12V USB Hub, Help! - Page 2

daviboy · 06-02-2008, 03:22 AM

there is 1 i found on ebay, el cheapo, it comes with an AC adaptor but it is transformed to +12VDC which u can happily tap off your regulated DC power supply in the car, dont run it directly off the cars 12V, Dont want to see the results of the devices once you crank the car.

http://cgi.ebay.com.au/ws/eBayISAPI....:X:AAQ:AU:1123

chrislamb · 06-02-2008, 03:53 AM

daviboy,

I can't see where it says that this ebay hub is 12V.
Sure it uses an adaptor but it could be 5v.

daviboy · 06-02-2008, 04:27 AM

yeh it doesnt state anywere on the link that it uses 12V but i emailed the seller and he quoted that it does. Why dont you just run 5v off the PSU? and use the existing hub? As easy as running a Fig8 cable to the rear of the car

epugh · 10-21-2008, 03:56 PM

Hey all,

The 4 port USB hub that is 12VDC (http://www.usbgear.com/computer_cabl...53%2C210%2C212) works great EXCEPT I don't have a computer in my car acting as a host controller.

So the port only works in the low speed/low juice 1 amp mode, and wont' go into 5 amp mode. If I plug in my laptop, great, but otherwise it stays at 1 amp. So it works fine for my GPS, but my iPhone won't charge cause it needs more juice.

I am using my iPhone as the computer brains on my setup, so I am looking for a hardware/dongle that will tell the USB hub that it should be in 5 Amp mode all the time. No joy so far. Any ideas?

Eric

DeltaFX · 10-27-2008, 01:00 PM

5 amps mode ? Uh? What are you talking about ? USB host/hub are 5V 0.5A maximum per line.

There's no low speed<=>low juice relation AFAIK, my old usb-powered zip250 is only USB1.1 and draws its 500mA.

or am I missing something ?

epugh · 10-27-2008, 01:51 PM

Doh! You are right, I meant milliamps. I think my hub is only giving me 100 mA, but when I plug in my computer as upstream, it gives the full 500 mA. So I need a way of telling it to give me the full 500 mA, but without plugging a computer in.

http://en.wikipedia.org/wiki/Universal_Serial_Bus#Power was what I was reading up on the modes...

Eric

DeltaFX · 10-30-2008, 12:42 PM

For "normal" devices (mice, usbstick,kbd, hdd,webcam) one usb port can output up to 500mA. Such a device requieres one unit of power at connection, that's 100mA,then it can negociate to ask for 500mA, 4more units. Special devices, and if the host(usb controller) allows, can negociate for more than 500mA (5 units). These devices are for exemple battery "smart" charger: if everything works fine, the usb port can output 1.8A.

But even if the device needs 600mA, and if the host can output 600mA, inserting a hub is always a problem. The hub needs power.... for itself. That's 1 power unit. Only 4 power units remains available for peripherals. Xternally powered hubs are differents in that they allow 5 power units per subline. But that doesn't mean they can deal with "special device's needs" It depends on how the hub was designed and how it deals with power request. Some simply don't stick to that part of the standard, the don't allow beyond 500mA requests, some can't even if they are transparent in the daisy chain (they transmit requests to the host) because of their PSU.

And as you probably discovered by wourself, alone they are just stupid. Without a Host (a pc /mac...) they have no way to understand request by themselves. Imagine a battery charger that asks for 1A, when connected an "ideay-perfect-standard-stickyl" hub will transfert that request to the comp, then if request is granted, allow 10 units to the device, either from the host if the host can, or from hub's PSU, if the PSU can..

Alone your hub can't probably output more than 500mA per line in "dumb mode" (not 'smart charger mode') and without a host it can fulfill 'highpower' request.