Re: 12 Volt Conversion Resistor

Posted by John T on June 15, 2006 at 06:40:21 from (66.244.90.5):

In Reply to: 12 Volt Conversion Resistor posted by Duane WI on June 15, 2006 at 05:48:55:

Duane, a typical rating for a conventional straight (NOT a heat sensitive variable resistance Thermistor) Ignition Ballast Resistor is around 1.5 to 1.85 ohms. Ideally, to serve as a pure 50/50 static voltage divider to drop 12.6 battery volts in half leaving 6.3 across the coil, it would be somewhere near the same ohms as the coils primary (measured between its lil + and - terminals). The thing youre wanting to do to
prevent premature burning up of the points and not overheat the coil is to limit the coil/points current to around 4 amps or so, which at 12 volts requires around 3+ ohms of TOTAL (coil + Ballast) resistance in the ignition primary circuit. With that alternator, the battery voltage may run a lil higher then using a genny, so a lil over 3 ohms TOTAL (coil + ballast) ignition primary resistance is what I would use to extend point life and not run the coil too warm....... The correct answer to your question really requires you know the coils primary resistance, but this ought to get you in the ball park and the spark should still be sufficient if you err slightly on the safer (more ballast) less current side of these suggestions.

If this info is correct ?? (copied it somewhere from a YT Mag post)

NAPA # ICR-13 or Standard Ignition # RU-10
are rated @ about 1.77 Ohms to 1.87 Ohms

Other sources are Tractor Supply or Rural King etc.

Wire it in series ahead of the coil after the ignition switch and youre good to go. The alternative would be to buy a full 12 volt rated (internally ballasted) coil that requires no external ballast but the ballast is cheaper.

John T

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