Charge USB devices from your PC, whether it is running or shutdown.

It seems like everything, whether it is your iPod, digital camera or a PMP, has a USB charger. No need looking for your wall wart charger and an empty wall outlet, just plug it in the USB port of your computer. While this works great most of the time, what if your computer is shutdown? Do you start up the computer just to charge the device or do you look for the charger? Now you have a third option.

When your PC is shutdown, all power supply rails are also shutdown with the exception of the +5vdc standby (+5vsb). The +5vsb rail supplies power whether the computer is running or shutdown. While the typical motherboard draws 500ma from the +5vsb rail, most power supplies are capable of supplying 1.5 - 2.0+ amps for +5vsb. We will be taking advantage of this excess capacity.

The needed parts: a USB jack, a 10k ohm resister and some wire.


Although a 20 pin motherboard connector is pictured, the same instructions also work with a 24 pin connector. Unplug the power supply from the motherboard and locate pin 9 on the power supply plug. This is usually a purple wire. This will be our 5vdc supply. Pin 7 (black wire) will be our ground.



Here I have tapped into those wires using red for +5vdc and black for ground.


The USB jack has 5 wires; red, white, green and 2 blacks. The white & green are soldered together then connected to one end of the 10K ohm resister. The other end of the 10K ohm resister connects to the red wire. (The 10K ohm resister is required by some devices to activate charging mode.) Both black wires are connected together.


The red wire from the power supply connects to the red wire on the USB jack and the black wire from the power supply connects to the 2 black wires.


Insulate the connections with heatshrink tubing or electrical tape. Mount the USB jack somewhere that is easy to reach like in an empty drive bay cover. Note that this USB jack is for charging only and not for transferring files to/from the computer. If the computer has multiple users it would help to mark this jack as “charging only”. Now, whether your PC is running or shutdown, you will be able to charge your USB devices.

Nice writeup. It will definitely come in handy!

very nice

Wait, you COULD connect it to a regular usb jack, just connect the +DATA and the -DATA to a mini DPDT relay actuated by one of the 5V or 12V HDD jacks. Those turn off when the mobo is turned off, right? so when the mobo is turned off, the relay is inactive and the +/-DATA are grounded to the resistor to the red wire... otherwise, they're connected normally.

Also, who turns their PCs off anymore?

Thanks Cerberus, this was just what I needed. It took me about 15 minutes to complete and saved me from buying a new power supply to get this feature.

thanks again
~DT

Is there a way to do this to a laptop. I would like to charge my ipod while on an airplane with no in-seat power available. Turning on the laptop would just drain the battery more.

I don't know if anyone mentioned this yet...

Cerb... you are featured on hackaday!!! Congrats!!!

it was mentiond in t3h chat room

I'm not an electrical engineer, but afir laptops have a similer standby line, however, because it's designed to run off battery it's probably tight, and a stretch to try this.

Your best bet is to use this (http://www.daydeal.com/product.php?productid=16431) coupled with this (http://www.usbcell.com/, or any rechargeable battery).