Phase Converter to run Three Phase Welder

I don't know if this question has been asked, but I think it prolly has. I bought at an auction five Miller 450 amp Delta mig welders and one Lincoln 400 amp mig welder. I want to try them out and see if they have any problems before I try and sell the Millers and keep the Lincoln. My phase converter makes 54 amps of power and my electrican thinks I could damage the phase converter by trying the welders. I told him I don't know if it would or not, but I wasn't going to turn it up all the way just enough to run a few beads to be able to show a buyer that they fire up and can stick two pieces of metal together. The phase converter is a phoenix 20 HP. What say the experts here because I sure don't want to burn it up???
Thanks everyone.
Rick

If the buyer insisted on testing with one inch plate and his own roll of wire, I'd be nervous.

If you were just running thin wire on 1/4 plate, I can't see any problem with the proposal.

And you do have proper overcurrent protection, right?

Yes, We were thinking of a 60 amp breaker, so if you draw more you trip the breaker and not kill the phase converter, we will still be able to weld and test the machines. I plan to keep the linkcoln. We had thought about a 125 amp breaker, but that monster would have taken 3 spaces in the panel ( a smaller sub panel with just the larger breaker is not out of the question )

Hmmmm....

I'm no welder expert by any means, but isn't the weld output of 400amps at around 20volts?? If so, that 400amps at the output would be only 40 amps at a 200v input, no?? so seems with a 90% efficiency in the welder (probably 95% in reality right Dave Kamp?) your 230v RPC should not be bothered by the full 400 amp output of these - in my opinion....