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When traveling, I probably will have the iPad 2, iPhone 4S, a USB backup charger, and some misc devices such as a Kindle Fire and a Sony digital camera that uses USB to charge its battery.

So instead of hooking them all up to the computer to charge them overnight, in the event that I actually need to charge every one of them that night, is it possible to use Apple's 10W USB charger that Apple makes (it is 100V to 240V compatible):

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and then hook it up to any USB hub, such as this Belkin 7-port one:

enter image description here

and be able to charge all the devices listed above at the same time? (by the way, it seems that the smaller Apple USB charger with the green dot is 5W, so probably that one is not very powerful to charge all devices at the same time).

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Belkin just launched this... But still too expensive. store.griffintechnology.com/ces-2013/powerdock-5-device-charger –  user38144 Jan 8 '13 at 15:19
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4 Answers

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You typically will need one high-powered (5W) USB port for each of such devices to charge efficiently. The iPad alone requires more to charge, hence the non-standard 10W adapter. In addition, the USB hub itself is not likely to provide the necessary wattage to any of the ports (these usually are low-powered ports), so chances are not even one device will efficiently charge when connected alone to such a hub.

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I saw people writing reviews on Amazon that the included power adapter is not charging devices well, but what if I use this Apple 10W USB Charger and not use the included adapter with the hub? Supposedly, the 10W should be distributed to all the ports (divided up)... so if one port needs 5W, and the other needs 5W, then it can charge 2 devices? Are you saying if 3, 4, or 5 devices are connected to the hub, then it actually requires about 15W, 20W, or 25W? (and if all 7 ports are used for charging, then 35W at least?) Is the 5W what a typical PC or Mac USB port can provide? –  動靜能量 Jan 3 '12 at 20:23
    
The main point is that the iPad alone would draw most of the 10W for charging efficiently. In my experience an iPad can charge with less (I use the 5W adapter sometimes), but at a very slow rate, overnight will not suffice for a complete charge. Add some extra devices drawing power in the mix, and there is no way your suggested set-up will work well. –  Gerry Jan 3 '12 at 20:33
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Also don't assume the hub will actually 'distribute' the 10W. It's far more likely it will only draw 5W from the 10W adapter and distribute that. –  Gerry Jan 3 '12 at 20:34
    
aha... the problem is that most hotels only provide 1 or 2 outlets, so to charge 4 or 5 devices at the same time using 5 chargers (using 5 outlets) it is hard... some USB ports I see on Amazon is providing 12.5W, so maybe it is good for charging 2 or 3 devices, while the iPad 2 will need its own charger. –  動靜能量 Jan 3 '12 at 20:36
    
really? I thought the voltage is 5V, and whatever current it draws, it depends on the device... if it is not over heating. The 10W or 12.5W is just the maximum power it can provide. So 10W is 2 Amp (using the formula Power = Voltage x Current), and if one device draws 0.8 Amp, while another device draws 1.2 Amp, it is all automatic? –  動靜能量 Jan 3 '12 at 20:40
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Apple use some tricky schemes to identify battery chargers and compatible devices. The sense resistor is common and it is what is responsible for the message

enter image description here

with some combinations of devices.

See the fun they had working out the right sense resistors when designing the MintyBoost. (and do check out ladyada.net if you like this sort of thing, there are some very clever hacks)

I don't think your iPad will charge at all with the hub. I have a Belkin Dual USB Charger and when connected the iPad just says

enter image description here

because it detects that it is not plugged into a high power USB port. Apple provide some explanation about high power in this technical note - basically the port starts out supplying the usual 500mA maximum and will supply extra power if capable.

The USB hub is almost certainly not a high power port, even if it is a powered hub. And it won't have the correct sense resistors to tell the iPhone/iPad that it is a device capable of charging it. So even if it could distribute power from the 10W adapter the devices could not recognise that they were connected to a 10W adapter.

If you only carry one charger then it should be the 10W adapter but you really need to connect the iPad directly to it. While the iPad can charge from the 5W adapter it will take much longer and you would probably not get a full charge on your device.

I think your ideal combination of charging devices is one Apple 10W adapter and one Apple 5W adapter, or two 10W adapters (I don't see the point of buying the 5W adapters since they are the same price and the 10W can do everything the 5W can do, it's just a tiny bit larger.)

Then you should be able to charge 5 or 6 devices a night with no problems.

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No, in fact most devices won't charge at all unless the hub is connected to a USB host.

When a USB device is plugged in it first determines if it's plugging into a USB host or hub, or if it's plugging into a charging device. This is signaled by the state of the data lines on the USB port.

If it's plugged into a charging device, it simply starts charging. Again, the state of the data lines tells it enough about the charger so it knows how much current it can pull - this is how an iPad knows it's plugged into an iPhone/iPod charger and charges more slowly. The data line state is a key that says, "This charger only supports 1A."

If it's plugged into a USB host or hub, then it has to talk to the host device (usually a computer, or a computer through the hub) and request power. The hub or computer might only be able to supply 100mA, or 500mA, or on newer USB ports 1A or 2A. The key point, however, is that the device has to talk to the computer and get permission to use that power.

The hub cannot give permission, it simply passes the request along to the computer.

So if you don't plug the hub into a computer then nothing attached to the hub will be able to receive permission. The hub doesn't match the state of the data lines of a charger you might plug it into, so nothing attached to a hub that's attached to a charger will ever get permission to charge, or will ever think that the hub is a charger.

There are devices which disobey the USB specification and attempt to charge anyway, and they might be able to charge under such an arrangement.

Apple devices, however, will never charge unless attached to a charger that follows Apple's charging spec, or a computer with sufficient current output.

There are a number of multiport chargers available now, though. Google for "usb 4 port charger" and you'll find many inexpensive options that will work with Apple devices, and be more compact than a charger and USB hub anyway.

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"state of the data lines" is a little misleading here. Their state is a binary 1 or 0, what is actually measured to determine charge capability is their voltage. The MintyBoost link in my answer shows actual resistor configurations and voltage levels for 500mA/1A charge rate selection. –  Adam Eberbach Mar 30 '12 at 2:20
    
Actually different companies use different methods, but it's relatively common to use resistors to bias them to a certain voltage on each, thus the state is not strictly a binary solution. I didn't explain further because it's interesting but largely irrelevant. The details can be found out if needed, this is a simple explanation. –  Adam Davis Mar 30 '12 at 2:52
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Wouldn't using the cable in the following link (http://www.canadacomputers.com/product_info.php?cPath=95_97&item_id=040817) plugged into a normal 5W powered hub do the trick?

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Of course you would have to convert the mini USB to a 30-pin connector somehow through either soldering or using adapters... –  Marrrl Feb 17 '13 at 19:33
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