Thread: Strange USB Issues - USB Doesnt "Stay Alive" In Car

Originally Posted by mnwcsult

Go into Control Panel. I am presuming you are using Windows as your OS.

Select System, then Device Manager. Find "Universal Serial Bus controllers" and click on the plus to open it.

You are looking for "USB Root Hub", you will have as many as you have hubs. Click on the first one, the click the Power tab. It will tell you whether the hub is self powered or powered. And the Total amount of power available: 500 mA per port. So a four port hub "should" be able to sink 2000 mA, or 2A. Thats 2A times the number of four port hubs available.

You will also see what devices are attached and their Power Requirements. Say a Bluetooth adapter around 50 mA. Another hub connected to it 400 mA. USB hard drive 500 mA.

My guess is that the ones drawing 500 mA can probably draw a lot more. I have a hauppauge USB TV stick. It's documentation suggests that it be on a hub by itself if the hub is unpowered. Experience shows me it can coexist on a powered hub with a Bluetooth adapter.

I also have a Seagate FreeAgent USB drive that derives all of it's power from the hub and can be the only thing living on it powered or otherwise.

What is happening is that certain devices will draw more current than their ratings show, hard drives in particular. And will monopolize the entire hub.

You will have to try different combinations to see what is actually stable. You may also want to power all of the hubs through a voltage regulator.

Good Luck

Thank you very much for all of the information.

Well after the writing of my last post in this thread I did go into device manager and for the USB devices I clicked the power tabs and set everything to >NOT< turn this device off... They were all set to disable or turn off the device to save power or something like that.

Now at the moment, I havent had any issues. But I have noticed that sometimes at boot up, the four port hub does not "initialize" itself it windows properly and the device manager shows it with a yellow question mark, indication "this device has malfuntioned". After a restart, it all works fine again.

What I have in the hub is Lilliput, USB GPS, and an empty extension cables for easy input of a flash drive.

I am going to test this for a few days and if I still have issues, I will try replacing the hub with another brand and see what happens.

Let's stay within specs. usb_20.pdf 7.2 A (2.0) high powered device can use no more than 500mA and assume no more is available. Low power should be no more than 100mA. The power listings in Windows will show the maximum each device defines itself as using, and is often less when running and more on inrush, usually when starting. A hub is usually going to use 100mA, leaving 400mA to its ports when not self powered. Although there is an exception. Many motherboards now allow for much more from the root hub's ports, but the problem is that most hubs have current limiting built in so they are still limited to the 500mA max.

Why not just hook the GPS up directly to the computer?

Also, from experience, it isn't such a good idea to put the monitor on a USB hub. It's one more thing to go wrong and the screen is your input when driving. If the hub craps out and music is blaring you're screwed.

In the begining the screen was on it's own USB. Then when I got the GPS it was easier to get a hub and attach it up front without running a seperate line. Plus I didn't think it was that big of a deal. I use a ATI Remote Wonder in the car for volume and track skip, etc. So just in case I do have a physical mute button

I recently ran a old SCSI cable from the front to back to give me some wires. The cable has like 25 leads in it. So I might wire everything seperate a d just do away with the hub all together. I just use alot of USB.

Ah, so 2 out of 3 of my scenarios were correct?

The problems started when the hub and long USB cables were installed.

Well I had the exact same setup before on another computer I had before, with the hub not connected to a power source. After I hooked the hub up to a 5v line, my issues seemed to go away.

That still doesnt explain why it worked in the house without the 5v line attached, but if its working now its hard to complain

The difference is that now there is interference to deal with in the car.