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Old 11-16-13, 12:45 PM   #149
NiHaoMike
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A permanent magnet alternator (not most automotive alternators) is ideal. I got mine at a surplus store many years ago (I think it was intended for wind power, got it at some crazy low price like $15), boosted the efficiency by swapping the ordinary diodes for some Schottkys out of old PC power supplies. Synchronous rectification would be even more efficient but orders of magnitude more complex.

If the load is 120V, a high voltage alternator would make more sense. Twibright Exciter If the load is mechanical in nature, a direct mechanical connection (if you can match it up well enough) would be best although that's often not possible. But for low voltage loads like electronics, a low voltage alternator makes the most sense.

Something else to consider is MPPT. Like solar and wind, you have to match the effective source impedance for best efficiency. But neither solar nor wind MPPT controllers would work with a bicycle since the source characteristics are different. DIY is really the only option there. I had to do it as part of my senior design project (along with the grid tie inverter), but it was very difficult to make an algorithm that remained stable over a wide range of inputs. For example, my first implementation (try to hold input voltage at about 16V or so, but decrease the limit down to 10V in order to hold a 3A minimum current) worked great when I tested it, but oscillated wildly when my friend Sarah tested it.
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