Coil ohms?

heapy

Member
Hello I have a 1975 Rover P6 V8 automatic.
I am wondering what coil I should have on there?
it's getting 12 volts to the coil with the ignition on, so therefore not ballast resist.
I have a few non ballast resistor coils but across the terminals they are all 3 ohms.
The one on the car despite making arking noises reeds 1.5 ohms and 7k ohms at the HT. The other coils are around 7 or more K ohms.
Do you think I am able to use these newer coils despite the difference in ohms at the low tension or buy yet another new coil!!
I'd rather use one of the many nice shiny new coils I have in the drawer but don't want to burn anything out!
Many thanks.
 
3 ohms is a normal unballasted coil running a permanent 12v feed. 1.5 ohms is for a ballasted system running ~9v. The 3 ohm coil would be the correct one to use with your system.
 
How did you measure the voltage at the coil? Measuring the feed to the coil even with ballast in place, if using a digital meter with the points open, would be battery voltage because there would be virtually no current draw. Or did you measure with the engine running. As said primary resistance of a standard HA12 coil is 3.0 - 3.4 ohms , ballasted is 1.3 to 1.5 ohms . This is according to a Lucas workshop instruction leaflet I have
 
Thanks for responding.
Ah that's strange then. It has the usual 2 wires for balast circuit on the positive terminal, the 1.5 ohm ballast coil I've just learnt, but with the engine running it's still over 12v..
It's been been on long journeys but hasn't cooked the coil either!?!?
I did switch over for 5 mins to a standard coil and this made no difference either.
Clearly the cars a ballast set up originally but something is a muck me thinks?
 
To roverp480's point. You want test voltage with the points closed. Apologies if I'm teaching your grandmother how to suck eggs:

1] Rotate engine until points are closed. (You'll need the distributor cap off to see)
2] Set up volt meter by taking both low tension wires from coil and connecting to volt meter
3] Turn on ignition but don't start engine.
4] If check voltage. If voltage is showing ~ 9v you have a ballast system. If it shows 12v you have a non-ballast system.

The idea being that you have it disconnected from coil and points closed before measuring supply, otherwise the voltage may show a full 12v from earth. Ballast resisters or normally on the ground side of points ignition systems.
 
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