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Checking Solar Cell Amperage Output

Discussion in 'General Electronics Discussion' started by Dustin Smith, Dec 26, 2012.

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  1. Dustin Smith

    Dustin Smith

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    Jun 27, 2012
    I have some very small solar cells rated at 0.5V 250mA.

    This is what I did.
    I connected 6 cells in series.
    I hooked that up to a crapped out 3V motor, one that is rusted and won't turn.
    I connected my amp gauge in the circuit on the positive side of the motor.
    I only read around 120mA in full sun.

    I hooked it up to a good motor, but because it's good it only drew like 58mA.

    Can I skip the motor and just use my fluke multimeter directly with the solar cells? How can I check their maximum current output properly? I want to verify that they can do what they say to help me plan some projects.
     
  2. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Jan 21, 2010
    Well, you can just connect your multimeter directly across the output and measure the voltage and then the current.

    What you have then is the open circuit voltage (zero power) and short circuit current (again, zero power)

    If you graph these along with some points in between (I'd be aiming at loads drawing between 50% and 80% of the short circuit current you can get a graph of voltage against current.

    With a little math you can draw a more interesting graph of power against current.

    Remember that you need to do this with constant illumination, and that the graph will only be accurate for that level of illumination.

    Often cells are often rated by both open circuit voltage (say 0.55V) and short circuit current (say 1A). These are under ideal lighting conditions -- i.e. never achievable outside the lab -- and are not achieved at the same time.
     
  3. Dustin Smith

    Dustin Smith

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    Jun 27, 2012
    Steve... So, for the open circuit current, are you saying that when I hook up a load, the voltage output of the cell will drop?

    So, let's say I'm getting 240mA of current under a consistent lighting at 0.56V. So I plot that down. Then I choose a load rated at 120mA (50% of the short circuit of the solar cell) and then measure the draw of the current and the voltage across the load (or coming out of the solar cell?) and plot that down? And then repeat with 80%, then I can see the results of voltage use against current use. Sorry if I'm getting it wrong, I'm not so good with words, I'm more of a visual learner. One of the reasons I'm interested in graphing.
     
  4. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Jan 21, 2010
    open circuit voltage -- there can be no open circuit current!

    If 240mA is the short circuit current, that will be at 0 volts.

    You can't choose a load rated at 120mA. You need to choose a load that will draw 120mA. The easiest way is to attach a variety of loads and measure the voltage across them and the current through them so that you get several data points.

    The most important data points are likely to be those between 50% and 80% of the short circuit current.
     
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