Test #5
measuring the current draw in the USB cable (how hard the phone is charging) when powered by the dynamo hub. The result fluctuates rapidly, but appears to generally stay within 0.23 to 0.37 amps. By modern smartphone standards this is very poor and would take a very long time to charge the phone. The 7805 regulator works by simply converting excess voltage into heat. Higher the input voltages AND higher current throughput will both increase heat production, requiring a heatsink for an application like this. (linear regulators such as the 7805 are very inefficient when used with higher voltages or currents; they are best used for reference voltages or low-current voltage regulation. In the modern era, there are far more efficient switch-mode converter circuits readily available. Search for buck converter to learn more)
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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
