Re: 12 volt coil without resistor

Posted by RAB on January 15, 2006 at 02:40:17 from (195.93.21.6):

In Reply to: 12 volt coil without resistor posted by deene on January 14, 2006 at 17:46:57:

Deene,
Not sure what you have bought and certainly no idea as to the application. So just to explain why there are different coils.
6 volt coils for 6 volt applications.
12 volt coils for 12 volt applications.
6 volt coils + ballast resistor for 12 volt applications.
12 volt coil with internal ballast resistor (actually a 6 volt coil) for 12 volt applications .

The main thing is to understand why to have a six volt coil for a 12 volt job.
It is simply for better STARTING spark. End of story.
The way it works is at starting, a 12 volt coil may not get enough voltage (due to heavy current drain of starter) to produce a strong enough spark. So the designers fit a 6 volt coil which will give a good spark on a reduced voltage, 12 volt system for starting.
But normal running would very quickly burn out contacts and/or coil, so they added a resistor to drop the current through the coil during normal running. It was called a ballast resistor in this application.
So your wiring will feed the coil directly from the starter solenoid (bypassing ballast resistor) only when the starter motor (solenoid) is energised (starting engine) and through the ignition switch via the ballast resistor for normal running.
Now what you actually need is determined by how or what your application has been designed or modified for.
Regards, RAB

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