[Al Skierkiewicz]

Sorry I wasn't able to check the boards yesterday.
Alternators are not motors. What the original article suggests is that you couple the 130 amp Ford alternator to a constantly running compressor motor such that the alternator is running at 6k-7k RPM. The output (voltage and current) of an alternator is a function of the field current and input speed. As the article suggests, you need to connect a battery starter such that the field is supplied current to start and a second circuit (supplying field current) to continue generating current. Please note the mention of the addition of a current limit. The article was written to auto repair specialists who have an understanding of the way alternators function so some things are expected to be understood and were left out of the discussion.
As to the alternator, you should be able to get one at a junkyard. Be sure to get a high current rated alternator if you can't get the one specified in the article. Please also note that the article suggests you can weld up to 1/4" with this setup but 1/8" is a better bet. The unspoken caveat here is that this will work for small fix it jobs, not continuos welding like when assembling a robot base from square tubing. The diodes can't take that kind of abuse for more than a few minutes at a time.