On Thursday, October 30, 2014 1:05:18 PM UTC-4, wrote:
Puget Sound Energy (PSE) has had complaints
from neighbors about voltage spikes or drops, my friend wasn't clear
on this, but they showed him a graph which I have yet to see.
Thanks,
Eric

It sounds as if the problem is the voltage sagging. You need to see the graph. If the problem is that the voltage drops while he is welding, then a rotary converter will not help. A inverter welder will be more efficient and maybe would not cause the problem.

Dan