solar AA charger Newbie need help

Discussion in 'The Projects Forum' started by Soon, Jan 26, 2010.

  1. Soon

    Thread Starter New Member

    Jan 25, 2010
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    Hi, i am using a 6V 200ma solar panel to charge 4 aa battery, is it possible? Can a zener diode and a led use to use as a indicator to show it is a fully charge? is there other diode than zener diode to prevent reverse flow? How to prevent overcharge?
     
  2. Bernard

    AAC Fanatic!

    Aug 7, 2008
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    What type of battery? Is 6V open circuit voltage, or under 100mA load? 6V might be a little low for 4 AA's, Ni-mh's.
     
  3. retched

    AAC Fanatic!

    Dec 5, 2009
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    also you lose about a volt through your diode. So the battery is only seeing about 5v. charging 3 AA's should be ok. What type of batteries?
     
  4. Soon

    Thread Starter New Member

    Jan 25, 2010
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  5. Bernard

    AAC Fanatic!

    Aug 7, 2008
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    A zenor diode is designed to " break down" at a specific voltage when reversed biased & hold that V over its operating current range; but it is not perfect, V increases slightly with increasing current . A plot of a 1N1766A [ 6.2V @ 1W]zenor shows the V climb. If a ZD of proper V were placed in parallel with the battery as v increased current would gradually transfer from battery to Z. A synthesized Z might work . A normal Z such as NTE 5117A, 5.6V @ 5w might work. A 1N1766A ,selected for 5.9V@ 100mA is under test now but clouds are moving in.
     
  6. Soon

    Thread Starter New Member

    Jan 25, 2010
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    [​IMG]
    Postive side of battery to led, negative side of battery to solar panel negative, how to know it is fully charged?
     
  7. Bernard

    AAC Fanatic!

    Aug 7, 2008
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    In my simple zenor diode[Zd]- charge limiting test, the Zd, cathode to batt. +, is in parallel with battery & solar panel. When battery V is low, all available current flows to batt., as V climbs more current switches to Zd; when target V is reached all current is suposer to go to Zd. A few figures available before clouds came.
    Battery mA---- Zd mA---- V
    82------------ 7--------- 5.90
    114---------- 14--------- 5.92
    105---------- 54--------- 6.07
    30----------- 15--------- 5.89 losing sun
    6.5 target V, 4 NiMH 2000 mA hr batteries
    Zd may work for low power system.
    LED in series with charging ckt wastes V . Solar panel used for test is 800mW 6V, 11V OC, 150 mA SC, peak power @ 7 V. 15X15 cm.
    To show " full charge" one way is to use a comparator, refference V source, V divider & current limited LED.
     
    Last edited: Jan 30, 2010
  8. Soon

    Thread Starter New Member

    Jan 25, 2010
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    i will remove the led. I think i can use comparator as there is no stable source. Sorry, I don't get you about the zd, so what rating should i use?
     
    Last edited: Jan 31, 2010
  9. Bernard

    AAC Fanatic!

    Aug 7, 2008
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    ' Carried test one more step with bench P supply. I Zd 105 mA, I battery 6 mA, battery 5.9V. A 1N4007 was added to allow better match to Zd, also acts as blocking diode. If implemented, Zd needs to be power rated to same as solar panel, colsest ' could find is 5W, NTE5119A, 5%, 6.2V, same for blocking diode 3A, 1N5400, or for lower drop NTE586, .52V @ 3A, shottky. A workable solution, but not verry good due mostly to componet tolerances. With your panel it will take two sunny days to charge 4 AA, NiMH batterys but we do not know what your load is. Also need more to charger to limit battery discharge, when to connect - disconnect load. Added an approximation of your panel I vs V, & power.
     
  10. Soon

    Thread Starter New Member

    Jan 25, 2010
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    Hi Bernard, i read from a site saying we can only charge not more than 10% of the battery capacity. Isn't your circuit is overcharging it?
     
  11. Audioguru

    New Member

    Dec 20, 2007
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    An old Ni-Cad battery cell can be over-charged for years at 10% of its mAh rating but a modern Ni-MH cell should have an intellegent charger turn off the charging when the cell is fully charged.
     
  12. Bernard

    AAC Fanatic!

    Aug 7, 2008
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    I believe that if you charged the battery over several days with no load , they might get a slight over charge, the big problem is getting enough charge. For 70% charge @ .1C [200mA ] takes about 14 hrs. Panel will struggle to deliver 200 mA for 3-4 hrs, & sunset will ahut it down. Better to be sure to remove load[ unknown] when battery discharges to 4.4V.
     
  13. Darren Holdstock

    Active Member

    Feb 10, 2009
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    Sorry to be the bearer of bad news, but NiMH batteries really don't like being trickle charged as the sole method of charging - you won't find a battery manufacturer who recommends this method. Some NiMH chargers employ a small trickle charge as the 3rd step after a high-current fast charge, followed by a somewhat lower current top-up charge, but this is merely to counter the self-discharge characteristics of NiMH cells, and then it is recommended that the trickle-charge be stopped after a day or two. Trickle-charging on its own will ruin the cells.

    If an NiMH battery needs to be on charge for long periods then the recommended method is to top up the charge with (relatively) high-current pulses as and when required.

    Another battery chemistry may be more suitable for a solar panel source, try looking into Li-ion or lead-acid. Again these will need a more complex charging regime than a simple trickle charge, but at least they're not as awkward as NiMH.
     
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