Charge Pandora With Bike Dynamo?


zapman

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Hi!

This is a question that's addressed at all electronics pros out there:

Is there a chance I can charge Pandora's battery while I ride my bike via the dynamo? I want to travel around and use my Pandora (as soon as I get it ;) ) in combination with a (Bluetooth? USB-Stick?)-GPS receiver and openstreetmap-based software.

On my bike, I have a rather modern Shimano DH-3N72 dynamo that delivers 6V/ 3W. As the Pandora can be charged via USB, and USB provides 5V I thought there must be a way to charge its battery while biking ;)

So there are several questions actually:

  1. Do you think it could work? If the answer is YES:
  2. How do I limit my dynamos output to 5V instead of 6V (or maybe 6V would be ok, too)?
  3. Would it harm the battery if the voltage fluctuates between 3-5V? (When I go below maybe 15km/h the dynamo won't reach its maximum voltage)
  4. Is 3W enough to power the pandora (no wifi, lowest screen bightness, no BT etc) or maybe I can only charge it with 3W when it's turned off?
  5. How much more power drain can be expected when activating bluetooth (wireless GPS instead of USB-GPS)?
  6. Do you see any other problems that may arise with my idea?

Of course I would install a switch that the dynamo powers the lights OR the Pandora..

So, what do you say?

Thx for your feedback!
 
zapman said:
Is 3W enough to power the pandora (no wifi, lowest screen bightness, no BT etc) or maybe I can only charge it with 3W when it's turned off?
Can't answer the voltage question, but under standard use the Pandora should only use up to 2 watts (based on 4200mah battery and proven 10 hour usage), and peak to 3 watts with everything running full power (not including plugging anything into the USB, which is an automatic 2.5 watt draw). If you can get a stable 3W supply, that should be more than enough to keep it charged.
 
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I think most bike dynamos put out AC (my cheap 6 V / 3 W did), so you'd have to rectify it, which would probably drop the voltage below 5 V DC because of RMS or some electrical phenomenon.

If you can find a dynamo that has a USB output, that would probably work, but I think designing your own will be complicated at least, and since the USB standard supports something like 2.5 watts of power, it will be loading your dynamo pretty heavily if the Pandora's turned on.

Worth a shot. Let's see if anyone who knows more about EE can help you...
 
it'd be cool to get some sort of outdoors charger that could be sold as an acsessory. Like one of those solar power phone chargers or wind up torches. I have a torch that you charge by shaking it up and down which moves this bit of metal inside through a wire coil. I call it my wank torch.
 
or, how about a device that holds aa batteries and charges the pandy from that? Originally it was gonna run on aa batiries and that was cool cos you could buy them anywhere and use your pandy but now you cant so this would be usefll for those travelling.

Or a little steam engine with a dynamo so if you were lost in the woods you could get wood to power up the engine and charge ur pandy!!
 
Turnip said:
it'd be cool to get some sort of outdoors charger that could be sold as an accessory. Like one of those solar power phone chargers or wind up torches.
We've had a number of discussions about solar chargers here. The conclusion we always come to :
* Cheap Solar panels will not work at all.
* Expensive ones probably will, but very slowly. (Perhaps a 2/3 charge with a full day of direct sunlight.)
* You could buy a LOT of AA batteries for the price of a usable solar panel.
 
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grasshop.JPG


just needs a dynamo


anyone know how many aa bateries you'd need to supply a pandora with enogh power to run without its main battery? I had one of the early sony minidisk players and it came with a black plastic thing that you screwed to it and held 2 aa's which you could use to run it. Twas usefll.
 

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Turnip said:
anyone know how many aa bateries you'd need to supply a pandora with enogh power to run without its main battery?
Two or four can be made to work :)
The two battery design uses a boost circuit to bring the 3 volts up to 5, while the four battery design attaches the 6 volt supply directly to USB which shouldn't cause a problem, but I'd be careful with it.
It may actually be worthwhile to combine the two: use the two battery design wired in series with the boost circuit, but wire the extra batteries in parallel to get twice as much juice.
 
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Thx for your thoughts!

As I don't want to use any external batteries, especially that link (and the comments in the 'how-to') is very helpful:

darfgarf said:
just thought this might be relevant to your interests:
http://www.instructables.com/id/How-to-Charge-Any-USB-Device-by-Riding-Your-Bike/

Now I'll have to learn some basic electronics I guess..
 
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