For some time I wanted to build a MOT stick welder. Well I got a transformer from an old microwave oven and tore the secondary wingdings out. Rewound the secondary with # 12 AWG left the primary winding intact. So I needed another transformer I found on in an old 12 volt battery charger this thing is huge.I tore the secondary winding off and damaged the primary winding. so I replaced the primary winding 180 turns and the secondary winding and they must wind in the same direction. Here is where I messed up since this transformer was much bigger I used # 10 AWG for the secondary note the other transformer done with #12 AWG wire. Well the secondary's must be wired in series while the primary needs 120 volt from two different sources.
I got it hooked up got one rod burnt looked over and smoked the little transformers secondary winding. Rewound 18 turns with #10 AWG and I am welding away just fine.