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Bicycle Generator

by tmackay Jul 10, 2017
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can you give me more details about the electronic components? is for example important which moter? sorry for the questions but I'm new to the soldering area.

Sure, if you're going to go out and buy one, I'd suggest getting a purpose built generator. While they are very similar in design, they are optimised for different applications. Motors generally have smaller number of turns of thicker wires which is good for dumping current into, but will only generate small voltages when turned. If you do choose to go down the re-purposed motor path, look for a motor with low KV value, 100KV-400KV or so, mine were 340KV and I wouldn't want to go much higher. The KV rating of a motor is the ratio of RPM to input voltage, and it more or less applies in the reverse direction, ie. lower KV means higher voltage generated for a given RPM.

Then there is the frequency of the AC voltage generated which will be higher for a motor due to the many sets of coils compared to a generator which will typically have one per phase. This means the rectifier diodes chosen need to be fast, like Schottky diodes. As for circuit diagrams, do a search for 3-phase rectifier and you'll get the idea. Dump the rectified output into a nice big capacitor (decent voltage rating too, I was easily getting 50 volts output) and run your voltage regulator off the smoothed output. A generator would probably be already rectified DC and won't need the diodes, with smoother (or at least lower frequency) output too that could probably feed a voltage regulator directly (they usually have their own input capacitor).

I was aiming for low power sustained over time, for charging batteries, at around 45W and sized my generator accordingly. A fit cyclist could probably manage a couple of kilowatts in short bursts, but you'd probably want something more robust to handle this, like a belt driven car alternator or two.