any danger from using 2 power sources at same time?

[MarkHaysHarris777]

for some reason i have an issue with lacking power to boot one of my boards. if i use the micro usb power source i don't have enough power to complete a boot, after it reaches a point the boot sequence loops. if i use a power supply through the euler pins, same situation, boot loop after a certain point in the sequence. however, if i use a power source through both the micro usb & euler pins at same time the boot is always successful. after boot i can disconnect one or the other and the board runs fine. i have been doing this for about 3 weeks now without any obvious damage. but i thought i'd mention it to the group and see what feedback i get. i'm mostly interested in if i will eventually burn up the board someway but i'd also like thoughts on just why this is working thanks.

You will not hurt the pine board, but you might damage one of the psu(s). If you are going to tie two power supplies together always go through a power diode in the positive lead of each supply;  also, you might consider putting a PI filter on the supply. 

The micro usb port is NOT sufficient to supply the proper current to the pine board; however, the euler bus should work fine-- you probably do not have an adequate supply.  Use a good 5v @ 2.5A PSU (not a charger) and make sure that the supply line is relatively short (less than one meter) 18 awg two strand braid. 

There is a sticky in the DC Power In subforum which talks to the PSU issue, and one that specifically talks to the issue of powering successfully via the euler bus.