USB Power Adapter

[gwynevans]

Originally Posted by JSWolf

I know how the cable works. But do you know what the power specification that comes out of that barrel plug is? Do you know if it might be risking your 700? Unless you know what comes out of that plug, don't use it. NEVER use any charger that you do not know what comes out of it. So what is the spec for that barrel plug?

That cable's just a physical converter, so the output will be the same as the input, so the question really is, what the chance that the USB adapter is out-of-spec? Given it's a name brand, pretty low, I'd expect.

[JSWolf]

Originally Posted by gwynevans

That cable's just a physical converter, so the output will be the same as the input, so the question really is, what the chance that the USB adapter is out-of-spec? Given it's a name brand, pretty low, I'd expect.

It's not that it's out of spec. The problem could be too low power and that could cause a problem.

[thibaulthalpern]

Originally Posted by JSWolf

I know how the cable works. But do you know what the power specification that comes out of that barrel plug is? Do you know if it might be risking your 700? Unless you know what comes out of that plug, don't use it. NEVER use any charger that you do not know what comes out of it. So what is the spec for that barrel plug?

As I mentioned before, what comes out is 5V because that's what USB standards dictates. And you can look at the plug too. And you can also read the specifications. That's not low. The Sony PRS-700 can charge by plugging in to the USB port or DC port. 5V and 5.2V is not a big difference and besides, it's not as if the Sony reader has one charging mechanism for USB and one charging mechanism for DC port. IT's both the same charging mechanism with two different ports.

[gokalp]

Originally Posted by JSWolf

It's not that it's out of spec. The problem could be too low power and that could cause a problem.

Low voltage is almost never a problem with a modern device. Lithium batteries are usually 3.7V, and any modern design has a diode and a fuse in series with the charging circuit. If you apply a low voltage, or even short that port (i.e. 0V), it simply does not do anything as the diode does not turn on. In other words, you cannot discharge the battery externally.

If you apply a high voltage, several things can happen:
1) If the charging system has a regulator between the battery and the port, it charges ok.
2) If there is sufficient series resistance, the battery will charge fast. Note that this will wear out the battery faster.
3) If the series resistance is low, but there is still a fuse, you'll burn the fuse. A simple fuse exchange can fix this though albeit with some soldering.
4) If none of the above apply, most probably you will damage some IC and/or battery. However, I have not seen any device which does apply to this category in the last 5 years.

[Shaggy]

Originally Posted by thibaulthalpern

As I mentioned before, what comes out is 5V because that's what USB standards dictates.

Don't assume it's 5V just because that's what the standard says. Yes, the USB power spec says 5V, but there are many 3rd party USB chargers these days that are built for specific devices (cell phones, MP3 players, etc) that DO NOT follow the spec. The power they output works fine with the 3rd party device they were designed for, but it will not necessarily be even close to the official spec.

There are many cases of devices which have adopted the USB plug format for their cables, but don't adhere to the power standards.

[Shaggy]

As I mentioned above, you need to be careful with these 3rd party chargers.

According to Apple's support site, the "Apple iPod Power Adapter" ( with firewire or USB port) outputs 12V at 1A, which clearly violates the USB power spec.

http://support.apple.com/kb/HT2537

I don't know if this is the exact same charger mentioned previously in this thread (it looks a little different), but you need to be sure what the power output is before trying to use these on devices that they weren't specifically designed for.

[thibaulthalpern]

Originally Posted by Shaggy

As I mentioned above, you need to be careful with these 3rd party chargers.

According to Apple's support site, the "Apple iPod Power Adapter" ( with firewire or USB port) outputs 12V at 1A, which clearly violates the USB power spec.

http://support.apple.com/kb/HT2537

I don't know if this is the exact same charger mentioned previously in this thread (it looks a little different), but you need to be sure what the power output is before trying to use these on devices that they weren't specifically designed for.

Wrong kind of adapter. That one is no longer made. The reason that one you pointed out might be giving out 12V is because it is also useable for Firewire devices. Apple has not made iPod that runs via FireWire for a couple of years now.

The one I'm talking about clearly is printed with 5V output. It's printed clearly right on the adapter.

[Shaggy]

Originally Posted by thibaulthalpern

The one I'm talking about clearly is printed with 5V output. It's printed clearly right on the adapter.

Then you should be good to go.

In general though, don't just assume it's 5V. Make sure it's either printed on it or that info is given on the manufacturer's/seller's site somewhere. There are other examples besides the out of date one I found on Apple's site where USB chargers don't follow the spec.

[tompe]

Originally Posted by Shaggy

T
In general though, don't just assume it's 5V. Make sure it's either printed on it or that info is given on the manufacturer's/seller's site somewhere. There are other examples besides the out of date one I found on Apple's site where USB chargers don't follow the spec.

Really. It is called an USB charger and do not follow the specification?

[Shaggy]

Originally Posted by tompe

Really. It is called an USB charger and do not follow the specification?

Really. As I mentioned, lots of device manufacturers (cell phones, mp3 players, etc) are adopting the USB format for their connectors, but the third party chargers that they designed for their device don't necessarily follow the USB power specs.

If it's being sold as a "universal" USB charger, then it's probably fine. If it's a charger that was specifically designed for another device and just happens to have a USB connector on the end, then it's a good idea to verify the power output.