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.

Alex

79xj6