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Question about Dynamo charger and recharging batteries.

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Discussion in 'Power Electronics' started by noneya456, Mar 3, 2011.

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  1. Mar 3, 2011 #1
    noneya456

    noneya456

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    Mar 3, 2011
    First, I have a couple of these little AA flashlights from Hong Kong
    http://cgi.ebay.com/3-Watt-1AA-torc...2442578?pt=US_Flashlights&hash=item33637c9ad2
    They are pretty bright for their size & price- and so far seem to be reliable.

    I want to use this dynamo charger/radio to charge a set of AA batteries that I can use in the mini flashlights I have incase of emergencies.
    http://market.solarrific.com/product_p/01108.htm
    The specifications say "Charging external products: Voltage Output: 5.6 V Maximum output power: _ 2.5W Mobile phone talking time after 3 minutes cranking: 2-8 Minutes"
    The device uses a round tip dc cable and comes with a normal size and mini-usb adapter. I will be using the normal USB adapter.




    My question is about the compatibility of the Dynamo with the following products...

    This usb charger charges 2 AA batteres in the '5V usb range' (in description) but seems to have no overcharging protection. I'm almost positive this will be compatible with the Dynamo Charger and it's 5.6v output
    http://www.amazon.com/Targus-Usb-Aaa-Battery-Charger/dp/B0025X1ASG

    I like this one more though (with overcharging protection) but the descriptions mentions nothing about 5v. Would there be any issues with using the 5.6v dynamo charger with this item?
    http://www.amazon.com/Kikkerland-US012-Battery-Charger-Batteries/dp/B001M5P5NY

    Then there is this charger which has the positive side of partially eliminating self discharge. LSD cells they are calling them.
    http://www.amazon.com/Sanyo-Eneloop...ZYXO/ref=sr_1_2?ie=UTF8&qid=1299026974&sr=8-2


    Is it realistic that 20 consecutive minutes of cranking from the specifications of the Dynamo Charger that I could atleast get an hour of charge in my 2 batteries for my mini flashlights? Or maybe even 1minute of power for 1 min of cranking?


    They also make these single usb batteries but I don't think they could handle taking 5.6v themselves when an real AA battery is between 1.4-1.6v. Or would it recharge faster?
    http://www.amazon.com/Moixa-MXAA02-USBCell-Rechargeable-Batteries/dp/B001RPZQ5G


    I'd really appreciate any educated suggestions!
     
  2. Mar 3, 2011 #2
    (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Before I wade through your links, I guess I've got to ask: "What's wrong with any of the plethora of hand cranked torches that you can buy?"
     
  3. Mar 3, 2011 #3
    (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    OK, I've waded through your links and I think you're barking up the wrong tree with respect to the battery charging issue.

    A small hand cranked torch I have contains 3 small NiMH cells (about N size I think) which are charged by the hand cranked generator. There is no fancy circuity involved at all, just a diode.

    Practically speaking, nobody is going to crank it for long enough to get anywhere hear a full charge anyway, so the risk if overcharging is incredibly remote.

    That single cell torch will employ a boost regulator to get approx 3.5 volts from a single cell. Using three cells will give you sufficient voltage without the need for a boost regulator.

    I would advise having some form of low voltage cutout because I killed the batteries in one of my hand cranked torches by accidentally leaving it turned on.

    I'd actually consider using a single lithium cell. The forward voltage drop of the LED would ensure that you can't easily over discharge it, and being a single cell, you don't have to worry about reverse charging a "weak" cell. (in fact I'll consider this if any of my current torches die again).
     
  4. Mar 3, 2011 #4
    noneya456

    noneya456

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    Mar 3, 2011
    There is absolutely nothing wrong with any of the dynamo lights on the market.

    I guess a better way to phrase what I was more interested in was...
    How can I charge a single, or two, AA batteries using the dynamo charger I specified?
    I already own the dynamo (great little product, charges all my products except some smart phones) and I'd really like a way to use it to pump some juice into a AA or AAA battery. I am aware I probably won't ever fully charge it with the dynamo but I'm sure at 5.6v output by the dynamo that I can fill a AA battery somewhat.
     
  5. Mar 3, 2011 #5
    (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Ah, now I understand.

    I would tend to suggest that you simply place 2 or 3 batteries in series and connect the generator's output (via a bridge rectifier) to the batteries.

    You probably won't be able to overcharge them.

    You may be able to charge a single battery at a time too. I'd give it a go and connect a multimeter in series with the batteries to see what charge current you're getting.

    Oh, and for those "smart phones"... If you're talking about an iPhone, then you can get USB adapters that will fool the phone that it's connected to an apple charger. It's basically a couple of resistors connected to the data lines.
     
  6. Mar 3, 2011 #6
    noneya456

    noneya456

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    Mar 3, 2011
    Thank you very much for your help!
    I'm not sure what a bridge rectifier is. A quick look up showed a 4 prong AC device. That can't be right?

    I'd definately be the most interested in charging a single AA battery
    The dynamo specifications say it outputs 5.6 volts _ 2.5W through the dc round tip. There are also a usb and mini usb adapter that fit on the round tip dc. I was told that typically usb adapters will limit dynamo charging to 5.6V at 500mah

    Wouldn't charging a single AA with 5.6v be way too much?
    If not wouldn't one of these work with the usb adapter?
    http://www.amazon.com/Moixa-MXAA02-USBCell-Rechargeable-Batteries/dp/B001RPZQ5G

    Also, thanks for the info on the smart phone adapters!!!
     
  7. Mar 3, 2011 #7
    (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Jan 21, 2010
    Something is required to ensure that the battery doesn't try to drive the generator. This may already exist in the generator.

    If you connect it to a battery and see no current flowing, then you're OK. Otherwise you'll need a diode (it looks like the output is already rectified, so a bridge rectifier would be overkill)

    The voltage will fall from 5.6V under load. It should not be any problem to charge the battery with a higher open circuit voltage.
     
  8. Mar 4, 2011 #8
    noneya456

    noneya456

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    Mar 3, 2011
    Right, I understand. I attempted to hook it up to a single battery in a series with my voltmeter but the pieces are just too small to work with. I just can't seem to rig it up as I don't have the necessary tools especially without stripping some of the wire work of the adapters.

    However, wouldn't it be safe to assume the 2 AA USB battery chargers I listed have something in place to make sure the power doesn't output from the usb- it only travels inward?
    And what about the single USB batteries I listed at the end of my post? They won't leak or explode will they? haha
     
  9. Mar 7, 2011 #9
    noneya456

    noneya456

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    Mar 3, 2011
    And what about the single USB batteries I listed at the end of my post? They won't leak or explode charging them at 5.6v at 500mah will they? haha
     
  10. Mar 7, 2011 #10
    (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Jan 21, 2010
    No, 5V is the correct charging voltage for them. 5.6V may be acceptable.
     
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