I gotta be honest with you folks, I don't like the way this thread is going. There are a lot of younger/inexperienced members here, so I need to make this message clear:
If you do not know PRECISELY what you are doing with household (mains) electricity, do NOT mess with it! DID YOU KNOW- A car battery actually carries enough current to KILL you? DID YOU KNOW- Under the wrong circumstances, LESS THAN 1 AMP can kill you? DID YOU KNOW- A fuse or circuit breaker will NOT react anywhere NEAR fast enough to save your life? DID YOU KNOW- Even a low-voltage circuit like a doorbell or thermostat circuit can cause a fire? I cannot stress enough that "fooling with" "cheating" or otherwise not using electrical devices for the specific intended purpose is BEYOND stupid. Leave it alone. Your life, your loved ones' lives, your pets' lives, your homes, your possessions are worth so much more than the cost of having a qualified electrician sort out your electrical issues for you!
I know exactly what I am doing. SOME others here may as well. MOST here do not. And to whichever of the above fellas talking about cheating a twistlock- Nothing personal, but I would throw you off my jobsite so fast, you'd create a sonic boom.
Enough said.
To the op- please either have a competent, qualified electrician install the appropriate branch circuit, or trade in your welder for a 120 volt unit.