USB Power Limits

Dell should consider documenting the amount of power that's available through the USB ports of their laptops.

Currently, no information about maximum power shows up in the specs or system documents for Latitude systems. All that's said is that they're "USB-compliant."

As a result, I only found out that they supply much less power than a desktop system's USB connection by connecting a 500 milliamp device and watching my new laptop (repeatedly) power itself off.

One line of documentation could have saved me some hassle and the system some wear and tear.

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4 Replies

RE: USB Power Limits


All of the available information we have for your system is located on our website under the System Specific Support Pages. Just go to:

and enter your system type or service tag. Technical specifications, documentation, files downloads, and spare parts are all located here.

If you would like to make a suggestion to our engineers, you can do so by going to:


Select Communicate with Dell, E-mail Dell Support, and then the option that says You have comments or suggestions for our development team.

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RE: USB Power Limits

As I've already indicated, USB power capabilities do NOT seem to be included in the system documents for the Dell Latitude. That's why I brought up the subject here.

I'll move on to engineering support.

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Re: RE: USB Power Limits

Did anyone ever figure out the exact details of host supplied usb power on latitude d800?  Does it matter if the laptop is plugged in or not?  Does any port supply more power than others?  I have a 2000 mA Axim X5 I'd like to charger via USB sync charger connected to dell latitude d800.
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Re: RE: USB Power Limits


The power output is dependant on the USB version it uses.
The system has USB 2.0 which from the USB2.0 standard can provide different power outputs.
The USB 2.0 standard states that a desktop system *must* supply 500mA of power to each port.
But, it is different for a portable system because it can be run on battery and does not have
a fixed power supply. So, according to the USB 2.0 standard the USB ports can provide as little
as 100mA of power to each port and still be meet the USB 2.0 standard.
The power output can increase when using the AC Adapter because you are then running off a
*fixed* supply. So the power output can depend on whether you are on battery or the AC adapter.
But, as long as a portable system still supplies at least 100mA of power, then it is still meeting
the USB 2.0 standard. All this information can be found on the USB.ORG web page.
Here is a way you can tell how much power each port is providing.
How do I check a USB ports power output?

Win2000 and XP:
1.Click on Start, Control Panel, System.
2.Click the Hardware tab, Device Manager button.
3.Click the + next to Universal Serial Bus Controller.
4.Right click on USB Root Hub and click properties.
5.Click on the Power Tab.

Hub information:
Provides information on whether the usb hub is self powered.
Provides Total Power available for *each* port.
USB 1.1 and 2.0 standards state each port should have 500 mA available.
But this is dependant on the type of system you have.
Portable systems can provide as little as 100mA of power to each port,
and still meet the USB standards.

Attached Devices:
Provides information on how many USB ports are available.
Provides information on how much power a USB device connected to that
port is drawing at any given time.

Because of USB 2.0 technology you may have from 1-4 USB Root Hubs listed
in the device manager. There are separate controllers for USB 1.1 and 2.0.
If your system supports USB 2.0 you may have several USB Root Hub entries
in device manager because of the separate controllers.
If you want to check the power drawn from a particular USB port,
make sure to check each listing of the USB Root Hub.
Also, portable systems may only have one USB controller but still have several
USB Root Hubs listed in device manager. You will still need to check each each
USB Root Hub to see which one your USB device is connected to, and what the power
output is.
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