USB Power Limitations?

[Jakalwarrior]

What happens when you ask too much power from your USB ports? I have an external blu-ray drive, 1 LED lit laser mouse, 1 keyboard, and sometimes my charging phone plugged into my computer at once. I have noticed that when using the front panels my blu-ray drive doesn't get enough juice to read some DVDs or any Blu-rays, but all CDs. Plug it into the back, directly into the motherboard, and it can read everything. This leads me to believe I am pulling close to the max from my USB plugs? or am I wrong?

Anywho, what happens when you ask for too much power? does it get regulated and some stuff not function / brown out without damaging the system? or does it burn out the traces in your motherboard like when you put too much fan on a fan header? My CD-Drive has auxilary power input available through a DC in port, but that would be one more annoying wire added to my rats nest.

 

[Joe Average]

500 mA per port is pretty much the spec, but if you're plugging in a bunch of devices that actually pull that much (each one) yes, you're going to overload it, and fast. A powered USB hub would be the best answer in that situation; get one and use one single USB "uplink" from the PC to the powered hub, then plug whatever into the hub, shouldn't have any problems at all.

Mice and keyboards don't draw much at all, perhaps 50 mA. The phone - if it's trying to charge off the USB port - will draw the 500 mA; if you can set it to not charge off USB and use the AC adapter, you'd be better off I suppose. Optical drives will most definitely pull the 500 mA without even thinking about it; that's a lot of hardware running off one source of power. If you have a separate power supply for the optical drive, you'd best be using it before you simply kill/overload the ports/controller in the PC/laptop forever.

When you require more than the ports can handle, either you get data corruption or the ports simply don't function at all. Windows (or whatever OS you're using) will typically inform you that there's a current issue (current as in electricity, that is).

 

[Menelmarar]

Each port should support around 500mA, or 2.5W IIRC. Each one should be fairly independant of the others.

Technically they could support more depending on how your devices are wired. It probably violates the USB spec, but a manufacturer could probably directly wire your power supplies 5V rail to the USB ports and provide shittons of power out of each port.

When you ask for too much power, something drops. Usually voltage drops, and then the device will not work. Generally no damage occurs. The power draw and difference for little PC peripherals isn't going to be big enough to burn out traces or wires.