can I charge a small battery with a micro solar panel?

Discussion in 'Power Electronics' started by humpataa, May 4, 2018.

  1. humpataa

    Thread Starter New Member

    May 4, 2018
    3
    0
    Hi guys,

    I am new to this board as well as to working with electronics. So please excuse if this is a stupid question and / or has been answered before. I have been searching here and via Google but I am still not sure.
    I do have a small vario (a small instrument that beeps when raised or lowered by checking the air pressure) that has a 750mAh battery and lasts around 10 hours in normal operation. It has a 5V USB slot to charge it.
    Since the instrument is - when used - at clear sunlight most of the time, I thought about adding a small solar panel to increase running time ...

    The battery is a LiPo 3,7V 750mAh, protected against over- and undervoltage.
    I have found a solar panel that would perfectly in size:
    https://www.aliexpress.com/item/10P...ar-Cells-Panel-For-DIY-Toy-3/32644315533.html

    Now the question is: will it work when I connect the wires of the panel directly to the battery?
    Or would that be not too good for the battery (I have read about LiPo being a little touchy)?
    How about connecting it to the USB port instead?

    Any help is greatly appreciated.
    Dieter
     
  2. ericgibbs

    Moderator

    Jan 29, 2010
    5,722
    1,066
    hi hump.
    Welcome to AAC,
    The datasheet on that link recommends a 5V panel for 3.7v battery.
    So it should be OK.

    E
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  3. ebp

    Well-Known Member

    Feb 8, 2018
    1,837
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    It would work, but ...

    The protection circuit usually should not be relied on to limit the final charging voltage. Typically the circuits are designed so they cut off charging at a voltage somewhat above the usual full-charge voltage so that they don't interfere with the normal charger fully charging the cell. For example, full charge is often considered to be 4.2 volts per cell. The protection circuit might not disconnect the charger until the voltage reached 4.35 volts. This is low enough to prevent disaster (fire, cell rupture), but too high to be good for the cell. Charging to such a high voltage will shorten the life of the cell significantly after only a few cycles.

    The panel only puts out 30 mA, so it would take something over 25 hours to charge your battery. You could connect some panels in parallel for higher current.

    I suspect you can find some ready-to-use low-cost charging circuit boards that you could put between the panel and the cell.
     
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  4. humpataa

    Thread Starter New Member

    May 4, 2018
    3
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    Thank you for the quick answers.
    And connecting the panel to the USB wouldn't help / work?
    I guess the USB port has some kind of protection ...
     
  5. ericgibbs

    Moderator

    Jan 29, 2010
    5,722
    1,066
    hi hump,
    I would not connect directly to the USB, unless you absolutely sure that you battery module has over voltage protection, that works.

    The solar panel I suspect would only give 5v to 6v, if used in bright sunlight, so that should be OK
    E
     
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  6. humpataa

    Thread Starter New Member

    May 4, 2018
    3
    0
  7. ebp

    Well-Known Member

    Feb 8, 2018
    1,837
    641
    That board uses the specific charger IC I was thinking of, but I couldn't recall the part number. The board also has protection circuitry, which you don't need since you are using a cell with built-in protection, but it shouldn't cause any problems. You can probably find boards with the same IC without protection circuitry, if you prefer.
     
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