Solarpanel and charging

Discussion in 'General Electronics Chat' started by FroceMaster, Nov 14, 2015.

  1. FroceMaster

    Thread Starter Member

    Jan 28, 2012
    400
    4
    Hi.
    Have this solarpanel that generate 12-30v with no load,
    How would be best to extract 5v 500mA from this.
    Either with 7805 or zener diode, or any ???
     
  2. MikeML

    AAC Fanatic!

    Oct 2, 2009
    5,450
    1,066
    What current will the panel deliver in bright sun if it is connected to a 12V car battery (using the battery as temporary test load)?
    What is the nature of the load? Does its current demand vary, or is it steady at 1/2A?
     
  3. spinnaker

    AAC Fanatic!

    Oct 29, 2009
    4,866
    988
    A linear regulator is the wrong way to go. You will dissipate most of the energy in heat. What you want is a switching regulator. The easy way to go is to pick up on of those USB chargers for the car and hack it apart. They are designed for 12V in and 5V out. They usually use a 34063 which is an older switcher and not the most efficient. You could also pick up full modules from eBay or just build your own.
     
  4. FroceMaster

    Thread Starter Member

    Jan 28, 2012
    400
    4
    Have used something like that.
    I have no battery to 12v
    I have solarpanel with 12v out and a battery 3.2v for windgauge.
    Need to charge this battery
     
  5. MikeML

    AAC Fanatic!

    Oct 2, 2009
    5,450
    1,066
    Ok, take the panel, connect it to a 20Ω resistor. Measure voltage across resistor in bright sun.
    Try it with a 100Ω resistor.

    What battery chemistry?
     
  6. FroceMaster

    Thread Starter Member

    Jan 28, 2012
    400
    4
    Hi
    Lithum ion.
    He have tried to put a 3w 12v bulp over the solarpanel. 5.5 ohm. Voltage drop to 0.09v 2.96 mA.
     
  7. wayneh

    Expert

    Sep 9, 2010
    12,093
    3,031
    In bright sun? That's pathetic. Perhaps you are not measuring the current properly? Post a photo.
     
  8. FroceMaster

    Thread Starter Member

    Jan 28, 2012
    400
    4
    Correct done volt parrelel over the bulp. Amp in series.
    Have no sun these days in denmark so use very bright light to light the panel up.
    21.5v with no load.
     
  9. wayneh

    Expert

    Sep 9, 2010
    12,093
    3,031
    Ah, OK. It's difficult to get enough light to simulate sunlight.

    Let's back up now and talk about what your goal is. You mentioned wanting 5V and 500mA from this? That's 2.5W of output power and obviously cannot happen at low illumination.

    Your best bet is a buck converter that will allow your panel to operate at ~24V where it is most efficient. As long as you have enough light, the converter will provide a steady 5V at the output with a high conversion efficiency. You can find buck converters on e-bay. Many, many choices and very cheap.

    It's still possible that your panel will not deliver enough power to meet your goal.
     
  10. Roderick Young

    Member

    Feb 22, 2015
    408
    168
    How large is the panel, physically? If the short circuit current is about 3 mA, that's a very small or weak panel. You might be able to trickle charge a battery by connecting the panel directly, with no other electronics.
     
  11. FroceMaster

    Thread Starter Member

    Jan 28, 2012
    400
    4
    The battery to charge is a 3.2v lithiun ion 700 mAh.
    Solarpanel is around 15×20cm
     
  12. tom_s

    Member

    Jun 27, 2014
    285
    333
    20w max using a marine grade panel that size. personally, post #10 best option, i doubt you have marine grade panel.
     
  13. jjw

    Member

    Dec 24, 2013
    173
    31
    20W from 0.03m2 panel?
     
    Roderick Young likes this.
  14. tom_s

    Member

    Jun 27, 2014
    285
    333
    Roderick Young likes this.
  15. Roderick Young

    Member

    Feb 22, 2015
    408
    168
    Ah, 14 x 20 inches, yes, that makes sense. Kyocera is also a reputable manufacturer.

    If I were doing this, I would just get a small buck regulator based on the LM2596. You can buy them on eBay for not very much, for example: http://www.ebay.com/itm/LM2596-Buck...470941?hash=item5d51b05c1d:g:XyoAAOSwLa9UXJBL . There are even some with a built-in USB socket, if that's what you're trying to power. Search "lm2596 usb" and you'll find them.
     
Loading...