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Microwave Transformer Arc Welder.

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quicksilver

Sun Jul 13 2008, 06:03PM

Registered Member #1408 Joined: Fri Mar 21 2008, 03:49PM
Location: Oracle, AZ
Posts: 679

This is one time when I can talk with a little knowledge because I was a welder as a young man and what you are talking about are two processes. Regular arc welding is called SMAW or shielded metal arc welding using an electrode covered with a dry flux and yes, AC is just fine for hot deep welds. The other thing is known as resistance welding or spot welding & you can tell by the name how you will need to set up your system.....

I have a newer Miller buzz box (AC by the way!), & 2 old Lincolns in a shed and took a look because this is an interesting idea and I hope this thread continues.......(AC will work just dandy by the way I used to use AC for rough stuff) and the old AC/DC Lincolns spat out about 250 amp and 50 volts - the REAL old one went to 400 amps and about 70 volts.

When we needed special stuff however, that's when you need to deal with DC due to your electrode choices! DC can be damn important. You will need to get to Home Depot and buy an electrode holder/clamp and a helmet/gloves, remember. You will be using a pretty damn hot arc even at 75 amps.

I took a look & what I'm seeing is from your mains you have an inverter that goes to your transformer-setup. Inverter circuit control, then output bridge rectifier and inductor for your fine tuning the clap that will hold the electrode are ALL SUPER heavy duty. I have not seen these items commercially available outside welding supply situations. I've seen a lot of them in dumps and junked welders but this stuff is HEAVY!

Could you rewind a MOT to get what you need? No not a single MOT but a few? YES! I'm not totally sure but lets say that a 75 amp threshold will exists on the smallest electrode available. You must experiment with electrodes to see what you'll need to work with but the Electrode of choice for EASY AC usage will be some thing like a "E6013". They can use wither AC OR DC and they are cheap (like 10 cents or whatever)! If you can buy smaller than 1/8 inch do so. The thinner, the lower your current level for a good penetration.

I'm going to dig up my material which had original schematics from all the manufacturers and statistics on what transformer, SCR, rectifiers, etc they actually use; if you're interested. My son wants to light one up to try them out so i will have all the materials to let you know what's what.

Basically I'm pretty comfortable saying that at a low end 75 amps and 1/8" E60series like E6013 is what you're going to need. You WON'T need more than about 50 volts & you'll be working in around 20-28 V for 1/8 stick electrode. So that's where you want to design for.

ahron11

Sun Jul 13 2008, 08:00PM

Registered Member #1572 Joined: Fri Jul 04 2008, 11:14PM
Location:
Posts: 19

Hey, I understand what an SCR does, but why do you need to have 2 of them in an arc welder. I mean is it just a switch or what is the use for it in an arc welder. Also would it be possible to hookup a light dimmer on the primary side of the transformers to control what is output on the secondary. Also what would I use an inverter for? Also as of now I want to keep it as simple as possible, and then upgrade it when I get more money. So right now all that I would probably be using for welding is AC.

ahron11

Mon Jul 14 2008, 03:02AM

Registered Member #1572 Joined: Fri Jul 04 2008, 11:14PM
Location:
Posts: 19

Hey, I have decided to look around and see if a dc arc welder would be worth making. The only thing that I need serious help with is finding some good deals on Stud Diodes to use for it. Since I will probably have to make my own bridge rectifier, I will need to acquire some high current diodes. above 200A if possible. I dunno, whatever would be suitable for this project. I am thinking of making a welder with 5 1000W MOTs, with each secondary giving out about 8 volts each, which would give me a 40V 125Amp welder. Please tell me what you think, and also try to find some sources for these large diodes, but it would be nice to pay a very small amount of money. Thanks so much for all your help!
Also, would it be possible to hook up two SCR's anti parallel to one another, and then put some smoothing capacitors after it to give a good source of DC for welding?

Dr. SSTC

Mon Jul 14 2008, 04:41AM

Registered Member #1407 Joined: Fri Mar 21 2008, 07:09AM
Location:
Posts: 222

ahron11 wrote ...

Hey, I have decided to look around and see if a dc arc welder would be worth making. The only thing that I need serious help with is finding some good deals on Stud Diodes to use for it. Since I will probably have to make my own bridge rectifier, I will need to acquire some high current diodes. above 200A if possible. I dunno, whatever would be suitable for this project. I am thinking of making a welder with 5 1000W MOTs, with each secondary giving out about 8 volts each, which would give me a 40V 125Amp welder. Please tell me what you think, and also try to find some sources for these large diodes, but it would be nice to pay a very small amount of money. Thanks so much for all your help!
Also, would it be possible to hook up two SCR's anti parallel to one another, and then put some smoothing capacitors after it to give a good source of DC for welding?

use a couple of large bridges in parrralel there aroung 35 amps for 5 bucks

quicksilver

Mon Jul 14 2008, 02:27PM

Registered Member #1408 Joined: Fri Mar 21 2008, 03:49PM
Location: Oracle, AZ
Posts: 679

As you design remember a few things....over build so that you have some room to work with and use the largest amount of real arc welder materials affordable; like clamps or cables. Be very conscious of the workload exceeding the strength and stability of the equipment. This is referred to as "duty cycle".

I see a lot of design challenges being there to overcome. The actual technique will come if you learn from simple procedures. But striking the initial arc will always be a challenge especially in unique positions. Start with a simple flat plate of steel and "scratch" a very short (1/4") and raise up as you see the arc through the visor (eyes NEED protection). Depending upon the current, etc you will be working with a VERY short arc of perhaps the diameter of the electrode. Be prepared for working with a 1/8" arc! It can be done very easily but there is a "feel" to working that close and not touching the work surface.

The actual ROOM to wind your secondary may not exist on a single MOT but may exist if several are used. How these several are to work in unison and maintain a reasonable duty cycle will also be a design challenge. However you must continually consider the challenge of overheating. Testing along the way should be VERY short. Overheating and over-reaching the design boundaries of such a thing are one of the principal design features of arc-welding equipment. There are now many forms of solid date "Inverter" type welders! They can almost do the same thing as the old fashioned transformer but have advantages in weight. The needed components may NOT be out of reach as there are some VERY high amperage components made now than in the 1970's.

I have heard of home-made welders several times but the design problems may best be met by studying an existing arc welder and looking at the energy limiting elements within the design. Adjustments are made with SUPER heavy duty components. It may be a good idea to obtain a junked one first. The components may not all be dysfunctional! In fact a neighbor has one that he uses quite regularly that is a fusion of two junkers and some homemade stuff that is every bit as good as a high quality commercial unit - better than many! Picking your parts will be important as some adjustable components wear with too much regularity.

Best of all this is a very inexpensive form of welding dating back to engine driven AC/DC welders of the 1930's ship yards! The magic is actually in the inexpensive electrode which is a stick of steel, etc which is coated with a dry flux (they MUST be kept dry!). When an arc is struck this flux creates gases which allows the arc/plasma to maintain & penetrate. Experimentation should be conducted at VERY short intervals with great emphasis on safety of the eyes, hands and from the gases from the electrode. Very short intervals of testing are also mandated due to learning what your duty-cycle range will be.

Only my opinion but if you could get a junked one you'd be very close to building your own by seeing how the high current issues and heat were deal with professionally. BIG Welding supply places often have junked ones to compare with the new models and if you find a place that repairs them, they may have a vast amount of junked SMAW's from people wanting to fix their old one and being talked into upgrading! These units were only $200 and less, new when copper was not in short supply. You could easily get one for free if you were to haul it away.

ConKbot of Doom

Mon Jul 14 2008, 09:10PM

Registered Member #509 Joined: Sat Feb 10 2007, 07:02AM
Location:
Posts: 329

I have seen a small spot welder made from a single MOT, rewound of course.

The maker had the core wound with #4 or #2 AWG welding cable (welding cable for maximum flexibility in wrapping it) only 4-6 turns fit if I recall correctly, an he used a deep reach vice grip with insulation added for the clamp
for reference
I think he used brass bolts, though I'm sure the electrodes from a 'real' spot welder could be used too, that and a timer relay for turning the MOT on and off, and a separate foot switch to trigger the timer.

Experimentonomen

Mon Jul 14 2008, 09:23PM

Registered Member #941 Joined: Sun Aug 05 2007, 10:09AM
Location: in a swedish junk pile
Posts: 497

I made a spot welder out of a single MOT, which was replaced with a real alternately laminated core.

quicksilver

Thu Jul 17 2008, 02:38PM

Registered Member #1408 Joined: Fri Mar 21 2008, 03:49PM
Location: Oracle, AZ
Posts: 679

ahron11:
I believe that the thread on filter caps may have some bearing on the use of a MOT in either welder design capacity. When I peer into a buzz box it seems that big old transformer yields a filtered energy prior to use! {Unless you're just going to make a big AC "scorcher" & trust in the electrode to and a hand sander to make a clean puddle}

Winding the secondary will always be the challenge but that may be less of one when several MOTs are used. Realistically, duty-cycle won't be as efficient as a single transformer I imagine in any event but with planning: you can see that spot welders would be made QUITE effectively. You MAY be able to make something that is halfway between both a spot welder and a SMAW. Something that "tacks down" some steel for rough work or holding purposes. It might even be extremely efficient and useful for fast holding of emergency repair.

Billybobjoe

Sat Jul 19 2008, 11:42PM

Registered Member #396 Joined: Wed Apr 19 2006, 12:55AM
Location: Pittsburgh, PA
Posts: 176

I'm surprised no one has linked to this site yet -

Yes you can buy plans (I've bought the Resistance Furnace plans and would recommend this guys stuff - they are really cheap and comprehensive) but really you shouldn't need to for this.

Quicksilver: I'm not sure what you're trying to say but a large choke is what one would use to smooth the DC output after rectification. A large bank of filter capacitors (and it would have to be huge for that current) would detonate the electrode when you tried to strike an arc.

A word of advice - building one would be fun, but personally I would look around locally first for a used one- I got one on Cragslist for $75. A 250 amp model with a 100% duty cycle up to, IIRC, 100 amps (I rarely have to worry about it). Adjustable current, and it came with a stick holder and ground clamp. The whole thing was probably worth it just for the scrap copper or an adjustable ballast. Just something to think about . . .

Also, I would HIGHLY recommend an auto darkening helmet. Very useful, especially for a beginner because striking an arc blindly is difficult, dangerous and leads to messy welds.

IamSmooth

Sun Jul 20 2008, 02:02AM

Registered Member #190 Joined: Fri Feb 17 2006, 12:00AM
Location:
Posts: 1567

I got a nice arc welder off of Craigslist for $99 which included extension cord, helmet, 100's of 6013 sticks and the welder. Mine goes to 200A. If you want serious welding your system will need to be able to handle close to 10kw of input power (220v @ 50A).

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