Posted by MarkB_MI on August 21, 2013 at 02:42:55 from (75.198.86.200):
In Reply to: HOT COIL posted by J.Keim on August 20, 2013 at 14:07:40:
Lots of misinformation here. Let me start out by saying I think you are using the original coil (or one intended for use with an external resistor). The original "six volt" coil is going to run hotter than a "12 volt no external resistor" coil because there is more current running through the six volt coil. So you probably need to either replace your coil with a "no external resistor" coil or add a ballast resistor. From a functional point of view it makes no difference which you do, although it's a lot simpler to change out the coil. Any decent auto parts store will carry a generic coil for this purpose.
It is not true that a so-called "12 volt" (no external resistor) coil is better than a "6 volt" coil plus external resistor combination, even though it as been repeated as gospel here so many times I've lost count. What's the difference between a coil that requires an external resistor and one that doesn't? It should be obvious: the latter has a higher internal resistance! How the resistance is added is irrelevant, whether it's done using smaller gauge wire in the primary winding or some sort of resistor inside the coil. (I think it's the former, but it really doesn't matter.) The inductance of the two coil types is identical, so the only difference is internal resistance. In fact, from an electrical point of view, it doesn't matter whether that resistance is inside or outside the coil. The "no external resistor" coils are easier to install than an external resistor, but in no way do they provide any better spark.
Why have a resistor at all? The added resistance does two things: First, it reduces the current through the points. Second, it adds damping to the circuit so the voltage transients that occur when the points open decay faster. Together, these effects make the points last longer. And, as you've discovered, the coil doesn't get as hot.
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