Transformer for spot-welder buildup

No - one leg of 240 to "240", the other leg of 240 to "0"

Yes

Maybe. It depends mostly on the output voltage. A couple of volts is good. Much more means that the 1.2kva won't be enough current, which is the main parameter.

1.2kva is marginal, but that rating is almost certainly continuous use and a spot welders duty cycle is so low that you can draw much more than that. E.g., if the out is rated for 1000A at 1.2v, you could draw 2000, or 3000 amps for the second or so that a weld takes & then let it cool while readying the next weld. The duty cycle might only be 10 - 20%. The unknown is whether your secondary winding can supply it. It looks like it from the pictures. Do you know the guage or dimensions of the secondary winding?

I made my spotwelder from MOT's and my output voltage is 2 volts (IIRC) and it draws 17A at 240v, giving 4kva input and 2000A output (less core loss). See it here:

Bob

From the looks of things the unit should go much higher than 1.2 kva in spot welder use. But the secondary winding looks to be multiple wraps, probably won't be low enough voltage to get the amperage you want.

Ignore the 200 terminal, hook the two hots of a 240 line to the 0 and

240 term> Be much obliged if I could get information and comments about this

See if you can post a picture of the nameplate. The little metal tag on top in this photo:

pix/100_1319.jpg

Your guess about the connections appears to be correct. I usually take an ohmmeter and check continuity (and rough resistance values) between each pair of terminals and each terminal and the frame. Just to make sure nothing will bite me when I hook it to 240V.

For smaller transformers, I'd put a resistance in series with the primary for the initial power-up. The only thing that will be easily obtainable for

240V would be two 120V light bulbs in series. This will limit the energy if there's a short in it.