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points and resistor

1

1948jr

Member
this tractor had a12 volt gen. and 12 volt reg. did it come out with a built in res. or 12 volt points or are all points 6 volt?
 
Points should be same. Be sure the coil has internal resistor marked on it. I always change points, condenser and coil when I change over to 12 volts. You can use a inline resistor if you don't want to buy new coil. I always use the internal resistor coil. This way you don't have the resistor wired inline to coil.
 
The points do not care if it's 6 or 12 volts. Only the coil cares about the voltage and needs a resistor if it's not a true 12 volt coil. Where are you getting your points from?
 
Points dont work on 12volt the resistor drops the voltage to about 6 to 8 volts on the points 12 volts will burn your points
 
The resistor drops the voltage down for the coil. Not the points. I have ran points on 12 volts with a true 12 volt coil for years and had no problems. The technology to manufacture a true 12 volt coil didn't exist until the 1970's. That's why most all cars and trucks made until the 1970's had a ballast resistor to keep the coils from overheating. GM's first 12 volt coil was the HEI around 1975. Ford did not produce a 12 volt coil until the TFI system in 1985. Even though Ford went to electronic ignition in 1974, the Duraspark system cranked on 12 volts but ran on 9 volts because the coils would over heat on 12 volts.I can't think of any tractors that had true 12 volt coils right off hand.
 
Minneapolis Moline used a "true" or "direct" or "no exernal resistor required" 12 volt coil (approximately 3 ohm primary as opposed to 1.5 ohm on the 6 volt system) as early as 1953. It was a Delco-Remy system.
 
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.
 
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.
 
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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