How to Make a Mini Welder Without Microwave Transformer?

How come when a regular car battery is shorted it does not have the same effect as when a 12 volt wall transformer in shorted. I'm trying to make a mini welder but can not figure out this concept, I found no help online and figured this would be the best place to ask how many volts would be necessary from a dC wall transformer to properly melt a piece of solder as if it were a regular welder.

It does have the same effect, with the problem that it delivers as high amps as possible – no regulation and it may ruin the battery if the car battery is discharged too far. A transformer tends to be self limiting due to inductance