james singleton":3edjfj76 said:
To All, while on the subject of resistence wires, ballast, coils, etc., I have a couple of questions that maybe someone more knowledgeable than myself can answer!??? Someone on another website posted that "if you want the most out of an electronic ignition, a true 12 volt 'high' performance coil is needed." Question(s): What is a true 12 volt high performance coil rated at ??? Is 40,000 volts considered considered a "true high performance coil??? 60,000 volts????.....
Way back in the early days of automobiles, Mr. Kettering and associates at the Detroit Electric Company (later known as Delco) detirmined by much experimenting that breaker points could handle a max of about 3-4 amps of primary current, much more than that and they had lots of trouble with burning, pitting, and poor reliability.
Since six volt systems were the norm, that put some constraints on the total system. Three amps at six volts was all you could put into the coil, therefore the coil had to be designed to work within those limits. Since R=E/I and we know the voltage = 6 with a current limit of 3, the primary windings of the coil had to have a resistance of about 2 ohms or slightly less. Then add as many windings to the secondary side to jump the output voltage high enough to fire a spark plug under compression load.
When the 12 volt systems were introduced, it made the job somewhat easier for the designers. Trouble is, the points could still only handle about three amps. Some additional resistance was needed to keep the current flow down now that we could push the current with twice as much voltage. Enter the Dreaded Pink Wire
Or ballast resistor. Or the coil could be designed with added resistance inside; some manufacturers chose this method.
Later, with the development of breakerless ignitions, the primary current could readily be increased. This was accomplished by reducing the primary resistance of the coil, some of them are as low as .5 ohms. This gives a LOT more current which allows the designer to build a much hotter output unit.
Why not just add more windings to the secondary to get more voltage? Because voltage isn't what lights the fire, current (measured in Joules) is what build the fire. And if we increase voltage via transformer action the CURRENT IS REDUCED as per Ohm's Law. So it is really a balancing act for the designer to get enough voltage with enough current to get the fire built. The higher the voltage input the easier this is to accomplish. Capacitor Discharge (CD) ignitions send 300-400 volts to the primary side of the coil. This gives a REALLY good zap!
High Voltage ratings sell coils, but high current delivery gets the job done.
General Motors came out with their famous HEI ignition first, Ford belatedly followed suit with the TFI some years later. The coils are functionally identical. Pretty tough to beat either one.
Joe
