Need help trying to buy a USB hub!

Discussion in 'Buying Tips, Advice and Discussion (archive)' started by CrackedButter, Feb 25, 2005.

  1. CrackedButter macrumors 68040

    CrackedButter

    Joined:
    Jan 15, 2003
    Location:
    51st State of America
    #1
    AND... it isn't what you think.

    I am eyeing up a certain USB hub and it is telling me it is USB 2. Plus I don't need a power adapter if I don't use more than 100 mA for any single port. This is fine until I check out the details of my scanner, it reports 2.5 watts. :confused:

    How do I make sure the hub will handle the scanner and for that matter 2 ipod shuffles?

    Now I was told a formula to figure this out.

    Volts x amps = watts

    or

    Watts x Volts = amps

    This isn't my field of knowledge, so i'm hoping somebody here knows the answer to this.

    Now i know the amps, and basically I need to know if the 2.5 watts is higher than 100mA, if its under, I can buy the hub without an external power supply. Btw, I don't want the power supply to begin with, hence the issue here.

    I live in the UK and the electrical current is AC.
     
  2. strider42 macrumors 65816

    strider42

    Joined:
    Feb 1, 2002
    #2
    Bus powered hubs cause problems. Get a self powered one, that is, one with its own power supply. I don't care what devices you are using it with, a self powered hub just works better.
     
  3. Mechcozmo macrumors 603

    Mechcozmo

    Joined:
    Jul 17, 2004
    #3
    Scanner has its own power supply so it doesn't matter.
    Shuffles will draw off of the hub. So they need to draw less than 500 mA combined (USB 2.0 standard and what Mac's dump out per port).
    But get a powered one. That way you do not have any issues. Because trust me, it is a pain. I had a USB 1.1 hub that when I first set it up for my dad gave errors that the devices weren't getting enough power. After a bit, that was fixed thankfully.... but still a pain.
     
  4. CrackedButter thread starter macrumors 68040

    CrackedButter

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    Jan 15, 2003
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    51st State of America
    #4
    My scanner doesn't have a power adapter. It uses the USB port only.

    If the answer is to get a powered usb hub then I won't bother. Thanks for the help.
     
  5. Mechcozmo macrumors 603

    Mechcozmo

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    Jul 17, 2004
    #5
    What kind of a scanner do you have that doesn't use an A/C adaptor?
     
  6. johan_tanying macrumors member

    Joined:
    Nov 28, 2004
    #6
    First: if the device is usb-powered you will most likely need a powered hub. A scanner is more often than not using some kind of light source, electric motors and so on.

    Second: is it possible to buy a hub that does NOT include a power brick/adapter? Sometimes they say it is optional to use them but do not count on it (I agree with the above poster - non-powered hubs are likely to be a pain in the a__...
     
  7. CrackedButter thread starter macrumors 68040

    CrackedButter

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    #7
  8. Mechcozmo macrumors 603

    Mechcozmo

    Joined:
    Jul 17, 2004
    #8
    The other devices on the hub cannot draw more than 400 mA then. Good luck trying to do that. You may be able to do it by having each one plugged in at different times, and then plugging/unplugging and turning off what ones draw the most power. And add like a USB mouse or something to that circuit, those don't draw a lot.
     
  9. mkrishnan Moderator emeritus

    mkrishnan

    Joined:
    Jan 9, 2004
    Location:
    Grand Rapids, MI, USA
    #9
    The scanner draws 2.5W off the 5V power bus on the USB? Doesn't that mean that it uses 500 mA (by itself), or have I been out of engineering for that long? :eek: Even in the 1.5W standby mode, it's going to draw 300 mA. Where did you get the 100 mA figure from, CrackedButter?
     
  10. CrackedButter thread starter macrumors 68040

    CrackedButter

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    Jan 15, 2003
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    51st State of America
    #10
    The 100mA figure is from the website that is selling the usb hub.
    It seems you have found the voltage, and it proves that the scanner isn't right for the hub.

    Thanks for the calculation.
     
  11. mkrishnan Moderator emeritus

    mkrishnan

    Joined:
    Jan 9, 2004
    Location:
    Grand Rapids, MI, USA
    #11
    Any time, although it probably wasn't the answer you wanted to hear. :( I hate having sixty power supplies connected. ;)
     
  12. CrackedButter thread starter macrumors 68040

    CrackedButter

    Joined:
    Jan 15, 2003
    Location:
    51st State of America
    #12
    I'm still going to buy it though. There are other devices which will benefit from the extra ports. With my devices I have; 2 ipod shuffles, pen drive, (the scanner) mouse and a usb card reader because of my digital camera using 2 types of memory card.

    All I have is the 2 USB ports on the iBook.

    This new usb hub is also a 19 in 1 card reader, it will help consolidate my afforementioned list of stuff. So it was helpful simply by knowing the power usage.
     

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