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A kinetic phone charger project

kostas

Oct 17, 2012
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Hello,

in my school we are setting up an enterprize, which will produce kinetic phone chargers and sell them.

The idea is that in a wooden box we'd fix a bearing with a magnet on it and put wound up magnet wire around it, the two terminals then would go to a 3.7V battery, then through a LED, a 5v voltage regulator, and into a usb cable which could charge phones.

Could you please explain which wire of the solenoid would be positive and which negative, how should it all be set up, im probably missing a lot of resistors or capacitors.

Id be greatful if you kept it simple, thank you. :)
 

BobK

Jan 5, 2010
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A magnet going back and forth thorugh a coil will produce AC. You would need to rectify it. I also hope your customers are ready to shake vigorously for a couple of hours to charge their cell phones!

Bob
 

kostas

Oct 17, 2012
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A magnet going back and forth thorugh a coil will produce AC. You would need to rectify it. I also hope your customers are ready to shake vigorously for a couple of hours to charge their cell phones!

Bob

Ok i have bought some rectifiers, what will they do to the AC and where should i solder it to,
thanks
Kostas
 

kostas

Oct 17, 2012
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Also would the diode bridge of 2Amps and 1000V be sufficient?
Kostas
 

BobK

Jan 5, 2010
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Ohh yes, i remember these, it makes much more sense now, so i guess these will do http://www.ebay.com/itm/2A-JX2W10-B...068?pt=LH_DefaultDomain_0&hash=item53ef5493dc
so to take that a step further, if the battery is of 3.7V would you need to have some component inbetween the diode bridge and the battery? voltage regulator of some kind?
thanks
Kostas
Yes, you would need a charging circuit.
Also would the diode bridge of 2Amps and 1000V be sufficient?
Kostas
I doubt that 2 Amps or 1000V would be exceeded. If you have a multimeter, try putting a smoothing capacitor after the bridge and measure the voltage you get.

Bob
 

BobK

Jan 5, 2010
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By the way, I am probably being a little too subtle, but I don't think your project is realistic. However, I would encourage you to experiment with it and see what you learn.

Bob
 

kostas

Oct 17, 2012
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Its ok, i do want to acomplish it either way, it counts if you try, and it is interesting. How many uF should the smoothing capacitor be?
Kostas
 

kostas

Oct 17, 2012
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So, as i understand the voltage must be 3.7 and not more or less to charge the battery right?
would a voltage regulator do?
 

BobK

Jan 5, 2010
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No, Lithium Ion batteries are charged first with constant current until it drops off then a constant voltage of about 4.2V. It is not a simple circuit. However... You generator is not likely to produce the current needed to charge in constant current mode, but it probably could be used to "trickle charge" the battery, which is a lot simpler, but it will take many hours of shaking.

Bob
 

CocaCola

Apr 7, 2012
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If you want to charge modern phones through a USB cable you will need a regulated 5V for the USB at a minimum of 1A, 2A preferable for modern smart phones that will seek the higher current if available when charging, or else they will drop down to a real slow charge that will take extra hours...

If you want to charge the 3.7V lithium batteries directly you will need to implement a lithium smart charger circuit, there are chips specially designed to do this...

As hinted this is a fun experiment to educate yourself with but not real practical or realistic in the end...
 
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