DIY 8m usb cable need help..

Discussion in 'Jailbreaks and iOS Hacks' started by xiaohong, Jun 22, 2011.

  1. xiaohong macrumors newbie

    Jun 22, 2011
    hi guys need a little help... as the title said, i diy a 8m usb cable.. i don intend to use it to sync but only to charge, i understand the maximum length of usb spec is 5m but i tot it only affect data transfer? i only wan a long cable to charge from a distance, i just merely added the length of the cable only, i measure the voltage after i fix up the 8m cable to iphone4 spec, 5v,grd and the data line on 2.8v,2v i can charge my ipod nano 1st gen, but when i plug in my iphone4 it says charging not support with this accessory..

    actually all i wanted was a long single wire about 8-10m long to a usb to do charging on my stuff like iphone4, mp3 etc.. every other device seems to be able to charge except my iphone4..

    anyone can give some guidance on this?

    P.S. sorry on the bad english..
  2. labman macrumors 604


    Jun 9, 2009
    Mich near Detroit
  3. xiaohong thread starter macrumors newbie

    Jun 22, 2011
    hey thanks for the info but i want to diy instead of buying one.. if not i would not have post here for some help.. thanks anyway...:)
  4. ulbador macrumors 68000


    Feb 11, 2010
    Chances are, over that distance, you are losing too much to resistance for it to actually be able to charge. I know iPhones in particular are very finicky about the voltages/amps you pump into them. I know I had a USB charger that would charge every USB device I had except for the iPhone.
  5. Prodo123 macrumors 68020


    Nov 18, 2010
    Maximum length of a USB cable is 5m. You cannot go over it. Since the iPod cable is a derivative of the USB standard, it also cannot be longer than 5m, even with extension cords. Sorry!
  6. ulbador macrumors 68000


    Feb 11, 2010
    That's primarily due to the degradation of the actual data signal. It would be a little different if the cable was used solely to provide power, though there would still be a limit somewhere where the resistance of the cable reduces the voltage/amperage enough to the point where the device on the other end refused to charge. That would be dependent entirely on the device and the tolerance of the charging system.
  7. sbddude macrumors 6502a

    Sep 27, 2010
    Nor Cal, USA
    why not use an extension cord for the AC power, then plug in the charger and use the normal usb cord

    like this:

    outlet <-----110v extension cord--->iphone charger<--usb-->iphone
  8. xiaohong thread starter macrumors newbie

    Jun 22, 2011
    thanks for the help guys.. so you are saying that the longer cable the more resistance there is so the signal drop? but i measure on my multimeter it shows the same voltage with no drop.. i know AC extension cord is a solution but i wan it to be light and small so i can bring it along with me when i'm out of home...
  9. thespazz macrumors 6502a

    Jul 5, 2007
    It will show the same voltage because the source is setting the voltage throughout. The current is what matters and that is most definitely decreased.

    V=IR simple ohms law--the 5v USB port is making voltage constant, so when resistance increases, current must decrease. your phone will charge very, very slowly.

    Edit: current is charge/second. As it decreases, you transfer far fewer charge units per second. Your phone will take forever to charge--possibly damaging the internals.
  10. jpetticrew macrumors 6502a


    May 13, 2009
    I'm no electrician, so I really can't help you out... But I am curious about why you'd need a 24 foot USB cable?

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