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Old 12-16-2010, 06:24 AM   #1
Fastolfe
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Sony Reader micro-USB charging

Hello everybody,

When I try to recharge my PRS-650 with a micro-USB cable, I'm a bit puzzled by the charging messages (or lack thereof) on the screen, and the exact meaning of the red charging LED. The user's manual isn't helping much. I've experimented a bit and here's what I noticed:

- When I'm trying to charge the device from a live, running laptop, the display says "charging battery". Battery charges, screen shows "charging complete" when it's done, no problem

- When I'm trying to charge the device from a sleeping laptop (but that still provides live USB ports, exactly for the purpose of recharging a device without having to run the laptop), the display says it refuses to charge.

- When I use a dedicated micro-USB charger, the kind that comes with cellphones, the display doesn't say anything at all, unhelpfully, but the red LED by the power switch lights up. The device seems to charge okay, and the LED eventually turns off and the device seems fully charged.

Now, both in the case of the sleeping laptop USB port and the micro-USB charger, pin #1 provides 5V and enough power to sustain charging, but the difference seems to lie in the fact that, with the micro-USB charger, pin #2, #3 (the data lines) and pin X are shorted, which is the usual way a cellphone knows whether it's connected to a full-featured USB port or simply a power supply.

So, I figure the Sony Reader acts the same way: if it doesn't sense pins 2, 3 and X shorted, it assumes there's a computer behind the plug, tried to connect to it, and when the laptop is sleeping, it fails and refuses to charge for some reason. If it senses pin 2, 3 and 4 shorted, it lets itself be charged but doesn't say anything on the screen, presumably to let the user read while charging.

The question then would be: why does it refuse to charge when pins 2, 3 and X aren't shorted but there's power available? After all, it's quite common to charge a device from a sleeping laptop - no sense in keeping the laptop running just for that - and people may want to read while charging off of a sleeping laptop too.

It would also explain why some people seem to have problems charging from certain types of aftermarket chargers: not all of them seem to bother shorting pins 2, 3 and X, especially cheap aftermarket cigarette lighter plug USB chargers.

The other question is: with a micro-USB charger, there really is no indication on the screen that the charging process is going well (if it is, I'm not even sure). There's only that red LED and the fact that it seems to charge okay, but that's all. Can I rely on that to carry on charging the device that way? It's handy, to charge the reader in the car, but I don't want to damage the battery.

What do you think?
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Old 12-16-2010, 08:11 AM   #2
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When using a mains charger, as well as the red light being lit, I also see a different battery indication in the bottom-right corner (this is on my PRS-650). Instead of the usual indication of the charge level, it shows an arrow into the battery to indicate charging. As you say, the red light goes off when fully charged. I've never checked, but I'd guess the bottom-right battery indicator would also change back to normal once fully charged as well.

I believe there may be some kind of issue that means it shouldn't be charged from a sleeping laptop? Not sure on this, but there have been other threads that discussed it - I could have the wrong end of the stick on this, and I'm sure other forum members will be more knowledgable than me on it.
Personally, even before I heard of that issue, I've always charged it on the laptop only while actively uploading books (or otherwise using the laptop for email and such), and used a mains charger if I want to leave it to charge for a while unattended.
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Old 12-17-2010, 03:27 AM   #3
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I think you'll find that hibernating laptops are in such a deep sleep that they do not provide power out through the USB port.

Regards, Alex
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Old 12-17-2010, 04:01 AM   #4
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Quote:
Originally Posted by AlexBell View Post
I think you'll find that hibernating laptops are in such a deep sleep that they do not provide power out through the USB port.

Regards, Alex
Hibernation is not the same as sleep/standby, and in the case of the former, the computer has actually copied its memory state to HDD and completely powered down (meaning no USB ports are powered).
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Old 12-17-2010, 04:16 AM   #5
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Actually, in my laptops and all the others I've seen, the USB ports always provide power, even if the laptop is completely shut down. Some laptops offer a BIOS setting to power down the USB ports when the machine is off, and with some others, you can tell the OS to power down the USB ports at sleep time and it works, but not hardware lets you do that.

This is actually a feature. The idea is to let people use their turned-off laptop as a battery brick to recharge cellphones or mp3 players. While it is indeed useful for that purpose, it's also a pain in the rear if you have an external mouse or keyboard, as you'll have to disconnect them manually when you switch off the machine if you don't want them to drain the battery.
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Old 12-17-2010, 04:20 AM   #6
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Most cell phone (except Apple for sure) work to charge the 650. In fact, I have an iGO AC adapter with the Blackberry tip and it works great to charge the 650.
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Old 12-17-2010, 02:25 PM   #7
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It may have something to do with the current being put out by the device going to the reader. I have noticed this too. The Sony wall charger that came with my PRS950 has a output of 1500 mA @ 5 V. The wall chargers for my cel phone accessories are 500 mA, which is also the max by spec that can be drawn from a computer USB 2 port on a computer. It appears the readers are smart enough to recognize what they are plugged into and give different indicators to give a idea of how fast you are charging.
At least that's my guess.
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Old 01-03-2011, 02:27 PM   #8
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Hi! Posted the solution how to charge from the sleeping laptop/any usb wall plug. Please check: http://www.mobileread.com/forums/sho...&postcount=124
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