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Power adapter for USB 3 4-port hub

Hello all!
I bought a USB 3.0 hub with an external power supply.
The hub has 4 ports, and one of them supports Battery Charging Specification. The power adapter has specs of 12V and 1.5A.
I contacted the manufacture regarding this power adapter. For me it seems it won't provide full power for the USB hub. See my math:
4 ports * 900mA = 3.6A - 1.5A (from power adapter) = 2.1A missing. Well, the USB port from computer (when on) could supply 900mA, so at the end I would miss 1.2A. Is it right?
And, I'm not considering the Battery Charging Specs above! Otherwise I think I'm missing even more power...
The manufacture replied to me saying that 12V at 1.5A can handle 4*5V at 900mA. So 12V provides more mA to 5V ports? I have no idea...
Could someone help me with this math?
Seems that this hub wouldn't support 4 peripherals drawing 900mA each. Or even worse, charging something at 1.5A and using other 3 ports at 900mA each.
Thanks!
6 answers Last reply Best Answer
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  1. I think the specification is clear: "Every device functions initially as low-power—but may request high-power, and gets it if it's available on the providing bus" The minimum requirement within usb specs is 3*100mA+1*Battery Charging
  2. noidea_77 said:
    I think the specification is clear: "Every device functions initially as low-power—but may request high-power, and gets it if it's available on the providing bus" The minimum requirement within usb specs is 3*100mA+1*Battery Charging


    Thanks, but my question is not about the USB 3 specs but if, having this power adapter, I'll be able to use 4 ports at 900mA - if my math is correct. Thanks for your help anyway.
  3. igorjrr said:
    noidea_77 said:
    I think the specification is clear: "Every device functions initially as low-power—but may request high-power, and gets it if it's available on the providing bus" The minimum requirement within usb specs is 3*100mA+1*Battery Charging


    Thanks, but my question is not about the USB 3 specs but if, having this power adapter, I'll be able to use 4 ports at 900mA - if my math is correct. Thanks for your help anyway.

    And the answer is no.
  4. I'd appreciate if someone could provide more detail on this... thanks.
  5. Best answer
    igorjrr said:
    Hello all!
    I bought a USB 3.0 hub with an external power supply.
    The hub has 4 ports, and one of them supports Battery Charging Specification. The power adapter has specs of 12V and 1.5A.
    I contacted the manufacture regarding this power adapter. For me it seems it won't provide full power for the USB hub. See my math:
    4 ports * 900mA = 3.6A - 1.5A (from power adapter) = 2.1A missing. Well, the USB port from computer (when on) could supply 900mA, so at the end I would miss 1.2A. Is it right?
    And, I'm not considering the Battery Charging Specs above! Otherwise I think I'm missing even more power...
    The manufacture replied to me saying that 12V at 1.5A can handle 4*5V at 900mA. So 12V provides more mA to 5V ports? I have no idea...
    Could someone help me with this math?
    Seems that this hub wouldn't support 4 peripherals drawing 900mA each. Or even worse, charging something at 1.5A and using other 3 ports at 900mA each.
    Thanks!


    igorjrr said:
    I'd appreciate if someone could provide more detail on this... thanks.



    I know this reply is extremely late. But I'm looking into modding one of my HUB's and I can provide a bit more detail on this. Hopefully if/when you get this you'll be able to teach someone else this as well. Or perhaps someone will stumble upon this thread and my reply will help them... never know. (so, sorry for a potential grave dig.)

    Okay so...

    If the power is 12 volts and 1.5 amps you need not worry about the volts or the amps...

    What you do is convert them to watts...

    12 volts times 1.5 amps = 18 watts

    What you do with that is pretty much obvious. Okay now 4*5volts at 900 mA is fairly simple to figure up (900 mA is only 0.9 amps):

    There are 4 ports right? But we need to figure out how many watts is in 5 volts and 0.9 amps

    5 times 0.9 = 4.5 watts

    4.5 watts times 4 ports is still only 18 watts which leaves you with nothing left.
  6. Thank you! Yes, I learned that it's not only the amperage that counts, but also how many volts... all together comes to Watts to do the proper math...
    Your math is absolutely right, so 12V with 1.5A can handle a USB hub with 4 ports (5V each) with 0.9A.
    Thank you! :)
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