The blacksmith's plasma table

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05 May 2024 04:06 #299778 by rodw
Replied by rodw on topic The blacksmith's plasma table

 I only have one question though. With the Stahlwerk's HF starts, could it fry the THCAD ? It didn't seem to affect much my multimeter when I tried it.

Also, is there a way to upload directly a video on the forum ? I'd like to show you the machine !

 

The THCAD can handle 500 volt overvoltage which is higher than your plasma cutter will generate so you won't damage it unless you connect >5v to the encoder side (Ask me how I know, 24v is enough to kill the encoder input, but I could use another encoder input on my 7i76e from the plasma firmware)

Upload your video to Youtube and link to it

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05 May 2024 07:47 #299784 by polskleforgeron
I did'nt yet, I just tried with the multimeter to read the arc voltage, and a simple circuit with a battery and a led to see if the reed relay was correctly activated. I'm going to wire to the THCAD today I think. I might lack the 2.5M resistor though. Could you tell me again which rating it should be ?

I am going to follow this wiring diagram (second one) for the THCAD-2 : forum.linuxcnc.org/38-general-linuxcnc-q...-questions#gallery-2

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05 May 2024 07:48 #299785 by polskleforgeron
Yes thank you I understand that now. A lot of confusion due to language and ressources being mostly in english. But I think I got it now :)

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05 May 2024 07:50 #299786 by polskleforgeron

How did you wire the THCAD to PLasma?
 

I did'nt yet, I just tried with the multimeter to read the arc voltage, and a simple circuit with a battery and a led to see if the reed relay was correctly activated. I'm going to wire to the THCAD today I think. I might lack the 2.5M resistor though. Could you tell me again which rating it should be ?

I am going to follow this wiring diagram (second one) for the THCAD-2 : forum.linuxcnc.org/38-general-linuxcnc-q...-questions#gallery-2

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05 May 2024 07:52 #299787 by polskleforgeron

I'm not sure I fully understand the difference between ground and earth. 
 


They are the same thing, it's just a difference between UK/Aus/NZ English and American English.

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05 May 2024 09:25 #299793 by Clive S
2 x 2 W resistors will be fine

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05 May 2024 13:27 #299803 by tommylight
@Rod,
He mentioned several times he has a HF/HV start plasma, the THCAD manual clearly states not to use that combo.
Having cleared that cautionary tale, THCAD can work with HF/HV start as can be proven by probably 10 i have in use daily, just some care must be taken when wiring to choose a suitable point where the HF has less effect, usually at the rectifier output or at the built in HF filter/protection.
And additionally a few days back i wired a THCAD10 directly to outside connectors on a new cheap china inverter plasma with HF start, THROUGH 2 resistors and added a 0.22uF/350V capacitor across the THCAD input just to be on the safe side, and it also filters the readings a bit. Used it for 2 days, all good, probably did over 200 starts as i was tuning voltage/feed/air so made a lot of 100x10mm rectangles.
Just to be clear, do this at your own risk, any mishaps usually end badly.
A 0.1uF capacitor would be better, did not have one with such high voltage.

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05 May 2024 21:17 #299848 by rodw
Replied by rodw on topic The blacksmith's plasma table
Perhaps it would be best if the OP takes his own advice and replaces his plasma cutter with a non-HF start machine. Ideally with CNC connectors built in, After all he did not want to open the machine up and play with voltage dividers.

The kind of stuff you do under the covers Tommy is not entry level stuff!
The following user(s) said Thank You: tommylight

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06 May 2024 01:18 #299868 by tommylight
OP has a choice between a HF start and a HF start with CPC port.
I worked with Stamos, it works fine, Stahlwerk before it also worked fine, meaning over a year of use for each, none of them mine personally.
Now under the covers, there were two reasons i did the last deed:
-New plasma under warranty, cheap Kzubr for 320 Euro, 60A, so could not open it.
-I had a THCAD collecting dust, so i risked it, it survived unscathed! :)
I was pretty sure it would work as i did add a capacitor across the THCAD input to short whatever HF gets to it and after the resistor drop should not be much to deal with, but the biggest surprise was it actually does 60A flat! That is in both 220V and 380V, and that raises a worrying question: what happens when someone less experienced gets it and plugs it into 220V and starts using it drawing over 30A from the mains! We (Europe) has a limit of 16A for anything 220V, so that will melt the plugs in a very short time.
380V is all good as it does roughly 18-19A, and we can do 16 or 32A depending on the socket size, probably should be fine with the small socket as it mostly will cut with 40-45A.
Again under the covers, i am mentioning all this as it applies to this topic, the plasma sources are all the same.

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06 May 2024 10:14 - 06 May 2024 11:55 #299928 by polskleforgeron

@Rod,
He mentioned several times he has a HF/HV start plasma, the THCAD manual clearly states not to use that combo.
Having cleared that cautionary tale, THCAD can work with HF/HV start as can be proven by probably 10 i have in use daily, just some care must be taken when wiring to choose a suitable point where the HF has less effect, usually at the rectifier output or at the built in HF filter/protection.
And additionally a few days back i wired a THCAD10 directly to outside connectors on a new cheap china inverter plasma with HF start, THROUGH 2 resistors and added a 0.22uF/350V capacitor across the THCAD input just to be on the safe side, and it also filters the readings a bit. Used it for 2 days, all good, probably did over 200 starts as i was tuning voltage/feed/air so made a lot of 100x10mm rectangles.
Just to be clear, do this at your own risk, any mishaps usually end badly.
A 0.1uF capacitor would be better, did not have one with such high voltage.
 

Thank you again for your explanation, but it's a bit technical for me and I'm not sure to understand.

When you say "just some care must be taken when wiring to choose a suitable point where the HF has less effect, usually at the rectifier output or at the built in HF filter/protection", do you mean that I shouldn't take the arc voltage the "simple" way from the ground clamp to the torch electrode, but instead get the wiring inside the Plasma cutter ? I think maybe I can do that..

Also when you say you plugged the cheap china plasma through 2 resistors (both 1MO 2W) with a capacitor (0.1uF and what power rating ?) shorting the two, would it look like that :
 

I've added some pictures of the plasma's cutter inside :
 
 
 

 
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Last edit: 06 May 2024 11:55 by polskleforgeron.

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