Re: Q. re: CircuitMaker (Student)

On Aug 15, 2:16 am, Kris Krieger <m...@xxxxxxxxxx> wrote:
"David L. Jones" <altz...@xxxxxxxxx> wrote innews:f3f0720d-b5bf-4873-8c28-43bc45b7b988@xxxxxxxxxxxxxxxxxxxxxxxxxxxx:

On Aug 14, 10:01 am, Kris Krieger <m...@xxxxxxxxxx> wrote:
Hi, I'm fooling around with CircuitMaker student version. I'm
curious as to whether anyone can tell me why a battery is not both a
voltage source and a current source - I thought that current was
necessary to calculate re: powering things, so this is confusing to
me.

A current source provides a *constant current* into a load, (ideally)
regardless of what that load is.

A voltage source (or battery) will provide whatever current the load
requires. So while the battery is providing a current, it is not a
constant current source, as the current won't be the same with
different loads.

Oh...oh!, OK, because current is a function of voltage *and*
resitance...?

Correct!
Start with simple "linear" loads like a resistor and a DC source that
you can analyse with ohms law. Electronics starts with learning to
apply ohms law and Kirchhoff's laws like 2nd nature. Don't start using
a simulator until you know the basics inside and out.

Other loads and AC sources are the next step and will get more
complicated, and that's where the simulator might start to help you
out.

A voltage source provides a *constant voltage* into a load, (ideally)
regardless of what that load is. A real battery is a voltage source
with an internal series resistance.

Because no material is resistence-free, right? Whcih would be the reason
for Joerg's note that "If needed a little resistor is added to simulate
the impedance", right?

Correct. Many people make the mistake of using a simulator which can
often use "ideal" components. Then they are shocked when their circuit
does not work when they actually build it for real.
Take the battery for example. Not only does a practical battery has a
series impedance (or resistance, make sure you learn the difference),
but that impedance changes as the battery discharges and also changes
with temperature.

In fact it's worse than that - not only are components not "ideal" in
practice but the way you construct the circuit in real life (on a
printed circuit board for example) can have a massive effect upon the
circuit operation.

Simulators can be BIG traps - beware. That's why you'll probably get a
lot of experienced guys warning you not to use them.

(Yes, I'm still in the Dummy stage... =:-o )

I can't remember how CircuitMaker
actually treats a battery symbol, best to use a proper constant
voltage source if that's what you really want.

It has a symbol that looks like the standard Battery symbol in hte
electronics texts, and you can choose to have the + and the - shown (good
for us beginners ;) ), plus you can specify teh VOlts. THe Default is
10V, but you can right-click and change that parameter to, say, 1.2V,
which is what I'm fooling with.



So a battery (or anything else) can't be both a constant voltage
source and a constant current source at the same time, they are
mutually exclusive.

Also, does anyone know whether I'd therfore have to add both a
battery, and an accompanying current source...?

Not together as the same source, no. You usually use either a voltage
source or a current source depending upon the sub-circuit you are
trying to simulate.

Dave.

OK, as I speculated in reply to Joerg, current changes because it's a
function of Volts and Resistence?

Correct again. This is ohms law at work, learn it like the back of
your hand.

Maybe what I need to do is keep looking through my Google search (I'm
currently running a search of
"SPICE" AND (electronic OR electronics)
and look for refernece materials, becasue I'm starting to think that the
current-voltage question is both a fundamental and a peculiarity of the
software structure and how it handles Power (watts). What's confusing me
with the simulator is I finally <!> understood, after some helpful
explanations by folks in the "basics" NG, that *Power* In has to equal
*Power* Through/Out, so, a subcircuit can "finagle" amperage and
"convert" it into voltage, or visa versa, but in the end, Watts Equals
Watts (did I mention I was starting from Zero with tryign to learn some
electronics...?) ANyway, so I thought I could use a simulator to analyse
a simple circuit in a ways that follows that rule.

I'm Googling
("SPICE" AND (electronic OR electronics))
and looking for tutorials, references, and so on, so maybe I ought to do
that first, since I'm starting to think that I ahve soem fundamental
confusion re: what "Spice" is actually supposed to do.

I think you'd be best to avoid simulators until you have a better
grasp on the basics.
Pen, paper, calculator, breadboard, multimeter and lots of good
beginner books is what's needed (more than one because you won't
"click" with all of them).
The simulator will never replace the breadboard and multimeter, you'll
learn a lot a lot of useful practical stuff using actual hardware.
But simulators do provide an easy and quick means to modify circuits
and measure stuff that would otherwise take a lot of time and
expensive equipment.

Welcome to the world of electronics, have fun.

Dave.
.

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