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Thread: Coil problem?

  1. #21
    Join Date
    Aug 2004
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    Christchurch, NZ
    Age
    57
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    2,207
    Quote Originally Posted by Dek View Post
    Update. Ordered a new coil from Pertronix and popped it on, problem solved! It now pulls again in 5th from 1000 rpm and smoothly throughout the rev range in all gears. Noticed on the instructions which I naturally read after I fitted it, said on 1.5 ohm coils for 8 cylinder racing and normal applications to remove resistor, as with 4 and 6 cylinder racing applications. But for 4 and 6 cylinder normal applications to keep resistor in place. Anyone know the rationale behind this? I kept my ballast resistor in place as it seemed to run ok with it.
    Dek

    The coil is an inductor, it resists changes to current so when you switch it on, the current starts low and increases the longer you leave it on (until it saturates). The time that the coil is on for depends on dwell angle so a coil on a four cylinder is turned on for twice as long as that on an eight cylinder (per spark). The current can increase to the point where it damages the components in your electronic ignition unit. The ballast resistor also serves the purpose of limiting this peak current and thus protects the electronics. As the revs increase, the on time for each spark decreases and so the current flowing through the coil decreases too and the ballast ceases to have much effect.

    In short, leave the resistor in if it is running just fine; it will do no harm.

    Hope that helped.
    Last edited by mylesdw; 16-10-18 at 02:34 AM.
    Cheers

    Myles D-W

  2. #22
    Join Date
    Jun 2004
    Location
    Northampton
    Posts
    1,415

    Thumbs up

    Quote Originally Posted by mylesdw View Post
    The coil is an inductor, it resists changes to current so when you switch it on, the current starts low and increases the longer you leave it on (until it saturates). The time that the coil is on for depends on dwell angle so a coil on a four cylinder is turned on for twice as long as that on an eight cylinder (per spark). The current can increase to the point where it damages the components in your electronic ignition unit. The ballast resistor also serves the purpose of limiting this peak current and thus protects the electronics. As the revs increase, the on time for each spark decreases and so the current flowing through the coil decreases too and the ballast ceases to have much effect.

    In short, leave the resistor in if it is running just fine; it will do no harm.

    Hope that helped.
    Thank you Myles for that tutorial. I now know more about coils and ballast resistors than I ever did! I think that was the advice from Pertronix when I first fitted the system without any explanation but nice to have you confirm it. Cheers.
    Dek

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