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Thread: USB Componet Power Usage

  1. #1
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    USB Componet Power Usage

    Been searching around here and Googling, and found some numbers but would like a "warm fuzzy" about them.

    Issue is, I am thinking about ditching my two adapter powered USB hubs for one bus-powered hub, I am too cramped on space and my need for USB devices is reduced. I was at 5 USB devices, now just three.

    I need to run a XMPCR, Soundblaster MP3 USB sound card and one of those cool little Mini kyboards (the one that is smaller than a PlayStation controller). The Xenarc TS will run off the other UBS port on my M10000 mother board and the hub will be in the other one.

    I don't really have room to tap into the USB headers on the m/b, and a small bus-powered Hub is the best alternative.

    I know the power limit on a USB port is 500mA (total of all devices) for each port, right? So the touch screen will have 500mA and the hub will have 500 mA.

    I found info (reliabilty factor questionable) that the power draws would be as follows

    XMPCR - 365 mA
    Sound Blaster MP3 - 160 mA
    Mini-Keyboard - Unknown (but I would think, maybe 50 mA at most)

    So this puts me at 575mA which obviously is over the limit.

    Questions:
    1) Does anybody know accurate mA ratings for these three devices?
    2) If I am at 575 mA will I have issues with the three devices?
    3) Since the mini-keyboard will be (nearly never used) that would drop me to 525 mA.... am I okay then?

    Any thought you have would be appreciated.

  2. #2
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    Anybody?

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    Banned xdjxklusivex's Avatar
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    dont know **** about usb stuff i just keep on pluggin em in but i would just give it a shot and see wat happens dude

  4. #4
    What can I say? I like serial. Curiosity's Avatar
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    I seem to recall a few old threads about this. Basically, bus powered = 500mA total for all ports - 100mA for the hub itself. Adapter powered = 500mA per port. You can also look in device manager, under USB and find your hub. In the properties is a "Power" tab which shows each device and what it reports as its max power usage. I'm thinking about just chopping up an extension cable to make one I can put inline and connect to my DMM just to get better readings on everything.

    Anyway, think of the motherboard as a hub, and any self powered hub has 500mA output per port. If you connect a device (any device, including hubs) to a port, you get 500mA max, so the source power to that hub will be 500mA. Using an adapter with 2A to that hub will give it 2000mA total over all the ports - 100mA. Now if you connect a hub to that hub, you get the same thing, 500mA total.

  5. #5
    Variable Bitrate roadhog's Avatar
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    How much does the touchscreen use?
    would it work from the hub?
    I would guess that it doesn't use much, and then you could put the power hogging xm on it's own m/b port.
    Just a passing thought.

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    Quote Originally Posted by roadhog
    How much does the touchscreen use?
    would it work from the hub?
    I would guess that it doesn't use much, and then you could put the power hogging xm on it's own m/b port.
    Just a passing thought.
    Duh....

    That is a really good thought, thank you.... put the hog by it's self and then pair up the lesser ones on the hub.....

    So that makes me think, and I am slightly conflicted by the posts above.... from the motherboard (on the back side ports)... does EACH USB port get 500mA, or is that the total for all USB ports?

    Thanks to all for your comments and thoughts.

  7. #7
    Variable Bitrate roadhog's Avatar
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    Hmmm. Not sure, but the USB specs suggest that each port should be able to supply 500mA @ 5 volts. I have heard that motherboards in general are a little under-prepared for providing the maximum current, but only rumour and heresay... I suppose that could be on the reasoning it's cheaper to provide a powered hub than replace a burnt motherboard.
    I have to say that were it me I'd follow my own advice (honest!) and provide a seperate +5 volt power and GND to the hub from my computer PSU.

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    I agree Roadhog... as I said I currently have two adapter powered hubs and am all setup to supply the 5V for a hub, the problem is that I can't find a SMALL compact powered hub, and I see so many SMALL non-powered hubs that would work just great.

    I am in a very tight space and all volume added is bad... doing a complete "in-dash" install....

    Something like this....

    http://www.radioshack.com/product/in...entPage=search

    narrow, thin and would work great for me.. but not adapter powered.

    That is my delemia....

  9. #9
    What can I say? I like serial. Curiosity's Avatar
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    They make small ones with adapter
    http://www.newegg.com/Product/Produc...82E16817111831

  10. #10
    Maximum Bitrate DeltaFX's Avatar
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    To make Usb things clear :

    Each controller allows 500mA max (under 5v). Usually, an onboard controller controls 2 USB headers.

    So if you have a mobo with 6 usb port, you certainly have 3 controllers, and then, 3 times 500 mA to share.

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