this site, using parts from old Microwave ovens, you can build an arc
welder. We don't endorse this downloadable PDF book, but you may find it useful.
They are selling plans for about 9 bucks. The plans include details for
small 120 volt portable units all the way up to 250 amp, 240 volt units. You can
easily scale the design up even more if you wish.
What you get is the inside scoop on microwave oven scavenging, the basics of
electricity, and dozens of high quality color illustrations and schematics to
get you on the fast track to building this very useful shop tool.
The design also incorporates an exclusive solid state controller using low cost
parts easily purchased on eBay or other online sources. The author claims to
have 5+ years perfecting the design and it works! You won't find better
information on this controller than right here.
And if AC welding isn't enough, there is also a chapter on building the
heavy duty DC rectifier bridge so you can weld with DC (direct current).
Please note that this is a large pdf file to download (4.6MB).