(Solved) How to charge your iphone 3G/S with any 5V power supply.

Discussion in 'Electronics & Electrics' started by mhgarage, Jul 9, 2009.

  1. mhgarage

    mhgarage Member

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    UPDATE: Problem solved in post 3. People have been having trouble charging their 3G and 3GS with 2g accessories for two reasons: 1) Firewire charging no longer works and 2) The iphone 3g requires a voltage > 2v on both data lines. This solution lets you create an adapter cable that you can use to charge your iphone anywhere.

    So I have an external battery pack I used to use with my ipod classic. It's really good - charges via USB and outputs to a standard ipod plug.

    It doesn't work with the new iphone.

    But the cable, that came with the battery pack, works from the computer to the iphone to charge it.

    So there is some issue with the power from the external battery pack.

    As I understand it, the iphone 3g no longer lets you charge via firewire, but the output of my battery pack is 5.5v 1A. Not firewire voltages!

    So there is a problem here.

    Basically the cable is OK as it works from the computer to the iphone (and works from the battery pack to my ipod classic)

    But the cable doesn't work from the battery pack to my iphone.

    ideas?

    EDIT: This doesn't solve it, but does have some more info
    http://www.tzywen.com/modules.php?name=News&file=article&sid=696
     
    Last edited: Jul 9, 2009
  2. 2xCPU

    2xCPU Member

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    I think your link will solve your problem.

    2.
     
  3. OP
    OP
    mhgarage

    mhgarage Member

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    An update for anyone who would like to make their iphone (3g) or 3gs charge from any USB power source (e.g. car usb adapter, battery pack, plug pack).

    Basically, you need to understand what pins correspond to in a USB plug:

    Female
    http://www.geocities.com/k7hkl_arv/PC_USB_Connectors_Pinout.png

    Male
    http://www.riccibitti.com/pc_therm/USB_A_pinout.jpg

    Step 1:
    Get a spare usb extender cable (male at one end, female at the other). These often come with usb modems and old USB thumb drives.

    Step 2:
    Check that it matches the pinout given above with a continuity tester (multimeter works fine).

    Step 3:
    Find 4 X 100kOhm resisters. The values are not so important, but they need to be quite high. Dig up your soldering iron and solder and a knife.

    Step 4:
    Strip the USB cable in the middle, and identify which cable corresponds to what with the continuity tester (in mine, orange = 5v+ black = GND 2Xwhite = data and yellow = case

    Step 5:
    Cut the data cables, and tape back the ones coming from the computer side. You don't want them any more. The D+ and D- below refer to the data cables extending to the female side of your new cable.
    You want to assemble the following circuit:
    [5v+] ---(100k)---[D+]---(50k)---[D-]---(100k)---GND
    Just bridge the cables in the middle with the resistors. Use two 100k resistors in parallel for the 50k value.

    Step 6:
    Check your circuit resistances and make sure when you plug it in that the voltages are correct (roughly 2-3 volts on the D connectors and over 5V on the + connector, all with respect to 5v- (GND)

    Step 7:
    Take a deep breath and try it out. You need to use a data cable from your extender to the iphone as most 2G charger cables just carry the the + and - and forget about the D+ and D-. It should work! It is also backwards compatible, as it just mimicks the USB port of a computer.

    I have charged my iphone 3GS and my ipod classic from a battery pack now, no problems.
     
  4. Siftah

    Siftah New Member

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    As with everything in life, there's more than one way to skin a cat too!

    I directly modified my charger after reading some of the comments and threads linked to here. I also documented the process so it's hopefully of use to others too: http://wiki.siftah.com/IPhone_3G_3GS_USB_Cigarette_Lighter_Socket_Charger
     
  5. Jon187

    Jon187 Member

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    GOLD mate! I suspect this is why my Navman won't charge from a non-Navman USB cigarette plug charger.

    GOLD!

    I'm going to do Siftah's mod tonight. I have a very similar charger from Dealextreme.com

    JT
     
  6. Siftah

    Siftah New Member

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    Good luck, hope it works for you!

    Be sure to post back and let us know too, I'd like to update the page with links to vendors/models of charger which can be modified as that could be handy for people too :)
     
  7. Jon187

    Jon187 Member

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    Will do. I bought my resistors today. I bought 1/2 watt and 1 watt resistors. I hope to use the 1/2 watt because of size restraints. Do you think that will be a problem?

    Mine was purchased from Dealextreme. Not the one in your link but the white one that puts out 1amp (costs like $3 USD delivered).

    I'll post results tonight (maybe pics if I remember).

    JT
     
  8. JaC

    JaC Member

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    1/2W will still be plenty. The total power wattitude dissipation is 0.1mA between the 3 resistors.

    P = V^2/R = 5*5/250000 = 0.0001W
     
  9. Siftah

    Siftah New Member

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    I think the ones I used were only 1/4 watt but there's a fair bit of space inside the casing so I suspect you'll have no problems even if you're using the 1 watt resistors.

    It's my understanding that the current is being drawn through the 5v feed to the iPhone, so there isn't a great need to use resistors that are rated more than 1/4watt, if that!

    My electrical knowledge isn't great though, so if anyone else can comment... :Paranoid:
     
    Last edited: Jul 22, 2009
  10. Siftah

    Siftah New Member

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    As I said in my last post - I don't believe it's an issue as the current is being drawn through the 5v pins, not the data pins - the iPhone is just sensing the voltage on the data pins.

    However, your maths don't correspond to mine... I work it out much more closer to 2watts! :)
     
  11. dakiller

    dakiller (Oscillating & Impeding)

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    You better recheck yours then, because JaC's is right

    You can use resisters as small as you can physically get
     
  12. Jon187

    Jon187 Member

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    Did the mod, gave me 2.4v on each of the data pins but the stupid Navman still doesn't charge with it.

    Charger works with all my other phones etc so I havne't broken it!
     
  13. Joelati

    Joelati Member

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    About to rip my hair out

    Heya folks,
    I'm about to rip my hair out.

    I am trying to build a small Nokia to Iphone charger adapter that will allow my iphone to work with any old nokia phone charger. I have so many around (particularly a car charger/bluetooth handfree kit), that it would be a great thing to get working.
    Basically I want to create a cable comprising of the female version of the nokia connector with the male iphone dock connector at the other end.

    The back of the nokia charger says it outputs 5.7v at 500ma, but the multimeter reads just over 6v without load.

    I have read as much info as i can about voltage dividing, and have done the math to try and get a circuit built similar to the usb cable requirements to power the iphone with 5v, 2.8v for the D- (pin 25) and 2.0v fir the D+ (pin 27).

    I am using a voltage regulator (LM1117T-5) to drop the voltage down to 5v as a starting point to make it easier to copy the numerous iPhone USB charger examples people have provided on the internet.

    However, no matter what combination I try of resistors to create a voltage dividing circuit, I can't get it to work.

    It seems as though as soon as the iPhone starts to draw load from the power adapter, all the ratios for resistors change, and the iPhone tells me the accessory is not capable of charging. For example, I use measure the D- as 2.8volts, but then as soon as I connect the iphone, it changes to over 3 volts.

    Is there something I'm missing? My knowledge of electrical circuits is at its limits.
    Do I need something else in the circuit to maintain the correct ratios so when the iPhone starts drawing current, it's own resistance doesn't throw off the whole thing?

    Any help would be greatly appreciated. I've wasted a lot of time and life on such a simple thing.

    Cheers,
    Joel
     

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