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simplest portable battery charger

Discussion in 'Power Electronics' started by PsiCo, Jan 17, 2013.

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  1. PsiCo

    PsiCo

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    Jan 17, 2013
    Hi all

    I need help with a concept i have been working on Please - my understanding of electronics is very basic (non exsistant)

    I want to make a simple Solar 1.5 V AAA battery charger. Emphasis is on size + weight.
    just 1 single AAA li-ion rechargable battery charged by (i am thinking ....) 2 of those little solar powered calculator solar strips (ave 3.6Vdc @ 1.5 Watts Max)
    in my mind the unit would be tiny-like a Tic-tac Container(60x35x15mm-fits 3x AAA batt) - or even smaller, to just charge a single AAA battery - it would come in very handy when camping

    theres always a "flattest" battery in my bunch - with this i could solve the problem by just leaving it on a rock in th sun at my camp ,while I enjoy my day. charger working quietly...

    When i get back to camp - my flat battery is fully charged.YAY!!

    A standard AAA battery charges @ 2.8Vdc with 120 - 150 mA - says so on the back of my normal Energizer Mains powered AA / AAA Charger

    In a perfect world I would love if it could also charge an AA battery ,but at 2.8Vdc with 260-300mA - i dont think 2 solar calc strips will be enough - again from the back of my Energizer mains Charger - its max power use is 8 Watt - with 4 AA batteries in - im plan on using 1 x AAA

    I live in South Africa - Cape Town. Here we have almost cloudless days for about 9 months of the year - ive found info that states :960 watts per squre meter is what the sun puts out on a sunny day - a calculator solar strip(12% efficiency) is about 1 square inch = 1.58 Watts - WE GET FULL SUN HERE ....

    A friend suggested just wiring the 2 solar strips in parallel ,connecting the battery in parrallel with these + a 5K / 10 K resistor to limit current (in series on the Positive....right??) this seems viable, but very "bushmechanic" like to me
    Should there maybe be a 2.8V diode (zener?) in series with the resistor - to limit the voltage as well?

    would this work - or is the resistor size wrong? to little power from 2 strips?
    Also - what sort of power (heat) would the resistor + diode have to deal with?

    Small + cheap + hopefully very easy to make - a usefull addition to any campers gear / "bug out" bag
    adding a third solar strip is viable - if needed - just makes the unit a bit bigger possibly - not preffered...

    Hopes this gives some people ideas..
    thanx in advance
     
    Last edited: Jan 17, 2013
  2. BobK

    BobK

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    Jan 5, 2010
  3. PsiCo

    PsiCo

    2
    0
    Jan 17, 2013
    sorry then - NIMh...geezz
    does that mean it needs some sort of controller chip... :(
    so much for simple to build...
    would love a circuit design if at all possible.
     
    Last edited: Jan 17, 2013
  4. BobK

    BobK

    7,682
    1,686
    Jan 5, 2010
    You can trickle charge them at 0.05C, but that will take about 24 hours to charge. Otherswise you really need a smart charger.

    (0.05C means 0.05 x the capacity in maH, so if capacity is 800maH, charge rate will be 40ma)

    Bob

    p.s. the solar cells from a calculator will probably not produce anywhere near 40ma.
     
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