Quote:
Originally Posted by Don Moyer
Hi Dave, thanks for your explanation regarding the role of inductive resistance in the primary ignition circuit whenever the engine is running. I have a follow-up question regarding the way coil manufacturers add internal resistance. You seem to imply that they add a separate resistor inside the coil. It was my understanding that coil manufacturers vary internal primary resistance by simply using heavier or lighter gauge wire in the primary windings. Would this alter the heat buildup/distribution concern you described? Don
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Hi Don,
I know that in years gone by that coil manufacturers added actual resistors in the coil cans to increase the overall resistance and limit the current. Its not hard to find info on those on the web.
Regarding what they do now.... I'm not entirely certain, but I suspect in most cases they are not using actual resistors in the coil, but that they are using resistance wire in the coil for the primary winding.
https://en.wikipedia.org/wiki/Resistance_wire
If you are a huge company like Bosch, its not a big deal to have your wire manufacturer run a batch of wire to your specification that results in X ohms per hundred feet, etc.
The Bosch Blue 00012 coil that I cut apart did not have a visible resistor in the primary winding, however the wire was not fine. It was probably 20-22 gauge wire. If it was pure copper wire it would have taken hundreds of feet of 20 gauge pure copper wire to get 3+ ohms of resistance.
http://hyperphysics.phy-astr.gsu.edu...es/wirega.html
The turns ratio between the primary and secondary is usually about 100:1, so that in itself puts a limit on the number of primary turns.