Regarding the following circuit, SPICE calculates the current I3 through R3 as 3.333A.
I try to solve that myself and can only reach that result if I first set V1 as zero(short) and solve for the current and then set V2 as zero(short) and solve for the current. Then the total sum through R3 becomes 3.333A.
But there are some parts which are not yet clear to me.
How can we set V1 or V2 as short? How can the current produced by V1 can pass through V2 at all? As far as I know they can do that in AC small signal analysis but here we have DC currents. How come a theoretical voltage source or a power supply in real pass DC?
If I was asked this question I would first remove V1 and solve for the current through R3 and then remove V2 and solve for the current through R3 and add these currents. But that would give 5A which is not the case.
So my thinking is somehow not matching the results, because I cannot imagine how current produced by V2 can pass trough V1 or vice versa. I would think the power supply would block such current. And even if not the case, here V1 = V2 how come current flows through the voltage sources?