Re: Placement of Ballast Resistor

Posted by Gene-AL on January 17, 2006 at 10:01:40 from (65.4.38.60):

In Reply to: Re: Placement of Ballast Resistor posted by Farmerfred on January 16, 2006 at 19:21:11:

Farmerfred:
I don't know that this will answer your questions, but one of the problems of a points-coil-condenser (Kettering) ignition system is that the heavy current draw of the starter drops the battery voltage. How much voltage drop depends mainly on the age and condition of the battery, including whether it's fully charged or not. A lower battery voltage means less current flow in the coil when starting, and if the battery voltage drops too low, the plugs will get only a weak spark or simply won't have enough voltage from the coil to fire at all.
Other than just living with a tractor which won't start on an aged or undercharged battery, one solution for some improvement has been to add a resistor (or a resistance wire) between the ignition switch and the coil, use a coil designed for a voltage lower than the battery, and short out the resister by some switching method during starter operation to apply the full (but lowered) battery voltage to the coil. If the resistor were left out entirely, too much coil current during normal running would tend to overheat the coil and also force the points to break much higher currents which shortens point life.

I'm not familiar with the so-called "infamous" Ford *N ballast resistor, but I guess it could have a high positive temperature-variable resistance, which has low resistance when cold, then a higher resistance when heated by coil current, thus applying higher voltage to the coil when starting cold, then lowering coil voltage and current back to normal for the coil when warmed up. I don't know that this is accurate, but such a resistance would work.

The condenser's voltage rating is likely at least 200V or higher to withstand the much higher voltages across the coil's primary winding during magnetic field collapse when the plug fires, so there would be no need to change it for different voltages (6V to 12V).

My take... Hope it helps.

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