Are USB adaptors interchangeable?
October 26, 2012 12:02 PM   Subscribe

Can I use an iPhone or Kindle adaptor for my iAudio 9 mp3 player?

I have an iAudio 9 mp3 player. As with many of my electronic devices, it charges by plugging into a USB port on my laptop. I also have an iPhone and a Kindle which charge the same way, however, I have been able to procure adaptors that I can use to directly charge from a wall outlet with these two devices. I'm sure you've seen these; you just plug the USB connector into the adaptor and the adaptor directly into the wall.

My question is, can I use one of these adaptors for my iAudio 9? I don't know if there's something special about the power conversion for the various devices, so I don't know if I will hurt the mp3 player (or the convertor) if I try. Any electricity gurus out there have any thoughts?
posted by blurker to Technology (8 answers total)
I use my Kindle and iPhone adaptors interchangeably and haven't noticed any problems!
posted by estlin at 12:05 PM on October 26, 2012

USB carries usually no more than 1 amp and all modern devices have a regulator that basically tells the adapter what power it takes, so I wouldn't worry about it. Certain devices like my Nexus 7 are very finicky and like being plugged in to their OEM adapter, but most are interchangeable without causing any damage.
posted by disillusioned at 12:07 PM on October 26, 2012

Yep, I do this all the time with no problems. I even ignore the warnings in products to only use the provided cable. Living on the edge!
posted by selfnoise at 12:09 PM on October 26, 2012

More data, in case it matters --

The iPhone adaptor indicates an output of 5V and 1 amp. The Kindle calls out 5V and 0.85 amps.

Sorry to threadsit, but more data is always good, right?
posted by blurker at 12:20 PM on October 26, 2012

As far as I know, using an adapter that's rated for a higher number of watts or amps than what your device needs is fine. It will only take as much as it needs. However, some devices like the iPad will charge really slowly or even refuse to work with an adaptor that supplied too few.

When I charge my iPad with my iPhone's "brick", it takes hours and hours - somewhere around a full day - to charge completely. The 10W "brick" that comes with the iPad charges at a much more normal rate.
posted by tkolstee at 12:32 PM on October 26, 2012

Yeah, I think the worst-case scenario (or certainly worst likely case scenario?) is it takes a long time to charge or doesn't charge at all. So give it a shot! See what happens!
posted by mskyle at 12:58 PM on October 26, 2012

The bare minimum USB power draw is around 100 mA, devices are expected to use that much just to function. The upper draw on a USB (the one on your computer) is supposed to be around 500mA, and in theory smart devices are supposed to request the bump from 100 to 500 mA, but in practice they often don't. My stupid battery charger will draw 500 mA without asking at all, my old Blackberry phone would only charge at 100 mA unless it could chat with a special system driver and then it would see fit to go ahead and draw 500 mA and charge 5x faster.

Some smart devices have special wall warts that have enough circuitry in them to let the device know that it can draw a 500 mA or even larger current, some other wall warts are just dumb and are just rated at 500 mA (the max without negotiation).

Some 'special' cables do tricks like shorting the Transmit/Receive wires together to serve as a special notice to the device that they aren't plugged into a computer and can go ahead and draw 500 mA without asking for it. Some others use a specific resistance between the T/R wires to signal the device that it's plugged into a specific charger that can provide 1000 mA or more.

So in all likelyhood, your mp3 player will charge at least at 100 mA, maybe it will go up to 500 mA, but probably not any more (and it probably never drew more than that anyway unless it came with a 'special' charger and cable originally); if it is mostly meant to charge from a computer it's 500 mA max.

And like tkolsee said, having more mA available is no problem, the device only draws what it needs. Having less mA is no problem, it either doesn't work at all, or it charges really slow. What you don't want to do is use a special cable that tells the device it can draw 1000 mA and plug it into a wall wart that can only provice 500 or 100 mA, that could possibly fry the wall wart.
posted by zengargoyle at 1:11 PM on October 26, 2012 [1 favorite]

Just because I saw this on HN today, A dozen USB chargers in the lab has a teardown and test of a handful of the common vendor provided USB wall warts, a few of the generic ones, and quite a bit of technical info on the various non-standards signaling mechanisms between devices and the chargers. It's a bit technical in places, but a bit more thorough than the Wikipedia section on USB charging standards.
posted by zengargoyle at 6:42 AM on October 28, 2012 [1 favorite]

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