7 Replies Latest reply: May 6, 2013 6:19 PM by shredofme
linux_dr Level 1 (0 points)
I am the very happy and satisfied owner on an iPhone 4, but am seeking mobile backup power for on the go use (and to limit unnecessary charging cycles in preparation for being away from an outlet). To that end I just purchased a Griffin "TuneJuice" charger for use with my ample collection of AA NiMH batteries. The TuneJuice expressly claims compatibility with NiMH and NiCd batteries as well as Alkaline and Lithium ones. Regrettably, even with fully charged brand new NiMH AAs the TuneJuice showed me no love with rechargeable batteries on my iPhone 4 and is being returned to from whence it came tomorrow. (It appeared to work fine with the included Alkaline batteries, but I have no interest in using it in that capacity.) That said, I'd like a solution that does work well with rechargeables.

Unless someone has any great alternative product suggestions, I expect I may be building a homebrew alternative. My initial diagnosis is as follows:
+ NiMH batteries are rated to deliver about 20% less voltage than their alkaline brothers.
+ the TuneJuice's 3 AAs in series was already under-volting the USB interface with the 4.5 volts 3 AA alkelines supply
+ even an overcharged NiMH battery delivers about 7% less than what a half-used up alkaline is rated at (a fully charged NiMH will typically deliver just under 1.4v when newly charged, but will quickly fall to between 1.3 and 1.2 volts.)
+ as charging with alkaline batteries did seem to work, I expect the voltage difference was the culprit.

So my main question is:

1. What are the allowable voltage ranges for charging an iPhone 4 (or iPods/iPhones in general) over USB. What are the minimum and maximum current an iPod/iPhone can draw while charging?

I realize that USB is spec'd to 5 volts, and as particular as I am about taking good care of it, I'd like to give it 5v 100% of the time, but the truth is that batteries do fade before they are mostly dead, and I imagine that interrupting a partial charge would do more harm to the iPhone's battery then let it finish charging at 4.9volts.

As NiMH batteries are rated at 1.2volts, but often deliver as much as 1.4 initially; I think 5 AAs in series (delivering, in the theoretically maximum case of alkelines, 8 volts; and more typically 5-5.5 volts with a less than full charge) can be voltage-regulated down to a steady 5 volts. If I had 2 sets of 5 AAs in parallel, I could remove one set to charge while still using the other without impacting to target voltage. (sets of 4 AAs would be much more convenient, but would mean that my delivered voltage could drop as low as 4.6 volts as the batteries begin to die. Is this within allowable parameters? Am I really just going overboard on this? Please provide any suggestions. I'd honestly rather buy than build.)

So having done a small amount of cursory research on homebrew USB to charge iPods and iPhones I have 2 related follow-on questions:

2. At one time, low-current reference voltages of 2.5v and 1.8v were required on the data pins to initiate charging. Are these reference voltages still required? Is there any official documentation specifying those?

3. I have been more than happy with the service I've received as part of my AppleCare warranty and wish to do nothing to invalidate it. Assuming that I am careful to check my work to ensure that I'm generating the voltages I should be, would anything I've described above invalidate my AppleCare warranty? How would it be different than charging an iPod/iPhone on any 3rd party vendor's USB port. (I concead that as a hobbist and solo artist I'm more likely to make mistakes than a company using 6 sigma processes to produce a run of several million units, but that's not what I'm asking.) In short, will this void my warranty?

iPhone 4, iOS 4
  • linux_dr Level 1 (0 points)
    Just thought it might be helpful to include some links and relevant tags. (Is there a tagging mechanism? I must have missed it.)

    Here is the Griffin webpage for the TuneJuice: http://www.griffintechnology.com/products/tunejuice

    Tags: USB voltage range rechargeable batteries AA NiMH "Nickel-metal hydride" current portable charging homebrew hobbiest specification "voltage regulator" "over engineered" solder charging accessories NiZn "Nickel-Zinc"
  • Andrea Rimicci Level 1 (120 points)
    I suppose you will use IC 7805 as voltage regulator. Technically, you can serialize so much batteries until you reach (when batteries fully charged) the max input voltage for the 7805, to realize a working charge-only female USB plug.

    About warranty, it does not allow attach your phone to unknown sources, as homemade usb-like ports. Most likely, if your phone gets any electric problem, warranty is voided.

    Third party usb plugs are OK when they have the USB logo on, it means the plug meets USB requirements, and the device has been certified on that.
  • linux_dr Level 1 (0 points)
    After more research I have found, and now ordered the:

    Tekkeon TekCharge MP1550

    This seems to be very close to what I described above. I also contemplated trying Nickel-Zinc rechargeable batteries in the charger I am about to return. NiZn batteries have a nominal voltage of 1.65v which would give me 4.95v which would be perfect if not for reading that on a very fresh charge, they can hit as high as 1.85v (would yield 5.55v) which sounded dangerously high to me... Also I'd need all new batteries and chargers which is costly.

    I think I have basically arrived at my final solution, but I would really still like to hear answers to the following:

    1) Can anyone provide reviews on the Tekkeon TekCharge MP1550 or any similar products? (I guess part of what is above is somewhat a review of the Griffin TuneJuice.)

    2) I would still like to see something OFFICIAL from Apple stating at exactly what voltage-range the (in this case) iPhone 4 is designed to be charged safely, and how much current it will draw to charge. (for instance "the iPhone 4 can safely be charged at any voltage between 4.2 and 5.1 volts, and will draw between 250 and 800 mA while it is charging."... Hmm that sounds so perfect, too bad I'm not Apple. Lol)

    Any answers to either of these two questions would be greatly appreciated. (I may repost these two questions separately, as the other stuff above may scare off any useful responses. Thanks again with all the help so far.
  • JoeZinVA Level 2 (430 points)
    If you want to cut down on reusable batteries, you can also use an iPhone battery pack case. Energizer has a PowerSkin case (1500?) NiMH built in which can provide up to 200 hours of standby time or 5 hours of talk/Internet time.
  • Andrea Rimicci Level 1 (120 points)
    linux_dr wrote:
    ...1) Can anyone provide reviews on the Tekkeon TekCharge MP1550 or any similar products?...

    I think google will helps you better on that.

    2) I would still like to see something OFFICIAL from Apple stating at exactly what voltage-range the (in this case) iPhone 4 is designed to be charged safely...

    iPhone serires (all) are designed to charge with USB plug. It means, they are Power V-bus devices, and official USB specs will rate from 4.75V to 5.25V the voltage range, at max current output (500mA).

    If you curious about USB specs, here an interesting article:
  • TranceMist Level 1 (0 points)

    You may be interested in the Guide 10 battery pack from Goal Zero




    It is normally used with their solar pannels, but could also be used for the purpose you describe.


    The batteries can be charged from USB or from the solar pannel.


    I have been using this with the Nomad 7 solar panel and when these batteries are fully charged, they will fully charge an iPhone 4 that is fully discharged.

  • shredofme Level 1 (0 points)

    Dear Linux_dr

    I just ordered this bike light :


    As it has a big battery I want to add another function to it which charging my iphone on the go.As you will read it has 4x 18650 Battery which makes the out 4x3.9=15.6 volt.

    What is the best option to bring the voltage in the range of 5 volt to make itappropriate for iphone charge?

    What about the current.

    Have you got any idea?