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Carbon Arc Cutter

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Kolas

Mon May 08 2006, 02:23AM

Registered Member #102 Joined: Thu Feb 09 2006, 08:15PM
Location: Raleigh, NC
Posts: 169

hi guys
while working on my homeade pole pig, I realzied a steel box would be needed to hold the oil. Thus many hairy situations arised, like welding (properly), feed throughs. and how to make the holes for all this.

With the help of Chris(not Russell) I settled on a way to kill two birds with one expensive, and over heated stone. Carbon arc cutting is very similar to welding, but instead of a stick, a carbon rod is used. Blah blah blah...

Now to the real reason for the post. Pictures of the full wave rectifier under construction.

The transfromer I will be using (not photographed yet) suplies about 30V, and is rated 500A continuous. so here is the subsequently sized device for rectification...
Yes, yes, I apologize for eh poor qaulity photographs.

Dr. Shark

Tue May 09 2006, 09:41AM

Registered Member #75 Joined: Thu Feb 09 2006, 09:30AM
Location: Montana, USA
Posts: 711

Your telling us that you've got a 15kVA transfomer standing around? Wow, that must be a hell of a beast and easily be capable of tripping some breakers. Why do you want to rectify it, should an AC arc not be just fine for cutting?

Kolas

Wed May 10 2006, 02:46AM

Registered Member #102 Joined: Thu Feb 09 2006, 08:15PM
Location: Raleigh, NC
Posts: 169

Yeah, the tranny is a beast alright. I'll be sure to make a video, and take plenty of pics. The reason I rectify is because alternating current wouldnt cut well. also I'm told that when the cutting electrode is -, it pushes the molten steel out of the way.

Anyone with thoughs on how to put a pilot arc on this, so striking the arc is more easy?

oh, and i will ahve to patch directly into the main breaker with this operation. of course current shoudl successfully be controlled by the saturatable reactor i have.

Kolas

Hazmatt_(The Underdog)

Wed May 10 2006, 08:54AM

Registered Member #135 Joined: Sat Feb 11 2006, 12:06AM
Location: Anywhere is fine
Posts: 1735

striking an arc would be similar to mig or tig with a HF HV source. The HV HF source is coupled to the LV side with an inductor. Or there are also very large 'trigger coils' that do the same job. Its a fairly large inductor of heavy guage wire of about 20T #8 square magnet wire on a ferrite or heavy rod, overwound with 5 or 6 turns of a very heavily insulated silicone wire where the HV pulse is discharged through, like a camera flash circuit, except that you are modulating a HV pulse onto the LV side.

You should be able to pick one up from a welding supply I think, although the replacement cost may be really prohibitive.

The first time I saw one of these tig 'trigger coils' I didn't know what the heck it was for, but a good friend of mine told me the whole story behind it. Its pretty neat stuff. I would look to Lincoln Electric and ask them for the part number. Their staff is excellent with technical questions. They helped me when I needed Tungsten electrodes.

So, there ya go.

Plasmaniac

Wed May 10 2006, 10:52AM

Registered Member #206 Joined: Sat Feb 18 2006, 03:17PM
Location:
Posts: 72

I'm also buiding a welding machine right now. Unfortunately, the 1mm thungsten electrodes are too thin though they are rated for 10-60A. I think I'll try a carbon rod later.

here some pics:

Argon
my pilot arc transformator (around 2kV and a few 100mA output)
here you can see my high curernt source

I'm looking for some MOTs right now, so I can make a better high current suplly. Right now, I'm using 60V 20A/120V 10A

This is how it looks like if you forget turning the argon on...

I made the nozzle from a 12cm piece of 8mm brass rod with my drilling machine and a dremel. It took half an hour and everything in our basement (including me) looked very shiny...

Kolas

Wed May 10 2006, 02:42PM

Registered Member #102 Joined: Thu Feb 09 2006, 08:15PM
Location: Raleigh, NC
Posts: 169

oh, that pilot arc is mighty cool!
is your HV source HF?
how can i do this with my 500A source, i assure you, i dont have the ferrite for such a core.
also, how does the HV not overcome the breakdown voltage of your rectifiers.

kolas

G^3

Fri May 12 2006, 02:36AM

Registered Member #97 Joined: Thu Feb 09 2006, 05:40PM
Location:
Posts: 61

To stop the HV a choke and a capacitor like this guy is using should do the trick. http://www.geocities.com/CapeCanaveral/Hangar/6160/welder/arcstarter/hf.html

I don't understand why a ferrite core doesn't saturate or something like that when used like this.

Marko

Sun May 14 2006, 03:20PM

Registered Member #89 Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145

my pilot arc transformator (around 2kV and a few 100mA output)

Doesnt' seem like something lou'l like to hold in hand like a pencil.

Plasmaniac

Sun May 14 2006, 03:48PM

Registered Member #206 Joined: Sat Feb 18 2006, 03:17PM
Location:
Posts: 72

The insulation is about 2mm thick, so this is no big problem. If I touch it I'll get some neat HF burns and that's all because of its relatively high frq of 20kHz (yes conditional I -> "It is possible and also very likely that the condition will be fulfilled." why? because I'm stupid and never managed to not touch a HV supply...

...

Sun May 14 2006, 06:45PM

Registered Member #56 Joined: Thu Feb 09 2006, 05:02AM
Location: Southern Califorina, USA
Posts: 2445

I would really hate to touch the output while connected to that battery pack... Why in the world do you need it to start that far away?

In any case, this looks like once it is done it will be quite a beast... Just out of curiosity, why did you use SCR's for the rectification instead of normal diodes?

As to the ferrite core saturating... It probably does; but it doesn't matter since once the lv ark is going you don't need the hv any more, so it doesn't matter what is going on with the ferrite core...

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