I've been welding a lot with spoolguns (flux cored wire), stick electrodes, and car batteries recently. These methods are pretty excellent for dirty, strong-e-nuff welds that are as portable as a couple of car batteries and some jumper cable.
Adding an inverter makes it possible to control the output in exciting ways
The prius inverter is quite robust. On this project as well as with derpbike, it's been subject to a number of situations it'd never see normally inside a car:
- repeatedly tripping the built in overcurrent shutdown
- plugging it into the wall
- covering it in grinding dust
Furthermore, it's nice to use. The pins are nicely labeled, the logic side is isolated from the power side, and all of the hard power electronic stuff (gate drive & layout) is done for you. That's why this device is a steal at the going ebay rate of $200. (less for a slightly dinged-up one)