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Old 07-10-2019, 09:13 PM
Dave9111 Dave9111 is offline
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>> what was the original internal resistance of the VW coil

Bosch says the 00012 coil is a 3 ohm coil, but it measures more, 3.4 to 3.6 ohms and that's with a good Fluke meter.

I have a new alternator on the engine and it runs just below 14 volts at speed.

Pertronix says that they want less than 4 amps of current. The bogus thing about that is that the current is not DC when the engine is running. The inductance in the coil along with any resistance in the coil or external creates an RL network.
https://en.wikipedia.org/wiki/RL_circuit

The inductance of the coil will resist the change in current flow (inductors don't like current changes). So the current flow is not calculable by a simple voltage / resistance calculation. That only works when the engine is not running but the ignition is on and the ignition is triggered.

I believe the Atomic 4 will fire the ignition twice every revolution. So at 1500 rpm, that is 25 rotations per second, and 50 ignition firings per second, or 50hz. Household AC current is 60 hz. So the current through the coil is pulsed DC.

I'm ok with my existing setup. The Accel coil is 1.4 ohms and the resistor is between .6 ohms to 2.5 ohms depending on the amount of heat in the resistor. I have quite a few hours on the Accel and resistor setup and that worked fine.

I dissected a Bosch coil that failed on a Ford Tractor I had. Turns out the coil failed from water intrusion. The top of the Bosch 00012 coil is not well sealed probably because its potted in epoxy. Unfortunately the epoxy had cracks in it and it was not well potted. It might have worked fine in a dry environment, but not on a tractor that is exposed to rain once in a while.
I have pictures if anyone would like to see the internals of a Bosch Blue 00012 coil. The quality of the parts look good. The quality of the potting not so much.

I retested the Bosch coil I took off the boat that had failed. I bench tested it and it seems to work fine now. But I won't be using it on the boat anytime soon.
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