Thread: Ballast resistor or not?

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When I was changing my Mopar flattie over to 12 volt, I got an article off the internet and it said if you are using a modern 12 volt aftermarket coil, you do not need a ballast resistor because it is built into the coil. Well, I smoked the coil last night so i'm wondering if I do need one or how I can determine if I need one. It was a new coil and only ran a handful of times. Anyone have any experience with this?

The ballast resistor is used to keep from burning up the points and is only in the system when the ignition switch is in the run position. If it was eliminated I would think you'd burn up the points before you smoked the coil.

The resistor is there to knock the voltage down to 8 volts so the coil won't be damaged. If your new coil has an internal resistor, it should be printed or stamped on the outside case. If there's nothing there, it's possible you have a regular coil that wouldn't handle the 12 volt and went poof. Mislabled box, switched somewhere along the way, when comparing an internal to an external resistor coil? Don't know just a guess. If your using an early style ignition, with a resistor, you should have a single wire from the distributor to the coil,(neg. side) and two wires to the opposite terminal of the coil.(pos. side) Of the two wires, one will come from the resistor that will supply 8 volt, or close to it. And the other wire will come from the starter solenode to supply 12 while cranking the engine over to start it. There's a terminal on the solenode that is energized only while your cranking the engine over, I'm not refering to the trip wire from the key switch that is used to start the engine, that's a seperate terminal on the solenode. So, now that, that is as clear as mud, you likely didn't need that part anyway. Some systems that used the internal resistor coil, just had one wire to the pos. side of the coil, and no jumper from the starter. Didn't need it, it had 12 volt all the time and knocked it down to 8 volt internally. No "boost" in voltage could be gained like you would get with the external system. So now it remains to figure out, is the coil the wrong one, or just a faulty one. Warranty can be a bit tough to get on electrical componets sometimes, best of luck though. Sniper

The ballast or condenser acts similarly to a snubber by 'snubbing' out voltage transients during the act of opening the points. These transients occurr due to the points being connected to an inductor (the primary coil circuit). Electrical inductors don't like the current to change so they can jack the voltage way up to compensate. Without the ballast it is possible for this inductor to develop voltages that are too high for the coil primary insulation causing short life or even instant failure.

Kitz

This helps a lot. Thanks, everyone.