THCAD-10 and voltaje divider ratio.

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26 Aug 2021 22:52 #218834 by paulsao
Hello, I have a thcad-10 and I bought a Chinese plasma that has the following connections for thcad cnc, but apparently the ratio is 1: 1, how can I verify this or calculate so that it works well? I attach the photo of my plasma machine
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26 Aug 2021 23:01 #218835 by PCW
You would need to add external resistors to extend the range of the
THCAD10 to your desired full scale voltage.

For 200V full scale, an external 1.91M Ohm resistor would be correct

You could also use a 1.91M or a 1M and 909K in series
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27 Aug 2021 09:02 #218874 by billykid
I had read in a post with thcad10 to use two 1 megohm resistors one on + and one on -. is this correct or two in series on the negative?
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27 Aug 2021 10:29 #218890 by tommylight
I would use two, one on each line.
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27 Aug 2021 11:52 #218902 by rodw
Can you also check the resistance from the arc voltage pins to the electrodes? 
I would expect there will be some resistance so bring the current down to non lethal levels. Usually 100k on both sides.
Any resistance needs to be deducted from the calculated values mentioned here....
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27 Aug 2021 18:45 #218932 by paulsao
I need only the calculated resistors or those kindly mentioned by PCW, or I also need to place the 2 resistors of 1M in the inputs of + and - of the THC ?, supposedly the output of the plasma machine is ready to use and I should not expect explosions or smoke :) in my th-cad

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28 Aug 2021 10:05 #218978 by billykid
As Rod said there should be some resistances on the arc voltage socket. you should measure with a ohmmeter  between pin 1 and ground and between pin 2 and the torch electrode.
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11 Sep 2021 22:30 - 11 Sep 2021 22:31 #220265 by paulsao
I finally have the plasma cutter in my hands, I made the respective measurements and I get a resistance of 40k between the cnc output pins and this is 40k.
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Last edit: 11 Sep 2021 22:31 by paulsao.

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12 Sep 2021 11:14 - 12 Sep 2021 11:17 #220289 by rodw
So assuming you have 40k resistance on both electrodes, you need to count the sum (80k) in the resistance you use for the thcad scaling.
Last edit: 12 Sep 2021 11:17 by rodw.

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