Talk:Electronics/Voltage and Current

This is found in batteries. (a battery could also be considered a current source, depending on perspective. i think we should not include batteries yet and only focus on what "voltage" and "current" mean.  then we can move on to ideal voltage and current sources, and then real sources.)

(Is there a difference between series and parallel voltage assuming there are no current splits? Depends if you mean ideal voltage sources or things like batteries.  Ideal voltage sources can't be placed in parallel.  This would be the same thing as saying 5=3.  Real voltage sources have some internal resistance, Rs, which would load the other battery's ideal voltage source.)


 * Is there a difference between ideal and real sources besides a resistor?


 * Nope. An impedance, actually.  But basically the same thing.  It's a hugely important difference, though.  *Very* important for beginners to understand.


 * I don't get it. You mean the maximum current a power source can output? How else does internal resistance affect the output of a power supply?


 * Impedance contains information about capacitance and inductance, in addition to resistance. Power supplies and cells (a battery is a stack of cells) can be quite different.  Even mere resistance will affect the battery's temperature, which will in turn affect the resistance.  Additionally, batteries are chemical devices and are impacted by the chemical processes that take place inside.  As a result, the voltage characteristics of batteries evolve during their lifetimes.  Also as a result, different types of batteries recharge differently.  A nominal 9V battery will not actually produce 9V during the entirety of its life.  Real batteries are quite complex.  We simplify thinking about them because most of that stuff seldom matters.  If you wanted to build a battery operated robot that would sit idle for months at a time and do something useful when its battery was going dead, then many of these things would begin to matter. --Rs2 22:41, 31 Mar 2004 (UTC)


 * Likewise, with other real voltage sources, like the output of an op-amp, it is important to realize that it has an output impedance, which cannot be separated from the ideal voltage source. The impedance has effects on op-amp stability, power handling, maximum current/voltage, loading, etc.  We model real voltage sources as an ideal voltage source (which just creates a voltage between two conductors, regardless of anything else) with an impedance permanently attached.  A real battery has inductance, capacitance, and predominantly resistance right at the output of a perfect voltage source, meaning the battery will give different voltages depending on what it is loaded with, etc.  We should mention in the article that a short circuit across an ideal voltage source would produce infinite current and vice versa. - Omegatron