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Questions about a USB hub and basic electricity

Discussion in 'Hardware' started by GbeTech, Oct 12, 2014.

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  1. GbeTech

    GbeTech Thread Starter

    Joined:
    Aug 27, 2007
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    Hi!

    I'm considering buying a USB hub. My knowledge in electricity is about 0, so I'm not sure about the preferred power specs of each.


    So there's that one, 7 ports, with a 12V/3A power adapter.


    7 ports, 5V/4A.


    9 ports, 12V/5A



    The last one has only one port designed for charging, and the rest of them may not be good enough.


    From the second one (4A):
    From the third one (5A):
    Are they talking about the amp parameter? The third product says specifically that the special port is capable of 2.1A. So how much do the other ports supply?


    I thought the device can provide X ampere total, regardless of how it's divided. (by all ports, or taken by just one)
    Is there an amp limit to each port?

    What are your thoughts? Thanks.
     
  2. managed

    managed Trusted Advisor Spam Fighter

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    First Name:
    Allan
    You are correct, the total current (1000mA = 1Amp) output of a powered hub shouldn't be higher than it's power supply can deliver.
    But some Usb devices don't need the full 500ma maximum current that a Usb 2.0 port can deliver so in practise you may be able to use all the Usb ports on the hub even if they can't all deliver 500ma.

    Usb 3.0 can supply up to 900mA per port but here again the total current should not be higher than the hub's power supply can deliver.

    Any electrical device will only use the current it needs to operate, possibly a lot less than the power source is capable of delivering. The Voltage a device is rated for should be the same as the source's though.
    So a laptop charger that is rated for the correct Voltage and at least the same or higher current output needed for a particular laptop will work ok, the laptop will only take as much current as it needs, even if the battery is removed or is charging.

    This is a good explanation of Usb hub current ability :- http://en.wikipedia.org/wiki/USB_hub#Power
    Usb ports designed for charging devices can deliver more current, more info on all this here :- http://en.wikipedia.org/wiki/USB#Power
    'Normal' Usb ports are 5 Volts but see the table at the above link for some other types.
     
  3. GbeTech

    GbeTech Thread Starter

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    Thanks!
     
  4. managed

    managed Trusted Advisor Spam Fighter

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    Allan
    You're welcome.
     
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