Take the 2-minute tour ×
Super User is a question and answer site for computer enthusiasts and power users. It's 100% free, no registration required.

I have a few heavy duty devices and a powered hub and I wonder what's the flow of current in those things.

share|improve this question
    
Read the USB power specs, they state the upper and lower limits.. –  NickW Jun 3 '13 at 16:57
    
NicW that's not the question. e.g. the spec accepts a tree of hubs but the supply may still run out of Current even with less than 500mA on each device. –  leladax Jun 3 '13 at 17:44

1 Answer 1

No, they do not. A properly designed powered hub will fulfill the USB specification's requirement of providing 500mA maximum per port; if you connect a device whose current requirement exceeds that value, then the resulting behavior depends on the hub, but in general it simply will not source more than 500mA, and it certainly will not draw additional current from the hub's upstream connection.

USB hubs do exist which are capable of providing greater than 500mA on some or all ports, e.g. to support the iPad's 2A charging requirement, but they are invariably described as such; if the hub you're asking about isn't, then the only safe assumption is that it can't.

share|improve this answer
    
"in general it simply will not source more than 500mA" This is far from reality. Keyboards with 104 LEDs are known to violate the USB standard and they work almost everywhere, and in most cases that they don't, they aren't explicitly cut off but they just get the power supply to its knees. –  leladax Jun 3 '13 at 17:36
    
Also that wasn't the question. e.g. the spec accepts a tree of hubs but the supply may still run out of Current even with less than 500mA on each device. –  leladax Jun 3 '13 at 17:46

Your Answer

 
discard

By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.