On Wednesday, July 25, 2007 at 02:24:43 +0100, Brad Karp wrote: >Greetings, all. > >We're using about a dozen net4826 boxes here, and we need to connect >a few USB devices to each box via a single USB hub. > >We power each net4826 box using PoE supplied by an HP PoE switch, >through a D-Link DWL-P50 PoE "splitter" (12V output). (As you know, we >need the splitter because the net4826 isn't PoE standards-compliant, >and the splitter puts the power on a pair the net4826 can use.) > >We originally intended to power each net4826's USB hub over USB >itself, and the USB devices from that USB hub. But we found the USB >devices in the numbers we need draw too much power for that, so we've >had to fall back on powering the USB hub by other means. > >Since we have PoE readily available, we decided to power each USB hub >using the 5V output of a dedicated D-Link DWL-P50 PoE splitter (each >supplied with power by a dedicated PoE switch port). > >We use D-Link DUB-H7 USB hubs. > >So in full, the picture is: > > PoE 12V > port0 ------------> DWL-P50 ----> net4826 > / | > HP PoE switch | USB cable > \ | > port1 ------------> DWL-P50 ----> DUB-H7 USB hub > PoE 5V > >Note that no USB devices are hanging off the hub in any of the cases >I'm describing. > >We find that while the net4826 can talk to the USB hub when the USB >hub is *not* externally powered (i.e., unplug the 5V cable in the >above picture), the net4826 fails to talk to the USB hub when the USB >hub *is* externally powered. > >In fact, it's worse than that: when we power the USB hub using PoE, >and connect its USB cable to the net4826, the net4826 hangs >immediately, and resets upon our disconnecting the USB >cable. Moreover, we seem to have *permanently* killed the internal USB >hub on at least one of our net4826 boxes by connecting an externally >powered USB hub in this way.
Perhaps the GND levels of the DWL-P50's is different when set to 5 or 12 Volt output? That would cause a short-circuit current that destroys the USB port. You can measure the voltage between GND of two adapaters without the Soekris and USB hub connected. If you measure (very close to) 0 V between both GND outputs, you can't use them like this. Maurice _______________________________________________ Soekris-tech mailing list [email protected] http://lists.soekris.com/mailman/listinfo/soekris-tech
