This question already has an answer here:

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?


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).

marked as duplicate by Ƭᴇcʜιᴇ007, Ramhound, techraf, DavidPostill, mdpc Oct 20 '16 at 23:27

This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.

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    @Ramhound, no, that question was about a hub that is not connected to a PC, but some ports might be "charging ports" still. The OP question is about OTG port to be a host, yet, instead of supplying VBUS, it should consume VBUS to charge itself. USB OTG/BC specs define this middle role with a goofy term "accessory charging adapter", which is too broad to make any common sense, but it is what it is. – Ale..chenski Oct 18 '16 at 21:41
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    Your two scenarios won't work. In the 1st, the pen drive would work, but you can't provide power to a downstream port and have it charge the tablet. In the second, the charging power would be limited to the current of one USB port and the tablet would not see the pen drive. – fixer1234 Oct 19 '16 at 6:46
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    The marked duplicate does not address this question. This question merely had a title that did not accurately describe it. Voting to reopen. – fixer1234 Oct 23 '16 at 23:15
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    @techraf, tablet computers are not necessarily off-topic devices. The question is a generic one dealing with connecting both power and a storage device to a computer via USB, which is applicable to on-topic devices. The fact that the computer mentioned in the question has a tablet form factor isn't particularly material. I don't see any reason why the question would be off-topic. – fixer1234 Oct 23 '16 at 23:56
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    @techraf, I think you missed the point about using the hub to also connect a storage device. The issue here is that you can theoretically charge a tablet (or toothbrush), through an appropriate USB port on a hub, or you can connect the hub a different way to attach a pen drive to a computer (my toothbrush can't use a pen drive). But you can't do both simultaneously. The reason for that last point is the gist of the question. The question is not about charging through a hub. – fixer1234 Oct 24 '16 at 0:08

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]

  • I barely understand concepts in electricity but I feel that this answer is the solution (even if it means that I can’t have what I want). So... do you know any “accessory charger adapters” on Amazon? If I enter that phrase in Amazon search, will I get correct results? Also I wonder how to translate it to other languages. – 7vujy0f0hy Oct 18 '16 at 21:03
  • I’m not the most competent person to judge answers in this thread but I select this answer as a solution. (I can’t vote with my reputation score anyway.) – 7vujy0f0hy Oct 18 '16 at 21:12
  • The manufacturers seems to be also fuzzy in proper identification of their devices, so it appears to be a tough task. Try this one from Amazon, amazon.com/Lollipop-Charging-Adapter-Function-Samsung/dp/… , and look for similar. – Ale..chenski Oct 18 '16 at 21:22
  • From description of that Lollipop adapter: “Please take note: Extra power only charge for accessories such as mouse keyboard etc, can not charge for smartphone or tablet.” But: “OTG and charge at the same time.” Confusing. – 7vujy0f0hy Oct 18 '16 at 22:06
  • Anyway, thank you for very useful search keywords! – 7vujy0f0hy Oct 18 '16 at 22:13

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.

  • I know that USB hubs can be used to charge USB devices using power stored on host’s battery. This scenario is, however, opposite: I want to charge the host. Also, are you sure that the pendrive will be visible to the tablet in configuration suggested by you? – 7vujy0f0hy Oct 18 '16 at 20:23
  • I an not certain about the device I suggested. Since you didn't mention the model/type of the tablet, drive, or tablet. But, it certainly seems very likely that you should be able to buy something that will work for your needs though, and I am pretty sure you can't simply randomly plug a charger into a hub and expect useful results. – Zoredache Oct 18 '16 at 20:30
  • Generic no-name Windows tablet from Alibaba.com and a generic pendrive. They are all the same really. I do already use a “random” USB hub plugged into a charger to split the power and charge multiple guest devices and it has been working without fault for a few weeks. – 7vujy0f0hy Oct 18 '16 at 20:35
  • That is a definite no. Power flows in one way only, and what you are suggesting makes power flow into opposite directions causing a collsion and thus short circuit. You'll fry your hub if its not properly protected. – LPChip Oct 18 '16 at 20:37
  • @LPChip: Which solution specifically are you cautioning about? (1) Plugging a random USB hub into a charger to charge multiple guest devices (not related to this thread)? (2) OP configuration? (3) @Zoredache’s solution (powered hub)? – 7vujy0f0hy Oct 18 '16 at 20:43

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.

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    flows in one way, from + to - Except if you talk to a physicist who will tell you that it is negative to positive. – Zoredache Oct 18 '16 at 20:45
  • In OP, I offered two configurations (one, two). Which one violates these principles? It cannot be both because one is the opposite of the other. – 7vujy0f0hy Oct 18 '16 at 20:46
  • @Zoredache If this is true, can you then explain why when 2 wires with a + lead touches, it creates a spark, and when two - leads touches it doesn't? – LPChip Oct 19 '16 at 14:54

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.

  • I know that powered USB hubs can power guest devices. Can they power the host though? – 7vujy0f0hy Oct 18 '16 at 20:30

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