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Wiring a USB connector to charge phone w/ Solar panel.

Discussion in 'Android Lounge' started by Colchicine, Aug 25, 2011.

  1. Colchicine

    Colchicine Android Expert
    Thread Starter

    I purchased a small solar panel charger today at Harbor Freight, they were on clearance for $6.50!! I read some reviews where people have added a USB plug and they have used it to charge their Android phones. I'm working on doing the same thing.

    Solar Panel Recharger

    I have above-average knowledge/experience with electronics, but I'm no expert and I still like to make sure I don't eff up my phone. I wanted to confirm that all I really have to do to connect the the positive and negative wires respectively.

    This website said something interesting: "Dedicated charger mode:A simple USB charger should short the 2 data lines together. The device will then not attempt to transmit or receive data, but can draw up to 1.8A, if the supply can provide it."

    USB pinout and wiring @ pinouts.ru

    I don't like the idea of the word "short" but it did say elsewhere: "Contrary to popular belief, D+ and D- operate together; they are not separate simplex connections."
    I don't fully understand that statement, but I can see how it relates to shorting the D+ D- wires together and it being just fine.

    One more question, the solar panel doesn't have a 5volt setting, just a 3 & 6v setting. I'm assuming that if I use 3v, it won't meet the minimum of 4.75v needed to charge. And I'm assuming the 6v will initiate charging, and that the protective circuits will keep the voltage above 5.75v from damage anything.

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  2. Harry2

    Harry2 Extreme Android User

    D+ and D- works only together and build a bidirectional driver.
    If you want to go deep in that "shortening D+ with D-" you should google for 'USB Enumeration'.
    This shortening is the simplest implementation of it.
    The HTC chargers are a good example of it :)

  3. Colchicine

    Colchicine Android Expert
    Thread Starter

    Se habla ingles?
    Sounds like you agree with wiring the D+ & D- together?
  4. Colchicine

    Colchicine Android Expert
    Thread Starter

    Update! Got things wired up this morning and tested it out, first with a dumbphone.

    I turned off my Incredible and plugged it in but got no battery charging light on the LED. Powered it on and plugged it in and it started charging. With the data wires shorted together, I got a message within 10 seconds that the power supply was not standard and to avoid damaging the phone, it should be unplugged. Without the data wires shorted, I got that message about 60 seconds after plugging it in.

    Also, it will not charge at 3 volts, only on the 6 volt setting.

    I'm going to ignore the warning, since I've gotten the same thing on an LG charger meant for a dumbphone. Nevertheless, can anyone provide any further insight?
  5. Harry2

    Harry2 Extreme Android User

    My solar panel couldn't directly charge my phone too.
    But this solar panel can charge my portable charger's battery.
    I think, this is the better way because you have to be patient until the battery is fully charged with a solar panel (think in days, not in hours ;)).

  6. John Redcorn

    John Redcorn Android Enthusiast

    As far as I know, shorting the pins is a way to signal to the phone that it's plugged in to an AC charger and not a PC, letting the phone know it can ask for more than the 500ma a PC provides. From what it looks like in the pic that thing says it outputs 150ma at 6v. You're not going to even get 500 out of it so shorting the pins shouldn't have any effect.

    Also as some added insurance you can regulate the output voltage of that to 5v with a zener diode. google for something like: usb battery zener diode voltage regulator

    6v may not be high enough to get a regulated 5v from a regulator circuit though, might have to go to 9v on the solar cell.
    Colchicine likes this.
  7. indybail

    indybail Well-Known Member

    You are braver than I am. Does anybody know what the energy savings are?
  8. John Redcorn

    John Redcorn Android Enthusiast

    if your 1A wall charger is putting out a steady 1A @ 5v for 8 hours a day. (nowhere near that much) that's 5 watts, probably slightly more watts on the 120v side due to inefficiencies but call it 5 for simplicity.

    5 Watt * 8 hours = 40 watt-hours per day * 365 days = 14600 watt hours per year=14.6 kilowatt hours per year.

    Kilowatt hour costs me about $0.095 tax and all, so at my price a very power hungry phone uses about $1.38 for 14.6kwhr per year.

    That's not at all to bag on the OPs project or anything, I'd totally do something like this knowing that it doesn't really save money, it's fun to put stuff together and it'd be great for camping or zombie apocalypse like scenarios.
    indybail likes this.
  9. Colchicine

    Colchicine Android Expert
    Thread Starter

    The way you explained that was VERY good, and I wound up NOT hooking those two wires together.

    Next question: Since I have a second solar panel I wired a Y that allows the 2 chargers to hook into my one USB. It doubled the voltage but I don't have a way to measure the mA. Shouldn't two chargers double the amps? All the literature on the webernet shows 1 power source and multiple loads to describe series vs parallel, but not my situation with 2 power sources and 1 load!

    Note that I didn't specify a use, and energy savings was not one them. Given my location (look at my info, I'm in a near direct path of Hurricane Irene) I was going to use this to charge our phones when the power was off. The last big hurricane we had, we went for 13 days without power but we all had dumbphones then. The hurricane is directly to the side of us now as I write this and we haven't lost power yet. On top of that, I was given a free generator on Friday, so it's all moot. But like John said, it's fun to put this stuff together keep fresh on electronics.

    In addition, I like the idea of being able to charge my phone when I'm doing field work. The review on the HF website said that he puts the solar panel on top of his back pack, charging his phone the whole time he's in the sun.
    indybail likes this.
  10. ambientdroid

    ambientdroid Well-Known Member

    Cool project.

    I look forward to the day when touch screens can double as solar panels so your phone charges when it's sitting on the dash of your car or a desk.
  11. Harry2

    Harry2 Extreme Android User

  12. Harry2

    Harry2 Extreme Android User

    If you use the same output voltage for parallel to load there should no problem: Same voltage, double current (better said: the sum of both currents) :)

  13. Colchicine

    Colchicine Android Expert
    Thread Starter

    Thanks Harry.

    I meant to comment that using the solar panel to charge a reserve battery is theoretically inefficient compared to charging the phone's battery directly. Energy takes on many different forms, but usually when it is changed from one to another, there is a loss of energy.

    So the pathway would be Solar > electrical > chemical > electrical > chemical.

    Electrical and chemical is listed twice because you're using a battery to charge another battery.

    This whole concept may be moot if charging your phone directly is impractical in the first place, but hopefully it gets your gears churning!
  14. Harry2

    Harry2 Extreme Android User

    Hi Colchicine,
    you have course right with the loss by the longer energy chain :)

    But what does this energy loss matter?
    I charge my portable charger's battery during the day (with the solar panel on the backpack :) ) long enought until the portable battery is full enought to charge my phone at night.

  15. Colchicine

    Colchicine Android Expert
    Thread Starter

    Don't get me wrong, Harry, I don't doubt that your system works fine. I've been accused of overthinking, and the engineer side of my brain screams Inefficient!
  16. gfinockio

    gfinockio Newbie

    I just ended up buying a solar-powered battery, and use that to charge my phone. It takes about 16 hours of sunlight to get 4 hours of phone battery life...
  17. Harry2

    Harry2 Extreme Android User

    With my first solar panel I had the same disappointing experience :)

    But solar applications are very dependent on the quality of the solar panel.

    My last solar purchase was a high tec solar panel which also can directly charge my phone. It can provide about 450mA. So the solar panel will need the same time as charging the phone on the PC USB socket.


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