January 26

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.

The basic parts – check out those massive diodes!

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).

Close up of the diode, these suckers are Huge! The measure in at 3 inches across.

The heat sinks for the diodes and the cooling fans in the back ground.

The heat sinks are prepared.

Using copper strapping to make the connections have as low resistance as possible for the massive welding current.

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.

Schematic Layout

Completed Rectifier in the welding cart.

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.


The finished DC rectifier showing connection end


Rectifier showing Choke and cooling fans


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.