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> Probably Fried The Charging Circuit
arzgi
post Sep 6 2011, 07:15 AM
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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?

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rlubikey
post Sep 13 2011, 01:23 AM
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Bad luck having to go through all this grief. At least you tried but, as gromituk says, a bike dynamo is a complex source of power. You would most definitely have needed a smoothing capacitor, quite a large value, to supplement your rectifier pack as the frequency would be quite low at low speeds. Especially so as you have a hub dynamo!

The fact that you measured up to 4.7V on your DVM is consistent with the regulated 5V being periodically "interrupted" as the rectified, un-smoothed voltage fell to zero every half-cycle. I should think it was this that confused the charging circuit and brought about the failure.

I seem to recall that the Z needs a 1-amp power supply - perhaps someone can confirm this. Even so, all bike dynamos I have ever seen only produce 0.5-amps. (Even the 6-watt hub dynamo my Nearest & Dearest has on her bike is 12V @ 0.5A) You *could* make a suitable power supply using a switch-mode regulator to translate (in excess of) 10V @ 0.5A down to 5V @ 1A when you're pedaling fast enough, but I suspect this is quite a challenging project.

Richard
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arzgi
post Sep 14 2011, 09:48 AM
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QUOTE(rlubikey @ Sep 13 2011, 12:23 PM) *
Bad luck having to go through all this grief. At least you tried but, as gromituk says, a bike dynamo is a complex source of power. You would most definitely have needed a smoothing capacitor, quite a large value, to supplement your rectifier pack as the frequency would be quite low at low speeds. Especially so as you have a hub dynamo!

The fact that you measured up to 4.7V on your DVM is consistent with the regulated 5V being periodically "interrupted" as the rectified, un-smoothed voltage fell to zero every half-cycle. I should think it was this that confused the charging circuit and brought about the failure.

I seem to recall that the Z needs a 1-amp power supply - perhaps someone can confirm this. Even so, all bike dynamos I have ever seen only produce 0.5-amps. (Even the 6-watt hub dynamo my Nearest & Dearest has on her bike is 12V @ 0.5A) You *could* make a suitable power supply using a switch-mode regulator to translate (in excess of) 10V @ 0.5A down to 5V @ 1A when you're pedaling fast enough, but I suspect this is quite a challenging project.

Richard

Yepp, thanks to gromituk seems to work now. I made some modifications as gromituk kindly suggested and Zaurus accepts now the hub dynamo charger (yellow charging led lits and does not hamper charging by the plug charger). I have not tested on the road yet, it's been very rainy here past few days, and the water shield I've planned is still in proggress.
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arzgi
post Sep 15 2011, 06:29 AM
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Road test done, works perfectly, thanks again gromituk!

I tried with totally empty battery. Took about two minutes before charging led lit, but after that no problems at all.
Led starts to blink when speed is 4 km/h (2,5 mph), but already at walking speed 7 km/h (4,35 mph) stays on
constantly. Max speed I tried was 48 km/h (29,8 mph), still nothing to worry, yellow led still shines. At home plugged zaurus to its own charger, and charging continues.

I also tried the head light at the same time, but as I suspected, the light was very dim, and zaurus stopped charging.

Goal reached, but I wonder if it is even possible to use those two at the same time without second dynamo at
rear wheel? Bulb "eats" 2,4 watts, so no much left to zaurus. Perhaps then, if I change to led lamp?
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