aq_blues 07-21-2011 03:23 AM

Current flow from higher to lower potential

2 Attachment(s)
Hi All,
This morning I got my concepts shattered. I had started my engineering with this sentence: 'current flows from high potential to low potential'
This is evident in my first schematic where we see current flowing from +5V to -5V terminal.

But in my second schematic, I do not understand why the current would not flow from +5V to -5V termial. Instead, I see two currents. One flowing from +5V to ground and the other flowing from -5V to ground.

If anybody can shed some light, I would be thankful to him.
Thanks,

 Ron H 07-21-2011 04:39 AM

1 Attachment(s)
Current flows from + to -, as you said. See attachment.

 aq_blues 07-21-2011 06:14 AM

I understand the current flows. What I do not understand is, why the current would not flow from +15V terminal to -15V terminal. Why would it go to ground instead, where in the bottom it can see the -15V(which is lower potential than the gnd)(As said, Current flows from higher potential to lower potential and -15 is lower)

 t_n_k 07-21-2011 06:55 AM

The center bridging link in the second schematic effectively de-couples the upper & lower parts of the original schematic. The two "halves" are then effectively two completely independent circuits insofar as the current flow in each case is concerned. The fact that they share a common link is irrelevant.

Interestingly you have nowhere designated on the schematics what you consider to be your ground point.

 Jony130 07-21-2011 10:01 AM

1 Attachment(s)
simply add resistor between +5V and -5V

 ErnieM 07-21-2011 11:07 AM

Quote:
 Originally Posted by aq_blues (Post 382212) Thanks Ron for the reply. I understand the current flows. What I do not understand is, why the current would not flow from +15V terminal to -15V terminal. Why would it go to ground instead, where in the bottom it can see the -15V(which is lower potential than the gnd)(As said, Current flows from higher potential to lower potential and -15 is lower)
Here is another way of drawing your circuit:

Current requires a loop to flow. Voltage requires two points to establish a potential.

Neither exists between these supplies as they are connected at only 1 point.

 GetDeviceInfo 07-21-2011 03:43 PM

Quote:
 Originally Posted by aq_blues (Post 382212) Thanks Ron for the reply. I understand the current flows. What I do not understand is, why the current would not flow from +15V terminal to -15V terminal. Why would it go to ground instead, where in the bottom it can see the -15V(which is lower potential than the gnd)(As said, Current flows from higher potential to lower potential and -15 is lower)
the current does flow from +15 to -15, however, because the loads are not balanced, the difference in loop current flows through common.

 ErnieM 07-21-2011 04:36 PM

Quote:
 Originally Posted by GetDeviceInfo (Post 382319) the current does flow from +15 to -15, however, because the loads are not balanced, the difference in loop current flows through common.
Look again.
No current from the +15V battery goes thru the -15V battery.
No current from the -15V battery goes thru the +15V battery.

 GetDeviceInfo 07-21-2011 05:14 PM

Quote:
 Look again. No current from the +15V battery goes thru the -15V battery. No current from the -15V battery goes thru the +15V battery.

Current in the common leg is the sum of the two loops, and not actually flowing in both directions. Where does the difference flow?

 ErnieM 07-21-2011 06:32 PM

Huh, well you got me there. The difference flows around the outer loop. Simple KCL applied to the two nodes of the middle wire.

What I find surprising is my drawing actually changed the circuit by adding two paths side to side. This allows each current to flow in it's own middle wire and thus there is a zero outer loop current.

Here the topology change actually changed the currents. This is a first for me.

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