I have instability problems with my mega that is probably a memory issue ...
Anyway I realized that I was not following specification (7 -12 V) with my external 5V power adaptor.
So I connected my variable voltage generator.
With consol USB power also connected.
Current from external was
6V 0 A
7V 0.33 A 2.31 W
7.6 V 0.2 A 1.52 W
7.6 V still 0.2 A
So it was a little bit interesting to see that my 5V was not contributing at all when running just the mega and some small consumption sensors/shields (temp,ether,SD drive)
When activating a relay needing 0.160 A I had 0.100 A from 5V.
Seems like external was providing most Watts at 7V ....
An Uno/Mega has a opamp+mosfet circuit to switch between USB supply and external supply.
Switch point is set to ~6.6volt on V-in (or ~7.3volt on the DC socket).
Leo..
sidhabo:
I have external power on DC socket. My Mega seem to cut in external just above 6 V.
Yes, external supply already starts to contribute just above 6volt.
But that switchpoint from post#1 is when USB supply fully turns off, assuming external supply is good enough.
Because you need at least 6-6.5volt on V-in (or 0.7volt more on the DC socket) to make a stable 5volt.
Leo..
