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Thread: Powered USB hub 5v feedback

  1. #1
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    Powered USB hub 5v feedback

    I'm finishing up my latest install and find that my powered usb hub is feeding back 5v to my computer's usb ports. Typically this wouldn't be a problem but I'm using the 5v of the usb ports to know when the laptop is running or not.

    Do all hubs do this or is mine a cheap one that the manufacturer forgot to isolate the power rail?

    I tried putting a diode in the cable but the voltage drop is too great. I haven't tried a shottkey yet.

  2. #2
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    you mean the up stream usb connector, is sending power to the computer, from the usb hubs internal supply?

    this sounds like a USB design voilation...looking at a design.. the upstream power only a voltage regulator 5v to 3.3v to power the hub ic
    its 5v is NEVER connected to the 5v hub power for the downstream ports
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    Not 100% sure what is happening internally but if I plug nothing into the hub and don't plug the hub into anything, then power the hub on its provided power supply, there is 5v at the plug that you plug into the computer.

    This in essence is pushing 5v back to my laptop. I have read other places that other people have had instances where their computer fans and lights would stay lit when using a powered hub. I have a couple of hubs here at work I'm going to bring home and try.

  4. #4
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    It sounds like it is just a cheap hub that connects the computer-side (dongle) 5v rail to the port-side (ports) 5v. Basically, it would be a passive hub that had an external power supply added, without the circuitry being adjusted for that.

    In theory these should be isolated from each other with the PC supplying power to a relay that triggers the power supply to feed power to the ports or for the dongle to not have the 5v line doing anything and the power supply feeds a constant 5v to the ports.

    I'm actually building my own powered hubs by using a relay on the dongle's 5v line that will trigger the power for the ports. That way I can wire up to 10A of USB without worrying about my devices failing because the computer can't push that kind of wattage through USB.

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    Well, it definitely powers the devices off of the external power as I had too many to run without external power.

    All that said, I tested an old Radioshack 1.1 hub I had that I'm not using cause it is 1.1 and from my first carpc install... sure enough, no back feed. So I just purchased a new one from staples... no feedback. Damn you China. American (or other countries) may be expensive but at least it freaking works and corners weren't cut. And yes, my new hub has made in china stamped on it too but an American told them how to make it otherwise it would have cut corners.

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    Maybe you could post a pic or at least details of model and where you got it to alert otehrs not to buy. Any help when choosing components is a bonus!
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    Maximum Bitrate Mickz's Avatar
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    Quote Originally Posted by dmcdlrn View Post
    I'm finishing up my latest install and find that my powered usb hub is feeding back 5v to my computer's usb ports. Typically this wouldn't be a problem but I'm using the 5v of the usb ports to know when the laptop is running or not.

    Do all hubs do this or is mine a cheap one that the manufacturer forgot to isolate the power rail?

    I tried putting a diode in the cable but the voltage drop is too great. I haven't tried a shottkey yet.
    This was common on almost every hub that I tried including some expensive units. Here is part of an answer I just gave on another post.

    Some Hubs when externally powered “BEFORE” the PC has powered on (+5v USB has appeared from the MB) will bleed voltage back to the MB and other USB devices on the line. This can cause “SOME” USB devices to power up incorrectly and lead to strange issues with USB devices not ready or not functioning correctly.

    I gave up trying to find HUBS that didn’t and I now have the PSU +12 ATX line switch a small relay which then connects the +5V supply to the powered HUB input.
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  8. #8
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    Quote Originally Posted by PhilG View Post
    Maybe you could post a pic or at least details of model and where you got it to alert otehrs not to buy. Any help when choosing components is a bonus!
    Well, I bought it over 5 years ago on ebay for my last project. It has sat in a box for the majority of that time. It looks like this: http://www.amazon.com/Port-LED-USB-C.../dp/B0010LUJCC


    Quote Originally Posted by Mickz View Post
    This was common on almost every hub that I tried including some expensive units. Here is part of an answer I just gave on another post.

    Some Hubs when externally powered “BEFORE” the PC has powered on (+5v USB has appeared from the MB) will bleed voltage back to the MB and other USB devices on the line. This can cause “SOME” USB devices to power up incorrectly and lead to strange issues with USB devices not ready or not functioning correctly.

    I gave up trying to find HUBS that didn’t and I now have the PSU +12 ATX line switch a small relay which then connects the +5V supply to the powered HUB input.
    I purchased this hub and can vouch that it does not bleed voltage back: http://www.staples.com/Staples-7-Por...product_837529

    The hub is controlled by a relay but I cannot have the power to the hub removed before the computer is down or else devices will malfunction due to under power state. This will lead to the computer getting confused more often.

  9. #9
    Maximum Bitrate Mickz's Avatar
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    Quote Originally Posted by dmcdlrn View Post
    I purchased this hub and can vouch that it does not bleed voltage back: http://www.staples.com/Staples-7-Por...product_837529

    The hub is controlled by a relay but I cannot have the power to the hub removed before the computer is down or else devices will malfunction due to under power state. This will lead to the computer getting confused more often.
    I can’t view that from AU for some reason, however it’s a moot point anyway as some of the hubs I use are USB repeater hubs.

    As you say, removing power before the PC has closed can cause problems if there is a supply drop, however having the power switching controlled by one of the PSU-ATX supply rails overcomes all external hub power timing problems. Of course there always are other way to do this as well.
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  10. #10
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    I'm using a netbook. My shutdown controller is an arduino that monitors the usb 5v rail to know if the computer is off... thus my problem.

    Weird on the staples. Too close to the great firewall of china?

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