COIL RESISTANCE

[kauri]

I have been running the engine again and suddenly realised that the coil was getting red hot. I may have cooked it but on cool down it seems to work OK.

Now this is a coil with dubious history and I wonder if it is likely that it should be run through a ballast resistor. I have measured the resistance of the coil which is 1.5 ohms on the primary side and 6K ohms accross the secondary.

Does anyone know what the resistance of a normal 12V coil should be and what the resistance value the ballast resitor needs to be for a coil designed for use with it?

Cheers John

[kev]

1.8 to 2.4 ohms is the primary resistance of a high output 12v coil. Normal 12v coil resistance will be higher You may have a normal 6v coil. The reistance of the ballast resistor will be about 1.5 to 2 ohms I guess. Secondary resistance, as far as I know, is immaterial as it is just the transformnr secondary resistance which is much higher due to the higher number of turns, and the ratio of the primary to the secondary gives the HT output.

[kauri]

Thanks Kev

I tried a 1.5 ohm resistor with a lash up on the bench but the spark was pretty small.

Put two in parallel and it seemed to work fine so I will settle on 3/4 ohm. Now back on the car and it doesn't get too hot.

Cheers John