How many USB devices can I use? (Math inside)

**Maheriano** · 05-11-2009, 04:44 PM

I have a M1-ATX that has 10 amps on the 5 volt rail (USB). Each of my devices is on average 100 milliamps, does that mean I can plug in 100 USB devices on this rail? That doesn't seem right. Here's what I have:
- Xenarc 700TSV touchscreen
- Holux 213U GPS receiver
- MadCatz PS3 wireless thumbpad
- crappy Creative Labs webcam

I want to add a hub so that I can plug in a flash drive whenever I want, also USB sound card and possibly a rear view camera.

**colin** · 05-11-2009, 06:21 PM

First, see how much power your motherboard takes up on it's 5v rail, along with all your drives. The rest is what you can use on USB devices. Hubs also use a bit of power, and youll want to make sure you leave some leeway so that you don't over-use the 5v rail.

**bratnetwork** · 05-11-2009, 08:08 PM

You could always get an OPUS DCL11 POL PSU to power a USB hub so the devices don't draw off the M1

**Jitters333** · 05-11-2009, 08:18 PM

I wouldn't worry about the flash drive but the camera might need an external power source

**DeltaFX** · 05-12-2009, 05:37 AM

webcam are power hungry, more or less. My old Trust SPaceCam 380 draws 500mA.

**digital79** · 05-16-2009, 08:49 AM

According to this: http://www.beyondlogic.org/usbnutshell/usb2.htm, one USB port can provide up to 500mA of power.

Just because your PSU can provide 10A on 5V rail, does not mean you can have whatever is left over from that for USB.

If you need to use many power hungry USB devices, use externally powered USB HUBs, and plug those devices into them.

There are slight variation from 500mA rule, they are manufacturer dependent. Some can provide a bit more for a short period of time.