I do not know why Intel did not put a jumper on the board to allow powering the kit from J3. Just makes sense to me to do that.
I got tired of having 2 USB connections to my Edison kit. One for power (J16), and the other for access to the terminal (J3).
I know that you can also power it from J21 as well, but my point here is that I want one connection.
If your good with a soldering iron, you can make this mod to your board so you can power it, and have access to the terminal with just one USB connection.
Pin1 on J16 routs to the anode of diode Dx (not listed on silk). What i have done is route a wire from Pin1 of J3 (+5v power) to one side of a 500ma fuse. The other side of the fuse is then soldered on top of, and to the anode the same diode Dx.
NOTE: Intel may frown on this, and I am not responsible for any damage you may do to your board in the process or lack of common sense.