Joined: Jan 2009
Posts: 44,172
Likes: 6,404
From: New York, NY, and High Falls, NY, USA
Bikes: 1962 Rudge Sports, 1971 Raleigh Super Course, 1971 Raleigh Pro Track, 1974 Raleigh International, 1975 Viscount Fixie, 1982 McLean, 1996 Lemond (Ti), 2002 Burley Zydeco tandem
Not only is a dynamo overkill for the purpose, it doesn't necessarily even work at charging. The $30 rectifiers are problematic. Some phones won't accept a charge from them because the voltage varies so much.
I'm a huge fan of hub dynamos, but this is not the right tool for this particular job.