On Sun, 23 Nov 2008 13:06:24 -0800, Gunner Asch
wrote:



Whats the difference between an AC and a DC coil????

This is a guess rather than any semblance of expert opinion: in a DC
coil excited by a battery, max primary current is limited by primary
resistance or a ballast resistor. An AC coil would be driven by a
winding in the alternator that is of the correct phase w.r.t. the
engine (synchronized with engine rotation) so the alternating current
in the primary would be about a max when the points open. Current is
limited by primary reactance so primary resistance could be quite low.
Possible advantage: the voltage produced by that winding increases
with engine speed, as does the frequency. Coil impedance would
increase with freq but since voltage does too the peak current remains
about the same. A DC coil can have trouble getting up to current at
high RPM's unless it's significantly overdriven at low RPM's.