Potential Difference

Thread Starter

ben sorenson

Joined Feb 28, 2022
180
There are 2 sources.

Source (A) 5VDC @ Max 1000mA

Source (B) 20VDC @ Max 50mA

If the grounds of both "source(s)" are "common".

Would Pos source (B) flow to Pos source (A)
or
Would Pos source (A) Flow to Pos Source (B) because source (A) has a higher *current* potential?
 

crutschow

Joined Mar 14, 2008
34,048
It's based upon the voltage potential between the two, so the higher voltage always wins.
The current will equal the voltage difference divided by the combined series resistance of the two sources.

But, of course, you normally don't want to connect the two in practice, because it will likely zap something.

The current rating (potential is voltage, not current) has no effect on that unless there is a current-limit circuit in one or both of the sources.
 

BobTPH

Joined Jun 5, 2013
8,665
The 5V source might or might not be able to sink current. If it is a battery, the current into it would be a charging current. The could cause a fire.
 

k1ng 1337

Joined Sep 11, 2020
911
Current is the rate of flow past a point in space so there isn't really a current potential, only a voltage potential. To solve your circuit, we can model the voltage sources as having a series resistance by using Ohm's law. By starting with voltages and resistances, we can calculate how much current will flow.

Take a look at this LTspice simulation,

1) At node A, we see V1 is supplying 5V and 1A is flowing through R1.

2) At node B, we see V2 is supplying 20V and 50mA is flowing through R2.

2) At node C, we see V1 and V2 are connected therefore 37.03mA flows between R3 and R4. Notice how a positive current flows though R3 and a negative current flows through R4.

Putting this together, we arrive at the proof for circuit C:

(V3 - V4) / (R3 + R4)
(5V - 20V) / (5ohm + 400ohm) = -37.03mA

a1.pnga2.pnga3.png
 

k1ng 1337

Joined Sep 11, 2020
911
Here is the algebraic equation in the units the question was asked:

?A = (V1-V2) / ((V1/I1) + (V2/I2))

(5V-20V) / ((5V/1A)+(20V/0.05A)) = -37.45mA

The difference between this answer and my first answer (-37.03mA) is due to rounding. The total current will always be less than the maximum of the higher voltage source. In this case, V2 is sourcing 37.03mA and V1 is sinking 37.03mA. V2 can not source more than 50mA but it will source current because the total potential difference (5V - 20V = -15V) develops an electrical field in that direction.
 
Last edited:

WBahn

Joined Mar 31, 2012
29,867
There are 2 sources.

Source (A) 5VDC @ Max 1000mA

Source (B) 20VDC @ Max 50mA

If the grounds of both "source(s)" are "common".

Would Pos source (B) flow to Pos source (A)
or
Would Pos source (A) Flow to Pos Source (B) because source (A) has a higher *current* potential?
Other answers have assumed that you have also connected the positive terminals of each source together, but I don't know if that's what you meant or not. Plenty of other people have asked about current flow between batteries that are only connected at a single point. So please be more explicit -- a sketch is always helpful in getting your thoughts across.
 

k1ng 1337

Joined Sep 11, 2020
911
Other answers have assumed that you have also connected the positive terminals of each source together, but I don't know if that's what you meant or not. Plenty of other people have asked about current flow between batteries that are only connected at a single point. So please be more explicit -- a sketch is always helpful in getting your thoughts across.
I did take a leap of faith on that one but it was still a good exercise. :p
 
Top