Small solar panel cannot power little timer

Discussion in 'The Projects Forum' started by timdiy, Jul 1, 2011.

  1. timdiy

    Thread Starter New Member

    Jul 1, 2011
    3
    0
    hi I'm learning electronics circuits stuff and I 'm trying to wire a small solar panel to power a small timer or a small handheld fan and am having trouble.

    I disassembled the solar panel from a calculator. Both the timer and the fan are from a dollar store. I use multimeter to measure the solar panel and got roughly 2v under full light. The fan will run on two 1.5v AA batteries and the timer will run on one 1.5v AA battery.

    I wired the solar panel to the timer and nothing happens. For the fan I tried two solar panels but the fan doesn't run. I wired the two little calculator solar panels in series and it reads 3v. The two solar panel setup produces much more voltage than the battery and yet does not power the timer or the fan, why is that ?
     
  2. #12

    Expert

    Nov 30, 2010
    16,298
    6,811
    Lack of current. The solar panels can not keep the voltage up when they have to supply significant current. In this case, significant means 1 or 2 milliamps. The solar panels are just too small.
     
  3. wayneh

    Expert

    Sep 9, 2010
    12,127
    3,048
    It takes power to run a motor or other device. If the panel cannot supply enough power, the "open circuit" voltage you measure with your meter is pulled down by the load (go ahead and measure it, you'll see) and nothing happens. Your panels are far too small to power the devices you're experimenting with.
     
  4. radiohead

    Active Member

    May 28, 2009
    474
    31
    if you put some panels in parallel, you will get more current output
     
  5. timdiy

    Thread Starter New Member

    Jul 1, 2011
    3
    0
    how do I measure the current of the solar panel ? From this link :
    http://www.freesunpower.com/battery_diagrams.php

    would it damage my multimeter to measure Amps/current like it says ? Also in step 6 of the Amps measurement section what does it mean "can not be placed across the circuit like in voltage measurement..."

    How I measure voltage of the solar panel(this is "series" and "open circuit" right ?) :

    Code ( (Unknown Language)):
    1.  
    2. (-)Panel(+)_____(-)Panel(+)______(Red)Meter(Black)
    3.  |                                           |
    4.  _____________________________________________
    5.  
    According to the article, how does the diagram look like if I were to measure the Amps instead of voltage of the solar panel ?


    Radiohead : by "parallel" do you mean I should wire like this :
    Code ( (Unknown Language)):
    1.  
    2. (-)Panel(+)
    3.  |       |
    4. (-)Panel(+)
    5.  |       |
    6.  |       ____(+)Timer/Fan/Meter(-)
    7.  |                       |
    8.  |                       |
    9.  ________________________
    10.  
     
  6. wayneh

    Expert

    Sep 9, 2010
    12,127
    3,048
    The panels you are now using are not able to damage your meter, so you can get an idea of your max, or short circuit, current by connecting the meter as you have drawn. My meter has a 0.25A fuse to protect itself, and it requires a large panel to blow that fuse.

    Better form - unlikely to damage your meter regardless of panel size - would be to connect the panel to a load already known to draw less current than your meter can measure. Then put your meter in series with that load and measure the current. But this approach cannot really measure the short circuit current of a large panel.

    Best form is to connect the panel to a known load (eg. 0.1Ω resistor, rated for ~2X more the power capability of your panel) and measure voltage across that load. This avoids running high current through your meter, and this method will always work safely, in the sense of protecting your meter.
     
  7. someonesdad

    Senior Member

    Jul 7, 2009
    1,585
    141
    The calculator probably runs on a few uA of current, so your power needs are not being met by probably 3 or 4 orders of magnitude, at least. You can measure the current levels easily with a $5 Harbor Freight DMM -- see the AAC textbook for details.
     
  8. wayneh

    Expert

    Sep 9, 2010
    12,127
    3,048
    Those are free right now, with any purchase, if you can find the coupon. I've probably got a half dozen of these meters, all obtained for free or nearly so. No idea how accurate they are, but they seem pretty good and are certainly handy.
     
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