Given the many discussions on coils, resistance, measurements, etc., the site
quadtech.com/primer may be of interest to some on the list. It’s written at a
basic engineering level and so may be confusing, but it does have useful
comments on performing measurements. Those on the list who are engineers can
help others interpret its content as necessary.
One note: when the talk is of “complex” or “imaginary” numbers, fear not.
This simply is a way of representing how real things, like coils and
capacitors behave in relation to simple resistors – the latter are
essentially 1-dimensional, in that current through them increases immediately
as voltage across them does (I = V/R). Coils (inductors) are time-dependent
devices and have the interesting property that current starts out at 0
regardless of how much voltage is applied – this is why we have a “dwell”
spec in the ignition system, so voltage is applied for a long enough time
(dwell) to get the amount of current we want flowing in the coil. Capacitors
are opposite that, their voltage is 0 initially, no matter how much current
flows into them, but if we wait long enough, voltage across them increases to
the max voltage being applied and the current through them goes to 0 (unless
they’re leaky and bad).
Simple algebra can’t handle their time-dependent, current-voltage behavior, so
the concept of imaginary numbers is applied, resulting in going from
resistance to “impedance”, which you can simply think of as adding another
dimension to the 1-dimensional behavior of resistors. Coils and capacitors
are also logical complements of each other and, along with resistors, are used
to produce amazing combinations of effects, such as tuning in a TV station, or
generating a nice spark. In fact, automotive engineers have long used
electrical circuits to simulate complex structures, like suspensions –
capacitors representing mass, coils representing springs and resistors
representing shocks and general friction – the equations for the mechanical
behavior are exactly the same as for the electrical. Furthermore, since
voltage, current, coils and capacitors are complements, the math itself can
even be complemented, with capacitors representing springs and coils mass.
Maybe the Jag’s suspension was designed this way?!
Sorry for the length, but I thought some of us could use the info.