Solar Cell with Joule Thief

Discussion in 'General Electronics Chat' started by ouzcoskun, Jun 12, 2019.

  1. ouzcoskun

    Thread Starter New Member

    May 12, 2016
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    I have used a small joule thief with old solar cell. Its current increased from 0.15 mA to more than 20 mA. But I can only add them in parallel, and the voltage and the current increases. Do you have an idea to add them in series ? SOlar Cell&Joule Thief.jpg SOlar Cell&Joule Thief1.jpg SOlar Cell&Joule Thief2.jpg SOlar Cell&Joule Thief3.jpg
     
  2. BobTPH

    Senior Member

    Jun 5, 2013
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    What are the specs of the solar cell? What are you trying to power (current and voltage?)

    But most of all, what are you trying to do?

    Bob
     
  3. ouzcoskun

    Thread Starter New Member

    May 12, 2016
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    Thank you very much for your interest.
    I just want to charge 2 x AA or 2 x AAA NiMH batteries.
     
    Last edited: Jun 12, 2019
  4. BobTPH

    Senior Member

    Jun 5, 2013
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    And what is the output of the solar cell?

    Bob
     
  5. mvas

    Active Member

    Jun 19, 2017
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    Research "MPPT" = Max Power Point Tracking
    MPPT is a circuit that extracts Maximum Watts from the Solar Cells.
    Watts = Volts x Amps
    You need to maximize Watts, not just volts individually, and not just amps individually.

    The Joule Thieve may, or may not, be operating the Solar Cells at Max Power Point.
    There are many combinations of Volts and Amps , where the Watts is below Max Power.
     
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  6. MrSoftware

    Senior Member

    Oct 29, 2013
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    This is an example MPPT device. It comes setup for LiPo, check the datasheet for the charge controller chip, maybe it can be configured for NiMH?

    https://www.kr4.us/sparkfun-sunny-buddy-mppt-solar-charger.html

    Side note; if you have the option of switching to lithium batteries, you may find greater efficiency (less power lost to heat during charging, lower self discharge rate).
     
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  7. ouzcoskun

    Thread Starter New Member

    May 12, 2016
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    A solar Cell is 1,5 V with 16.50 mA
    With a joule thief 2.3 V with 24.18 mA
    When added in parallel 3.88 V with 26,24 mA SOlar Cell&Joule ThiefM1.jpg SOlar Cell&Joule ThiefM1.jpg SOlar Cell&Joule ThiefM2.jpg SOlar Cell&Joule ThiefM3.jpg
     
  8. ouzcoskun

    Thread Starter New Member

    May 12, 2016
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    Thank you.
     
  9. ouzcoskun

    Thread Starter New Member

    May 12, 2016
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    Thank you. I try to design my own charger.
     
  10. BobTPH

    Senior Member

    Jun 5, 2013
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    No it is not. That would violate the laws of physics.

    Bob
     
  11. ouzcoskun

    Thread Starter New Member

    May 12, 2016
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    Why not ? I just send you the pictures.
    Why would that violate the laws ?
     
  12. BobTPH

    Senior Member

    Jun 5, 2013
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    Because no circuit can put out more power than it takes in.

    1.5V at 16.5 mA = 24.75 mW

    2.3V at 23.16 mA = 53.3 mW

    Bob
     
  13. ouzcoskun

    Thread Starter New Member

    May 12, 2016
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    Ok. I see. Maybe it is increasing the efficiency of the solar cell. You know a joule thief is working like a buck booster.
    So do you have an idea about adding the cells in series ?
     
  14. BobTPH

    Senior Member

    Jun 5, 2013
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    I am not entirely sure what you are asking. Are you trying to charge multiple cells in series, or do you have multiple solar cells you want to place in series.

    Your solar cell will take 133 hours to charge 1 AA 2000 mAh. Charging two would take twice that.

    Bob
     
  15. Bernard

    Expert

    Aug 7, 2008
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    The pictures are nice but meaningless unless we know how everything is connected. Assuming 3.88 V is from 2 cells in series OC, open circuit, then under load V might be about 2.9 V , ready to charge 2 batteries in series.
    Disconnect charging when battery V = 3 V, about 2 weeks later ? Might be best to add a blocking diode between solar & batteries if leaving connections over night.
     
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  16. Audioguru

    Expert

    Dec 20, 2007
    11,247
    1,342
    The multimeter is designed to show smooth DC, not DC pulses from the Joule Thief circuit.
     
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  17. Bernard

    Expert

    Aug 7, 2008
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    My 2 " X 2 " solar cell OC = 3V & SC = 28 mA., at 33 deg. N.
     
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  18. ouzcoskun

    Thread Starter New Member

    May 12, 2016
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    Yes. Multiple solar cells with a joule thief on each, and I want to add them in series.
     
  19. ouzcoskun

    Thread Starter New Member

    May 12, 2016
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    Thank you. I have added also the circuit diagram. As below. SOlar Cell&Joule Thief4.png
     
  20. BobTPH

    Senior Member

    Jun 5, 2013
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    Well, that is definitely not the way to do it.

    Connect the - of the top one to the junction of the diode and capacitor in the bottom one.

    Connect the load from the - of the bottom one to the junction of the diode and capacitor in the top one.

    Like this:
    upload_2019-6-13_16-40-59.png

    Bob
     
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