I never really built much because of lack of funds, and materials, but I'd like to build a tesla coil one of these days or maybe just a van degraaf.
I did build a huge electromagnet once though, well I built lot of those but they are very easy and take about 5 minutes to do, but a good one takes longer. And this one was a good one. The first time I turned it on I could of lost my finger, since a bar just zoomed towards it and stuck to it, I could not take off the bar without turning the thing off! Those are hard on transformers though, since all they really are is a short circuit. Perhaps you can stick a resistor in there though, I never thought of trying it back then.
More recently, about a year ago I built a small solonoid but it was using AC current so all it was doing is pulling in the rod in the center.
Archived topic from Anythingforums, old topic ID:277, old post ID:2283