Mobile Device Charging issues and the ugly truth
If you have tried using a generic USB power adapter and wondered why they are not charging very quickly then this is probably the reason why:
After a lot of testing trial and error and buying various different USB chargers thinking they are not fit for purpose or making misleading claims about there about the stated output I decided to do some digging and found out the ugly truth about mobile device charging. The end result was that I have now modified three of my chargers and they now charge at more or less the same rate as the original charger that came with the device; Prior to this they were taking about 10-12 hours to carry out a full charge rather than the 2-3 hours they should have been.
My initial searching found reference to shorting out the data pins (pins 2 and 3) on the charger or placing a 200 ohm resistor across the pins I completed this mod to a couple of my chargers and great one started working correctly the other remained the same.
I then started to look at the pin-outs on the USB leads and noted that on the standard USB-B (pictured below)
Micro plug had a fifth pin.
Down to some basic testing I noted that one cable I had did charge at a slightly slower rate, so I took this cable out of the equation for testing. Some further reading around the subject revealed that the EU have been involved along with China and several big device manufactures and came up with a standard on USB and charging. The basic outcome of this was the following:
-The charging adapter would have a standard A USB socket on it
– The device would have a standard USB-B micro plug on it
-The devices must be able to detect when it is plugged into a PC and charge at a slower rate so that it does not overload the port For full details please click here
So what was the problem?
Whilst Apple adhered to the adapters having a USB-A plug on the charger there are other differences in the way they link the pins in the adapters, I can only assume this is the way in which the device detects when it is plugged into a PC. Therefore apple chargers for the ipod and Ipad have a different set up on there chargers. 
Some careful observation showed that when plugging the device into a slow charger the device would show up on the screen (To browse phone storage you must first unlock your device) essentially the device thought it was plugged into a PC therefore the device was immediately limiting the draw it would take down the USB cable .
The next step was to take a lead and chop of the Micro USB-B plug and strip back the cables. remove the charger from the wall socket and, by plugging in the cable and carry out some impedance testing using a multimeter. I noted the difference between a good charger and a slow charger. The difference being on a good charger, there was open circuit reading between 0 volts pin lead and the two data pins and the 5 volt leads and the two data leads (Pins 1 – 2,3 and pins 4 – 2,3) On a slow charger It was showing resistance therefore meaning that there was some sort of link between them.
I took a slow charger and with some careful metering out I found the resistors that were linked to the 0 Volt and the +5 Volt terminals. After removing these resistors and then shorting out the two Data terminals (2 and 3) I then plugged the charger back into the wall socket to ensure that I still had a 5 volt supply on Pins 1 and 4.
After carrying out the above the device started charging at the correct rate and no longer displayed the unlock screen. I tried the device out on a number of android devices including HTC mobile Kindle HD fire and some blue tooth head sets. All charged at a fast rate
So there we have it, these generic chargers that claim to support charging Apple Devices as well as others will work but at a reduced rate
Please note though by doing this you will almost certainly render the charger useless for charging apple devices, you have to love Apple!
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