Solar cell phone charger problem

Discussion in 'The Projects Forum' started by Michael.Riley, Feb 28, 2015.

  1. Michael.Riley

    Thread Starter New Member

    Jan 3, 2015
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    I have built a small solar panel, 12V no load output, 1.4 A short circuit current out put. I also built a switching voltage regulator based on an LM317 adjustable regulator. I bought a USB connector at Radio Shack (voltage only), but when I try to charge my cell phone or my Kindle, neither one indicates that it is taking a charge. I have checked that the voltage at the USB pins is 5V, and checked that I have the correct pin polarity ( At least, it is the same as my wall wart chargers.) I have checked the output voltage of the regulator while connected to the devices, and the drop in voltage is .01 V. I have no trouble running a couple of small fans (.18 and .16 amps) and a small LED flasher at the same time (I adjust the voltage output up for these 12V items). Any ideas would be welcome.
     
  2. MikeML

    AAC Fanatic!

    Oct 2, 2009
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    Most devices accepting charge look at the data pins to validate that charger is legit. If your data pins are unconnected, chances are your cell phone and Kindle just ignore the presence of the 5V because you are not tricking them into thinking that your charger is real...

    Apple started playing this stupid game to force people to buy Genuine Apple chargers.
     
  3. bushrat

    Member

    Nov 29, 2014
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    Post a schematic, it will help out figuring out what is the problem.
     
  4. Michael.Riley

    Thread Starter New Member

    Jan 3, 2015
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    I'll post a schematic as soon as I figure out how to convert a Diptrace *.dch file to something that I can send. However, the schematic is based on the following: http://www.circuitstoday.com/3a-switching-regulator, with a few minor changes, to wit:
    Q1 is a TIP42G 6A transistor; D1 is a Schottky dual, common cathode 15A; R1 is 4 1 ohm resistors in parallel; and L1 is an unknown value inductor, fairly large.
    Does that help?
     
    Last edited: Feb 28, 2015
  5. Michael.Riley

    Thread Starter New Member

    Jan 3, 2015
    15
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    I have a wall wart that appears to have only two pins, producing 850mA at 5V, that charges both my devices without an issue. I did manage to get the Kindle to show a charging symbol by jacking the output voltage up to about 8.5 volts and then turning the voltage back down to 5.5V, but it didn't actually charge it.
     
  6. bushrat

    Member

    Nov 29, 2014
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    Umm... just because you can, doesn't mean you should..
    upload_2015-2-28_16-15-12.png
    It works in simulation, and the only thing that I can think of is what MikeML said about apple chargers.
     
    Last edited: Feb 28, 2015
  7. djsfantasi

    AAC Fanatic!

    Apr 11, 2010
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    image.jpg Here's a schematic from the web that I refer to. It shows how to apply the proper voltages to the data pins, using voltage dividers. It's specifically for an iPhone.
     
  8. Michael.Riley

    Thread Starter New Member

    Jan 3, 2015
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    Have you found a post that gives the same voltage divider set-up for the Kindle Fire HD?
     
  9. djsfantasi

    AAC Fanatic!

    Apr 11, 2010
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    Google it, like I just did.
     
  10. Michael.Riley

    Thread Starter New Member

    Jan 3, 2015
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    I spent a couple of hours today trying to locate specs for the charging circuit of a Kindle without any luck. I thought that if you had already found such a site, you would be willing to share it.
     
  11. djsfantasi

    AAC Fanatic!

    Apr 11, 2010
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    Oh I would, but I hadn't. Sorry.
     
  12. tindel

    Active Member

    Sep 16, 2012
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    Per the USB Battery Charging Specification, section 1.4.7 - Dedicated charging ports shall short the D+ and D- lines. Iphones are 'special' and do not conform to the USB spec, that I'm aware of anyway.

     
  13. Michael.Riley

    Thread Starter New Member

    Jan 3, 2015
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    Thanks. That info may do it. Do you know if that is short to each other, or short to ground?
     
    Last edited: Mar 1, 2015
  14. bertus

    Administrator

    Apr 5, 2008
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  15. tindel

    Active Member

    Sep 16, 2012
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    Short to each other there is a diagram in the spec that shows that.
     
  16. Michael.Riley

    Thread Starter New Member

    Jan 3, 2015
    15
    2
    Thanks a lot, to everyone who responded. I took apart a dead USB wall wart to use the USB socket, found that the data pins were simply soldered to each other, and I went with that. Both my Kindle and cell phone now charge immediately through my regulator, supplied by a 12V power supply (A Heathkit ET 3200, believe it or not). When the sun comes out tomorrow I'll try my solar panel, but I'm sure it will work. Many thanks, again, to everyone.
     
    tindel likes this.
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