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Old 03-17-2005, 10:53 AM
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A question on coils

Converting 1950 ford to 12 volt system, since I will put a ballast resistor on the ignition side of the coil to drop the voltage from 12 volts to 6 volts.

My question is
Do I have to get a 12 volt coil or can I still use the stock 6 volt coil?

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Old 03-17-2005, 02:22 PM
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Doc Here,

Let me see If I have this correct, You have a 6 volt system, that has been upgraded to 12 volts, with a 6 volt coil and ballast correct?

If this is the case, Then yes, go to the 12 volt coil.

The reason is even with the ballast resistor, while the 6 volt may work (for awhile) the windings of the coil (internal resistance) is lower than that of the 12 volt coil.

This will produce more current draw, ergo, more heat, the coil will eventually break down. The output of the coil will be slightly higher than it needs to be which will put stress on the points over time.

Also remember , The Ballast Resistor was made to drop current at 6 volts not 12 volts. The load through a resistor at 6 volts is quite different than the load through a resistor at 12 volts (Ohms Law)

You Can get away with running the 6 volt coil, no doubt, but it can lead to unwanted surprises later on down the road. And for, What, 15 bucks or so...for a 12 volt coil...It Is a lot cheaper than the price of a hook home some dark winter's night.

I would upgrade the coil and ballast to 12 volts were it me. OR get a system dropping resistor and install it to drop the voltage to 6 volts BEFORE it gets to the coil and Ballast (as if the system was still running at 6 volts) But I think you may find the price of that big ceramic resistor is about the same price as a new 12 volt coil and ballast. So if it's the ONLY thing you need to run a 6 volts, I'd just change out the coil.

Hope it helps!

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