About the iPad power supply

by Volker Weber

Carl writes:

The iPad adapter is not your regular USB adapter. It's expecting 10v to charge instead of the 5v that your typical PC, and USB adapter delivers. So whilst Steve Jobs talks about standards, he likes to tweek them a little bit. Apparently on the Mac this isn't an issue, as it' recognizes when an iPad is connected and outputs 5v. Now I have discovered though, that if you do plug an iPad into a PC USB port and turn the screen off it will charge, very slowly.

Well, that's wrong. Apple does not supply 10 V. That would be rather silly. Look at the fine print:

iPad power supply
Photo: vowe

We are simulating the reading abilities of an old fart like myself. The top says 10 W, not 10 V. Easy to mix up. The bottom right says 5.1 V at 2.1 A. The iPad will adjust the 5.1 V to 5.0 just as any other USB device. But it is capable of gobbling up the power at up to 2 A. The iPad has a pretty large battery that takes forever to fill up if you only supply 500 mA as specified in the USB 2.0 specs. A dedicated battery charging port can supply a lot more .

So, it's not evil Steve Jobs. It's just that in the PC world, you have to pinch every penny to make a profit.


Ich bin mir sehr sicher, dass USB 2.0 mit max. 500mA und USB 3.0 mit max. 900mA spezifiziert ist, um endlich externe Festplatten ohne Y-Kabel nutzen zu können. Das habe ich so auch bei usb.org gefunden. Wo liegt mein Fehler diesmal? ;)

Markus Jabs, 2010-08-09

Nirgendwo. Ich habe totalen Blödsinn im Kopf gehabt. Korrigiert. :-)

Volker Weber, 2010-08-09

the whole thing is actually clever and interesting: there is a very good article here http://www.ladyada.net/make/mintyboost/icharge.html that explains "The mysteries of Apple device charging"

Giuseppe Grasso, 2010-08-09

Wer kam denn auf die 10V Theorie? Wäre lustig wenn man dann an ein 10V Ladegerät ein Iphone zum Aufladen gehängt hätte. *Bruzzel*

Ich musste aber den kleinen Unterschied auch erst lernen. Ich hatte das Ipad Ladegerät erst gar nicht ausgepackt und mich eine gute Woche darüber gewundert warum das Ding (am Iphone Stecker) so ewig zum Laden braucht.. :-)

Roland Dressler, 2010-08-09

Siehe oben die ersten beiden Wörter und den Link.

Volker Weber, 2010-08-09

Das der USB Ladeadapter mehr Ampere liefert ist aber durchaus üblich, zumindestens bei meinem aktuellen Smartphone und dem davor war der Ladevorgang mit dem Adapter schneller als am Rechner.

Das interessanteste in Sachen USB aber doch irgendwie nicht hab ich bei einem Motorola Razr gesehen, welches zwar einen USB Port zum laden hat, sich aber nur mit dem Motorola Adapter laden lässt.

Patrick Bohr, 2010-08-09

My Motorola Milestone also draws a lot more than the specified 500mA. Charging the device using my cheapish Dell PC at work takes half a day. Using the power supply reduces the timespan to an hour.

Michael Adams, 2010-08-09

Mein Razr liess sich mit jedem USB Kabel laden. Allerdings musste ein Treiber installiert sein. Kein Treiber - kein Laden. Und wenn das Gerät aus war (z.B. weil der Akku erschöpft war), dann sprach der Treiber nicht an und man war gebissen... (Bis man den Adapter zur Hand hatte)

Ulf Jährig, 2010-08-09

@Ulf: Unter Linux ging das auch ohne Treiber
@Vowe: Wie kommt der USB Lader im Sanctuary mit dem iPad klar (Ausser dass es ein grösseres Sanctuary braucht)?

Stephan H. Wissel, 2010-08-09

You're right Volker, and I'll be in trouble with my Dad the electrical engineer for making such a basic mistake.

However, it's more widespread than just PCs, many cars, 3rd power power adapters give the impression they are not charging, surprisingly a Mac in booted to Windows also doesn't give enough power. The amps expected by the iPad are well outside the USB specifications.

My point was and is if you stick the iPad into an available USB socket somewhere don't always expect it to charge.

Carl Tyler, 2010-08-09

Actually, the iPad is charging in many of those situations. But it is not charging enough to report a charge. That also happens with many devices, and it is called a "trickle" charge. The only trouble is if you discharge more quickly than you charge. :-)

Oh yes, and then there are devices which won't charge at all, although the power supply is strong enough, and the cable fits. Amongst them some Nokia device. As I once wrote: all hail to the USB charger.

Volker Weber, 2010-08-09

I made a power supply circuit to provide 5.1vdc and 2.1a to charge my iPad, according to the LM350 data sheet (adjustable regulator application, page 6). However, when I connect the iPad USB cable to it, the iPad does not indicate charging.

The input source is a 12v photo-voltaic system with several lead-acid batteries, so sufficient current is available. The LM350 is good for 3a. I adjusted the potentiometer so that 5.1v appears on the USB port. What could be the problem?

Sidney Tupper, 2010-08-22

I just read Giuseppe Grasso's comment about "The mysteries of Apple device charging" article, which suggests the solution to my problem. Thanks, vowe.net.

Sidney Tupper, 2010-08-22

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