USB LiIon/LiPoly charger

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jim
 
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USB LiIon/LiPoly charger

Post by jim »

i want to use the USB LiIon/LiPoly charger with a bicycle hub dynamo, 6V 3W.

i expect to build a rectifier starting with the most basic design and improving my understanding.

is a single diode, (half-wave rectification), enough to protect the USB LiIon/LiPoly charger and battery?

Half-wave rectification seems like the most basic design but a diode bridge or bridge rectifier also looks simple on paper.

can i use the USB LiIon/LiPoly charger as long as i rectify the hub dynamo charge?

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dbc
 
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Re: USB LiIon/LiPoly charger

Post by dbc »

Well, check the data sheet to see what the part expects for input voltage and waveform, if they spec anything. Off the top of my head, I would suspect that the charge controller chip could deal with some pretty ratty input, but it probably cuts out below some threshold voltage, and having the input rapidly transitioning across that threshold is unlikely to yield a happy chip. The other thing I'd watch out for is over voltage -- since you are planning to run it off a bicycle dynamo, when you get some significant speed up the voltage might get pretty high.

I'd be thinking full wave bridge, because it's a single part and a diode is a single part and the name of the game is really minimizing parts count, not schematic complexity. So start with full-wave rectified DC and hang a big beefy capacitor across it to keep the input to your charge controller from pulsating below its "happy threshold". If you need to protect it from over-voltage, hang a zener across the cap as a crowbar.

-dave

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jim
 
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Re: USB LiIon/LiPoly charger

Post by jim »

thank you dave,

i bought 3 different bridge rectifiers at radio shack and tested one by spinning the wheel by hand as fast as i could topping 8 volts.
i could not figure out from the MCP73833 datasheet if adding the capacitor would be required.

so my question to Adafruit is will 8 volts damage the USB LiIon/LiPoly charger?

if so, is the USB/DC Lithium Polymer battery charger 5-12V a better idea?

thanks

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dbc
 
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Re: USB LiIon/LiPoly charger

Post by dbc »

MCP73833 data sheet page 3:
"Absolute Max Vdd 7.0V" -- it is guaranteed not to smoke *below* this, no guarantees above.
"Supply Vdd" min 3.75, max 6.0V -- this is the nominal operating range.
Under-voltage lock-out in the 3.5V neighborhood.

Unless you can keep the supply ripple dips above 3.6V, and the max voltage below 7.0V, I think that chip is going to be unhappy.

-dave

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jim
 
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Re: USB LiIon/LiPoly charger

Post by jim »

thanks again dave, (embarrassed i missed that)

i bought a two 1000 uF, one 470uF, and one 220uF electrolytic capacitors today.
Now plugging in different resistors to limit the voltage below 7 volts, (without an LED in the circuit yet).

it was fun to see the capacitors hold their charge with my cheapo multimeter

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dbc
 
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Re: USB LiIon/LiPoly charger

Post by dbc »

Using a resistor as a voltage divider works, but wastes some of your available voltage headroom. Take a look at using a zener as a crowbar. Like maybe a 6V zener in series with a current limiting resistor of 10 ohm or so...

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jim
 
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Re: USB LiIon/LiPoly charger

Post by jim »

thanks again,
now i have a 2200 uF capacitor, a 5.1 V zener diode, and a 10 ohm resistor.
would a 6 to 7 V zener diode would be worth shopping for?

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Re: USB LiIon/LiPoly charger

Post by adafruit »

stick with the 5.1v they can drift high

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jim
 
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Re: USB LiIon/LiPoly charger

Post by jim »

thanks all for the quality help
http://www.flickr.com/photos/zyzak/5463798629/

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Re: USB LiIon/LiPoly charger

Post by adafruit »

do you have any photos of the actual project wiring?

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jim
 
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Re: USB LiIon/LiPoly charger

Post by jim »

blurry photo before glued shut. Should use silicone caulk instead of hot glue.

http://www.flickr.com/photos/zyzak/5471543588/

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