Electronics > Beginners
Power source, internal resistance and Ohm's law?
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Mr D:
Hi folks,

I'm just messing around EveryCircuit, trying to get my head around the basics.

When i create a simple circuit consisting of only a 1 volt battery and a one milliohm resistor, i get a nonsensical current of 1 kiloamp even though that is indeed correct according to Ohm's law (seems impossible to get so much current from a 1 volt power source, no??!!)

So i guess this is the result of EveryCircuit not simulating the internal resistance of the battery?

Is this normal in every simulator (nonsensical answers at the extremes), or do more serious ones take this into effect?

Or am i in fact talking nonsense?

Audioguru:
It is an example of non-real math.
1) There is no 1.0V battery available.
2) There is no 1milli-ohm resistor available.
Most Simulation programs do not use common sense. They can get 10A (!) from a little 2N3904 transistor that has a maximum allowed current of 200mA and works poorly at and above 100mA.
soldar:

--- Quote from: Mr D on June 04, 2019, 10:26:06 pm --- So i guess this is the result of EveryCircuit not simulating the internal resistance of the battery?
--- End quote ---

What did you set the internal resistance to? Because if you set it to zero then you got a result consistent with that.
MarkR42:
It's totally reasonable, because your software is simulating "ideal" components.

An ideal 1V battery has zero internal resistance.

Ideal wires have no resistance (or inductance etc)

An ideal 0.001 ohm resistor actually exists and is a thing. In real life these components are impossible, or at least, unlikely to work like that.

It's like the "spherical horse in a vacuum" joke.
ejeffrey:

--- Quote from: Mr D on June 04, 2019, 10:26:06 pm --- (seems impossible to get so much current from a 1 volt power source, no??!!)

--- End quote ---

It certainly isn't impossible.  I've used power supplies that produced hundreds of amps at 1V and they were pretty ordinary.  Few batteries can do that, but some can.  A lab I used to work next to had some single cell NiCd batteries each the size of a car battery.  I don't know what there ratings were (or even what they had been used for) but I imagine they could produce a staggering current.

Better simulators will have more sophisticated models available, but they won't necessarily use them unless told to.  If you just place a 1V battery you are almost always going to get the result you see because there isn't really any other sensible result for the simulator to produce.  Only if you provide a model of a specific battery, or create your own will it be able to provide a realistic current limit.  Even then, if you do something like a small signal AC simulation, it is going to ignore the large scale parameters that lead to reduces maximum current.
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