Hi Gang,

So I have a couple of CNX-P5USB hubs that basically work as advertised... Except for one issue -- power is flowing from the hubs back to my Car PC. I believe it is causing my DC-DC adapter to act funny, so taking advice from some other threads on the forum I cut the red line on my usb cable going into one of the aforementioned hubs... Well the hub didn't turn on, which is what I should have expected. Reading the device description;

The DC input includes reverse polarity protection, transient suppression, and an internal in-line, self-resetting fuse. A self-locking power cable is included. The P5USB can be turned ON or OFF either by the carís ignition line or by sensing the presence of +5V on the upstream host USB device (PC). This helps prevent battery discharge when the PC is left in Standby for extended periods of time. The P5USB includes an Shutdown Delay jumper which can be set to allow the P5USB to remain on for either 5 minutes or 25 minutes after the Ignition is turned off. This prevents the loss of USB connectivity during short stops if the PC is left running.
So the question at hand is if the hub requires the 5v to turn on, how do I prevent the current from going back upstream and have it power on?