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pauleddy

Wed Jan 05 2011, 12:46AM

Registered Member #2909 Joined: Wed Jun 09 2010, 12:31AM
Location: fort belvoir, Va USA ( south of DC)
Posts: 145

So I have had some Carbon electrodes for some time and I would like to use them for something so I have decided to make an arc furnace. But lacking a electric welder I have decided to build a vary High Current, low Voltage DC supply. I have this large transformer that Iâ€™m deciding either to rewind or use as is.
Here is a pic of it, along with a MOT for comparison.

Itâ€™s a spare from one of these supply I found at a junk site there where half a dozen of these but must were destroyed I had to get two and swap parts to get one working.

I also have two more of these diodes there rated for 250A IFAVM and 600A IFRMS so I think they will do.

And finally I have this 140000Âµf 50V smoothing cap.

So I would like any advice on how I should go about this. I was thinking a simple half wave system since I only have two diodes The only worry I have of using the transformers own windings and paralleling them, is that there is to different voltages coming out.
Any help would be great

Ash Small

Wed Jan 05 2011, 12:56AM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

How big are the carbon electrodes? (diameter)

pauleddy

Wed Jan 05 2011, 01:40AM

Registered Member #2909 Joined: Wed Jun 09 2010, 12:31AM
Location: fort belvoir, Va USA ( south of DC)
Posts: 145

its about .5cm thick

2Spoons

Wed Jan 05 2011, 09:48PM

Registered Member #2939 Joined: Fri Jun 25 2010, 04:25AM
Location:
Posts: 615

why do you need DC?

Ash Small

Wed Jan 05 2011, 10:38PM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

pauleddy wrote ...

its about .5cm thick

I found 6 mm electrodes run at about 50-100 amps, 8mm electrodes run at 100-150 amps.(any more and they burn away too fast)

At Corus Special Steels in Rotherham they have 3 electrodes about 10-12 inches in diameter.

klugesmith

Wed Jan 05 2011, 11:43PM

Registered Member #2099 Joined: Wed Apr 29 2009, 12:22AM
Location: Los Altos, California
Posts: 1716

Ash Small wrote ...
At Corus Special Steels in Rotherham they have 3 electrodes about 10-12 inches in diameter.

Ash Small

Thu Jan 06 2011, 12:36AM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

Cool videos, Rich. The electrodes at Corus may be 18 inches diameter. I've not been there on a shutdown since summer, 2006. It's somewhere in that region though.

Steelworks are amazing places to be. I'll never forget being underneath the blast furnaces at scunthorpe(furnace road) at 6am in January, while it's still dark, while they are discharging into the 'torpedoes'.

The cupolas at Sheffield where they did the stainless are pretty impressive too (I think they have shut down now)

The vacuum induction furnaces at Killamarsh (Ross and Caterhall) are my favourites, though. (Rolls Royce have some smaller ones in Derby, and in Bristol, I think, but I've not seen them, but they are not as impressive as the ones at Killamarsh). They are used for producing superalloys, inconel, hastealloy, etc.

pauleddy

Thu Jan 06 2011, 03:25AM

Registered Member #2909 Joined: Wed Jun 09 2010, 12:31AM
Location: fort belvoir, Va USA ( south of DC)
Posts: 145

Dc because I may use it for other high current project that may need dc and I have the parts for it.
So I'm should be shooting for a max of 100A I doute i can get that high
Now should I try rewinding or use the original winds?

Kolas

Thu Jan 06 2011, 03:56AM

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

hey there, interesting little project you've got going. I'm actually working on something very similar. It looks to me you have a ~1kw transformer core there.
Since I have yet to see any real numbers on the resistivity of an established arc, I would have to assume that your goal of 100A is not very feasible. (assuming 10V at 100A)

My best suggestion would be to acquire a ~2kVA welding transformer. These have very thick secondaries and are designed to be shorted. Also for a carbon arc lamp or furnace, I don't see any real reason to rectify it. If anything using AC will cause the electrodes to wear at the same rate. In a DC situation one of the electrodes will see all of the heating due to the kinetic energy of the electrons and the other will see hardly no heating.
Just my thoughts.
Kolas

Ash Small

Thu Jan 06 2011, 09:31AM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

I'd second this. A cheap welding transformer is exactly what you want.

You can also buy copper coated carbon electrodes from welding suppliers.

EDIT: You can always get some big diodes if you need to rectify it for anything else.

BTW, 50 amps should be plenty, but a cheap welding transformer will allow you to adjust the amps.

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