both of transformer driver chips (74ACT04)
have been damaged either by a spike in the 5V supply (exceeding 7V)
or a high voltage spike on the OUT+- terminals (hundreds of volts)
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13 May 2021 08:43 #208714 by RNJFAB
thanks PCW,

5V supply to the MESA board is seperate to the 24v sup for relay's and proximity sensors, and the 6v supply to the steppers and motors.

not sure how it would get a high voltage through the relay then into the MESA board.

Is this normal? is it just because of the cheap cut 50 plasma being used?

any reason why it would happen now (and so quickly, even after having hundreds of cuts with no problems) as I don't want to replace the board only to have it happen again.

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13 May 2021 10:09 #208720 by tommylight


not sure how it would get a high voltage through the relay then into the MESA board.

Plasma sources create huge amounts of EMI when starting, less during cutting.

Is this normal? is it just because of the cheap cut 50 plasma being used?

Does not matter, all plasmas do that (more or less)

Shielding and grounding a plasma cutter is the hardest thing to do properly, any issue with it will send you chasing gremlins ....
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13 May 2021 13:08 #208734 by PCW

Is this normal? is it just because of the cheap cut 50 plasma being used?


The Cut 50 is a HF start plasma source. HF start plasma machines generate
massive amounts of EMI when staring. Also depending on where you connected
the THCAD you can have 20KV or more of high frequency AC on the voltage
sense wires when starting.
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14 May 2021 09:38 #208788 by RNJFAB
Thanks Guys,

Looking at a new plasma would this be suitable for use with the MESA board?
sydneytools.com.au/product/uni-mig-kupjr...verter-plasma-cutter

cheers

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