Originally Posted by
steelbikeguy
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I have a vague memory of someone running tests in a manner similar to what the OP is suggesting. The open circuit voltage did rise in proportion to the dynamo's rotational speed.
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Steve in Peoria
About a decade ago, I was a bit frustrated with the high cost of USB chargers that were powered by a dynohub. So I tried to make one. And after two or three of them quit working, I put a volt meter on my dynohub output on a shallow downhill. It was over 30 volts and I was not trying to go fast.
From that I realized that if you had a USB charger in the circuit but were not using it to charge any batteries, you had better have a circuit that could handle pretty high voltage input. That was the day I decided to give up trying to build one and to buy one that was designed by someone that knew a lot more than I did about designing those things.
Originally Posted by
steelbikeguy
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Personally... for a dynamo that can be swapped between bikes, I was always fond of the old block dynamos of yore. They attached to a bracket on the fork and could be removed by taking out a single bolt. Yeah, it's still a bottle dynamo with all of their issues, but it was convenient. No wires either, unless you wanted to wire up a tail light.
My old Jos block dynamo...
Steve in Peoria
I have a few of these in a box somewhere in storage, but Union brand.
I had one on my errand bike. In fall after the end of daylight savings time, I often was riding home after dark. I was riding on well light streets, the incandescent light was not very bright but it was bright enough to be a good to-be-seen type of light.
I recall adding some zener diodes to it to prevent the bulbs from blowing out, but that was a long time ago, do not recall the details.
Not sure if you can still find used ones like these, it has been a long time since these were in common use.