Powering USB 2.0 Hub off HDD +5v Rail - Any problems?

sq_geek · 06-07-2004, 12:35 AM

Do you guys see any issues powering my USB 2.0 Hub (requires +5v) off of my HDD rail, which supplies +5v from the PSU. ???

I'm guessing the USB hub does nothing but regenerate the signals, so I doubt it would draw too much power during use.

What do you guys think?

Q_gamelogic · 06-07-2004, 12:53 AM

if you gonna let it get power from psu .... why not buy a self powered one .... one that works off the usb 2.0 power from mobo .. (that inturn gets it from the psu ) .... so .. seems kinda useless to get it from the same source

sq_geek · 06-07-2004, 01:32 AM

I couldn't find one.. Can you post a link for one of these "self-powered" ones?

Anyhow, it's too late.

What I did so far was hack off the 120vAC adapter head, and wired up some terminal clips to hook into the +5v molex adapter to get power from the PSU's +5v rail. Do you think this will suffice? I don't see how it is different from using the 120vAC adapter which ouputted +5v....

Kevin

Kermee · 06-07-2004, 02:01 AM

You should be fine. Just remember that each USB port on your hub is rated to 500mA by USB spec. Then add 500mA for some space. So a 4-port USB 2.0 hub needs 5V up to 2.5A regulated. Check your power-supply to make sure there's plenty available on the +5V rail.

fantomas · 06-07-2004, 02:05 AM

Quote: Originally Posted by Q_gamelogic

if you gonna let it get power from psu .... why not buy a self powered one .... one that works off the usb 2.0 power from mobo .. (that inturn gets it from the psu ) .... so .. seems kinda useless to get it from the same source

i heard (dont know if its true or not) that the hub that is self powered from the mobo splits the power (500ma) between each port....

NoPistonPC · 06-07-2004, 02:34 AM

The USB port on your mobo isn't required to provide more than 500mA. So if you plug in a 5-port bus-powered hub, it has to split up this 500mA among its ports. This won't be enough if you have several high-powered devices plugged in.

You did the right thing by buying a self-powered hub and wiring it directly into your +5V rail.

Here is a really article on self-powered vs. bus-powered hubs: http://www.microsoft.com/whdc/system/bus/USB/hubs.mspx

Defiler · 06-07-2004, 09:47 AM

Acctually I think Powered USB hubs can get up to 6As per port...I think the 500mA spec was on USB 1.x only. When USB 2.0 came out I think it was raised.

rando · 06-07-2004, 01:36 PM

Quote: Originally Posted by Defiler

Acctually I think Powered USB hubs can get up to 6As per port...I think the 500mA spec was on USB 1.x only. When USB 2.0 came out I think it was raised.

According to section 7.2 of the USB 2.0 spec at http://www.usb.org/developers/docs/usb_20.zip a single USB device can consume upto 5 unit loads. A unit load is defined as 100mA.

Defiler · 06-07-2004, 02:59 PM

Quote: Originally Posted by rando

According to section 7.2 of the USB 2.0 spec at http://www.usb.org/developers/docs/usb_20.zip a single USB device can consume upto 5 unit loads. A unit load is defined as 100mA.

Sorry, was thinking USB Plus power...

http://www.usbpluspower.org/

Kermee · 06-07-2004, 04:54 PM

+5V @ 6A's. 6 amps down 20 Gauge USB wires.

Sounds like fun!

beaverpants · 06-07-2004, 06:12 PM

Quote: Originally Posted by Q_gamelogic

if you gonna let it get power from psu .... why not buy a self powered one .... one that works off the usb 2.0 power from mobo .. (that inturn gets it from the psu ) .... so .. seems kinda useless to get it from the same source

actuly you dont want a self powered one.. it wont be able to run say a CD drive off a self powered one

sq_geek · 06-07-2004, 10:09 PM

well the DVD drive is self-powered, too.. I'll just have this IDE -> USB adapater (on ebay for $29) to convert and run the signal over the longer distance which USB can take me..

rando · 06-07-2004, 10:11 PM

Quote: Originally Posted by Defiler

Sorry, was thinking USB Plus power...

http://www.usbpluspower.org/

LOL, that uses completely different cables (since you certainly burn a standard USB cable with that kind of power). I'm not aware of any system boards using this standard so in a carPC environment, you'd still need an external USB+Power hub and that hub would still require external power (sigh). Moreover, since none of the typical USB devices support the USB + Power standard, high current devices would require an adapter to suck the power off the USB + Power cables. This looks like a no-winner, at least in the short term.