Naked Science Forum
Non Life Sciences => Technology => Topic started by: AllenG on 04/02/2010 20:19:00
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I know very little about the black art of electronics.
Could I use the hub dynamo on my bicycle to trickle charge a cell phone battery?
Specifically what I want to do is wire this (http://www.griffintechnology.com/products/powerjolt-reserve) up to dynamo hub with an on/off switch in between.
I know nothing about the charge rates of Li batteries, just that this (http://www.griffintechnology.com/products/powerjolt-reserve) is designed for a 12 volt car and that I have a 6 volt supply. Is it safe to assume that it will work but take twice as long to charge?
With many thanks,
--Allen
Oh, and this (http://www.sheldonbrown.com/harris/lighting/shimano.html) is the hub I have laced to my front wheel.
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As long as the charger thingy is compatible with your phone, I don't see how you could damage anything if you give it a shot (as long as you connect the polarity correctly).
However, I'm not sure it will work. The charger thingy seems to want 12 volts, whereas the dynamo only wants to put out 6 volts, but it might actually put out a higher voltage to a reduced load, so you might get away with it.
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I wanted to hook the spare battery to the charger so as not to fry the phone (the battery is cheeper & and doesn't have my address book to loose).
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I think the max charge the dynamo will supply is 6 volts. I may be mistaken but I think they are throttled in some fashion so they won't burn out lighting systems during a steep decent (presumably the faster the wheel turns the more juice it produces).
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Yes. It could be voltage limited, in which case you may be out of luck.
What's the voltage of the battery? If it's less than 6 volts we might be able to rig up a trickle charge circuit without the charger thingy. I'm a bit hazy (er, clueless) about charging lithium batteries, but I would think, as long as you keep the charge rate low enough, nothing too bad is likely to happen.
BTW - if the battery voltage is more than 6 volts, it's still not impossible, but it's going to get fairly complicated.
You could also replace the windings in the dynamo to jack up the voltage it puts out, but that might invalidate the warranty (not to mention that it would be a serious PITA to actually do)
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You will need to rectify and regulate the voltage output from a dynamo to charge a battery.
IIRC the output from a bicycle dynamo is AC, (needs to be DC to charge a battery), and the dynamo voltage varies wildly depending on the speed of the rotor.
[If your bke lights are LEDs rather than incandescent bulbs there will already be rectification and voltage regulation circuitry somwhere in the circuit].
http://pilom.com/BicycleElectronics/DynamoCircuits.htm
http://www.instructables.com/id/USBIphoneIpod-Dynamo-Charger/
How to make a bike charger for your iPod! ... http://geektechnique.org/projectlab/511
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Ah! So it's really an alternator then. Wonder why they call call it a dynamo?
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You will need to rectify and regulate the voltage output from a dynamo to charge a battery.
IIRC the output from a bicycle dynamo is AC, (needs to be DC to charge a battery), and the dynamo voltage varies wildly depending on the speed of the rotor.
[If your bke lights are LEDs rather than incandescent bulbs there will already be rectification and voltage regulation circuitry somwhere in the circuit].
http://pilom.com/BicycleElectronics/DynamoCircuits.htm
http://www.instructables.com/id/USBIphoneIpod-Dynamo-Charger/
How to make a bike charger for your iPod! ... http://geektechnique.org/projectlab/511
You're correct, dynamo hubs are AC. My rear light is LED but I think the rectifier is in the tail light unit and not in the hub. The lights stay on when I'm stopped. The LED's are running off of a capacitor.
Doing some reading Sheldon Brown (http://sheldonbrown.com/dynohubs.html#rectifier) has beaten me to the punch. So it is absolutely doable.
According to this site (http://www.ipodbatteryfaq.com/ipodbatteryandpower.html) the iPhone battery is 3.7 volts.
What do I need to do to make sure I don't over charge the battery?
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What do I need to do to make sure I don't over charge the battery?
A voltage regulator: this three legged thing ...
[ Invalid Attachment ]
http://www.instructables.com/id/Convert-a-generic-dynamo-flashlight-into-an-AA-bat/step7/Put-the-7805-regulator/
The regulator gives out (say) a constant 5 volts even though it is connected to a supply which can vary between 6 and 12 volts. The output of the regulator can be adjusted (with a potentiometer) so the voltage matches that of the charged battery.
Warning: if you get this wrong you could burn out circuitry in the ipod.
I'd try a circuit which recharged three AA(A) NiCd batteries (http://en.wikipedia.org/wiki/AA_battery#Primary_chemistry_and_capacity) in series (~3.6V) from the dynamo as a proof of concept:
worst case scenario you destroy three batteries worth a few of bucks rather than fry your ipod.
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To prevent overcharge, you need to have some idea about the batteries maximum charging current. It may be much greater than the maximum current the dynamo can produce, but it might be a good idea to know. NiCad batteries can handle enormous charge (and discharge) currents, but I don't know much about Lithium cells. I'll poke around a bit.
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Thank you gentlemen.
I'm on a steep learning curve here and this is greatly appreciated.
I'm going to try to cobble this together now that I have the direction of where I'm going.
With the X1 I'm going to see if I can safely charge the battery I linked in the OP with my hub.
For the X2 I'll see if I can charge the iPhone directly.
Hub-->Rectifier-->Voltage Regulator-->Battery
If I were to add a fuse to that would one put it on the AC or DC side of the rectifier?
Time for me to read more about Lithium batteries.
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There are products on the market like wwww.pedalpower.com.au
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It will be a great thing to charge a phone battery with a bicycle and I will also try to do this.
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In mobile charger there is converter which convert ac to dc.Dynamo is a dc source.So I think it is impossible to use as a charging apparatus of mobile.
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I don't think it will work. Your mobile might damage if you do try it. You better charge your mobile in a proper way. But you can experiment if you want too.. There is nothing wrong trying it.