Did a search and did not find this posted before so, here is how to build an ARC welder
http://www.dansworkshop.com/Homebuilt%20arc%20welder.shtml
It is interesting to note that he used his dad as the guinea pig
land rover field repairs to weld is one or two batteries connected in series, a set of jump leads connected to the battery, the negative to the metal
and the postive lead holding the welding rod. Can't be any simpler than that?