Posted by Bob on May 04, 2010 at 06:15:01 from (69.178.228.68):
In Reply to: coils posted by bspauld on May 04, 2010 at 05:54:27:
Yeah, that's about right.
'Cept the coil sold as a "12 Volt needs external resistor" is more or less a relabeled 6 Volt coil.
There IS a reason for the "12 Volt needs external resistor" coil. The use of an external resistor makes it possible to use a bypass setup to take the resistor out of the circuit during cranking to compensate for the low battery voltage available to the ignition system while the starter is hogging current.
Also, there's 2 types of ignition resistors used, a fixed resistor is often used with the bypass starting scheme, a "PTC" (positive temperature coefficient) resistor MAY be used in systems WITHOUT a starting bypass. It's resistance starts out low to allow for a HOT spark if the engine is cranked right away, (as soon as the ignition is switched "ON"), then it's resistance drops as it heats up to limit primary current for long point life and less coil heating.
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