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Effect of charging-only USB cables (ie that can't transfer data)?

I have recently come across two Micro USB cables that came with power banks, which were able to charge phones but didn’t support any data transfer. One came with a power bank from Realpower, the other one with a power bank of the Dutch Railways (I think the power bank is manufactured by Xtorm).
I found that using one of these cables has some interesting side effects:

  • When connecting the FP2 to my laptop (ThinkPad T60) with a normal micro USB cable, it charges with 500mA. But, when using one of these power bank’s cables, it charges with 1A from the laptop.
  • When connecting the FP2 to a Sitecom powered USB hub (ie the hub has its own AC adapter) with a normal USB cable, it only charges when the computer is on. With one of these power bank’s cables, it also charges when the computer is off.

For the USB 2.0 ports of a laptop from 2006, charging with 1A is obviously out-of-spec behaviour and it surprised me that it didn’t appear to do any harm to the laptop such as tripping the fuse of the USB port.

Is there any hardware expert here who can shed light on the safety of using these cables?

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Here is what happens when using a regular USB (2.0) cable:

  • When connected to a computer (or USB hub), the phone has to to “ask for permission” (using the data lines) before drawing more than 100 mA. When the computer is off, it can’t answer this request and the phone won’t charge. When it’s on, it will allow up to 500 mA to be drawn.
  • Chargers short the data lines in order to signal the phone that it is allowed to draw up to 1.5 A without any USB communication.

Your special no-data cables most likely short the data pins directly in the Micro USB connector. This way the phone always thinks it’s connected to a charger and will draw up to 1.5 A. This could theoretically damage your computer or USB hub, however most USB ports can handle quite some abuse. But it definitely violates the USB specification.

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I think most usb ports have overload protection but I wouldnt bet on it.

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