Test #1
Multimeter is measuring the DC voltage between the bridge rectifier and the LM7805 regulator. Power source is AC from the dynamo hub. The unloaded voltage is in the teens, but it is pulled down to between 7-8 volts when the phone begins drawing current. The LM7805 requires an input voltage about 2v higher than the nominal output voltage, or the voltage will drop. Using Schottky diodes for the bridge rectifier might help keep a little more headroom here, and at higher rotational speeds the hub should also produce a little more power.
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Circa 2008, USB chargers powered by dynamo hubs had not quite become available commercially, but various creative types had experimented with making circuits to use dynamo hub power for charging batteries or mobile devices. I had recently acquired my first dynamo hub, and wanted to experiment with trying to charge my phone (an iPhone 3g, also my first smartphone!) from the hub. I was relatively inexperienced with electronics at the time, and I think this circuit consisted of a bridge rectifier, a 7805 regulator, and a big capacitor. This is very inefficient and not very sophistocated, but I was able to prove to myself that a respectable amount of charge could be had even with such a crude approach. I never did take this further than the prototype stage, and within a year or so the Busch & Müller E-Werk became one of the first popular mass-produced chargers. Things have only gotten better since then!
About this test rig shown: The wheel is mounted in a homemade truing stand and being turned by a cordless drill spinning a 6" wooden disc held against the tire. The bike computer shows the approximate speed of the spinning wheel in MPH, and the multimeter is hooked up differently in each clip to show voltage or current when connected to either the dynamo hub or to a sealed lead acid battery (to compare the hub to a source of much greater current).
6 сен 2024
