usb : WHY don't most mobo's allow divert +5vSB current to +5??

[ananymous]

Hello,
I'm shopping for a new psu and just discovered that USB devices draw power from the +5vSB connection.
Frankly, I'm kind of surprised that there aren't more problems as a result of this! I don't need a psu for gaming so I have no reason to spend more than say $65 on a decent psu. In fact, one of the main reason I was shopping for a nicer psu in the first place is so that I wouldn't have to worry about plugging as many usb devices as needed.
If I spend $80 I can get one with 3 amps on the +5vSB, otherwise it's going to be 2.5 amps. This just seems exteremely low safety margin considering the proliferation of usb devices that people use, especially with high performance external drives and enclosures (why would anyone use a 5400rpm external drive anyway unless they are broke?).

I also read that older mobo's used to have a jumper to divert +5vSB power to the +5v connection...why the hell would this feature be discontinued now, shouldn't it be more common with all the usb devices people use?

Is the easiest solution to just buy a usb hub with external power? I certainly don't want another external thing around the desktop but like I said, I'm tired of worrying about whether or not my "modern" computer can actually handle the number of usb ports the *@#!!% mobo came with.

I'd appreciate any feedback on this subject...sorry it's a bit of a rant but I was set to buy a psu & then made this discovery :-(

 

[wirednuts]

unless youre charging 4 xbox controllers all at once, i really doubt youll draw 2500ma just with your usb devices. i know each device is allowed to take 500ma, but most pull like 50ma under normal use.

also, i thought that +5vsb jumper was to keep power at the usb devices while the pc is in sleep mode....

 

[VirtualLarry]

I have a HTPC, with a 300W PSU included in a micro-ATX case, with a Foxconn 780G mobo, and my USB ports cannot handle the power requirements of a MagicJack.

I have an IR reciever, and a Logitech "Unified" reciever plugged into the rear USB ports. I can plug a USB flash drive into the front USB ports, and it works, but plugged in the MJ results in "Device not recognized". Same if I use a high-quality USB extension cable and plug it in the rear USB ports. I had to resort to using an AC-powered USB hub.

That might be the only solution for you too.

 

[Zap]

If I spend $80 I can get one with 3 amps on the +5vSB, otherwise it's going to be 2.5 amps.

Just an aside... BFG had two PSUs that had IIRC 5A on the 5VSB. They were the LS-1000 and LS-1200 models.

It is possible to re-wire your front ports to be powered off 5V instead of 5VSB. Just strip out the black (ground) and red (5v) wires from the cable and tap into the PSU's 5V (red) and any PSU ground (black). See, they made it easy! Just match colors! Just make sure the other two wires (green and white) go into the same pins they did before on the motherboard.

 

[tcsenter]

also, i thought that +5vsb jumper was to keep power at the usb devices while the pc is in sleep mode....

It is. And its only intended to supply power for relatively low draw devices that will be used to bring the system out of sleep or standby (e.g. mouse, keyboard).