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  1. #1
    Star Lounger
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    USB Port power requirements

    I read an article that said that USB connections have power limitations. I do understand that external USB hubs sometimes required their own power supply.

    My question is what happens with USB PCI or PCIe cards in terms of how many ports can be supported.

    I am seeing four-port USB 3.0 PCIe cards being offered for sale but I wonder if they need an additional Molex connection. If I recall, a two port USB card is more reliable than a four-port USB card; correct me if I am wrong.

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  3. #2
    5 Star Lounger chowur's Avatar
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    Most likely on a 4 port you will need a,Molex connector.When checking out most cards in question.Make sure it has,Multiple translators installed on the card.This link can explain it;https://en.wikipedia.org/wiki/USB_hub
    Problems cannot be solved by the same level of thinking that created them. -Albert Einsten

  4. #3
    Super Moderator satrow's Avatar
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    Disclaimer: I only have USB2 ports but a USB3 external 2.5" drive (~6yo machine).

    USB standards require 0.5W per connection, this can easily be supplied by the PCI bus, providing any other PCI(E) cards don't push the power draw over ~100W < should be irrelevant if your PCI(E) graphics card is powered by Molex as well. I'd guess that a good USB3 card with 4 ports would draw ~10W max.

    Provided you have a good quality motherboard/PSU, I'd be more inclined to track down which USB3 chipsets to avoid, this was certainly an issue in the early days of USB2, a bad driver/chipset can cause all sorts of problems.

    If your motherboard has 'fast charge' USB ports, this may add further complications if enabled and used - again, chipsets/drivers.

  5. #4
    Platinum Lounger
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    The technology has hurtled along, as usual, and you'll probably find there are no issues with 4 port USB 3 cards, either power or speed.
    External hubs require additional power to provide the full USB specification on all ports.

    cheers, Paul

  6. #5
    Star Lounger
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    Thanks ALL. This makes a LOT of sense. I have heard of these issues before. I have a 650W PSU but I have 4 USB cards (2 USB2.0 and 2 USB 3.0) and connections to powered external hubs... NONE of which are always on. My next step is to realign all this to what I usally need. I tend to favor the cards that have a molex on them for the extra power.

  7. #6
    Silver Lounger mrjimphelps's Avatar
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    Anytime I get an external USB hub, I always get one with external power to the hub. The ones without external power generally aren't reliable.

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