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USB power

L

Ldu02171

n00b
Joined
Feb 26, 2007
Messages
1
Hi All,

This is my 1st post :D

I am currently involed in a university project in which we (my group) need to know how much power can a USB supply. From information on the internet, we found out that the average voltage is around 5v with a current rating of 3mA. Is this correct?

What we need to use it for is to power a solenoid with a stroke bewteen 5-10mm. Is this possible with just USB power? We are trying to power it from just connecting the unit to a PC without the need of an external power source, apart from USB, are there any other forms of power that we can use? firewire?

I hope you can help with our dilemma. Any information will be useful and our group would like to thank you in advance. :)
 
The USB specification provides a 5 V (volts) 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 4.35 V between the +ve and -ve bus power lines.

Initially, a device is only allowed to draw 100 mA. It may request more current from the upstream device in units of 100 mA up to a maximum of 500 mA. In practice, most ports will deliver the full 500 mA or more before shutting down power, even if the device hasn't requested it or even identified itself. If a (compliant) device requires more power than is available, then it cannot operate until the user changes the network (either by rearranging USB connections or by adding external power) to supply the power required.

If a bus-powered hub is used, the devices downstream may only use a total of four units — 400 mA — of current. This limits compliant bus-powered hubs to 4 ports, among other things. Equipment requiring more than 500 mA, hubs with more than 4 ports and hubs with downstream devices using more than four 100 mA units total must provide their own power. The host operating system typically keeps track of the power requirements of the USB network and may warn the computer's operator when a given segment requires more power than is available.
Click to expand...

Source: http://en.wikipedia.org/wiki/Universal_serial_bus
 
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