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Power for US hub?

Discussion in 'Electronic Repair' started by Terry Pinnell, Dec 12, 2010.

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  1. I've dusted off a 4-port USB hub I had lying but can't find whatever
    adapter it came with. What are the standard specs for USB 2.0 please? I
    want to replace a PC-powered hub with it.

    I have several old adapters at hand. One (which happily has the correct
    plug) has switchable outputs of 3V, 4.5V and 6V, with current capacity of
    300 mA at 6V. options. Would the 4.5V be OK?
  2. J. Todd

    J. Todd Guest

    No. The voltage spec is tight. Try to find a unit 5.0V, 2.1A,switching
    type. Linksys routers use them, for one.
  3. No. You really need 5 volts at 500ma for each port. Most things don't use
    5 volts anymore, they use regulators for lower voltages and 4.5 is just at
    the border of 3.3 volt regulators working or not.

    Besides a 4.5 volt unregulated supply could provide almost anything at no
    load (like 8 or 9 volts if it is really bad) which would be a problem.

    Lucklily 5 volt supplies are easy to get and cheap. You can get a 5v 1amp
    switching supply as a charger for a music player/cell phone. That will do for
    2-3 bus powered devices, or all 4 if they are self powered.

  4. D Yuniskis

    D Yuniskis Guest

    Hi Terry,

    5V at about 2+A -- for four *powered* ports; less if you
    can guarantee the devices plugged into the hub have their
    own power source(s). You won't be finding this in an
    old-fashioned "transformer" wall wart (you'll need a small
    switcher wall-wart)

    Most hubs that I have seen, lately, use a ~0.100 dia barrel
    connector (center positive) -- though I have seen others.
  5. Thanks all, glad I asked, as I hadn't realised it needed such a heavy duty
    supply. At worse, I'll get out to the shed and make one.

    BTW, if you'll excuse a related question, is it usual for USB ports on the
    front of a PC case to be less reliable than ports on the back? Perhaps
    with lower current delivery? That's my motive for deploying this powered
    hub. An operation that failed from the front worked OK from the back
    (connecting an iPad to run an iTunes sync). That wasn't the only thing I
    changed, so it's not conclusive. But from subsequent googling I've seen
    several suggestions that this difference is a real one.
  6. D Yuniskis

    D Yuniskis Guest

    Hi Terry,

    Again, it only needs that sort of supply if you have devices that
    1) need lots of power (e.g., a laptop disk drive powered from
    the USB port) and 2) don;t provide it themselves. Some devices
    (e.g., the sort of laptop drive I mentioned) have options for
    both. Mice, keyboards, etc. usually rely on the USB port for
    their (typically modest) power requirements.
    A lot of this depends on the vintage/manufacturer of the PC.

    All bets are off when it comes to an "add in" USB card (which
    would typically be USB2 or USB3 and most likely "powered" -- but,
    could just as easily be an ancient USB1.1 card, etc.)

    Some manufacturers put "good" (fast, powered) ports on the front
    of the machine leaving slower ports on back for the keyboard/mouse
    and giving the user more flexibility in what he can CONVENIENTLY
    plug into the front of the machine. Other machines may be the
    exact opposite with the philosophy that the fast devices you are
    likely to use will be semi-permanently attached and you'll just
    need the front ports for things like thumb drives (modest power

    The ports *in* keyboards are almost never capable of delivering
    and sort of power (I've seen some that won't support a thumb drive).
    And, of course, you are limited to the speed of the keyboard's
    connection to the PC (in addition to the hub/controller within the

    It is also not uncommon for connectors to be flakey -- the "pins"
    *in* the USB connector as well as the pigtail that invariably connects
    the "front connectors" to the motherboard (the rear panel connectors
    are more often than not directly soldered to the motherboard).

    And, of course, iPod cables are also notoriously flakey
    (not to mention the &*^[email protected]#*&$% "charge only" cables!)

  7. Baron

    Baron Guest

    Terry Pinnell Inscribed thus:
    Open up the machine and unplug the ten pin cable header for the front
    USB ports at the mainboard then plug it back in ! Could be the pins
    are dirty. Its surprising what a little oxidisation can do !

    Don't forget to take anti static precautions !!
  8. Thanks for those helpful follow-ups.

    The good news is that after more rooting around in the shed I found the
    adapter. A 6V, 2.1 A unit.

    Not so good is that the 'New Hardware Wizard' on my XP PC now reckons it's
    found new hardware and wants to install the darn thing. Why! The same USB
    devices are plugged into it as before, when it was running under PC power.
    And I'm darned if I have an installation CD for it. I thought USB hubs
    were simply plug'n play?
  9. PeterD

    PeterD Guest

    They are, it's trying to play it... So let it install and you'll
    probably do just fine.
  10. D Yuniskis

    D Yuniskis Guest

    Hi Terry,

    It will "install" support for the (external) hub.
    In turn, that may (silently?) reinstall the devices
    that you plug into that hub as they are now connected

    This shouldn't be a problem.

    Be sure to note/verify any power indicator on the hub.
    Some will only illuminate when a device is plugged
    *into* the hub.

    You can also check in "Device Manager" to see where
    the hub appears (by connection) and whether it is
    seen as a 1.1 or 2.0 hub.
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