Posted by 440roadrunner on March 29, 2009 at 10:37:42 from (98.145.76.31):
In Reply to: My coil's okay BUT.... posted by Kestrel in CT on March 29, 2009 at 10:20:52:
OF course it WILL. You have to understand a little about coils and ignitions. A coil in normal operation (running) is NOT a DC load. It is an AC circuit, because the points switching act sorta like "an inverter" or more correctly a chopper. This means that you have a pulse effect, more like AC than DC, and that the duty cycle is lower.
Second part is more difficult to understand. A coil has "inductance" and exhibits "inductive reactance" It is in fact the coil and condenser together that make the spark. If you ever see a tune-up pattern on a 'scope, you'll see the 'ringing' during the spark time. These oscillations are caused by the coil and condenser alternatingly trading off energy to each other--first the charged condenser (capacitor) discharges through the coil, which forms a magnetic field. Then the magnetic field collapses, generating electrical energy in the coil, which recharges the capacitor. This ringing goes on until electrical losses deteriorate to nothing, or else the points close again as the engine turns. The point is, that as an engine runs, a coil does not draw the same current (because of this inductance) as the points open/ close as it would if you replaced it with a pure resistive equivalent.
What all this nonsense boils down to is that a running coil DOES NOT draw current WHILE RUNNING in the same manner that it does when NOT RUNNING. The 100 percent draw (cureent/ wattage) of a coil when stopped is incredibly more than when running.
The only other thing that (on many engines) is that it may have a "ballast" or "coil resistor" which WILL help to mitigate some of this current, I.E. the more current that the coil tries to draw, the less the ballast allows it to draw.
In older motor vehicles, a coil/ resistor could actually cause a fire. Visualize the mid-late 60's or early 70's. Visualise the usual family truckster, with 1/8" of grease and oil all over the engine room. A hot resistor not a good thing.
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