Quote:
Originally Posted by Mike51Merc
OK, just to clarify, in a non-ballasted system, a 3 ohm coil would be called a 12volt coil and a 1.5 ohm coil would be called a 6volt coil.
If the systems are ballasted, a 12 volt coil would have 1.5ohms and the 6 volt coil would have less resistance (I used .5 as an example, but that would vary depending on the value of the resistor that gets added to it).
Current draw (amps) will vary depending on the voltage, but it is really total wattage (Volts x Amps) that has to be limited.
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Yep, if I am following your response correctly. It is the total resistance that has to add up. Most so called 6v coil will not measure right on 1.5 ohms and likewise with the ballast resistors. And all of these numbers are just at contain points in time anyway, a 6v system is not 6v, it is over 6v on a fully charged battery, under 6v when cranking the engine and over 7v when running at a cursing speed. The numbers are just for talking purposes, not detailed circuit analysis. What you are concerned about is mainly the current and keeping it around or below 4 amps. In a 6v system somewhere around 1.5 ohms will do that (there is also resistance in the wire, connections, etc.) and in a 12v system 3.0 ohms.
Another variable is the ballast resistor if one is used. The actual resistance changes with temperature. Some of the early car manufactures didn't use ballast resistor on the OEM style coils. All of the above relates primarily to "can" coils which do not require a ballast resistor (assuming it has the correct resistance). With the original Ford coils, they were a lower resistance value and coupled with a ballast resistor (I think the numbers were somewhere in the .8 ohm range). The ballast resistor had a lower resistance when cold which increased the amperage in the circuit to ad start up. As the current flowed through the resistor it would heat up and increase the resistance which lowered the current in the circuit to prolong point life.
So, again, there are variables all over the place in the ignition circuit and the resistance numbers used is just guidance as to what is needed.