Phaedras Posted December 22, 2004 Share Posted December 22, 2004 I just built a new MSD coil into my Loyale and of course read the instructions AFTER I had it all set up. MSD mentions that I need a "ballast resistor" so no "personal injury" or "product damage" will occur. Is this all just hot air, or is my coil eventually going to go nuclear? I have the newer crank angle distributor, if that helps. Quote Link to comment Share on other sites More sharing options...
All_talk Posted December 22, 2004 Share Posted December 22, 2004 Coils are designed to work with or without a ballast resistor and dont mix well with the wrong type ignition system. I dont believe the stock Subie system uses a ballast resistor, you could add one I guess, or there should be a similar coil that doesn't require one. The origins of the ballast resistor root in the days when cars were switching from 6 volt to 12 volt, I think that running without it will supply a higher than designed input voltage risking VERY high output voltage (personal injury) and coil burnout (product damage). I know that when switching the old VWs to 12 volt you can run the 6 volt coil for a while... but sooner ot later it would leave you on the side of the road. Gary Quote Link to comment Share on other sites More sharing options...
All_talk Posted December 22, 2004 Share Posted December 22, 2004 I wasn't quite right, there is a bit more to it, the following was extracted from this site: “Basically, a non-ballast coil is designed to produce full spark output with 12 volts on the input (+ terminal). A ballast coil is designed to produce the same spark output, but with only 6 to 9 volts on the input. With a non-ballast coil, the input to the coil is the same, 12 volts, whether the engine is running, or being cranked by the starter motor. With a ballast coil, the starter relay by-passes the ballast resister when the starter motor is spinning the engine, and applies the full 12 volts to the coil. Since the coil is designed to provide full spark with reduced voltage, the application of the full 12 volts produces a much hotter spark, which is an aid in starting. After the engine starts, and the starter motor is off, the coil voltage is dropped to the lower voltage, and the coil output is the same as for a non-ballast coil. The reason the ballast type coil is not run at the full 12 volts, for a hotter spark, is to prevent damage to both the coil and the points. With a non-ballast coil, power is applied to the coil directly from the ignition switch. Power to the ballast coil comes from the ignition switch to the resistance wire, and then to the coil. When the starter relay operates, power from the battery, is routed through the contacts of the relay, to the coil. This shorts out the resistor wire, by placing 12 volts on both ends of the wire. With the same voltage on both ends, no current flows, so no heat is generated. The current flow is shunted around the resistor wire. This bypassing of the resistor wire places the full 12 volts on the coil. “ In the sprit of complete information, I stand (self)corrected. Always the humble student Gary Quote Link to comment Share on other sites More sharing options...
NorthWet Posted December 22, 2004 Share Posted December 22, 2004 To extend All_talk's comments with my personal (not necessarily accurate!) understanding: The ballast resistor is there to limit current flow through the coil (possibly introduced when going from 6V to 12V, though I haven't had any 6V experience). Without the resistor, the coil would overheat quickly if you "parked" somewhere with the ignition on and your points closed. (Oops! my age is showing.) It could also overheat during normal running, given standard dwell angles. It also limited the current through those points, which would tend to burn and pit (tungsten pitting!!! ) if exposed to the full current from a coil in an unballasted 12V system. Please note that most starting circuits bypass the ballast so that coil sees the full 12V (or whatever is there while the starter is cranking). So, you might get away with running an "external ballast required" coil without a ballast, but probably not for long. And it *might* cause damage to your ignition module by exposing it to a much higher flyback voltage from the coil. Quote Link to comment Share on other sites More sharing options...
Vanislru Posted December 22, 2004 Share Posted December 22, 2004 use the old one from your coil bracket and you're good to go, I've run withou and not had any damage, but that's only for a 1000 cliks or so. Quote Link to comment Share on other sites More sharing options...
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