voltage across the coil
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Joined: Feb 2006
Posts: 86
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From: Sunnyvale Texas
voltage across the coil
Just finished installing a Pertronix distributor kit, doing away with points. I was told to check the voltage across the coil and i dont know what it should be. I checked it several times and once i got 12.5v and the next serveral times i got 5.5v to 5.7v. I suspect it could be the ignition switch, maybe, the set up is without a ballast resistor. Has anyone had the same problem? What should the voltage across the coil?
this is on a 68-327
I'm all
this is on a 68-327
I'm all
Le Mans Master
Joined: Jul 2006
Posts: 8,117
Likes: 104
From: charlotte north carolina
are you measuring the voltage with the engine running, or just with the switch on? i think what you are seeing is one voltage with the points open and the next voltage with the points closed. without a ballast resistor and the points open, if you attach the probes across the coil, you'll get some strange readings. also, depending on the quality of you meter, with the engine running, the voltage across the coil will change from zero(when the points are open-because there is no current flow) to 12 volts(when the points close and the only load in the circuit is the coil). with this voltage fluctuating between zero and 12, the meter will get stuck in the middle and give an "average" voltage. if you put an occiliscope on the coil you would see this, but an everyday voltmeter will give the reading (5.7) that you got. turn the engine so the points are closed, turn the switch to "on" and measure the voltage.
Thread Starter
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Joined: Feb 2006
Posts: 86
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From: Sunnyvale Texas
Thanks for the fast reply, i just checked it again and the max i got was 5.7v down to 3.5v. By the way this Pertonix Ignitor is a pointless system. These readings where after a short drive. But again thank you for the help
Le Mans Master
Joined: Jul 2006
Posts: 8,117
Likes: 104
From: charlotte north carolina
i see that your post indicated a pointless system-my mistake. however, the current thru the coil must turn on and off as the distributor functions, and the readings would still fluctuate between zero and 12. i would think that if the meter was attached across the coil and the engine rpm was increased, the apparent voltage would increase (because the meter wouldn't have time to "fall" back to zero).
Team Owner
Joined: Jan 2006
Posts: 37,637
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From: Crossville TN
The '68 car came with a ballast resistor. It did not come with integral resistance wire in the "run" circuit. So, if no other modifications have been done to the ignition system wiring, it should have full 12 volts delivered to the (+) coil wire. That means you should not have any problem hooking up the Pertronix system (as long as it requires the full 12 vdc as an input...check your installation instructions). If you are converting from a points-type ignition, a PO could have changed the wiring to a resistance wire like later C3's required. You really need to determine how this car is presently wired.
