Astronaut Don Pettit shows how he built a Van de Graaff generator using LEGOs, a rubber band, a electric driver, and some metal foil in this video. His device looks like it generates 20-30 KV based on the length of the electric arcs. He built it to study electrostatic fields in microgravity. It was cool to see a piece of charged foam orbit his structure like a satellite when negatively charged, and stick to when positively charged. It's a neat demo with very simple materials.