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PostPosted: Wed Oct 17, 2012 8:42 pm 
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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.

I found out that one should use a diode bridge and a smoothing capacity, but im lost on what to put inbetween the capacitor and the battery to charge it up.

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


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PostPosted: Wed Oct 17, 2012 9:04 pm 
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You can't get 5V out from a 3.7V battery unless you use some form of switched mode power conversion technique - nor will a 5V regulator work with less than 7V going into it.

The output from the 'generator' depends on many factors, turns-ratio, magnetic flux density, number of poles, rotational speed, air gap ad-infinitum.

The solenoid (generator) output will be 'alternating' but the bridge rectifier sorts the polarity to the capacitor.

You need to do a bit more research or provide more technical information if you want help from us.

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PostPosted: Wed Oct 17, 2012 9:09 pm 
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anything you sell will probably need a ce mark and comply with various regulations :dunno:

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PostPosted: Wed Oct 17, 2012 10:07 pm 
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How can I put this in simple terms? :scratch:













:cb Got it. Its a complete waste of time.

I shall expand on that:

You are attempting to make a phone charger that works by a magnet moving in / near a coil. So why does it need a battery?
Also as Kellys_Eye said, you would need to do some calculations as to the size of coil, the size of magnet to get enough voltage to charge a phone. By making a coil of wire and running a magnet through it will prove the principal works, but it wont give you any figures from the start, it will if you go for trial and error. Also you will find out about the coil, which wire is positive, and which wire is negative. (Try it and see, now figure why you get the answer you do)

You may want to try this, borrow some ones push bike that has a dynamo and lights fitted, turn the back wheel, does the light come on? (try it and see) Will this charge a phone?

A well known DIY store used to sell a torch, just like you are planning, they don't anymore, figure out why.

Let me ask you this: Assume you made it, and it works, how will it move? That means you would (well the person that has it) has to stand there shaking it. Human nature will say take the easy option, plug in a phone charger.

I would suggest, you do more research, not into what you can make but what people will buy.
In life, some people will set up a shop selling what THEY want. They soon close down due to lack of business, the reason is because they sell what THEY want, not what the people near the shop need.

Print this out and take it into class, and say some one said.....................

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