How can I make about 30-40 Volts DC ARC Welder using an alternator of a vehicle and/or a transformer of a Microwave oven. Please give me a detailed report including the conversion from AC to DC. I hope that it will be possible to weld thin metal sheets using such a device. The main idea is to repair car bodies without damaging the Zinc coating of the new plates and surrounding paint work.

 

Welcome to the forums! In all honesty? Why reinvent the wheel? Light duty arc welders are not expensive, much safer than what you propose, and will do the job. As with any electrical device having a UL certification could help should there be an insurance matter.

 

The least damage you can do with welding is by TIG and working with thing sheet metals really requires precise control. Something you won't get with a DIY welder made from spare parts. Also, any welding will damage the plating. In most cases you want to grind away the plating from the weld area before welding as the plating can contaminate and weaken the weld. Then there is the toxic smoke when you weld many types of plating.

Out in the jungle and need to weld? Yea, cable together some car batteries to make emergency repairs but for intentional, planned work especially on thin sheet metal there are too many inexpensive welders (new and used) to bother with making one from scrap. If you really want to do it cheap I would buy a used or not working welder and fix it.