THCAD selection including ohmic sensing

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14 Mar 2020 16:24 #160192 by calvin.d
Ok I am about to start integrating my torch
I believe I need a THCAD-300 because the torch voltage output is 1:1

If I want to do ohmic sensing, what is the right THCAD version ?

Thank You
Calvin

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14 Mar 2020 20:29 #160211 by tommylight

I believe I need a THCAD-300 because the torch voltage output is 1:1

Does it have a PC or Control connector ?
They will never have a 1:1 output to a connector.
1:1 term is usually used when wiring the THC input directly to torch output headers on the plasma cutter, so the output voltage at open circuit i anything from 150 to 280V.
If you plan on wiring that directly, please do make some pictures of the innards of the plasma source and post them here. opening them and working on them is extremely dangerous, so a lot of caution should be taken.
For the above you would need a THCAD300.
You can also get the THCAD10 instead of 300, it does require adding 2 more resistors inside the plasma but it is a lot safer to work with and can be used in pretty much all the plasma sources.

If I want to do ohmic sensing, what is the right THCAD version ?

THCAD5

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14 Mar 2020 22:17 #160217 by PCW
THCAD-5 and THCAD-10 can both be used for Ohmic sensing
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14 Mar 2020 22:24 #160218 by tommylight

THCAD-5 and THCAD-10 can both be used for Ohmic sensing

Thank you for confirming that.

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14 Mar 2020 22:41 #160223 by PCW
Basically the only difference is the value of the added input resistor needed for 24V full scale
(assuming a 24V supply is used for sensing)
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14 Mar 2020 23:19 #160233 by calvin.d
The back of the machine shows 1:1 as the ratio so I believe I need the 300v option, picture added

for the ohmic sensing side of the question, it seems like going with 5v and just adding a small 5v power supply to the system is the easiest option. Compared to getting a 10v supply or dividing down the 24v power the system to less then 10v



Thank You
C
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15 Mar 2020 01:40 #160245 by tommylight
Damn! Please do not touch those 2 pins while the plasma is on!
I really hope they bothered to put some resistors inside of that thing.
In that case a THCAD300 should do just fine and save you a lot of work.
Please also use proper isolation for that connector and make sure those two wires are not pinched or crimped somewhere.
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15 Mar 2020 01:50 #160247 by PCW

The back of the machine shows 1:1 as the ratio so I believe I need the 300v option, picture added

for the ohmic sensing side of the question, it seems like going with 5v and just adding a small 5v power supply to the system is the easiest option. Compared to getting a 10v supply or dividing down the 24v power the system to less then 10v



Thank You
C


Actually you want a higher sensing voltage, 24V or even 48V is suggested
Note that this needs to be an independent floating supply (no connections to anything else in the system)

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15 Mar 2020 09:14 #160269 by rodw
Can you measure the resistance from the electrodes at the front of the machine and those pins on the back of your machine?
I would expect that there is around 100k ohm resistance if its like any other machine that has raw voltage output so you don't kill yourself.

I think you should use a THCAD-10 so that you can account for this resistance. eg. follow the example in the THCAD-10 manual and then deduct the resistance (200 k Ohms?) from the calculated values.

Also using a THCAD-10/5 for ohmic sensing will require a component I have written but its not yet published.
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15 Mar 2020 11:20 #160283 by tommylight

Also using a THCAD-10/5 for ohmic sensing will require a component I have written but its not yet published.

Oh, you've been holding on us ! :)
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