coil, how hot is too hot

[66 E100 Pickup]

I'm running a duraspark 2 dizzy and module, with a later model 12 volt coil. The coil has a 1.0 ohm primary. It's wired directly to 12 volts and throws a big fat spark.

But it DOES get warm, mighty warm, about the same temp as the block (I'd guess 190 degrees +/-).

Anyone have a clue whether this temp is too much? Should I throw a 1 ohm ballast resistor in the 12 volt line and try to knock back the temp a bit?

John/Fresno

 

[69.5Mav]

Is it bolted to the block?

 

[66 E100 Pickup]

yes, the factory coil mount. But I've had it get that same temp after 10 mins run time, when the block is still mild to the touch.

John/Fresno

 

[Lazy JW]

190º sounds almighty hot to me. Not all DS2 modules/coils were created equal, as they did reduce the primary resistance of the coils in later models, and also compensated with improved dwell control. An early module with a late coil "could" cause things to run pretty hot. Just guessing though.

I wouldn't want my coil running that hot. At the very least, a spare coil and module on board would help my confidence level.
Joe

 

[66 E100 Pickup]

It's an AMC coil, 12 volt, 1.0 ohm primary, got it from someone on the site. The module is an aftermarket blue grommet, maybe Standard brand? Can't remember, but they cover a lot of years with the same module.

I suspect that the key info is the primary ohm number, which is the internal resistance to absorption of electrical energy. The lower the ohms, the faster the charge rate (needed for the high rpm/V8) condition.

My understanding is that once a coil is fully charged, the remaining time until discharge is a period of creating heat. A higher ohm coil takes a little bit longer to get fully charged, and therefore heats up less. So there is a balance needed in picking a coil that will not get too hot (and have a shortened life) and the other condition of maintaining a maximum spark at all times.

So...seems that the sixes, in a factory form, under normal conditions, have about 3 ohms total (1.5 from the pink resistor wire, and about 1.5 in the coil primary). That's also the recommendation for the Pertronix Flame Thrower coil, 3.0 ohms. They do say for performance builds and running, a 1.5 ohm total will get it done.

Since the question is all about "how much heat can a coil tolerate" I guess the answer is going to be "it depends" on such things as coil design, primary resistance, and cooling capability. The newer coils are certainly better designed, with cooling fins, lots of surface area, and generally low ohms (0.3 range).

I guess I'll find out if the thing burns up, in the meantime, carry a spare LOL.

John/Fresno