I've used my Zaurus 3100 as a gps device on long bicycle trips.
The gps-card I have (Billionton) sucks battery quite soon empty, so
decided to do a travel charger. My bike's hub dynamo gives 6 V / 2,4 W,
and thus 0,4 amperes, as I learned at school many years ago.
Added a diodebridge to smoothen voltage to dc, and a 5 V regulator
to ensure voltage won't get too high.
Then rode a test trip voltage meter mounted on handle bar. Voltage
newer rised over 4,7 volts even I pedaled 50 km/h (31 mph). I almost
never exceed that speed.
I thought it was safe to use the system to charge zaurus.
Soon on first trip I almost fell, fastening strap twisted connector
quite strongly. After that I could not charge even using the regular
plug charger, led wont lit up, bottom gets hot under power connector.
Took Zaurus to be repaired, has been there almost 10 weeks, not
very promising. First they said it can be fixed, last time a called
they were still waiting for spare parts.
After that secured the fastening belts, triple checked polarity.
Did a test drive at very low speed, but seems I've burn't also
my second Z's charging circuit. Sometimes yellow led lits, usually
just blinks when charging with plug charger.
Does not hamper my usual usage, I have an external charger.
Seems it's time to forget dynamo-charger, but I wonder what wen't
wrong. The plug charger gives 5 V and 1 A (readings on sticker, I also
measured 5 volts).
I newer measured the amperes of my bike charger.
I've seen graphs of hub-dynamo's speed vs. voltage curve, and it is quite
even. So thought it would never exeed 1 A.
Can someone who has deeper knowledge of electronics tell what was wrong?