Re: Ignition Coils, Still Confused?

Posted by Jim WI on November 06, 2000 at 10:34:32 from (192.159.76.19):

In Reply to: Ignition Coils, Still Confused? posted by BlueLight on November 03, 2000 at 14:19:19:

The OEM 6-volt coil used on some tractors (such as Ford 9N's) is actually designed for 3.5 to 4.0 volts. The purpose of the OEM ballast resistor is to drop the voltage down to that level.

There is a trick involved -- when the power is first applied, the resistor will have a lower value than after the power has been on for a while. The resistor heats up, increases in value (more resistance) and as a result, drops more voltage. When cold, this allows more power to the coil when starting and helps make up for the voltage drop caused by the starter drawing lots of power.

If you convert to a 12-volt system you can use the old coil if you add more resistance to the primary circuit -- either by replacing the OEM resistor or adding another resistor.

You can also use a 12-v coil (which may or may not need any resistor). If your 12-v coil needs a resistor and you don't use one, the life of the coil will be greatly reduced. If your 12-v coil doesn't need a resistor and you use one, the intensity of the spark will be reduced and may cause hard starting.

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