We've combined our classic hand crank generator with 2 sets of complete replacement drive gears. Now your students can furiously crank away without having to worry about broken gears! Gear replacement is fast and simple, and instructions are included. These generators demonstrate the conversion of mechanical energy into electrical energy. If you have 2 of them, they can be attached to one another using the included connecting wires to demonstrate multiple energy conversions and energy loss in a system. Max Voltage: 6.5 Volts DC