THCAD 10 to Herocut 55i (1:1)

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09 Jan 2022 12:57 - 09 Jan 2022 12:58 #231246 by rodw
Replied by rodw on topic THCAD 10 to Herocut 55i (1:1)
Did you check if there is any resistance between the electrodes and the raw arc outputs?
That would need to be included as part of  your scaling resistors to get the thcad scaled correctly.
If it does have say 100k on each pin, the external voltage won't be lethal so it will be safe to keep it all outside as you have now.
The Everlast and Thermal Dynamics machines I have had both had 100k resistance mentioned in  the manual and I measured that on the everlast with a multimeter.
Last edit: 09 Jan 2022 12:58 by rodw.

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09 Jan 2022 19:21 #231255 by Ekholm
I have now moved the resistors inside the machine. Thanks for the feedback
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09 Jan 2022 21:28 #231260 by rodw
Replied by rodw on topic THCAD 10 to Herocut 55i (1:1)
Did you use your multimeter to check if there was any resistance between the pins and the electrodes before you started?
YO really need to know that.

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10 Jan 2022 19:25 #231335 by Ekholm
Oh didn’t know that it was important, thanks! I measured 120kohm on both ground and plus. Do I need to compensate with a smaller resistor or how do I do it?

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10 Jan 2022 19:41 #231339 by rodw
Replied by rodw on topic THCAD 10 to Herocut 55i (1:1)

Oh didn’t know that it was important, thanks! I measured 120kohm on both ground and plus. Do I need to compensate with a smaller resistor or how do I do it?

Yes, you need to adjust as its part of the scaling resistance the THCAD sees.
Recalculate the full scale reading  as per the formula in the THCAD manual including ALL resistance in the circuit (eg 240k Ohm plus the resistors you added).

If its not satisfactory, adjust your resistor values to account for this.

I tested this on my plasma cutter and the adjustment is definitely required. Be sure to scale your software scaling parameters correctly

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10 Jan 2022 19:48 #231340 by rodw
Replied by rodw on topic THCAD 10 to Herocut 55i (1:1)
PS: For others contemplating this plasma cutter, there is no need to locate resistors inside the plasma case with this plasma cutter as the 120k resistance on each terminal ensures the current is non-lethal. In fact, there is no reason why the THCAD can't be located inside the main control box.

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10 Jan 2022 21:09 - 10 Jan 2022 21:13 #231345 by Ekholm
sorry for all the questions! I’m not following how I calculate this values. I found that there is a online calculator where I tried to add all information. I guess that voltage divider ratio is 1? 1.12Mohm +1.12MOhm?
and I don’t understand the frequency devider jumper settings. Should I use F/32? 
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Last edit: 10 Jan 2022 21:13 by Ekholm.

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10 Jan 2022 21:59 #231349 by rodw
Replied by rodw on topic THCAD 10 to Herocut 55i (1:1)
You read the manual. Use 1/32

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10 Jan 2022 23:16 #231362 by tommylight

Oh didn’t know that it was important, thanks! I measured 120kohm on both ground and plus. Do I need to compensate with a smaller resistor or how do I do it?

You can also include their value in and adjust the scaling accordingly without changing resistors.
No sleep so i'll leave that to someone with less caffeine in their bloodstream ! :)

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11 Jan 2022 11:32 - 11 Jan 2022 11:33 #231434 by Ekholm
Hi!
I’m not sure if I understand this correctly. But should I do it this way?
If I measure  the voltage between the nozzle and the ground clamp. Then I know the full scale voltage input (VFS)? And the maximum current (100uA)
then I can solve the REXT equation added in attachment . 

the example then shows a 4.9M resistor if VFS=500.

If I use this example should I take 4.9 M - (1M + 120k )=3.78M
and add another 3.78Mohm to each output pin?!


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Last edit: 11 Jan 2022 11:33 by Ekholm.

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