Test #6
measuring the current draw in the USB cable (how hard the phone is charging) when powered by the sealed lead acid battery. Due to the wiring of cables being used, the phone does not attempt to draw more than 0.5 amps. In this time period, Apple used resistor bridges on the data lines inside their own chargers as a way to signal the phone that it was safe to draw more current. (I hadn't learned about this yet.) Read more here: learn.adafruit...
For comparison, 0.5 amp is the typical maximum charge rate available from a USB port on a computer, and will usually feel "slow" compared to a dedicated wall charger, which often allows the phone to charge at 1 amp or higher. In the world of tablets and big screens, what constitutes an "acceptable" charge rate has only increased in step with ever-increasing battery capacity in devices.
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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
