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Discussion Forum

Ignition coil resistor

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09-30-2001 18:58:49

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When a resistor is connected in serries with a load (in this case the coil is the load ) --it functions as a current limiting device . That means that it limits the current to the coil .

Since it has a positive temperature coefficient , the resistance increases as the current tries to increase --in that way it again reduces the current flow .

Yes there is a voltage drop across the resistor , since when volts = current times resistance .
eg I= E/R 3.6 volts / .6 ohms = 6 amps while points are closed .

I measured the resistance of a new coil primary , .6 ohms .

It is like a light bulb , when you first turn it ON ,and you had an ammeter connected , the current would,at first be high ,and then drop down to a constant current .

So that means that when it is cold , more current flows ,and a hotter spark occurs .Or when the generator starts charging, the voltage goes up a bit, and yet the current through the coil remains the same , because the total resistance has increased .

Another factor that cannot be ignored ,is that the coil current is not steady current , but, pulsating current ,the pulse rate determined by the speed of engine rotation , opening and closing the points .

Pulsating DC is, in many ways ,the same as AC .which is why the coil is in fact a transformer .That brings into play such things as Inductive reactance and all that stuff .

The point is ,when you are checking static (engine not running) things change when it is running .

'hope this helps someone .

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