A(nother) ballast resistor question
Yes, the ballast has been around the block discussed a few times. I'm sure I've not read all of the threads.
Given (from Demon408 years back):
From the 1973 Factory Service Manual (FSM), in reference to the dual ballast resistor using electronic ignition, (note: the compensating side of the dual ballast resistor is the side that is in series with the coil positive): The compensating resistance serves the same purpose as in the contact [points] ignition system, that is to maintain constant primary current with variation in engine speed. During starting this resistance is bypassed, applying full battery voltage to the ignition coil
.
and (from killer6 of the same vintage):
I have explained this in another post, but here it is again.The function of the ballast
resistor is to compensate for hi CURRENT demand at idle and lower engine speeds.
This is caused by the longer actual dwell time the coil primary windings are subjected
to at low speeds,i.e. 30 degrees at 900 rpm lasts 4 times as long as it does at 3600
rpm,thus the saturation time is enuff to create excess heat. Since the coil has to be
engineered to saturate quickly enuff and deliver sufficient energy at the maximum
design rpm,the ballast provides the needed flexibility allowing low speed operation
by providing resistance that increases w its own temp increase at those same high
demand conditions.This reduces the the voltage and thus temp of the coil,keeping
it alive...
Engine speed change will take place at the drop of a hat...or the foot. Point is, it happens quickly and often. Considering all of the above (current compensation based on temp of the resistor) and that the word 'constant' is used in the FSM,
how does it work in real life?
The temp change in the ballast and thus the current drop of the voltage going through it is going to be a very slow response thing. That big hunk of ceramic will both hold heat for a long time and also be slow to heat up (both when compared to variation in engine speeds).
Best I get is that starting current in the ignition coil is higher than run current...long bits of unbridled current through a coil during run is not a good idea and long bits of un-resisted current when NOT running (left the key on) can be downright explosive.
Isn't the write-up in the FSM and the reference to
'... maintain constant primary current with variation in engine speed' rather a whole lot of words that don't have much to do with anything?
I am not asking about the 5th pin, zener vs: solid state regulation in the spark box, points, differences in coils that want 'some' outside resistance vs: none or something different, HEI being better, or anything other than heat as it applies to current regulation for a 'constant' coil saturation environment.
Words mean things...or they should. The FSM statement seems a whole lot engineer speak if not downright fol-de-rol.
