I need to run mine. Book says to run under a load every 6 months.
I use a 1000 watt flood light for a load.
Mine says to run under load once a month. I've probably went 6 without doing it and have never had to re-excite the magnets. My manual doesn't say how much load and kind of implies that it doesn't really matter, but I've always wondered if I should really load it up or just throw SOMETHING on it. I usually put my air compressor on it and maybe the wife's hair dryer if I feel like going in for it.