A bug calculating currents?

Hi,

can anybody have a look at this circuit and tell me why the three currents are different depending on where I place the GND? They all should be the same, shouldn't they?





On Multisim and everycircuit.org they are the same. Is it a bug?

The first and the second are the same and have the 15v power supply in short-circuit, so they are not evaluable, in the third, caculate the meshes yourself and compare with other systems.

blitobyte wrote:Hi,

can anybody have a look at this circuit and tell me why the three currents are different depending on where I place the GND? They all should be the same, shouldn't they?

On Multisim and everycircuit.org they are the same. Is it a bug?

As it was mentioned by Defran, the first two circuits are identical.

If the third one is seen, by any other simulator, being similar to these two circuits, I am afraid you missed something somewhere because SimulIDE gave you the right currents.

Be happy, this could be a good exercise for you to revise what you learnt about how to calculate the DC voltages and currents on a given circuit. I had to do such calculations (also in AC) too many times in my designs, about 4 decades ago, when I didn't have any tool to help me

Defran wrote:The first and the second are the same and have the 15v power supply in short-circuit, so they are not evaluable, in the third, caculate the meshes yourself and compare with other systems.

Hi Defran, you're right. I made a mistake pasting the second circuit: GND was to be on the right corner.

It's strange, though. SimulIDE considers a short-circuit if GND is connected to a power supply as long as it is not a battery. How come? I thought both, the fixed Volt and the Rail signs were two ways to indicate the power supply. Similar to the triangle usually used in schematics. But no!!

So what's the reason to have three different symbols?

Changing the power symbol for the battery one it doesn't matter where I place the GND, as it should be.

Thanks.

KerimF wrote:

blitobyte wrote:Hi,

can anybody have a look at this circuit and tell me why the three currents are different depending on where I place the GND? They all should be the same, shouldn't they?

On Multisim and everycircuit.org they are the same. Is it a bug?

As it was mentioned by Defran, the first two circuits are identical.

If the third one is seen, by any other simulator, being similar to these two circuits, I am afraid you missed something somewhere because SimulIDE gave you the right currents.

Be happy, this could be a good exercise for you to revise what you learnt about how to calculate the DC voltages and currents on a given circuit. I had to do such calculations (also in AC) too many times in my designs, about 4 decades ago, when I didn't have any tool to help me

Hi KerimF,

here are the 3 circuits with batteries and now the currents are the same. Let's say correct. At least they coincide with Everycircuit.org and Multisim... BUT NOT with itself, SimulIDE, if I use Fixed power instead of Batteries. Why!!??

You said: SimulIDE gave you the right currents, but it didn't or so it seems.

The difference comes from the fact of the - definition of voltage - that is done with the Voltage Source and the rails. The battery does NOT define voltage, it - adds - voltage.

You are thinking of the battery as a Ground attached to a Voltage Source with a resistor. These components - define - the voltage. The battery works as an adder of voltage, that is why you can use batteries in series.

Subcircuit of a "battery" using a ground and a rail



Tests:
(Pay special attention to the voltage readings)