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Bicycle usb-charger help

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Gotte

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Hi, I'm new here, and must admit I know very little about electronics. But I figured you guys might be able to help me.
I'm trying to sort out a way of charging a HTC hero smart phone from a bicycle dynamo (bottle) using it's mini usb function.
There are some options out there, but most either too expensive or unavailable in UK.

I've found what could be a potential winner, though - the Nokia bike charger:

Nokia UK - Nokia Bicycle Charger Kit - Specifications

I can get an adaptor that goes from the Nokia's 2mm jack to a mini-usb (from Nokia), and from my basic understanding of voltages, etc, it should do the job (I understand that when charging anything from a PC's USB, it's around 5v and 500mA (?)
Seeing as I can charge my HTC phone from USB, and the Nokia bike charger outputs 5v at 450mA, I'm guessing it should work.

Here's the blurb from Nokia:

Power generation:
Compatible with bottle type bicycle dynamos with 6V/3W and 12V/3W output
5.0V/450mA/15km/h. Maximum current 70mA
Charging starts at ~6km/h and maximum output is achieved at 25km/h. Charging stops when the speed reaches 50km/h.
Charging time depends on cycling speed, for example a Nokia 1202 with a 860mAh battery can be charged with about 20 minutes of cycling at a speed of about 10km/h (for the Nokia 1202 this would mean approximately 57 mins talk time or 74h standby time)



The only thing that worries me, though, is:

5.0V/450mA/15km/h. Maximum current 70mA

I don't know quite what to make of that. It says 5v at 450mA, but then says maximum current 70mA.

Can anyone help me explain this? Is it a mistake (maybe it should be 700mA), or does it refer to something else?

Thanks for that

Phil
 
It appears they are saying 5.0V/ 450ma maximum and 70ma if you are only going 15kph. If it is linier, that means you have to pedal at 96kph to get the full 450ma. I suspect you might have to be going downhill so see those results. :)
 
OK.. That makes no sense to me either.

I think there must be some mis-communication between their marketing and engineering departments.
 
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Thanks for that. I've been doing a bit a digging, and the Hero battery is rated at 1350 mAh. I'm guessing that's from the wall charger and not USB charging.
The hero charges from USB, which I understand should be about 5v at 500mA.
Will the rating of the battery be affected by the lower mA of the charger (450), or do you think it will charge, just slower (as with USB charging)?
I don't want to buy it only to find it won't charge at all.

I ask this as I once tried charging it with a hand cranked emergency charger, which actually seemed to take charge out of the battery rather than put it in.

Thanks

All the best

Phil
 
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Gotte said:
I ask this as I once tried charging it with a hand cranked emergency charger, which actually seemed to take charge out of the battery rather than put it in.

Maybe you were cranking it the wrong way ;)
 
The battey's capacity is 1350mah - ie a full(ish) charge is achieved after putting in 1350mA for one hour. 675mA for 2 hours will also charge it.

Your wall charger is probably 1A charging current - a USB port is 500mA max. The phone should be able to cope with a bit less than that - ie it still should charge.

Although there's only one way to be sure!

Andrew
 
Thanks for that.

I'm tempted to get it, but the last thing I could do with finding out is if I'll be able to change dynamos later. At the moment, I want a bottle dynamo so I can swap it between bikes with different wheel size, but later, I might get a hub dynamo for one of my touring bikes. If I did that it's be handy if I could just remove the phone adaptor part and wire it up to the new dynamo.
Don't suppose if anyone knows whether hub dynamos are different to bottle dynamos?
 
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