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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
    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
    -Thanks
    Mitch
    www.rush2112.net

    "Did you test it in carwings??"

    Sun, Come shine my way
    May healing waters bury all my pain
    Wind, Carry me home
    The fabric of reality is tearing apart
    The piece of me that died
    Will return To live again

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    • #3
      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.

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      • #4
        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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        • #5
          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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          • #6
            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!
            My 2007 Ford F350 Work Log located HERE

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            • #7
              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.
              Palm sized ainol MiniPC, 8" Transreflective PRO, Win10, Reverse camera, Dual 10HZ GPS RX's for Speed Display & Sat Nav, FM-DAB & Phone Modules, iDrive interface. T-Screen HVAC control, custom microcontrollers, microcode and FE.

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              • #8
                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


                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.

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                • #9
                  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.
                  Palm sized ainol MiniPC, 8" Transreflective PRO, Win10, Reverse camera, Dual 10HZ GPS RX's for Speed Display & Sat Nav, FM-DAB & Phone Modules, iDrive interface. T-Screen HVAC control, custom microcontrollers, microcode and FE.

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                  • #10
                    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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                    • #11
                      That explains it as I had a similar problem, I also have a micro controlling shutdown sequences and validating the requested state. Three of my other Microprocessor control systems were leaking a small voltage from the data interfaces ports back into the USB line. As these Micros have to also run independently of the PC system I had to modify the micro code to Monitor USB +5V and switch the data interface to the USB lines off whenever the PC was off. There really are so any things to consider with different installations and hardware. Makes answering a general question so difficult at times but I guess we do the best we can
                      Last edited by Mickz; 03-17-2012, 04:45 AM.
                      Palm sized ainol MiniPC, 8" Transreflective PRO, Win10, Reverse camera, Dual 10HZ GPS RX's for Speed Display & Sat Nav, FM-DAB & Phone Modules, iDrive interface. T-Screen HVAC control, custom microcontrollers, microcode and FE.

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                      • #12
                        Truth. This install was much more complicated because I included the micro controller. Seriously was a 1 step forward 3 steps back for most of the install. Luckally my arduino does not feed back on the 5 volt.

                        I did however find an issue where the arduino would not initialize its usb system if you didn't first power it off of the usb power then apply external power. I tested it about 30 times on the bench and ended up installing a switch in the kick panel of the car to kill power to the arduino in the event I need to reboot the system... After install I found that to not be a problem.. can't explain it. But I did find I couldn't have my lines hooked up from the usb 5v and to the laptop power header or it would cause the issue. I know those were not hooked up during testing...

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                        • #13
                          Isn't there a laptop startup/shutdown controller that uses the Ethernet port to monitor your ignition state? Seems like it might be easier to do that since your having issues with both your hub and the arduino all related to the USB?
                          1997 Acura CL (Capacitive Touch, GPS, DVD, HD Radio, Backup Camera)

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                          • #14
                            well, I'm not having issues any more now that I have a good USB hub. Ethernet doesn't supply voltage... how would it monitor Ethernet? I would think the link lines on Ethernet would be VERY low voltage/current.

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                            • #15
                              It doesn't supply voltage. You still need to use a power supply. It uses the Ethernet port to send the startup/shutdown signal. Its powered by your car battery. Good to hear you got it working.
                              1997 Acura CL (Capacitive Touch, GPS, DVD, HD Radio, Backup Camera)

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