usb power draw question

elemenoP · 01-02-2011, 11:24 AM

If I have a USB device (let's say a Sony Reader) and I connect it to my Macbook to charge, does it charge faster if my macbook is plugged in, vs on battery power?

Thanks,
eP

theducks · 01-02-2011, 11:32 AM

Quote:

Originally Posted by elemenoP

If I have a USB device (let's say a Sony Reader) and I connect it to my Macbook to charge, does it charge faster if my macbook is plugged in, vs on battery power?

Thanks,
eP

NO

USB puts out 5Volts Period
The port has a preset limit on how much current is allowed to flow. That is the sole limiting factor on charge time.

Will it kill your MBP (or any other brand) battery sooner when not plugged in. Yes. Both ways . Charge - Discharge cycles use up the Battery Lifetime (More equals Less

)

FF2 · 01-02-2011, 11:52 AM

Or it might not charge at all. I believe my netbook will popup a notice that it cannot charge an external device - depending on its battery level if the netbook is not plugged in.

elemenoP · 01-02-2011, 02:15 PM

ok, thanks!

I have also noticed that if the computer goes to sleep, the reader stops charging. Time to get a wall plug, I think.

eP

screwballl · 01-02-2011, 02:56 PM

Most devices only draw at most 500mA (milliamps) so charging from laptop battery itself is minimal. Considering it takes several hours for a full charge for most of our devices, the laptop battery will be low or unusable by that time anyways.

CWatkinsNash · 01-03-2011, 12:44 AM

Quote:

Originally Posted by elemenoP

ok, thanks!

I have also noticed that if the computer goes to sleep, the reader stops charging. Time to get a wall plug, I think.

eP

Some computers have advanced power settings that let you decide what happens to USB power when the computer is in various states. You might be able to change it on yours.

Doug Huffman · 01-03-2011, 09:07 AM

A KINDLE battery's capacity is 1750 mAh. My laptop's battery capacity is near 50 Ah. USB regulated voltage is 5 VDC. My laptop's battery puts out 12 VDC nominal. There are at least three generations of USB standards, with varying power specifications. A high power USB port should be able to charge your e-reader.

elemenoP · 01-03-2011, 11:24 AM

Actually I just discovered that my ipod can continue to draw power when my macbook is asleep, but my Sony Reader cannot. Why is this?

eP

FF2 · 01-03-2011, 12:01 PM

Different devices look for or detect different signals besides just power on usb connections. My Creative MP3 player could only charge from certain usb ports and only using certain ac adapters that provided some signal that the player was seeking. It was not just a matter of having the right voltage.

My Blackberry will occasionally throw up a prompt/message that there was insufficient power to charge it - has happened with both cigarette lighter sockets and usb ports on laptops.

Some devices will not work properly with usb hubs whether they are separately powered or not and sometimes the usb ports on the front of a computer and those on the back will provide different results. USB is not, well, always usb, I gather.

01-02-2011, 11:24 AM	#1
elemenoP Wizard Posts: 1,717 Karma: 3790058 Join Date: Oct 2010 Location: NYC Device: Kindle Paperwhite, Sony 650	usb power draw question If I have a USB device (let's say a Sony Reader) and I connect it to my Macbook to charge, does it charge faster if my macbook is plugged in, vs on battery power? Thanks, eP

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
PRS-600 USB Power	hansvanderveeke	Sony Reader	3	04-03-2010 09:59 AM
PRS-300 Very useful USB/power cable	chaley	Sony Reader	11	02-20-2010 09:19 PM
Newbie Question : Draw Graphics on Hanlin v3 Display	biodiesel	HanLin eBook	6	01-06-2010 12:17 AM
AC Power from USB - Will it work?	Killian	Sony Reader	26	08-28-2009 07:54 AM
USB Power Adapter	thibaulthalpern	Sony Reader	54	03-24-2009 10:44 AM

01-02-2011, 11:52 AM	#3
FF2 Wizard Posts: 1,105 Karma: 1025784 Join Date: Oct 2010 Device: WiFi Kindle3	Or it might not charge at all. I believe my netbook will popup a notice that it cannot charge an external device - depending on its battery level if the netbook is not plugged in.

01-02-2011, 02:15 PM	#4
elemenoP Wizard Posts: 1,717 Karma: 3790058 Join Date: Oct 2010 Location: NYC Device: Kindle Paperwhite, Sony 650	ok, thanks! I have also noticed that if the computer goes to sleep, the reader stops charging. Time to get a wall plug, I think. eP

01-02-2011, 02:56 PM	#5
screwballl NewKindler Posts: 504 Karma: 1865773 Join Date: Dec 2010 Location: NWFL Device: Kindle3 Wifi	Most devices only draw at most 500mA (milliamps) so charging from laptop battery itself is minimal. Considering it takes several hours for a full charge for most of our devices, the laptop battery will be low or unusable by that time anyways.

01-03-2011, 09:07 AM	#7
Doug Huffman Banned Posts: 102 Karma: 7860 Join Date: Nov 2010 Location: Washington Island, across Death's Door, Wisconsin, USA Device: KINDLE 3 WiFi	A KINDLE battery's capacity is 1750 mAh. My laptop's battery capacity is near 50 Ah. USB regulated voltage is 5 VDC. My laptop's battery puts out 12 VDC nominal. There are at least three generations of USB standards, with varying power specifications. A high power USB port should be able to charge your e-reader.

01-03-2011, 11:24 AM	#8
elemenoP Wizard Posts: 1,717 Karma: 3790058 Join Date: Oct 2010 Location: NYC Device: Kindle Paperwhite, Sony 650	Actually I just discovered that my ipod can continue to draw power when my macbook is asleep, but my Sony Reader cannot. Why is this? eP

01-03-2011, 12:01 PM	#9
FF2 Wizard Posts: 1,105 Karma: 1025784 Join Date: Oct 2010 Device: WiFi Kindle3	Different devices look for or detect different signals besides just power on usb connections. My Creative MP3 player could only charge from certain usb ports and only using certain ac adapters that provided some signal that the player was seeking. It was not just a matter of having the right voltage. My Blackberry will occasionally throw up a prompt/message that there was insufficient power to charge it - has happened with both cigarette lighter sockets and usb ports on laptops. Some devices will not work properly with usb hubs whether they are separately powered or not and sometimes the usb ports on the front of a computer and those on the back will provide different results. USB is not, well, always usb, I gather.