HelpA Solar Cell Charger Problem

Discussion in 'General Electronics Chat' started by Ray Hwang, Apr 15, 2014.

  1. Ray Hwang

    Thread Starter New Member

    Mar 30, 2014
    3
    0
    Recently I've got a solar cell.Given the proper sunlight ,the open-circuit voltage is 6.3V and the short-circuit current is 70mA.
    Now I wanna get a output voltage 5.1V.
    Use only basic circuit elements,diodes\transistors\capacitors\inductors\ICs,etc.No MCU and FPGA.
    No MPPT(Maximum Power Point Tracking) required.
    Could everybody give me some ideas?
    A freshman from East China Normal University.
    Lots of thanks!
     
  2. shteii01

    AAC Fanatic!

    Feb 19, 2010
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    497
    Stick 17 Ohm 5-10 Watt resistor in series, this will drop 1.2 volts, 6.3-1.2=5.1 volts.
     
  3. Ray Hwang

    Thread Starter New Member

    Mar 30, 2014
    3
    0
    The cell output is not constant,fluctuating between 0~6.3V .The target is that once the cell voltage is over a startup voltage,then the circuit works and stablizes the circuit output on 5.1V . The startup voltage should be as low as possible. I think the output end could be like this.

    [​IMG]

    But I don't know how to raise the low voltage to a higher one?
    Maybe I need a boost converter?
    And how to improve the efficiency?
     
  4. shteii01

    AAC Fanatic!

    Feb 19, 2010
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    That does not make sense. Solar cell is not a motor, it does not have startup. Sun is out, you get some voltage. No sun, no voltage.
     
  5. alfacliff

    Well-Known Member

    Dec 13, 2013
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    d1 is not needed, the solar cell is a diode already. you dont need the capacitor, and get a zenner to limit the voltage to what is safe for the battery.
     
  6. ErnieM

    AAC Fanatic!

    Apr 24, 2011
    7,386
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    My first question is what are you intending to use the output voltage for?

    What is the load?
     
  7. wayneh

    Expert

    Sep 9, 2010
    12,100
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    It is true that a blocking diode might be included in a larger panel, but it is rarely a part of a solar "cell".

    If there's no current source to cause reverse current into the solar cell, then D1 has no function except to smooth out a transient shadow on the solar cell, to power the load for a few seconds after the cell is no longer illuminated.
     
  8. Ray Hwang

    Thread Starter New Member

    Mar 30, 2014
    3
    0
    yeah sorry I forgot to mention that the load could be a Li ion or Li poly battery.I know it is not proper to connect the battery directly to the output,and an battery manage ic is required,but I think as the first step,to get a 5.1V could be more realistic
     
  9. Bernard

    AAC Fanatic!

    Aug 7, 2008
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    Depending on the battery, probably could connect panel thru a shottky diode to battery. Internal resistance of panel will drop V. At max power out V will be about 5 V. Disconnect at batt. V of 4.2V. After short test get a proper control chip. Home built Li [ except for LiFePO3 ] chargers make me nervous.
     
    Last edited: Apr 16, 2014
    Ray Hwang likes this.
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