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Question: How can I add power to a USB cable without using a USB hub?

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Background:

I have a USB device that runs on bus power. I don't know how much bus power it requires (I googled).

When I plug it into my Macbook Pro, it works.

When I plug it into my iPad Camera Connection Kit, it doesn't work.

Googling confirms that this device needs more bus power than provided is by iPad, but people say they have made the device work with iPad by using a powered USB hub.

So I bought a USB cable that has two male A connectors and one male B connector; the cable is marketed for connecting USB hard drives that require extra power: one male A has power and data lines, the other male A has only power lines.

I tried that cable with my iPad and USB device and it doesn't work; the device doesn't light up any of its LEDs.

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Maybe they were referring to an external power source (an adapter connected to a power outlet) that connects to external USB Hubs. –  Doktoro Reichard Sep 19 '13 at 18:58
    
Yes, they were. My question is, how do I add power to USB /WITHOUT/ a hub? –  themirror Sep 19 '13 at 19:00
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1 Answer 1

up vote 4 down vote accepted

It won't work. The problem is not that there isn't enough power available, it's that the host will not configure a device into a particular power profile unless it knows there's enough power available for that profile at the device port. So making more power available will not help. You have to use a device that can tell the host how much power it can provide, which only a USB hub will do.

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To develop a little. Since portable devices are battery-constrained, them may limit the amount of energy they can send through the USB connection. –  Doktoro Reichard Sep 19 '13 at 19:21
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