Monday, May 16, 2011

Fixing USB car chargers from eBay

A few months ago, in an accessory buying frenzy for my then-new N8, I ordered a couple of USB car chargers from eBay. The first one did not specifically say it was for the N8, but it didn't say it was for Apple either, so I took a chance with it. Disappointingly, it did not work. I ordered another one, this time in a bundle with a wall adapter and 3 micro USB cables. There was a choice of colours, so I ordered a pink one because that goes well with Subies. This model was advertised to work with the N8, but of course it didn't work. Some time passed. Recently, I helped put together two Minty Boost USB chargers, which showed that for some devices, pins 2 and 3 need to be shorted together. Inspired, I disassembled the pink one and soldered the pins together. Sadly, the N8 still wouldn't charge from it. Luckily I spotted this in a forum:
I found a similar problem: USB cigarette ligher (an expensive one) charger, and the phone (Nokia C7) won't charge. The solution was somewhat surprising. Some background info: in the USB plugs, there are 4 wires: +5 V, Ground, +Data, -Data. Only the first two is required for charging, but you have to do something with the rest. The spec says, they should be connected together either directly or through a maximum of 200 ohm resistor. However, in my charger (optimised for iPhone perhaps?) the +Data was connected to the +5 V through a 24K resistor, and likewise the -Data to the Gnd through a 24K resistor. Removing them and connecting the + and - Data through a 100 ohm resistor, the charger works perfectly. Too bad though, that you need a soldering iron for this...
Aha! After removing two resistors tying pins 2 and 3 to the power rails (and of course soldering pins 2 and 3 together), the charger works. The voltage between pins 1 and 4 is 5.24 V, and between 1 and 2-3 it's now 2.15V (it used to be ~3V). Mr Pink's circuit board. Green: solder bridge. Red: removed resistors. The other USB charger was trickier to disassemble because it is encased in a stainless steel sleeve, but after some prying it came apart. Same problem, same resolution, same results. Top: Mr Pink's resistors. Bottom: Mr Steel's resistors. There's no doubt in my mind that Mr Pink's components were placed and soldered by hand :(


  1. Excellent post. While looking for a solution to a non charging Nokia C7 via a cheapo auto 12v to USB charger, I came across your blog. When I looked into my cheapo charger, I found the same 24K resistors. Why are they built this way if it keeps the unit from charging?

  2. This is highly informatics, crisp and clear. I think that everything has been described in systematic manner so that reader could get maximum information and learn many things.
    USB car charger

  3. This comment has been removed by the author.

  4. Nice blog...Thanks for sharing this useful information about chargers….keep it up
    car chargers

  5. Smart phones are becoming indispensible by the day and hence so are the accessories associated with it. USB Type C Cable