Converting an inexpensive AC Welder to DC Service…
About 9 years ago I converted my standard Lincoln AC “Buzz Box” Welder into DC Service. I did this by building a massive full wave bridge rectifier. It has provided great service and welds very nice – DC welding is acutally quite a bit easier than AC welding, and in fact, this DC full wave Bridge is clean enough for Tig welding should I ever get the bug to do that.
Here is how I did it. (Excepted from my old original website hosted on Comcast – and it is still there even though I haven’t been a customer in over 9 years!)
Welding can be done with AC but for better welds and for work on thinner sheets of metal, DC is needed. Lincoln sells a inexpensive AC arc welder that can handle as much as 225 amps of current at about a dollar per amp. A DC welder of this current can cost twice as much, and a Mig welder of this current is way more. I decided to buy the cheap Buzz Box and then convert it to do what I want. First I built this DC arc conversion. Next I will build a Mig and Tig extension and then I will have a fairly complete welding system for very little money.
I acquired these four 300-amp,200-volt diodes from Ebay for $7.00 apiece. They originally sold for $90.00 each. You can get this stuff cheap and there. The old transformer will be used as the choke coil (see circuit diagram).
The terminals and heat-sinks must be connected such that the heavy current (as much as 225 amps) can flow unrestricted, and so that cooling is possible in both air or in a oil bath, and so that the whole is structurally sound. To insure all of this I used both aluminum and copper strapping scavenged from the transformer shown earlier. Notice how the aluminum is wrapped with the copper.
Below is a diagram of the full wave bridge. Again, while the circuitry is simple, the actual physical construction is challenging due to the heat dissipation requirements and the current carrying requirements.
A view of the completed air cooled full wave bridge mounted on its nylon header. The header is made from a nylon kitchen cutting board. The box is an old main-frame computer power supply box.
This welder has given me 9 years of great service – never overheated, and I have never had any issues with the rectifiers. A great way to build an awesome system and save money. Your just not going to be able to buy something of this ruggedness without spending a ton more money.