In a post on hack a day, “Doctor Bass” needed to do perform some welding on his electric bike but had not welded before and didn’t have the required welding equipment. Ingeniously he connected a battery made from from reclaimed DeWalt A123 liyhium cells to power his diy welding rig.
He has a huge adjustable resistor which is responsible for limiting the current. 80 Amps seems to work the best with the welding rods he’s chosen. It is worth noting that when he demonstrates the welder, the color of the wire used for positive and negative leads is opposite of convention. His positive wiring is black while his negative connection is red.
To start the welding process he connects a jumper-cable-like clamp to his work piece which serves as the positive electrode. To hold the welding rod he drilled a hole in a pair of vice grip pliers and bolted on the negative lead. This way the end of the welding rod can be clamped in the vice grips while his other hand guides the tip. So far he’s still practicing, but it looks like he’s nearly ready to take on the job at hand.
He certainly would have been better off using a power transistor, such as an IGBT module to limit the welding current instead of the resistor because the resistor loses energy by turning it into heat. The transistor will more efficiently limit the current.
You will also notice he is using the incorrect safety gear for face protection. The eye goggles do not protect hime from the extreme UV light emitted by the welding arc.
See the video here