turning my old arc welder into a mini spot welder

[flippityflop]

i'm trying to find more uses for my current arc welder which has the specs of
mode 1: 25V @ 50A and
mode 2: 23V @ 70A
(i forgot the cycles for each, but it's less than 60 secs or so)

so i figure i'd modify it to also function as a mini spot welder... i'm targeting about 1.5-3V @ 750A max

since my welder already ramps down the AC to above voltages, i figure it that there are other taps in the transformer that might go down pretty close to 3V.... well i opened the thing for the first time (and confirming my hunch that it's just one big transformer, as implied by it's low price 4 years ago), and found no other taps.

so i'm thinking maybe buy another large transformer core, say one taken from a microwave oven, rewind it's coil (and having the secondary a much thicker gauge), then connect it to my old welder; bringing 23 or 25V down to 1.5V.
but... i could've just connected the microwave oven transformer to the mains in the first place... like some diy-ers have done and blogged online.

so which is better, connecting the microwave salvaged transformer to the welder transformer first (2 stage) or directly to the mains??

would the other handle higher currents than the other configuration?

[pebe]

It seems logical to eliminate the welder transformer if you can and connect the micro tranny straight to the mains.

There are plenty of ways of making a spot welder from one. Go to Youtube and look for 'Spot welders'