What is the purpose of a USB hub's external power supply, and is it important?

Question

I have a D-Link 7-port USB hub that I use with my laptop. I recently broke the AC adapter, so I'm using it without any external power now.

I have six things plugged in (external hard drive, mouse, keyboard, USB speakers, iPod transfer cable, printer) but I haven't noticed any difference since unplugging the AC adapter. So what's the point of external power? Am I likely to experience some problems sooner or later? If so, I'll buy a new hub now, rather than wait for the problems to arise.

Thanks!

Answer 1

All USB devices require power.



The problem with USB hubs is that the hub is connected to one USB port to your computer -- 1 USB port can only provide about 500mA (2.5 volts) of power.

This power is shared equally between all the devices connected on your hub.

USB hubs with more than 4 ports typically come with an AC adapter to help boost the power output, so your devices will keep working.



iPods and printers are self-powered -- they either have batteries or their own AC power, so they rarely draw power from the USB port.

The same goes for mice and keyboards, depending on what you use, these kinds of devices typically don't draw much power either.



It is when you start using USB hard drives, thats a different story since HDD's consume more power than any USB connected device.

Right now you only have low powered devices connected -- you're probably bordering on using the maximum amount of power a single USB port can provide, so if you connect more devices your hub can become underpowered and stop working.

Answer 2

External Powered Usb Hub

Answer 3

Usb Hub With Power Supply

Answer 4

The power cable for your device is to make sure that every thing can run at their best speeds. When you have one of the seven devices pulling power it pulls it away from the others. When you run them they would have to run all at the same time. Its not going to happen all at once.



You do not use the printer to print every moment, right? The speakers do not sound like high wattage either and the mouse uses very little power in comparisons to the other devices.



Image running a table saw on a 110v but what the manufacturer recommends is 220v. It will run but when you push that board into the blade. Its going to bind or slow down and you have to use it slower than you would.



Speed that we perceive is a perception like the "glass half full or half empty", however I usually say, "the dude the glass as liquid in it!" neither a matter of one or the other negative or positive as the half or half idea is. It's simply a observation of fact liquid in a glass.



I'd suggest instead of taking the chance of burning out the single hub that your powering the device off of, and possibly causing some issues with lack of power on another device. Try to buy the cord from the manufacturers website or get an entirely new hub. Reason being if you ever run all devices at once it might affect it. Is that a all-in-one type of printer? Or if you change out one of the devices with some thing that requires more power.

Answer 5

some devices require more power than a non-powered hub can supply. That's why certain devices need to be plugged into the rear panel USB port instead of the ones on the front or on the keyboard. I'm surprised the printer works. When you have that issue, that'll be the reason...then you deal with it.

Answer 6

As long as you don't run all 6 devices at once you should not go over the 500mA limit (100mA per most devices.)







Power

The USB 1.x and 2.0 specifications provide a 5 V supply on a single wire from which connected USB devices may draw power. The specification provides for no more than 5.25 V and no less than 4.75 V (5 V±5%) between the positive and negative bus power lines. For USB 2.0 the voltage supplied by low-powered hub ports is 4.4 V to 5.25 V.[29]



A unit load is defined as 100 mA in USB 2.0, and was raised to 150 mA in USB 3.0. A maximum of 5 unit loads (500 mA) can be drawn from a port in USB 2.0, which was raised to 6 (900 mA) in USB 3.0. There are two types of devices: low-power and high-power. Low-power devices draw at most 1 unit load, with minimum operating voltage of 4.4 V in USB 2.0, and 4 V in USB 3.0. High-power devices draw the maximum number of unit loads supported by the standard. All devices default as low-power but the device's software may request high-power as long as the power is available on the providing bus.[30]



A bus-powered hub is initialized at 1 unit load and transitions to maximum unit loads after hub configuration is obtained. Any device connected to the hub will draw 1 unit load regardless of the current draw of devices connected to other ports of the hub (i.e one device connected on a four-port hub will only draw 1 unit load despite the fact that all unit loads are being supplied to the hub).[30]

Answer 7

If you are connecting lots of peripherals that all require power, this external source will be required because the single USB port that you are using to power your hub cannot provide the amount of power needed to run 7 devices.

Answer 8

it all takes 5 volts but for ipod usb cable it takes 5 volts and 2.5 watts