The Revolution is an awesome way to get the most out of your dynamo. It is designed to run in parallel with your lighting system to charge any of your USB-rechargable devices and features:
Best in class efficiency
High Speed Overload Protection
Simple Installation
Shock and vibration toughened
Waterproof
Gold-plated USB connector won't rust or corrode
 
Starts charging at 5.5 km/h
Full charging at 14.4km/h
Max current: 1 Amp
Weight: 37 grams
Dimensions: 54mm x 35mm x 14mm