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Ballast Resistor - further ramblings

From: Hank Dozier
Remote Name:
Date: October 10, 2002


Adam...You are correct that the ballast is bypassed when the starter is engaged. This is done to give the maximum charge energy into the coil under the cyclic voltage drops as the starter spins. Also, since the starter is grounding such a high current, this can also "float" the ground back to the battery, which would also reduce the effective voltage available to the coil. Some coils (Ford E-cores and GM cap-mounted HEIs) do not require a ballast resistor, as their primary winding resistance is about 1.2-1.5 Ohms. However, almost ALL oil-filled coils require a ballast, since their resistance is only about 0.4 to 0.7 Ohms, and they will overheat if left with continous current flowing through them. Bottom line is, if in doubt, put the ballast in there. You can always remove it if you find you have cold weather starting issues with a half-charge on your battery.


Last changed: July 19, 2018