|
John, the capacitor (condensor) is there to balance the inductance of the coil. Without the capacitor, some primary current will always attempt to bridge the opening points causing not only a weaker spark to be generated, but also transferring metal between the point contacts themselves - kinda like a mini-arc welder. With the capacitor, this 'bridgeing' current then simply charges the capacitor instead of arc welding between the opening points and wasting spark energy needlessly. This 'appears' to make the spark hotter with the capacitor than it is without the capacitor as initial spark voltage will be higher and faster to build up with the capacitor than it would be without it. One benefit of having a proper sized capacitor VS coil inductance is that the points last longer. Without the capacitor, a pit and a matching peak will build up on the points themselves. When the capacity of the capacitor matches the inductance of the coil then there is no pit or peak creation on the points. This last part is from an old Motor's Repair Manual (1967). I'm not sure if I can chime in with your theory on the capacitor 'kicking' energy in though. It certainly helps getting things started faster, but as Duane will attest, one can observe the spark voltage on an engine oscilloscope and watch the spark for its whole duration. It's always only one polarity for standard point/coil ignition systems. In order to kick in extra energy there would have to be a polarity reversal as well and that is not observed on engine scopes. Temporarily, battery voltage across the capacitor is exceeded if that is what you mean by 'kicking in', but that in itself doesn't help make a hotter spark as there is almost no current involved. Voltage swing back also occurs due to the capacitor but that happens after the spark has fizzled out, again viewable on an engine scope. Further, I know of no electronic ignition system that requires or recommends the use of the 'old' capacitor - as if to say that it is no longer a neccessary component and only useful for point systems. The entire amount of energy available for spark generation comes from the stored energy in the coil's inductance only. The capacitor only keeps some of that energy from wasting away across the opening points. My main trouble with internal ballast resistor coils is the concept of them in the first place. Until you and Clooney exposed me to this, I had not ever even considered their existance. The way the 3 ohm coil should be built (and I just assumed it always so) is to use a longer length of smaller copper wire for the primary winding than is used in the 1.5 ohm coil. But the way something _should_ be built and the way it actually is will always be a factor - so the possiblilty does exist for a 1.5 ohm coil to have an internal resistor of 1.5 ohms for a total of 3 ohms. And it could be that this is the way it has always been done as that would certainly be the cheaper way to make a 3 ohm coil when you already have a factory making 1.5 ohm coils. As to where the resistor exists in the schematic of such a coil, I would not like to have say for sure until I get it in my hands, but I would assume and hope it is in the same postion as you have suggested. Since the switch from 6 to 12 volts also occured about the time the switch from positive to negative ground occured and the fact that 3 ohm coils didn't make their appearance for several years after those two happened first, I would have to suggest that all 3 ohm coils are made for negative ground with rare, known(?), blatent exceptions allowed? Thus, reto-fitting one to a positive ground tractor would result in the wrong polarity of the spark, which is a much more important aspect than where the resistor actually is. So I would have to disagree with the blanket statement '- to distributor always'. Despite how the resistor argument complicates things, a retro-fitted positive ground system needs the + side of the coil going to the distributor points. This would put the resistor between the capacitor/points and the coil windings which is no small concern as it would halve the charging rate of the capacitor outright. This should result in a somewhat less energetic spark than if you were to retro-fit with an external ballast resistored coil (1.5 ohm). The idea being to keep the resistor on the ignition switch side of the coil at all times for the hottest possible spark. Only solution I can see for this dilemma is to never retrofit 12 volt, postive ground systems with 3 ohm coils, instead use only 1.5 ohm coils with an external ballast resistor on the ignition switch side of the coil. Stick with 6 volt, postive ground or go whole hog with 12 volt, negative ground are a couple of other angles that work, the latter being the one I chose for my non-parade, working 43 A, with that ugly alternator hanging out the side. One other option for the 'Green Police' might be to use resistor wire from the ignition switch to the 1.5 ohm coil and then just don't tell anybody? Just my 2 cents worth and my opinions, no big deal if you or anyone else disagrees. I certainly felt the need to 'weigh in' on this and thanks for the invitation. A very good, interesting topic and one I'll continue to track in the group. Especially when someone starts opening up some of these 3 ohm coils, I would have never thought that there even might be a resistor in there without you two - thanks for gettting me to think a little bit. If they went bad more often I would have a couple to sacrifice to the cause.
|
