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Old 09-23-2011, 01:26 PM
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ndutton ndutton is offline
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A word of caution

Before we start piling on a bunch of resistance on the input side of the coil we need to consider the output as well. Having a cool running coil that puts out a weak spark is not a solution. Accordingly, not any random resistor will do.

I can speak only to my system and how I intend to approach this new strategy:
  • I'll do a visual spark check off the coil lead to the block before changing anything.
  • I'll accurately measure internal coil resistance at rest and coil input voltage with the alternator under load, engine at 1500 RPM minimum.
  • I'll do the calculation with a target amperage of 3.75 amps (see edit) and add a resistor to achieve that balance as close as possible.
  • Repeat the coil wire spark to block test for comparison.
  • Run the engine for 1/2 hour and read coil temps every 2 minutes (already did this with the current system) and compare.

Regarding coil spark output, as I recall the standard points type coils were 28K volt. The Pertronix Flamethrower I installed as part of the conversion to electronic ignition is a 40K volt coil so I'm thinking I could tolerate a 30% output reduction and still run as well as when I had the old points ignition and original coil.

Dang this is interesting.

edit:
To repeat, I eventually lowered the target amperage to 3.4 amps for a wider margin of safety.
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Neil
1977 Catalina 30
San Pedro, California
prior boats 1987 Westsail 32, 1970 Catalina 22
Had my hands in a few others

Last edited by ndutton; 10-05-2011 at 12:01 AM.
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