How to tell the capacity of a USB Hub?

We have a laptop with a 12 ports of USB hub, plugging to external LCD, HD, printer, keyboard, mouse, iPhone, etc.... It was working well without a problem for about 6 months till the monitor started blacking out. We figured it may be because of too many peripherals plugged to the USB hub so we unplugged the iPhone. And yes, it fixed the issue. But just today, several months from the last incident, the monitor again started blacking out. We then fixed the issue by unplugging one more peripheral -- HD.  
We are so puzzled since if it is the USB hub's capacity issue how come it takes many months to act up? More importantly, do you know how to fix this issue?
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☠ MASQ ☠Commented:
Check the USB Root Hub properties in Device Manager on the "Power" tab to see what is available and what's being pulled through the hub.

It may be you have a single device plugged that's exceeding its specification, which should be easy enough to track down by a process of elimination, or it could be a problem with the Hub/PSU

If you're already at the limit of what the hub can deliver then a smart device like a phone that regulates its own "downstream charging" requirements might push the hub over the edge with an uncharged battery but sit innocently in the hub when fully charged.
Sounds like power issue, that  USB HUB is overloaded (maybe capacitors that provide power to USB HUB are in bad shape). iPhone is charging over USB, and I guess that HDD has no external power supply.
my recommandation is always : for usb 2 hubs - use a powered one; otherwise it's limited to MAX 5Vat 0.5 A = 2.5 W, and most laptops don't even supply that much

if you're on usb3 - there you have more power - so if you have an usb3 port - use that one
see here how it's calculated :

The USB 1.x and 2.0 specifications provide a 5 V supply on a single wire to power connected USB devices.

A unit load is defined as 100 mA in USB 2.0, and 150 mA in USB 3.0. A device may draw a maximum of 5 unit loads (500 mA) from a port in USB 2.0; 6 (900 mA) in USB 3.0.
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CastlewoodAuthor Commented:
My powered hub is 2.0.
So in my case the external monitor getting black out means this monitor tried to draw more than 500mA? Or some other connected devices drained the power out of the hub??
Almost all devices draw power from your USB hub (any device that has no it's own power source), so most likely it is combination of too much power draw and aging of equipment under constant load. When components age max power that device can provide is reduced....
☠ MASQ ☠Commented:
It means the hub couldn't provide enough power for all the connected devices, it doesn't automatically mean that the monitor is at fault.
it is starnge that a powered hub has this problem - are you sure the power adaptor is still working?
CastlewoodAuthor Commented:
What did you mean by "it is strange that a powered hub has this problem"?
May I take the liberty of answering for nobus in his absence.

A "powered usb bub" is one that is supplied by 5 volts of power by means of a power supply unit (transformer) that plugs into your wall socket and a small jack that plugs into the hub.  USB devices draw their power from the power that is being supplied to the hub from the separate power supply unit.  If you add together the current in milliamps or amps that all the peripheral devices connected to the hub need to draw, the power supply unit must be able to meet this current and more.  The external power supply unit should also be able to supply a steady 5 volts to the hub.

A "self-powered usb hub" is one that has no external power supply and is only fed by the usb socket of the computer that it is connected to.  USB sockets on a computer are usually limited and unable to supply the current drawn by multiple USB devices plugged into it.  To meet the demands of all the devices plugged into the hub you need to supplement the power from the computer's USB socket with power from an external source.

So, what nobus was saying is that an externally power USB Hub normally supplies enough power to all its sockets even if fairly power-hungry peripherals are attached to it, and he is wondering whether you have a faulty power adaptor.

You get the same thing with external usb hard drive enclosures.  Older 3.5 inch IDE usb hard drive enclosures invariably have a power supply adapter plugged into the wall socket, whereas external 2.5 inch laptop hard drive enclosures are normally completely portable and don't need any more power than the computer's USB socket supplies.

Download the 32-bit or 64-bit version of Nir Sofer's USB Device Viewer, depending on whether your operating system is 32-bit or 64-bit, and unzip it to a new folder:
Right-Click the following link and use the appropriate browser menu option to download and save the file "usb.ids" to the same folder where you unzipped the previous file:
This file tries to provide the program with details of known devices.

Run "USBDeview.exe" and configure the layout to suit using the "View" menu.  It is usually best to "show gridlines" and optionally to "mark odd/even rows" for easier reading.

Under the "Options" menu, make sure that you have ticked:
"Show USB Hubs"
"Retrieve USB Power/version Information"
"Mark Connected Devices".

The connected devices should show at the top of the list in green.  There are loads of columns, but if you scroll to the right you will find Power and USB Version columns.

You can use the Edit menu > Select All, then File menu > Save Selected Items to save a text-based report.  You can also use the View menu to save an HTML report of selected lines or all of them.

BE CAREFUL what you click on.  This program allows you to change drive letters, disconnect devices, open the places they appear in the registry, and so on.  I am only recommending this tool as the means to provide a report.
Tx Bill, you explain it better than i can
you can also see the power used in device manager, by selecting the usb device properties  - there is a powerr, or energy tab

what model of usb hub do you have?  that should clear up any fog around it
CastlewoodAuthor Commented:
My 2.0 hub is: Plugable USB 2.0 10-Port High Speed Hub with 12.5W Power Adapter and Two Flip-Up Ports

Did you guys mean usually a powered hub should have way sufficient electricity for its connected devices?
The specifications for your hub are:
5 volts, 2.5 amps, 12.5 watts
5 Volts for USB is the standard.  The important rating you are interested in is Amps.  It's odd that they use Watts as the main specification in the title, however:

Volts x Amps = Watts
5 volts x 2.5 amps = 12.5 watts.

As long as the cumulative amperage requirement of ALL the devices connected to the hub at one time does not exceed 2.5 amps, then the hub SHOULD be capable of fulfilling the power requirements of them, AS LONG AS the power adapter is actually working properly.

Make sure that the USB cables to each of ther devices are as short as possible.  Look at USB 2.0 in Table D under the section header: "5: Cabling and maximum cable length" on the following page for maximum cable lengths:

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this also means that you have 5x more power than a hub without PS - which only has 2.5 W total

can you measure the power adapters output ?
and if it has a power light, is it burning?

also  can you list the devices connected to it?
Danny ChildIT ManagerCommented:
buy this USB power meter - very cheap on ebay, and test each device in turn...
It appears to be generic, so doesn't have part numbers, but works very well in my experience.
Thank you Castlewood
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