MobileRead Forums - View Single Post - Sony Reader micro-USB charging

Fastolfe · 12-16-2010, 05:24 AM

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?

12-16-2010, 05:24 AM	#1
Fastolfe Bookworm Posts: 98 Karma: 55796 Join Date: Dec 2010 Device: Sony PRS-650	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?