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What I do have (default way of charging tablets: A) vs. what I want to have (B or C):

USB charging scenarios

Can I have it?

It’s a simple thing, so why not?

How else can I use a tablet together with a portable hard disk (or with any USB device in fact) when I run out of battery power?

Update

Marking my question as a duplicate of “Can I charge USB devices from a powered hub that isn't connected to a PC?” is wrong (as @AliChen explains on my behalf in a comment below).

In fact, I already use a USB hub connected to a universal USB charger to split electric power and charge multiple devices. And that hub is not even powered – it’s passive. So I know the answer to the other question very well – even without reading it.

This is different from using a single USB socket to charge a tablet and connect that tablet to a pendrive at the same time (presumably by the means of some kind of USB hub).

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7vujy0f0hy
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4 Answers4

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No, what you "want" is not that simple. Most hubs are not designed to conduct the current backwards from downstream ports to upstream. Even if some cheap hubs do have the direct connection, the tablet will not recognize the cable as a charger cable, will continue to be in HOST mode (which means supplying VBUS, not consuming), and obviously will not charge itself. So the case (2) will not work for this reason.

In case (3) the tablet will take charge as from a regular 500-mA port. However, there will be no any USB connections.

To have your tablet to be charged and simultaneously be in host mode, a special arrangement is required. In USB charging specification it is called "accessory charger adapter". For some more details you can see this item. However, your tablet must support this "accessory" mode, which may not be the case.

ADDITION: The devices are available at Amazon with keyword search [OTG and charge at the same time]

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Ale..chenski
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You can purchase USB Hubs (example) that will provide sufficient power to charge a tablet. Do not plug a charger into some random hub, not specifically designed for that purpose, it almost certainly won't work, and many fail catastrophically.

Zoredache
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USB is a technique known as "Universal Serial Bus" Like every port, electricity is required to make things work. The reason USB comes with a male and female form, is because the female port sends out electricity.

USB uses 5volts on its power port, and a very low voltage (don't know the specifics, but probably blow or close to 1 volt to use as data transmission.

That said, Electricity flows in one way, from + to -.

When Electricity flows from + into another + the circuit overloads as it short circuits. Depending on protections in place in the devices, it will likely damage one of the devices, but in more safe cases, it will simply not work.

In one of the comments on another answer, you mention you want to do the reverse, for the exact same reason, that is not going to work, because again, power flows in one way, and that'll cause for a collision.

LPChip
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You shouldn't plug the charger in randomly. As he said, almost the only way is to buy a hub with power supply for your tablet. Another way would be welding an adapter for this. For this, you should Google for schematics of this adapter.

jukisu
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