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  1. derwin's Avatar
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       #1  
    I've built a solar charger. Or at least, that's what my multimeter tells me. However nothing ever comes without problems.

    I bought a 6V, 5A solar panel off eBay. It's pretty compact and comes with the positive and negative wires. I tested it with a multimeter, and sure enough, a solid six volts comes in when tilted at the sun.

    I read about USB charging on the Internet and learned that most devices need somewhere from 4.75-5.4V to charge safely. So I found a USB extension cable and cut it revealing the 5V+, GND, D+ and D-. Using alligator clips, I connected the negative of both the solar panel and the USB cable together, as well as the positive but with a diode wired in to keep the energy from leaking in the other direction. I connected it again to my multimeter and now I was getting around 5.2-5.4V. This seemed perfect, so I plugged in my Pre. Well, I was left a bit ...

    The Pre immediately recognizes it, chimes, and displays the "Charging Battery" banner. But the phone then simultaneously slows to a crawl. And by crawl I mean .5 frames per second, and then its eventual and tragic lockup that forces me to remove the battery and restart. I tried to short the D+ and D- together, but I feel like I'm missing something.

    I'm so close! What can be wrong?
  2. #2  
    I have had similar problems with heavily taxing the car charger I got from monoprice. I'm sure someone else can explain it in more detail, but I believe the voltage has to be better regulated than .2v. I tested the touchstone and have been getting between 5v and 5.01v during charge.
  3. #3  
    The multimeter isn't drawing any significant current. You need to test the voltage under load (ie, when plugged into the phone and charging). My guess is the voltage drops below 5V when the phone is actually pulling current.
  4. #4  
    Quote Originally Posted by azeeb View Post
    The multimeter isn't drawing any significant current. You need to test the voltage under load (ie, when plugged into the phone and charging). My guess is the voltage drops below 5V when the phone is actually pulling current.
    It is supposed to supply 5A though, and that should be plenty since the Pre only needs about 1A.
  5. #5  
    Quote Originally Posted by derwin View Post
    I've built a solar charger. Or at least, that's what my multimeter tells me. However nothing ever comes without problems.

    I bought a 6V, 5A solar panel off eBay. It's pretty compact and comes with the positive and negative wires. I tested it with a multimeter, and sure enough, a solid six volts comes in when tilted at the sun.

    I read about USB charging on the Internet and learned that most devices need somewhere from 4.75-5.4V to charge safely. So I found a USB extension cable and cut it revealing the 5V+, GND, D+ and D-. Using alligator clips, I connected the negative of both the solar panel and the USB cable together, as well as the positive but with a diode wired in to keep the energy from leaking in the other direction. I connected it again to my multimeter and now I was getting around 5.2-5.4V. This seemed perfect, so I plugged in my Pre. Well, I was left a bit ...

    The Pre immediately recognizes it, chimes, and displays the "Charging Battery" banner. But the phone then simultaneously slows to a crawl. And by crawl I mean .5 frames per second, and then its eventual and tragic lockup that forces me to remove the battery and restart. I tried to short the D+ and D- together, but I feel like I'm missing something.

    I'm so close! What can be wrong?
    You need a voltage stability circuit 5 amps is to much to dump in to it unregulated. I made a diagram for you this would work just fine something like the Pre or any USB device for that matter you just cant dump in voltage with out some kind of regulator I made a little list of what you need too also see pic I have attached to this post... With this set up you can also use 4 aa c d battery's and charge your pre as well.


    1x 7805 Voltage Regulator
    1x 0.47F 50V Electrolytic Capacitor
    1x 0.1F 50V Tantalum Capacitor
    1x 20V 1A DO-41 Schottky Diode
    1x 1.3mm DC plug
    1x 1.3mm DC socket
    1x Copper glad PCB, 3″x4″

    1x Plastic box at least 2.8″x1.8″x0.8″, any type you can find will do
    1x USB female connector (cut off from an USB extension cable at a length of 20cm)
    Attached Images Attached Images
    Last edited by gitit20; 07/14/2010 at 10:38 PM.
  6. derwin's Avatar
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       #6  
    Thanks for the information. Where do you recommend purchasing these exact parts?
  7. plee3ac's Avatar
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    #7  
    Quote Originally Posted by gitit20 View Post
    You need a voltage stability circuit 5 amps is to much to dump in to it unregulated. I made a diagram for you this would work just fine something like the Pre or any USB device for that matter you just cant dump in voltage with out some kind of regulator I made a little list of what you need too also see pic I have attached to this post... With this set up you can also use 4 aa c d battery's and charge your pre as well.


    1x 78M05 Voltage Regulator
    1x 0.47F 50V Electrolytic Capacitor
    1x 0.1F 50V Tantalum Capacitor
    1x 20V 1A DO-41 Schottky Diode
    1x 1.3mm DC plug
    1x 1.3mm DC socket
    1x Copper glad PCB, 3″x4″

    1x Plastic box at least 2.8″x1.8″x0.8″, any type you can find will do
    1x USB female connector (cut off from an USB extension cable at a length of 20cm)
    The 78M05 is not a low dropout linear regulator. It has a min dropout of 2V, so the input must be at least 7V to output 5V. Since your solar cells (and also 4 AA, C, D batteries = 4 x 1.5 = 6V) can drop down to below 7V under load, I would not recommend using this regulator.

    Instead, after some googling, the National Semiconductor LP3855 appears to have a better dropout of only 0.24V and can handle a maximum of 1.5A (the 78M05 is only rated at 0.5A).

    Perhaps this would be a better solution.

    Hope this helps... plee3
  8. #8  
    Quote Originally Posted by plee3 View Post
    The 78M05 is not a low dropout linear regulator. It has a min dropout of 2V, so the input must be at least 7V to output 5V. Since your solar cells (and also 4 AA, C, D batteries = 4 x 1.5 = 6V) can drop down to below 7V under load, I would not recommend using this regulator.

    Instead, after some googling, the National Semiconductor LP3855 appears to have a better dropout of only 0.24V and can handle a maximum of 1.5A (the 78M05 is only rated at 0.5A).

    Perhaps this would be a better solution.

    Hope this helps... plee3
    m was a typo meant to just use a reg 7805
  9. plee3ac's Avatar
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    #9  
    The 7805 does handle 1A, but still has a minimum 2V dropout thus requiring a minimum of 7V input. A 6V input from a 4 cell battery pack or from the solar cells will not work.

    You need to use a low dropout (LDO) regulator like the one I suggested earlier.

    -- plee3
  10. #10  
    Quote Originally Posted by plee3 View Post
    The 7805 does handle 1A, but still has a minimum 2V dropout thus requiring a minimum of 7V input. A 6V input from a 4 cell battery pack or from the solar cells will not work.

    You need to use a low dropout (LDO) regulator like the one I suggested earlier.

    -- plee3
    I have made me one of the set ups and its outputting 5 volts ok? a good clean even 5v and the chip i used is 1.5 amp no doubt yours is a better choice prob but that's all i had laying around. And i have not had any prob thus far. i use it for charging all my usb stuff when camping and what not also i will mount it on my motor cycle too since it does not have a cig lighter i just hook it right to the battery haha and i know 12 volts is more then the 4 aa c or d battery's but i get a good clean 5v from it under load when using the 4AA i will get about 3 charge cycles out of them before they are too weak to do anything.

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