ignition coil ballast resistor

[Bill Goddard]

I have tried to search this question but no results. I have a 12v system on my four-door leatherback. I am trying to choose the proper coil. I have a 12v coil that says it has a resistor built in. The ohm reading across the terminals is 3 ohms. I understand a 6v coil should read 1.5 ohms so I think 3 ohms is right for a 12v coil/ 12v system. This would mean the 12v coil would deliver the same amperage as a 6v coil. Am I right? Thanks for any help Bill Goddard

[katy]

You got it.

[Jim/GA]

You are correct.

Another option is to take the 6 volt coil, that reads ~1.5 ohms across the primary, and add a 1.5 ohm ballast resistor to the power feed wire going to the coil. Those 2 together (in series) will then measure 3 ohms and work well on 12 volts. Having that extra 1.5 ohm resistance inside or outside the coil doesn't change how it operates. This lets you keep the original 6 volt coil, instead of buying a new 3 ohm coil.

[Herb Concord Ca]

Jim is right, however using an external ballast resistor, helps with power (heat) dissipation. A good thing.

[Bill Goddard]

I appreciate all the responses above. They have cleared up the question for me. Oddly, I have a 12volt coil labeled as "super hot " that measures 1.5 ohms so I installed it with a 1.5 ohm ballast resistor. The resistance now measures 3 ohms on a 12v coil. It seems to be working. Bill Goddard

[rotorwrench]

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This is basically what auto manufacturers did after they switched the cars over to 12-volt systems back in the 50s. Some manufacturers used the wire wound ballast resistors and some used the resistor wire clear up into the early 70s.