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Re: Resistor on a 12v To-20 Ferguson
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Posted by John T Electrical Engineer on May 14, 1999 at 07:23:49:
In Reply to: Resistor on a 12v To-20 Ferguson posted by Craig Collins on May 14, 1999 at 03:16:03:
Craig, heres all the straight stuff. What you read from me or others is correct about a ballast resistor needed on a 12 volt system using the old 6 voil coil, because the ballast drops approximately half the voltage with 6 left across the coil as it was designed for. Now, ignition points are physically just a current switch (not a voltage device) and the voltage withstand ratings regardless if 6 or 12 volts were across it are more than satisfied. Theres practically no difference in insulation or separation requirements needed for 6 versus 12 volts DC, so theres little if any difference in the points on 6 or 12 volts. If a coil is rated for 12 volts you dont need a ballast resistor but some 12 volt coils still had an internal ballast for the purpose of reducing point current if it were a point type ignition. So, if you use a true 12 volt coil you can do away with the ballast. Still, if in place, it would reduce the current through the points extending their life. I have seen them with 12 volt coils and still a ballast and they ran fine and the points would draw less current and last longer that way. The problem is not with 6 or 12 volt points, its with current through them which is what eventually burns them out, not how many volts are across them when theyre open. Try it at full 12 volts and if the coil is a 12 volt designed for a point type ignition, things will be fine. If you experience premature point burn out, add the ballast, which will reduce spark energy somewhat, but extend point life. The answer has to be two sided because its hard to sit here and know the coils resistance or the exact coil type, since if it were designed for elec ignition, there wouldnt be such a need to limit its current the way necessary if it were designed for points. John T in Indiana
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