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Solar Charging for Android Phone

Discussion in 'General Electronics Discussion' started by Piratio, Jun 17, 2013.

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  1. Piratio

    Piratio

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    Dec 3, 2012
    I know this has been done before. But I want to make my own charging station.
    I have the all the parts needed as I thought it would be fairly simple. but my only problem right now is that I'm using a USB Sync cable because I'm low on money and it was only 8 dollars. I know that it has the power to charge my phone, because I've used it before, but I'm not sure where to put which wires. There are 4 of them in contrary to the Solar Panel that has the Red and Black.
    In order to move forward I was wondering if I could get anyone to help me identify which way to hook these wires up. Pictures of what I'm working with are attached.
    Thanks
    Will post finished project when done :)

    EDIT: I am not using that single cell for the power. I have 2 of them. But I didn't think showing 2 of them helps my case any.
     

    Attached Files:

    Last edited: Jun 17, 2013
  2. BobK

    BobK

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    Jan 5, 2010
    What are the specs of the solar cell? I doubt that even 2 of them provide enough power to charge a phone in less than a few days. Also, you can't just connect the solar cells to the phone, you need a voltage regulator in between.

    A typical plug-in phone charger provides 1A at 5V, which is 5 Watts. Solar panels provide about 200W / square meter under the best possible condtions. So it would take a 6 in sqaure to produce this amount of power with the sun directly overhead on a clear day.

    Bob
     
  3. Piratio

    Piratio

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    Dec 3, 2012
    The specs for the 2 small cells I'm unsure of the technicals, but each on puts out about 3.42 volts and I have 2. I also have a larger one that put out about 6.87 Volts that I rigged to an old RC car and it drove just fine, as long as it was in he sun.
     
  4. BobK

    BobK

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    Jan 5, 2010
    The cells look to be about 1 x 2 in? Is that correct? If so, they will, combined, be able to put out at most 0.5W or about 1/10 of what is needed for a fast charge.

    Bob
     
  5. Piratio

    Piratio

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    Dec 3, 2012
    Yes, it is.
    I measured the power output of it though, and it put off about 3.4 volts. Unless I measured wrong 3 times.
    That could be it, I'm here to learn not prove others wrong. Is there a specific way I could try to get a more accurate reading for this project?
     
  6. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Jan 21, 2010
    The problem is not so much the voltage, but the current. A typical phone will want 5V at about 1A to charge.

    The next measurement you need to take is the short circuit current.

    Just get your multimeter, set it to a current range (start with 10A and switch down as required) and measure directly across the cells in full sun.

    Now you have the open circuit voltage (as you measured above) and the short circuit current.

    The maximum power a solar panel will produce turns out to be at (roughly) 80% of the short circuit current and 80% of the open circuit voltage.

    If you get a figure of 5V or more and 1A or more, then you have enough power in full sun.

    I suspect you will find the power is much lower than you require.
     
  7. Piratio

    Piratio

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    Dec 3, 2012
    There we go. That's what I was looking for. I'll post a picture of the bigger cell I have for thoughts. :)
    Or the specs of it more or less.
    Sorry for bad picture. My camera sucks at closeups....
     

    Attached Files:

    Last edited: Jun 18, 2013
  8. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Jan 21, 2010
    All you need is 10 of those 0.5W panels and you will have *just* enough power to charge a phone in strong sunlight with a following breeze.

    20 of them and you'll be able to cope with a bit less than full sun.

    40 of them and it might even work with light cloud.
     
  9. Piratio

    Piratio

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    Dec 3, 2012
    The only issue being that I am going for a phone case..
    Impossible to fit 10 on there..
    But its possible. Some company made iPhone cases that were solar powered.
     
  10. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Jan 21, 2010
    There are a couple of ways to do it:

    1) use the solar panels to charge another battery (over a long period of time) then use that to deliver a short burst of power to the phone.

    2) implement your own slow charger for the battery (essentially (1) above wired directly into the iphone

    3) convince the iphone to accept a lower current.

    (3) is actually achievable to some extent. Google for the resistors needed to set the charging rate. You'd probably want to go to the lowest value to allow the use of the smallest panel.

    (2) isn't going to be possible unless you wire directly to the iphone battery.

    (1) is not as silly as it sounds. I once had an iphone case that included an extra battery.
     
  11. BobK

    BobK

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    Jan 5, 2010
    I doubt that there is a configuration that would allow charging at 80ma. I think your only hope to use that solar cell (the larger one) is to change an external battery as Steve suggested.

    You could trickle charge a battery made of 4 NiMH cells, then use this to charge the phone. If the cells are 2000maH, it would take about 30 hours of bright sunlight to charge then, and then they might be able to give one full charge to the phone.

    So, 5 sunny days for each charge of your phone. It hardly seems worth it.

    Bob
     
  12. BobK

    BobK

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    Jan 5, 2010
    I just noticed the title. Android phone. I thought we were talking about an iPhone here. If the android phone has a removable battery, you have another option. That is to remove the battery from the phone for charging. This would eliminate the need for an additional battery.

    You could probably get away with just using a 4.2V Zener diode to limit the voltage to the battery. The cell will not be able to supply enough current to worry about. But you are still talking about days for a single charge.

    Bob
     
  13. somanshumehta

    somanshumehta

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    Jun 22, 2013
    Whatever your type of solar panel.Since u do not say much about it ,get the output of panel converted down to 5V using DC-DC step down converter and now u need to regulate the current upto 900mA (typical for anroid phones),maybe in some cases 1A.
    A good design would take care of voltage exceeding the typical values,when the sun shines more brighter or when days go hot.
     
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