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Cxx0 Hardware / Probably Fried The Charging Circuit
« on: September 06, 2011, 12:30:50 pm »Quote from: arzgi
Can someone who has deeper knowledge of electronics tell what was wrong?A bicycle dynamo is a current source rather than a voltage source. Its current is proportional to its speed, rather than its voltage. This means that as its speed rises, it will want to push out more and more current (until it self-limits due to its impedance increasing with frequency, as it is inductive), and will produce more and more volts to do this. You therefore must ensure that the current it wants to produce is always absorbed. Unless your Zaurus was trying to take all the current that was available, the voltage at the input side of the voltage regulator could rise to a level at which the voltage regulator would fail, and these things tend to fail short circuit, dumping that high voltage straight into the Zaurus. What you should have installed was a shunt regulator such as a zener diode of, say, 10V across the input to the regulator (which would have to be quite a high powered zener to dissipate 3W). Some bicycle lamps have two back-to-back zener diodes in them to prevent blowing the bulb at high speed.
Did you fit a smoothing capacitor before the regulator? If not, you meter may have misread completely because it was trying to measure a relatively high frequency pulsating DC, rather than a smooth DC. Who knows how the voltage regulator might have performed under those circumstances, too. And it needs a non-electrolytic capacitor on input and output to prevent oscillations.