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Harry Ferguson Tractors Discussion Forum
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Re: points and resistor

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Jason S.

12-01-2013 06:13:09
174.237.8.67



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But it wasn"t a true 12 volt coil. There wasn"t an external resistor but the coil had resistance in the primary windings so it was the same as the coils you buy now that say no external resistor required. The resistance is internal. A true 12 volt coil has no resistance internal or external. A GM HEI coil when measured only has about .5 ohms of resistance.




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rvirgil_KS

12-01-2013 09:28:37
192.208.173.110



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 Re: points and resistor in reply to Jason S., 12-01-2013 06:13:09  
Sounds like a matter of definition.

Your statement "There wasn't an external resistor but the coil had resistance in the primary windings so it was the same as the coils you buy now that say no external resistor required. The resistance is internal." is correct.

However, comparing HEI system to the old points system seems to me like apples and oranges. Appears to me that any coil that will work, as designed, on a 12 volt tractor without extra external added resistance is a "true" 12 volt coil for that circuit.

Contrary to what many guys seem to think, there are no separate resistors in any coil from the points ignition era. A coil is a transformer with one end of primary and one end of secondary tied together. The designer controls the voltage or current capacity by the ratio of primary to secondary turns, the number of turns and the type of wire used.

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Jason S.

12-01-2013 10:24:19
174.237.37.233



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 Re: points and resistor in reply to rvirgil_KS, 12-01-2013 09:28:37  
But added resistance is added resistance. Whether its added internally in the coil by adding extra windings to increase resistance or adding external resistors to increase resistance where it was needed because of using a low resistance coil. I wasn"t comparing the HEI system, I was just using the coil as an example of one of the earliest low resistance coils that would not over heat on 12 volts. Bosch made some low resistance 12 volt coils also. In general an ignition system is better anytime you decrease the resistance. That"s why it"s better to use non resistor plugs and copper core spark plug wires. They will always provide better spark because of the lower resistance.

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