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The coil is a compact, electrical transformer that boosts the battery's 12 volts to as high as 20,000 volts. The incoming 12 volts of electricity pass through a primary winding of about 200 turns of copper wire that raises the power to about 250 volts. Inside the distributor, this low-voltage circuit is continuously broken by the opening and closing of the points, each interruption causing a breakdown in the coil's electromagnetic field. Each time the field collapses, a surge of electricity passes to a secondary winding made up of more than a mile of hair-like wire twisted into 25,000 turns. At this point, the current is boosted to the high voltage needed for ignition and is then relayed to the rotor.
Ignition coils are very rugged and reliable, but can fail for a variety of reasons. Heat and vibration can damage the coil's windings and insulation causing shorts or opens in the primary or secondary windings. But the number one killer of ignition coils is voltage overload caused by bad spark plugs or plug wires.
when they first started making ignition systems for engines, they used mechanical "points" to switch the voltage on and off. When the points "made" to allow the current to flow, they had a tendency to bounce, causing the voltage to build up erratically. When they were opened, though, the current was shut off very rapidly, giving the sudden change in current flow necessary to create the higher voltage to be induced. Nowadays, with electronic ignition systems, it could be done either way, but they usually stick with the "old" way just because it's what they're used to.
If you are missing either the power, or the switched ground, then you need to see what is wrong in the ignition system. The coil is likely ok. But if you have power to one wire, and a switched on/off ground signal to the other wire, with the engine being cranked, and the coil is not emitting a spark from the output side, then you have a bad coil.
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发表于 2011-6-3 13:42:20
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