perhaps I am asking for too much. Please do tell.

So I have a few usb chargers laying around. I realised that in these chargers I can charge iPhones and I can charge all devices that do not follow the "usb power delivery specification" (roughtly all usb1.1 and some usb2 devices).

What I can NOT charge is my android phone. Looking into why I ended up in this article.

So apparently Apple "did it again". I mean they gave the finger to yet another specification and did their own thing. Their thing is that they provide 2V and 2.8V in the data pins (D- and D+ respectively) of their usb chargers. If these voltages are not present the charger is not considered an apple product and apple products will fail to charge...

What is more the apple usb power delivery standard seems to conflict (according to the article) with the usb power delivery standard, which requires that a very small resistor (0-200ohms) must be placed between the D- and D+ data pins of the usb charger.

What is EVEN worse: some of the usb chargers I have never stated that they are targeted for apple only products! (I have already formally complained to them).

The question is, I see on ebay and elsewhere so "truly universal USB chargers that claim to charge both apple products and other products". What have they done in order to make their products universal?

Is it possible to hack my usb chargers to make them universal as well??

Thank you in advance for your help.

  • 1
    \$\begingroup\$ Apple's high capacity charging standard predates the USB power delivery specification... \$\endgroup\$ – Passerby Feb 4 '15 at 23:46
  • \$\begingroup\$ @Passerby true, the "usb power delivery" standard was only started being applied in 2012, but Apple is notorious for breaking standards. MY guess is they read preliminaries of the standard and decided to go the other way. \$\endgroup\$ – nass Feb 5 '15 at 0:18

If I read your post correctly, you want a charger that will both follow USB specifications and the Apple specs?

The article presents a very convoluted circuit. Only three resistors in series are needed: 430Ω, 150Ω and 360Ω. Together they make 940Ω which yields a current of about 5.15mA. you connect D+ and D- across the 150Ω resistor. The standard USB charge spec needs a resistor of less than 200Ω. So a 150Ω resistor is fine.

NOTE: I don't know if the voltages present on D+ and D- will effect a non apple device. It might work and it might not. If it does not, a double pole single throw (DPST) switch can be put across power (both ground and VCC) and the circuit to isolate it when charging non apple devices which will simply see a 150Ω resistor.


simulate this circuit – Schematic created using CircuitLab

A volt meter across R3 will yield about 2V and from R2 to ground will yield about 2.77V, close to 2.8. I doubt it's that picky. You could also throw in a 160Ω for R2 which would bring the D+ up a bit without dropping D- that much, about 1.98V.

The circuit will draw 5.15mA and dissipate 25.7mW. 1/8 watt resistors can be used.

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  • \$\begingroup\$ Doh! I changed my schematic and somehow forgot to label the 150Ω resistor R2. \$\endgroup\$ – Mister Tea Feb 5 '15 at 15:49
  • \$\begingroup\$ should you include the length of the usb cable in the resistance calculation? \$\endgroup\$ – jiggunjer Apr 20 '15 at 18:40
  • \$\begingroup\$ Nah. They are low enough in resistance that it won't matter. Even 2 meters of very thin 30AWG wire is about half an ohm. \$\endgroup\$ – Mister Tea Apr 22 '15 at 18:00
  • \$\begingroup\$ But half an ohm at 1A charge means half a volt drop. But I'll assume the data lines don't carry much current... \$\endgroup\$ – jiggunjer Apr 22 '15 at 18:35
  • \$\begingroup\$ Exactly. The wires used for signalling are carrying very, very little current if any current at all. They are simply a voltage reference. Of course, your +5V and common wires supplying the actual current need to be thicker to handle the current without dropping too much voltage. This is why some thin usb cables are stuck charging your device at <=500mA when you have a 1 or 2 amp charger. \$\endgroup\$ – Mister Tea Apr 22 '15 at 18:55

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