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USB generator Answered

I am building a small crank-powered generator for a college electronics class that will power a USB port. I know a USB port supplies 5V DC, and that my generator will obviously produce AC current, but I'm not sure the best way to convert AC to DC, then how to step my voltage up to 5 volts. My generator uses 6 wire coils in a circular pattern. 12 neodymium magnet rotate over the coils. This doesn't seem like the most efficient design ever, but that part is a stock university kit, the wiring is up to me. I've only been able to test each coil at a time, and each one produces .5-.7 VAC. Do any electricians out there have some tips? When all is said and done, I'll definitely be posting an instructable on this.

Discussions

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jj.inc
jj.inc

9 years ago

 You could can change it to DC with this AC to DC

Hey, cool project. I suggest that you take 4 shottky diodes and make a rectifier bridge. Then you could use the circuit from the MintyBoost to step up the voltage.

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tech-king
tech-king

11 years ago

i think everyone forgot something here, because you guys are so used to dc. this is ac! you dont need mintyboost; you need an old fashioned CW voltage multiplier. it can not only multiply the voltage, it will rectify it and, if you use large values on the caps, filter it. install a 7805 in series with the output and voila.
patent pending

remember, cwvm parts need to be greater than 2Vin.

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tech-king
tech-king

Reply 11 years ago

another brilliant idea brought to you by tech-king

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guyfrom7up
guyfrom7up

Reply 11 years ago

trickery! But it'd be less (or the same) efficiency as a minty boost

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tech-king
tech-king

Reply 11 years ago

hows that? it would be more volts, less amps. also, you dont have the inefficiency of a rectifier, which then needs a cap to smoother the power (and shunt it to ground)

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guyfrom7up
guyfrom7up

Reply 11 years ago

well, you'd still need a cap with a 7805, plus I read somewhere that 7805s are only around 50% efficient, while stuff like a boosting circuits are usually areound 95% (depends on chip) efficient. With either one you need a smoothing capacitor

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tech-king
tech-king

Reply 11 years ago

no, you dont. in a cwvm, the input is ac, the output dc. if you use large value caps in the CWVM, the output has little or no ripple. and 7805s are decently efficient.

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guyfrom7up
guyfrom7up

Reply 11 years ago

smooth enough not to cause glitches in the device you're charging? maybe use a buck circuit if avalable

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tech-king
tech-king

Reply 11 years ago

if you use high value caps (not a problem, seeing as 2Vin is less than 20 volts) you can get almost no ripple.

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fortneja
fortneja

Reply 11 years ago

Thanks for the help. I took another look over the later lab sections, and it looks like we will eventually be doing this exact setup. I'm too scared to try this on anything important (cell phone charger, ipod, etc), so I think I will whip some USB throwies to prove it works.

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LinuxH4x0r
LinuxH4x0r

11 years ago

Are you using your own coils? any pictures?

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fortneja
fortneja

Reply 11 years ago

They are pre-packaged coils from Tinitron. Here's a pic:

IMG_0183.JPG
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LinuxH4x0r
LinuxH4x0r

Reply 11 years ago

Ok, those look good. How is it powered? Wind? Hand crank? I agree with tech-king's idea

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guyfrom7up
guyfrom7up

11 years ago

you would have to use a couple bridge rectifier (google it, the one you want is the one that consisstist of 4 diodes). Before soldering the coil together, do tests with a bread board or aligator clips. You want about 3 volts at normal speed, then you could use a minty boost circuit (google it)

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zachninme
zachninme

Reply 11 years ago

Great minds think alike :P Thats almost scary...

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zachninme
zachninme

11 years ago

To convert AC to DC, you'll need a rectifyer, which is essentally 4 diodes. You can make your own from 4 diodes, or buy a chip. Once you get that going, and wire up all the coils, check the voltage, you may not need to do step-up conversions. If you do, you should be in the neighborhood to use the MintyBoost's circuity.