any danger from using 2 power sources at same time?

[dkryder]

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.

[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.

[dkryder]

both of the power supplies are 5v/3A. both work with my other pine64 using either the micro usb or euler. actually for 6 months the pine64 in question booted just fine with either supply using either micro usb/euler. it was not until after 6 months the pine64 in question begin the boot problems. so in my mind it points to some type of fault with the pine64. but then just out of trying everything i started to power one supply then the other and i was surprised it booted and even more surprised it did not fry the board.

power supply, https://www.amazon.com/gp/product/B006QY...UTF8&psc=1
micro usb adapter https://www.amazon.com/gp/product/B019CX...UTF8&psc=1

edit: the thing that comes to mind is a capacitor that may help provide additional juice during the boot sequence that is no longer good and thus this additional power needs to come from another source, enter the 2 power supplies, to get the board past the boot sequence at which point the board can operate at levels of current provided by one power supply. thing is it is no longer as easy as it once was to identify a blown cap so that sorta rules out visual inspection of the board, for me at least, particularly when where the cap is placed is an unknown. i can see it on a schematic that is available but that is not much help in identifying the physical location.

[MarkHaysHarris777]

both of the power supplies are 5v/3A. both work with my other pine64 using either the micro usb or euler. actually for 6 months the pine64 in question booted just fine with either supply using either micro usb/euler. it was not until after 6 months the pine64 in question begin the boot problems. so in my mind it points to some type of fault with the pine64. but then just out of trying everything i started to power one supply then the other and i was surprised it booted and even more surprised it did not fry the board.

power supply, https://www.amazon.com/gp/product/B006QY...UTF8&psc=1
micro usb adapter  https://www.amazon.com/gp/product/B019CX...UTF8&psc=1

edit: the thing that comes to mind is a capacitor that may help provide additional juice during the boot sequence that is no longer good and thus this additional power needs to come from another source, enter the 2 power supplies, to get the board past the boot sequence at which point the board can operate at levels of current provided by one power supply. thing is it is no longer as easy as it once was to identify a blown cap so that sorta rules out visual inspection of the board, for me at least, particularly when where the cap is placed is an unknown. i can see it on a schematic that is available but that is not much help in identifying the physical location.

The only other thing you could check ( and it requires a good scope ) is for noise in the supply. Some switching supplies are noisy because they don't provide adequate regulation or filtering. The other thing that can be a problem is the line -- like the one on your supply which is circular.  Even though the supply is rated at 3A is doesn't really provide 3A because the cheap line-cord has a thin foil wrap rather than a good ground conductor.  ( PSU manufacturers cut corners, sad but true )

A well regulated PSU with a PI filter connected to the euler bus ( 5v 2.5A ) with a relatively shorter line cord ( 18 AWG ) two conductor cable;  is what is recommended.

http://forum.pine64.org/showthread.php?tid=1981

See the above link -- the official RPi power supply works very well when connected to the euler bus;  if not, something is wrong on the Pine board.

note: connecting the supplies together will not fry the board, neither will have a rating of 3A.  The important factor is the supply voltage ;  if you exceed 5.1v your board is going to be in trouble. It should be rated for AT LEAST 2.5A--- more is fine.