Plasma torch test procedure

I have this plasma torch:
http://igor.chudov.com/projects/Welding/12-Plasma-Torch/
I am pretty convinced that it is a knockoff of Hypertherm PAC-130
torch, see
http://www.arc-zone.com//catalog/web_store.cgi?page=hypertherm10.html
So, I want to slowly make a plasma cutter. My first test/experiment could be as follows:
1) connect torch and pilot leads to power supply, electrode negative
2) Set power supply to 250 volts and 20 amps max.
3) Start compressed air flowing.
4) Turn on power supply
5) Nothing should be happening
6) Give it a little jolt of high frequency, the shorter the better
7) That should ignite the pilot arc
8) Blue flame should be coming out of the nozzle. That is the pilot arc. Watch arc for a while.
Does this sound like a sensible first step? I am aware that it would not produce the main cutting arc, but it could make a pilot arc. thanks
i
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On Wed, 12 Jul 2006 19:32:52 GMT, Ignoramus15962

Amps sounds high to me. I'd start with 5 amps. The volts might be a little high as well but it depends on what the torch is designed for. I've used one plasma that put that many volts out (didn't like it). Most I've seen run in the 100-150V range.

It's a start that's for sure. You'll find out soon enough if you've got to many amps flowing through the pilot arc.
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Is that 100-150V open circuit, or 100-150V cutting?
The relevance of this question to me is that if I need lower OCV than 250-290 volts, then I can change the way I connect my transformer secondaries and get higher cutting current, all the way up to 100 amps. I realize that 100 amps is useless for a chump messing around in his garage, but it is kind of cool. I thought that I needed almost 300 volts OCV. (I know very little about plasma cutting)
Anyway, I will definitely start with smaller amperage than 20 amps.

Thank you Wayne. I will start with smaller amperage. Going from 20 to 10 amps solves a lot of problems for me. (smaller relays, limiting resistors, heatsinks etc)
i
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And have the torch above a sheet of steel - with the return attached - and ready for fire cutting through and burning downward, or flame not cutting through and splatting metal sideways. It might just blast out a wide hole since you are holding it to high. Holding it close - say .1 or .15" off the surface..
Generally one doesn't fire it in mid air, it is possible but not good I suppose high voltage might eat up the pistol grip it it chars the plastic.....or cable.
Martin
Martin H. Eastburn @ home at Lions' Lair with our computer lionslair at consolidated dot net NRA LOH & Endowment Member NRA Second Amendment Task Force Charter Founder IHMSA and NRA Metallic Silhouette maker & member http://lufkinced.com /
Wayne Cook wrote:

-
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I'm fairly sure the torch is a Trafimet.

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I second Martin H. Eastburn's recommendation to have something to cut handy when you fire up your torch. It is definitely not good for a plasma cutting torch to have it running longer than absolutely necessary with the arc contained inside the torch. That can erode the innards of the torch unnecessarily.
How do you intend to control the arc current and voltage independently? I believe that the arc will have a voltage that is a function of the current and the torch design and operating conditions. I guess if you are using a variable power supply that will limit the current to your preset value and supply only the voltage that is necessary to sustain the plasma, you are ok, but be sure the PS can handle the power. Depending opon the design, running at high current and low voltage can dissipate a lot of power inside a power supply that is not designed for it.
10 amps sounds very low. Maybe OK for sheet metal. I haven't ever tried that. My cutter is rated at 40 amps and I use it near max most of the time. 10 amps is a pretty low powered cutter unless you are limiting yourself to sheet metal. Are you sure you want to build it with that limitation?
Have fun, and let us know how it works out and what your power supply is. 250 volts at 20 amps is 5 KW, which is a large power supply. If it works for you, others will be very interested in following your lead. What is your HF generator?
awright
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Sure. I will only get a flame going for a few seconds. There has to be a lot more circuitry and logic for transferring the arc to the work piece, than I have presently, so I just want to test a little piece of the torch's functionality.

Yes, but I can set maximum (open circuit) voltage.

I am pretty sure that it can handle power, at the very least up to 60 amps, but yes, a good point.

This is a 200 amp 100% duty cycle welder, so doing 60A is not a problem.

That would be 10A for pilot arc only.

It is a HF unit built into my Hobart CyberTIG that I heavily modified. Very powerful HF generator, I never run it at more than about 3-4 out of 10 setting.
i
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message

http://www.arc-zone.com//catalog/web_store.cgi?page=hypertherm10.html
thanks
My Hypertherm 900 cuts the supply if the arc doesn't transfer from the electrode to the earthed workpiece in about 5 seconds to save burning up the consumables - I suggest that you should incorporate this feature.
AWEM
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On Thu, 13 Jul 2006 22:40:18 +0100, Andrew Mawson

Good idea, yes, I will do it this way.
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