USB-powering an M6E

Discussion in 'General Electronics Chat' started by daneloctober, Mar 14, 2013.

  1. daneloctober

    Thread Starter New Member

    Mar 22, 2012
    Hello again!

    I was tasked to power an ThingMagic M6E reader module through USB ports from a laptop. The reader is configured to draw a maximum of about 800mA at 5V, so I figured all I had to do was connect it to 2 USB ports: 1 port for communication (FTDI to USB), the other for additional power. But then I discovered that you had to ASK the host to enable the USB port to give more current, otherwise, you only get about 100mA max from a USB port.

    The USB for communication (the one with the FTDI interface) I think is all set to get 500mA, but the other USB port, I've read that all I had to do was use a 200 Ohm resistor to practically short the D- and D+ pins so I can get more than 100mA.

    The question I have is, will the reader draw equally from both ports if I short the data pins on the port dedicated to provide additional power?... Remember, I will be drawing a maximum of 800mA. I'm not really sure what would happen if I draw more than 500mA from either ports... I guess the USB ports will shutdown or something...

    Here is a schematic of what I'm trying to describe:
  2. ScottWang


    Aug 23, 2012
    I bought the small portable HDD that did the same thing as you did, they reading and writing are ok, but I didn't measure how much current they draw.

    You may in series with two 0.1Ω into two +V of the USB ports, and measuring the voltage of 0.1Ω, and using I = V_0.1Ω/0.1Ω to calculate the current of each port.