According to the USB Battery Charging Specification, a device plugging into a USB port to charge may find itself connected to a source that is capable of data transfer as well as power, or it may be connected to a source that provides power only. If the source supports data, the device is expected to do a trickle charge only, but if the source does not support data, the device may draw more current because the source is likely to be a wall socket. (More detail on Wikipedia.)

So those of us who use USB car chargers with our Android phones really want the phones to charge as fast as possible. Unfortunately, most car chargers do not short the data pins together, which is the spec-compliant way to indicate that the power source does not support data. It would seem that this gets past manufacturers' QA because the iFail devices apparently ignore the spec and draw as much current as they want, regardless of the state of the data pins. This leaves Android users stuck with trickle charge off their car chargers, unless they go out and buy a specialized charge-only USB cable which shorts the data pins.

For those of us who want a car charger that supplies 1+ amps without needing a special cable, the Mediabridge dual port high output charger is easy to take apart and add solder to short the pins, and this post shows how to do it. I wrote this up because I've done it at least 3 times so far and I always forget the fastest way to put it back together. I am indebted to this review of the charger model in question.

First, take the device apart. Unscrew the metal tip, remove the collar ring, and then separate the two halves of the case by inserting the blade of a small screwdriver and twisting it to pry the case apart. Then you can pull the circuit board out of the case.

The charger, disassembled.

Next, short the data pins. The below photo illustrates where to place the solder. Specifically, get a small blob of solder onto the tip of the soldering iron, and then place this into the gap between the two middle USB pins, holding the tip of the soldering iron in contact with the pins long enough for them to heat up and attract the solder in order to form a good connection.

Shorting the data pins.

That's it, now we put it back together. First, extract the USB faceplate if it's still connected to one of the case halves (you might have to pry, if you were unlucky and it was glued) and lay it over the USB ports on the circuit board, illustrated below. It should snap on firmly. It is possible that both orientations will work; in the next step you may have to reverse the orientation.

Aligning the faceplate over the USB ports.

Now slide the faceplate into the half of the the case without the large post. If the faceplate doesn't fit snugly all the way around, try rotating the faceplate 180 degrees, but the circuit board must remain oriented closest to the case as pictured. Once this is done, nestle the attached metal clip into one side of the nose of the charger, and insert the loose metal clip on the other side.

Applying one half of the case.

Align the remaining half of the case with the edge of the faceplate and slide it on. Keep the nose end of the case open just enough to slip in the four metal buttons, and snap it fully closed.

Attaching the top half of the case.

Finally, place the collar ring. Drop in the piece with glass in it, cover it with the metal tip, and screw on the retainer ring. Done! Go test it.

On your Android phone, in Settings -> Battery, you previously would have seen something like this at the top of your screen -- "(USB)"

After the mod, this is what you should see on that screen -- "(AC)"

On a Galaxy SII, this increased the charge rate from about 450 milliamps to about 870 milliamps, which means it charged almost twice as fast.

Posted in: Electronics, Tutorials  

1 Response

  1. Deming Said,

    Same thing with these cheap ebay car cigarette lighter adapters I got from here:

    I dismantled it and found that both data pins were not shorted out. Will try soldering the pins together and hope it would work and will be able to charge my Galaxy S4.

    This car cigarette adapter I bought from Ebay is capable of 500 Ma, but I was only getting 300 Ma, which explains why my Galaxy S4 does not get charged, even though it shows the charging notification.

    I tried charging my phone on a Pc USB port (USB 2.0) rated at 500 Ma, and I was getting 460 Ma, which was able to charge my phone even with Wifi turned on.

    Posted on November 13th, 2015 at 3:56 am

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