Should I connect USB hub to power outlet?

[abrodski]

Hello!

I recently bought a USB 2.0 7 port powered hub.
I noticed that it works fine without being connected to the wall electric power outlet. Of course, I don't use scanners etc.
I just connect to it stuff like basic optical mouse, basic generic keyboard, flash drives, most generic Internet cam (an eye) and 3G Nokia phone that I use as a modem.

From what I understood, devices can get electric power from USB interface. So, if it works without an external power, then I can safely leave it that way or for some reason, its best to have external power on in the hub?

 

[sandorski]

As long as everything is working, there's no need. I'm not even sure what would require it, probably a USB HD.

 

[Firsttime]

Only so much power can travel through USB cables. So as long as you aren't using more power then the cable can carry from your computer to the hub no need to plug it in. That's my understanding anyway.

 

[VirtualLarry]

I would go for the extra security of plugging it in. Otherwise, you never know when USB devices might start to fail. For example, if you attempted to use all of them at once.

 

[corkyg]

Agree with Larry - the main issue is reliability! It is true that 5 vdc will flow through a USB port - from the hub or from the linked PC (laptop or desktop.) No question at all if it is a laptop - and, even a desktop will be more reliable when the USB hub is powered. That relieves your internal PSU and mobo of that chore. I have two floor tops, each with a 7 port USB hub, and each is connected to its own power source. Reliability is 100% for several years.

 

[abrodski]

So basically, as long as it works, then its optional? I mean, if I DON'T plug the power to the USB hub, then nothing can get damaged?

 

[JackMDS]

Well, if you are using an External USB HD, once something happen it can be too late for your data.

Rule of thumb, if you are using only an mouse and occasional flash drive, it probably be OK, more usage you better plug it in.

 

[Mark R]

So basically, as long as it works, then its optional? I mean, if I DON'T plug the power to the USB hub, then nothing can get damaged?

Pretty much.

USB is designed to provide power to devices. It does this dynamically - the PC monitors the devices on the port/hub and the amount of power available.

When a device is plugged in, it boots up into 'low-power mode' where it takes only a tiny amount of power. It then identifies itself to the PC, and tells the OS how many mA it will need to power-up. (A USB port can provide 500 mA total).

The OS calculates how many mA are reserved by other devices on the port, and if it can allocate the requested mA, it will send a command to the device telling it to power up. If the OS calculates that the power is not available (e.g. 400 mA is already spoken for by other devices, and the new device just plugged in requests 200 mA) then it the OS will send 'do not power-up' to the device, and the device will not function (or function in low-power mode).

The iPhone is a good example of this. If plugged into a USB port, it will request 500 mA for battery charging. However, if plugged into an unpowered hub (which needs some power for itself), then the OS will reject the power request, and the iPhone will pop up an error message saying 'Charging is not available on this accessory' - but you should still be able to sync.

There is a problem. Cheap, badly designed USB devices may mis-report their power requirements, or power-up immediately (even if the OS denies permission to power-up). This is common with low-end 2.5" hard drive enclosures. If a device like this is plugged into a hub, it can overload the USB port. If the USB port is overloaded, then circuit breakers on the motherboard will trip, disconnecting the USB port and all the devices on it. You'll then have to unplug the USB cable, and reset the circuit breakers (Windows will pop up a 'power surge' error box, giving you an option to reset the breaker).

 

[JackMDS]

May be we should look at it from the other side.

Unless it is a macho problem, i.e., I need to say at school: "Hey Dude I am Cool, I do not Plug the Hub". :hmm:

What the problem in plugging the 5V connection to the USB Hub is.

 

[Mark R]

What the problem in plugging the 5V connection to the USB Hub is.

Uses up a power point (probably several power points, given the size of the pregnant plugs commonly found).

Low cost power adaptors are often highly inefficient - I got one with a 7 port hub (maximum power requirement 17.5 W). With zero load, the adaptor sucked down 18 W, at full load, it was using about 42 W. At the power prices I pay, that's $2 per month in electricity costs (just for the hub alone, on the off chance that something might need to draw power from it). The adaptor also got so hot (not surprising given its dire efficiency) that I also had to wonder whether it carried a fire risk with it.

 

[JackMDS]

Uses up a power point (probably several power points, given the size of the pregnant plugs commonly found).

Low cost power adaptors are often highly inefficient - I got one with a 7 port hub (maximum power requirement 17.5 W). With zero load, the adaptor sucked down 18 W, at full load, it was using about 42 W. At the power prices I pay, that's $2 per month in electricity costs (just for the hub alone, on the off chance that something might need to draw power from it). The adaptor also got so hot (not surprising given its dire efficiency) that I also had to wonder whether it carried a fire risk with it.

All of this are a valid concern, if one more 5V low power adapter puts you in such a risk, it is a good reason Not use a computer or any other electrical unit.

 

[abrodski]

I want to clarify something here...I don't care about electic bills (since its a swedish govt. who pays them)...Nor I think there's a reasonable chance of fire in the house.
My problem is that when I plug the USB devices into the 7 ports powered USB hub sometimes they don't work. I can use them OK and suddenly, the mouse is dead. Or everything that was plugged into the hub. Or I use a 3G phone as a modem connected to PC through USB hub's port. And I lose a connection and every time I have to unplug and re-connect and then connect again to mobile broadband ISP.
And its not after any event. Just all of a sudden. Then I had to unplug the hub and put it back etc. Its a pain to do it every half an hour. But sometimes everything works OK for hours.
I don't know...I bought a hub here in Sweden. And its not exactly cheap 250 SEK which is roughly 25 Euro or 35 US$. Its a metal hub. And it gets warm, but not too warm.
I use Windows7 Pro. And I disabled power management options in root hubs and in the hub itself.
Also I went to advanced power setting and disabled "USB Selective Suspend"
When something is plugged directly into the laptop's USB ports, then those devices work just fine. Its only when I plug them into USB hub. Frankly, I regret that I bought a laptop with only 2 USB ports. If I knew that the USB hub is such a pain, I would have only gone for 3 USB ports laptop. And also, I noticed that it doesn't really matter if I plug the USB hub into power or not. So maybe its not even a power issue to begin with.
I get Windows errors that USB device is not recognized and then I see an unknown device in Device Manager. It happens often when I connect an addition device into the USB hub.
So maybe this thread should be closed and I should start a different one because originally it was about the power connection to USB hub...?

 

[JackMDS]

There is No simple direct answer.

It can be the laptop's USB interface, or a "quirky" Hub.

If someone around has a Laptop ask permission to try your hub and devices on another Laptop and see if it does the same.

 

[abrodski]

We only have a desktop at home...you think it's worth trying the hub on a desktop?
I don't think that the problem is with a laptop...I would think its either Windows or the hub.
Laptop's USB ports work fine.

 

[corkyg]

Worth trying? You have the hub - it can't cost you anything to try it. So, do it and report back.

 

[Modelworks]

Most of the hubs sold as powered and come with an adapter either have a switch on the side to switch to power by adapter or will auto switch when they detect the adapter.

A single port on a pc is limited to 500ma, often they are fused for 650ma in case of a short . So if you add a hub that can support 4 devices you get 500ma / 4 devices = 125ma for each port or a total of 500ma. That is where the adapter comes in . The adapter needs to supply 10W of power minimum to make each port 500ma.

I use a lot of devices that are powered by USB and at 3-500ma each. I found a powered hub that has no internal regulation but used a small 5Vdc wall adapter. I cut off the wall adapter and wired the power to the pc +5VDC supply. I now have usb ports on the hub that can each supply a few amps each. Don't do this if you do not know what you are doing, you could harm your pc or usb devices.

 

[abrodski]

Frankly, I don't think that overheating is an issue here...
A while ago, I was using the hub and everything worked just fine. And the temperature of the hub didn't make any difference or whether the device was getting an external electric power.
My impression is that the reason why devices that are attached to the hub disappear and therefore stop working is because for some strange reason they don't get enough power, REGARDLESS of whether they hub is powered itself or not.
I will tell you what exactly happened:
I had a 7 port hub connected to the laptop and I had in the beginning a keyboard, the mouse and 2 flash drives connected to the hub.
After that, I had the keyboard connected to the laptop's USB port and the hub was on the 2nd port.
Then I disconnected the flash drives and had a web cam, keyboard and 3G USB modem connected to the hub.
I went to the device manager and checked the propertives of 2 (?!) hubs that appeared in the list of the devices in PC.
In the 1st hub it was written:
The hub is self-powered. Total power available: 500 mA per port (?)
Attached devices:
USB Composite device 500 mA
USB Composite device 100 mA
2 ports available 0mA

In the 2nd hub it was written:
Generic USB hub (4 ports???) 0 mA
Logitech cam 100 mA
2 ports available 0 mA

Then I got the 3G modem CONNECTED to the ISP.
RIGHT AFTER that the keyboard died.
I also got a connection error in a modem (excl. mark in a task bar-No network access)...
Then I re-checked the previous generic hubs' properties.
In the 1st I had:
USB Composite device 500mA
USB Composite device UNKNOWN
2 ports available 0 mA
In the 2nd I had:
Generic USB hub (4 ports) 0 mA
Logitech cam 100 mA
2 ports available 0 mA
3G modem appears connected, but not operational.
I think that it was simply disconnected and then reconnected right away by the system...

 

[Modelworks]

Without an external power source the total for everything plugged into the hub cannot exceed 500ma. My mouse, a gaming mouse , uses 500ma by itself so if I plugged it into a unpowered hub I couldn't use any of the other ports because there would be no power left.



On most pc motherboards there are at least 6 USB ports on the chipset. The tricky part is knowing how those 6 ports are routed to the usb connectors. All the ports on a pc are not separate USB ports. Most of them are connected to internal hubs. If you have something like a laptop then it can be two separate ports or it could be 1 port shared using a hub internally providing two usb connections.

If it is an internal hub then you have 500ma per USB connector, but if you connect another hub to that connector externally you are still limited to a combined 500ma for all the devices because that port will only allow 500ma total regardless of how many hubs you connect without an external power source.

 

[abrodski]

Yesterday I finally checked my USB hub on a Windows XP desktop PC...Basically, same story...
SisoftSandra showed some mysterious ''enumeration error''...
In that XP PC's device manager it showed USB Root Hub (8 ports), underneath that-6 unused ports and below them USB Hub (4 ports???), below it-1 unused port and below USB Hub (4 ports) there was Unknown device, mouse and 2 unused ports.
In the end, as before, I managed to make everything work...but when I started surfing the web, everything stopped.