This project took me about 6 hours to complete, and requires some moderate electrical skills to put together. Some aspects of it are quite complex to most, so i'll try to use somewhat generic terminology for ease of understanding. Having been an industrial electrician for 23 years, this kind of stuff comes 2nd nature to me, and I struggle to explain myself good enough for the common homeowner sometimes. Anyway, here's a basic "how-to" on constructing a homemade welding machine from transformers used in microwave ovens.
Photo below - here's the only 2 that I could get my hands on. The one on the left is significantly larger than the other, and is the size of choice if it can be found. A transformer is nothing more than 2 different coils of wire that are separated by an iron core comprised of several pieces of laminated iron. These 2 coils are called the primary and secondary windings, and have differing numbers of individual wraps of wire. Generally, transformers are used to "step down" a high voltage to a more user friendly lower value - as is done with the one that takes several thousand volts from the utility pole and brings 240 volts into your home. The 2 windings are separated by an iron core, and current is induced from one to the other. (There is no actual physical connection between the two)
Photo below - here's a closeup of the windings in the small transformer, for reference. The one on the right is the primary, and the one on the left is the secondary. In it's original use (microwave oven), 120 volts is connected to the primary winding, and about 2,000 volts is produced from the secondary. This is due to the much greater number of turns (of wire) that the secondary winding is comprised of. But, the current carrying capacity of the secondary is really a small amount. Anyway, because we need to produce low voltage and high current for our welder, this secondary winding will need to be replaced.
Photo below - here's the larger transformer with it's secondary winding removed. Performing this task isn't easy - especially in your own backyard. For reference, I used a reciprocating saw with metal-cutting blade to cut the the entire loop on one side, then drove the rest out the back with a hammer and chisel. Again...this is quite difficult to do, and care must be taken to not damage the primary winding in the process.
Photo below - I wanted to make a carrying case for the whole thing, making it very mobile and compact, too. So, this plastic case was leftover from a cheap circular saw that bit the dust a few years ago, and would be just the thing needed to house everything. Using a dremel tool with cutting disc, several of the little plastic dividers were removed to allow enough room for what needed to go in.
Photo below - The transformers were fastened to a small piece of scrap plywood, then the plywood fastened to the case by installing screws from the backside. It's times like this that remind me why I never throw anything away, because sooner or later it will have a purpose at my house. Ha!
Photo below - Here's the 2 transformers with new secondary windings installed. Twenty coils of wire on each transformer is just the right amount to provide enough voltage to maintain a good arc while welding, and also provide plenty of current to make the welding rod burn into the metal good. Although several types of wire can be used, a #10 awg copper stranded wire is probably ideal for most people. It's current carrying capacity is 30 amps, and is readily available. However, I had access to some high temperature #12 awg that was rated for 50 amps of current, so that's what I put into mine. Hehe...
Photo below - here's the transformers connected to incoming power and outgoing leads. Since the primary windings won't pull much current when in operation, some smaller wire is used to connect 120 volts to them. Of course, the primaries are connected in parallel, but the secondary windings are connected in series. The series connection causes the secondary voltage of each to be additive, and also increases the current capacity. For reference - anytime the voltage is reduced to an electrical load, the current draw increases significantly. Since the two secondary windings (combined) have a 6:1 voltage reduction from that of the input to the primaries in parallel, the current capacity has been increased by the same ratio. Anyway, the output voltage measured 38 volts ac, (which is just about right for this application) and the current capacity created is greater than 60 amps (although it wouldn't be wise to force it to produce that much current for any length of time).
Photo below - A couple of small, 12 volt dc cooling fans from old computers were then mounted into the top of the case to pull heat out of the enclosure while welding is performed. Exhausting air is much more efficient than trying to force air into an enclosure, because you can easily control where the fresh air intake comes from. This allows you to direct the air path across an item within - which picks up the heat on its way out. Anyway, these little fans are powered by an ac adapter that was salvaged from some type of small appliance at one time or another.
Photo below - here's the unit closed up, and sitting as it will be while being used. I really like the looks of it, even if it was built by a complete redneck, as my friend Hambob would say. Ha! The carrying handle is quite convenient too, and the whole thing weighs less than 15 lbs.
Photo below - several holes were drilled into the very bottom of the enclosure - which were strategically located to direct all intake air directly across the 2 transformers. Since any exhaust fan has to receive its supply air from somewhere, this control method was definitely the most sensible.
Photo below - now for a grounding clamp and electrode holder to connect the small welding cables to.....I went to the freaky merchandise store by my workplace one day while at lunch, and I ran across these battery clamps that are used on a set of jumper cables for 25 cents each. Shoot....that was a no - brainer, and worked like a charm!
Photo below - I welded my first bead on a piece of 1" steel rod that had been cut off of the extension for the compost turner last winter, just to see how it worked. The #10 awg copper stranded wire that connects the clamps to the secondary windings of the transformers is good enough to perform under intermittent load cycles, and is rated at a temperature value of 194 degrees farenheit before melting. Just as a reference, the insulation type is THHN, 90 C.......
Photo below - here's a closeup picture of the little bead with the flux chipped away. A 3/32" 6013 rod was used, although I would have preferred 7014 or even 6011. Still, this was proof enough for me that the little homemade welding machine would be really handy around here in the future. Especially on some thinner material....
So, there ya have it - my homemade light-duty stick welder that is constructed from salvaged parts that can be found sitting beside the curb in any neighborhood throughout the country. For the record, my total investment is officially $0.50, if you don't count the labor involved. I hope to run across another transformer similar in size to the largest one, because the small one limits the amount of time that it can be used before getting a little too hot for comfort. Until then, I'll just keep the continuous welding to a minimum, which should keep it from hopefully burning up. When time permits, the homemade welding helmet will be constructed too, but not for a while yet.
This project was fun to do, and I hope you enjoyed it - especially people like Hambob, that really get a kick out of my projects.
Take care, and happy tinkering!
EG
