Build your own Arc, MIG and TIG welder 
You can build a welder with a modified alternator, a few resistors and some welding cables. Can be powered by a gas or electric motor. There are several of these floating around like the "weldernators". They basically work, but have little output control. They will also likely blow out the rectifier bridge as there is no protection from the output running away and no stabilizer for a better arc. These typically run at about 20V; that will work, but hard to maintain an arc.
The idea is to have a generic control board to allow any power source with current/voltage control to be used for Arc, MIG and TIG welding. It has a programmable slope and OCV just like the big welders have. Also it supports both Constant-Voltage (CV) and Constant-Current (CC) modes so TIG, ARC and MIG can be done. It can also be used as a fast battery charger.
http://diy-welder.com/buildit.shtml
