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  1. #1

    Default USB 1.1 - max current output?

    What is the maximum current output for a USB 1.1 port? (eg it is 500mA for USB 2.0).


  2. #2
    Join Date
    Dec 2004

    Default Re: USB 1.1 - max current output?

    Look under USB root hubs in device manager (under USB controllers). Click on the power tab

  3. #3
    Senior Member 1101's Avatar
    Join Date
    Jan 2008

    Default Re: USB 1.1 - max current output?

    Just FYI
    Most of the longish USB cables & extention cables are hopeless for transmitting(wrong word) USB power.
    Often you'll get too much of a voltage drop in the longer cable & the USB device wont power up, especially with USB powered external HD's

  4. #4
    IT Contractor
    Join Date
    Feb 2005

    Default Re: USB 1.1 - max current output?

    USB 1.1 and USB2.0 specifications both define a maximum draw of 5 unit loads, with a unit load being 100mA (therefore maximum draw 500mA). USB3.0 defines a unit load as 150mA, and a maximum draw is 6 units loads (900mA).
    Windows 7 x64 // i5-3570K // 16GB DDR3-1600 // GTX660Ti 2GB // Samsung 830 120GB SSD // OCZ Agility4 120GB SSD
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  5. #5
    Senior Member Paul.Cov's Avatar
    Join Date
    Aug 2006

    Default Re: USB 1.1 - max current output?

    I had cause to plug in a USB powerd dialup modem today, which was being kept on hand for emergencies.

    It almost caused an emergency itself when it went up in smoke.

    On the first computer (USB 1) it produced "Power Surge" warnings from the OS when plugged in.

    It was a computer known to have flaky responses to USB 2 gear, so I plugged it into a USB 2 computer, and it very quickly roasted itself. My skin still stinks from handling it, despite washing repeatedly.

    Pulled it apart, and it was all micro components like a cellphone has. Too tiny and toasted to determine which part failed.

  6. #6

    Default Re: USB 1.1 - max current output?

    Thanks for the answers and suggestions. Paul.Cov's experience suggests that the modem tried to draw too much current for USB 1.1 and triggered an overload response, whereas USB 2.0 was able to provide enough current to fry it. On the other hand Inphinity's info indicates that both provide up to 500mA. This is interesting as I had assumed that some (? most) laptops were fitted with USB 1.1 ports well after USB 2.0 became standard in desktops because 1.1 presumably used less current and therefore gave better battery life.

  7. #7
    amateur expert dugimodo's Avatar
    Join Date
    Dec 2005

    Default Re: USB 1.1 - max current output?

    Motherboard manufacturers don't seem to limit themselves to the specification, it's often possible to draw much more than 500mA and some even mention this as a feature (my gigabyte board has some kind of blurb about fast charge for usb devices).
    I've seen it described on one tech website as motherboards using current limiting circuitry across several usb ports so that 4 ports for example can supply 2A total with individual ports being able to exceed 500mA depending what else is in use across the ports.
    It makes sense as individual current limiting circuits would cost more.

    I think manufacturers are relying on the devices being plugged in having their own limiting circuitry if required, or simply not drawing too much current to begin with.
    Ryzen 2700X, 16Gb DDR4RAM, 512GB M.2 NVME SSD, MSI GTX1070

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