As other posters mention, the Ronk convertors seem very dependable AND popular in this area (NE ILL). I'd call the people here @ Ronk. They'll help you figure on size needed and will work with your electrician if he'll call them also.

http://www.ronkelectrical.com/pages/aap.html

I'm sure you'll like air system. They might not be fast enough for wet corn, but not sure of how you plan to use it. I just wish we'd put ours in many years before...but that's life.