From: Carl Byrns Newsgroups: news:rec.crafts.metalworking Subject: DIY arc welder- the post Date: 24 Mar 2000 10:51:53 EST I've gotten a ton of e-mail on this. Here's a copy of the original post: Note: I washed it through my spell checker and fixed some errors. Looks like fun to build. -Carl ------------------------------------------------------------------------ Some years ago my economic status was on the tight side and I had need of the use of an arc welder. A friend of mine had a portable DC welder manufactured by the Scott company, which he loaned to me. It was very interesting, as it was quite small and looked like a portable standby generator minus the roll cradle. It certainly wasn't the gas driven Lincoln arc welders that were common to contractors in that day (late 70s). Those monstrosities took up the better part of the bed of a full size pick-up truck The unit was advertised at 125 amps DC, and it was powered by an 8 horsepower Briggs and Stratton engine. It weighed less than 100 lbs, and it could be carried by one person, though it was it bit on the awkward side. Mounted on the engine was a small box about 10 inches on a side with a potentiometer and Miller brand type welding lead connectors. What was in that small box that changed 8 Briggs and Stratton horsepower into 120 amps of DC welding power? I really wanted to know that secret. Despite its diminutive stature I knew that you could actually weld with it as a contractor at work had one and I had personally observed it working. During the course of my using it, naturally, the belt broke. Of course this was no ordinary belt, it was only about 1/4 inch wide instead of the 1/2 inch or more of a typical "v" belt. I finally tracked down the Scott dealer, as this happened to be a quasi holiday, (Christmas eve day and Christmas was on a Saturday). The manager just happened to be working at his store/shop and while he was no longer the Scott welder dealer, he did have some parts, ie,. the belt. I drove over to this place and found a small assembly shop, that was making, you guessed it, portable DC welders of the Scott Welder type. Being the curious type I not only purchased a belt, but got a tour of the factory and found out what was in that box. Would you believe a Delco alternator, some diodes, heat sinks, and a small controller circuit. The owner explained how after he lost the Scott dealership, how he decided to make his own. He did some reverse engineering and a lot of messing around in his garage and brewed up his design which was called an APACHE welder. Anyway he bought Delco Alternators from GM with the stators not wound. He had worked out the appropriate windings and hired people to wind them for his operation. He explained the control circuit and even how he used the magneto of the engine to help the self-excitation process get started. Hot dog, I now knew how to build a welder. I had the engine and Chief auto parts had lots of Delco alternators. I bought a rebuilt 60 amp model, no built in regulator, and took it home. After tearing it apart, expecting to find fairly small wire in the stator, I was surprised to find that it looked like the same size wire the SCOTT guy was winding into his alternators. Great, I won't bother ripping that stuff out, I'll just slide some 32 gauge stuff in between for my field windings, throw in a bunch of rectifiers, pots, capacitors, and wahhla! I will have a welder. Well the long and short of it is, that you can make a welder this way. It wasn't quite as easy as I thought it would be, but I learned a lot about 3 phase power, Y connected and Delta connected, transformer effects, and bunch of other stuff. It wasn't entirely cheap either although my home brew machine was less than 1/2 of a new one, even if I had went out and purchased a new engine which I didn't. A real good scrounger could probably do this for less than $200 engine included. The engine is the single most expensive item. Delco alternators from the 60s and 70s without the built in regulator are the most suitable. It needs to be at least the 60 amp size or larger. You could use one of the newer integral mounted regulators, but in the past they were more expensive. That may no longer be true. I don't think Chrysler alternators will work as they are already delta connected where as the Delco ones are "Y" connected. You need the Delta connections. A 60 amp Delco alternator is capable of 110-120 amps if it is reconnected in a Delta configuration. They come "Y" connected. Basically you buy the alternator, take it apart, throw out the diodes and the regulator if it has one. Then find where the 3 phases of the stator are tied together and undo that connection. In a "Y" connection, one end of each of the 3 phases is connected together. In a "Delta" connection, the 2 ends of 2 phases are tied together. If the windings are drawn as a series of loops along a straight line, the 3 windings form the sides of a triangle, which is the symbol for the Greek letter delta. The "Y" connection schematically looks like a "Y". Changing this configuration will lower the output voltage and raise the current by a factor of 1.732 (square root of 3). This will give you an open circuit voltage of about 50-60 volts and about 20 volts when you are welding and maximum continuous output of 104 amps (60 x 1.732). The math and theory behind the actions of a 3 phase circuit can be rather daunting. If the reader is so inclined there are numerous books around that will explain far better than I ever could. Suffice to say it works and certainly isn't new. Almost all of the power grid in the US uses 3 phase circuitry. Your house typically has only one phase hooked up to it. You can safely overdrive the system to 125 amps if you keep the duty cycle down. I have never have had to stop and let the unit cool down in my use of it. The time required to change rods and restart would probably be sufficient to prevent melt down of the windings at 125 amps. The alternator has to spin a bunch to do this. You need about a 3 to 1 increase in speed to do this. This means at 3600 rpm engine speed, the alternator is doing about 11,000 rpm. Not to worry. Check out a small block Chevy. It depends on the gear ratio, but if you were blasting down the freeway in the old days (75 mph) the Chevy motor was doing 2500-3000 rpm. The crankshaft pulley is about the size that you are looking for, which means that the alternator is buzzing along at 9000 or so rpm. Stomp on it and passing gear will get you well above the 11,000 that your welder is running at. So the engineers at GM have already considered this form of abuse for you. The existing diodes are too small, so they get canned. You need at least 25 amp 200 volt PIV diodes. Get 3, stud-to-anode and 3 stud-to-cathode. Fortunately these are fairly cheap, few bucks, bigger is better, but anything over 50 amps is overkill. You need 2 heat sinks with plenty of fins like you see in large audio amplifiers. You mount 3 of the diodes of one polarity on one of the heat sinks and the other 3 on the other heat sink. If you don't insulate the diodes from the heat sinks then the heat sinks become a common conductor for the 3 diodes and one is (+) and the other (-). This assumes that the two heat sinks are electrically insulated from each other. If you follow this suggestion then you must follow the suggestion to buy the diodes as cathode to stud and anode to stud types. You can do it with all one type but it is more difficult and messier as a connection must now be made to the stud portions of the diodes and you need to electrically isolate the diodes from the heat sinks. Electrically isolate the heat sinks from the cabinet by mounting them on isolation shock mounts. These typically come either with threaded studs, or threaded inserts. I used ones that were about an inch in diameter and had 1/4-20 threaded studs on them. Connect your welding leads to the heat sinks. One is positive, the other negative. I bought some female connectors at a welding shop. They sometimes referred to as Miller style. They are a tapered brass rods that mate with a tapered sockets. I mounted these sockets on the side so that my welding cables were not permanent with the welder. The sockets come and red and black so that you can keep the polarity correct. You can get the shock mounts from Grangers. The diodes form factor is a D0-5 shape and most electrical/electronic supply houses carry them. A 1N1186 or 1N1188 should work fine. For excitation I found that the self excitation route was a pain, so I obtained a small permanent magnet motor. You need 3 amps at 16 volts. Burdens surplus catalog has bunches of them. I used a vacuum cleaner belts to drive the motor and made pulleys to give about a 2 to 1 increase in the crankshaft speed. This ratio will vary depending on what kind of motor you end up buying, but the permanent magnet motor will have to be driven at least the rated nameplate speed to get anywhere near the maximum nameplate current rating. A simple power rheostat will suffice to control the field although a simple power transistor circuit out of a Radio Shack book is a nice touch and it is what I evolved the circuit to. I made a small box about 12 inches on a side and 6 inches deep. On one of the 12x12 sides I cut a hole to match the shape of the alternator. Make the other 12x12 a removable door. The older GM alternators have 4 screws to hold them together. I removed the screws and made the hole in the box to fit over the end of the alternator with appropriate bumps to match the casing. I bored holes in the bumps to match where the screws went. Then I put the screws back in and now I had an alternator with a box on its back side. I mounted the heat sinks on rubber shock mounts which are electrical insulators and help protect the diodes from all the engine vibrations. If you drill some holes in the cover and on the bottom under the heat sinks, the fan on the alternator will now draw air over the heat sinks and keep the whole thing cool. I constructed a mounting bracket that bolted to the gasoline engine. The alternator sits above the crankshaft, although it could be mounted on the side. Alternators are not direction sensitive when it comes to generating electricity. However, the cooling fan may not be as efficient when operated in a reverse direction but the effect would probably not be harmful. Also the brushed are mounted off to one side for the direction of rotation. There are many approaches to mounting the alternator and it is a matter of preference and what kind of engine you mount it on. The welder will run 3/32 rod quite nicely and if you push it, 1/8". It is a little hard to get the arc started and an arc stabilizer from Burdens would probably help. I still have mine and I made a second one for my brother. I went so far as to make a foot control for it and used it with a tig torch. Works pretty good. I haven't fried any diodes yet. SURPLUS CENTER 1015 West "O" Street P.O. Box 82209 Lincoln, Ne 68501-2209 An Attempt at a little ASCII art. Welding leads ______________________ | ___| | | | | /_\ | | | | | _______ 0-----------------------------0--|---0 | | _/ \ | | | F (/) W _\ /_ | | | I (/) I _\ /_ | | | E (/) N _\ /_ | _ | L (/) D _\ /_ | \ / | D (/) I _\ /_ | | | (/) N _\ /_ __| | | (/) G _\ /_ | | |______ | __| _\ /_ | | | | | _\ Alternator / /_\ | | | | \ \ | | | | | / \ | | | | | o---\/\/\/\/\/\/\/\/\/-----0---------------0--|---0 | | | \ | | | | | \ ___| | | | | \ | _ | | | \ | \ / | | | \ | | | | | \ /_\ | | | | \ | |______| | | \ | | | | \----------------------------------0-------0 | | | | | | | | | | | _ | | | RHEOSTAT \ / | | | __/\/\/\/\/\/\/\/\/\/\________ | | | | ^ | |_____| | |______________| 12-16 volts |___________ |__________________________________|__ Welding leads An Attempt at a little more ASCII art. --------------------------- | Box | | ----------------------- | | | | | | |\/| ______ | | | |||| | | |-------| - - |||| | | | | | | ||||- | | | | | Alternator ---||||| | | | | | ||||| | | | | | ---||||| | | |Heat | | | ||||- | | |Sink | - - |||| | | | | | | |||| | | | | | | |||| | HOLES---> | | | | | || | | | | ----------------------- || | HOLES---> | | | | || | | | | | || | HOLES---> | |_______| | || | | | || | ---------------------------- || | ^ || | | || ______| | || | HOLES || | || | || | |||| | |||| | |||| | |||| | |||| | |||| |- |||| | |||| | |- ||||-------- | |||| | |||| ENGINE | |||| |- ||||-------- |||| | |||| | |||| |- |||| | |||| | |||| | |||| | |/\| | | | | | | ------------------------ |