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This question seems like it would have a logical answer, but I thought I’d ask to be safe.
As shown in the photo below, there exist externally-powered USB hubs (A) and USB power-adapters—like the kind that come with some GPS and other USB devices—(B).
Connecting devices like keyboards, mice, flash-drives, MP3 players, etc. to the powered hub (A) is not a problem, as expected. The devices simply turn on (eg light up) or charge, or even do nothing as the case may be.
But, what happens when you plug a device into a USB power-adapter like (B)? I’ve plugged MP3 players (and of course the GPS device it came with) into it and they simply charged. But what would happen if I plugged a mouse or flash-drive into it?
Logic says that they would not be harmed and act exactly like they would if plugged into a powered-hub, but is that indeed the case? (unusual, proprietary adapters notwithstanding) USB connectors only have four pins, +5V
, GND
, +DATA
, -DATA
; so presumably only the power pins would be connected, and thus it would be harmless (as plugging it into any other live port would be). Again, this is excluding unusual, non-standard devices/adapters since they would not be compatible anyway (you can’t use the pins for whatever you want).
Am I right?
Update
Okay, so I took the chance and tried plugging a flash-drive into the adapter. My idea was to use the orange LED in the drive, plugged into the adapter as a cute little, low-power night-light. Unfortunately I over-estimated the luminosity of the LED (I could have sworn it was a lot brighter). The first shot is of the drive with some ambient light (a 12-ultra-bright-white-LED torch with 3xAAA), and the second is of the hallway with just the drive’s light (at night of course).
I tried a different drive and it didn’t even light up (because there’s no data communication). I then checked both drives with my computer and they were both fine.
Oh well, at least I learned something. :-)
It's my theory that you would create a short circuit since there won't be any load or drop in voltage. I don't think that you would cause catastrophic damage per se, but you would most likely bust a couple of capacitors. Also, I think you are doubling the voltage as well. I haven't quite wrapped my (novice) electrical knowledge around it yet. – skub – 2011-07-28T04:02:43.600
@skub, I think Collin is on the right track about how it would be like if the device were connected to the hub by itself or to the computer while it’s off (my last system had powered front USB ports, even while off, so I could charge without turning it on). – Synetech – 2011-07-28T07:10:51.390
I totally mis-read the post. I thought he was going to plug A into B. HAHA! – skub – 2011-08-01T02:13:22.333