Pertronix hookup with ballast

[Avenger]

I see that the pertronix unit hooks up with a ballast by hooking up the negative to the negative on the coil and hooking the positive up to the ignition key on side of the ballast.. But how? The ballast has a blade connector on it and this is a ring terminal.. Or is there a better way of hooking it up that the directions do not specify?

Thank you in advance,
John

[67440Dodge]

Just come off the Positive side of the coil.. that's where the ballast connects to.

[Avenger]

I was figuring that would be the case but I was hoping someone would confirm it for me. Thank you for the help

[markz]

Just come off the Positive side of the coil.. that's where the ballast connects to.

I think I need to disagree with Mike on this one...........

Sound like the pertronix wants full voltage that's why it says ignition key side of the ballast. If you go to the coil you will have reduced voltage (actually will have some lower DC value with lots of ripple).

Am I right????

[67440Dodge]

Pertronix can work after the resistor, I've run them that way with no problems. It only requires 8V to operate.

[markz]

Pertronix can work after the resistor, I've run them that way with no problems. It only requires 8V to operate.

I would not be comfortable doing that. The voltage on the positive side of the coil is an average DC voltage with very high and low peaks (AC voltage ripple) based on the firing frequency. I would be concerned about the long-term reliability of the Pertronix with that happening. The Pertronix is designed for DC not DC with high AC component. It is a safer bet to connect it to a solid 12 volt source.

The voltage ripple I am referring to is dropped across the resistor.

If you remember the old point system (anyone that old?) when the points were open the voltage at the positive of the coil was battery voltage and when the points were closed the voltage dropped to what? 6V? 7V? 8V? That voltage cycling is always happening when the engine is running.

My opinion as an electrical engineer but I could be over-engineering it...........

[67440Dodge]

The sole purpose of a ballast resistor (besides blowing out when you're late for work and it's raining) is to drop the voltage for the points so they don't burn out as fast. It doesn't introduce an AC ripple into the system (only the alternator is capable of that), it just drops the voltage. The "ripple" you might be thinking of is the on/off/on/off signal seen at the negative side of the coil.

What would benefit John the most is if he bypassed the resistor (since the points are going away, it's not needed). He'd get a slightly hotter spark due to the increased voltage at the positive side of the coil, it'd eliminate any questions he has about whether it will be a problem, and removes a potential ignition failure point.

[markz]

It doesn't introduce an AC ripple into the system (only the alternator is capable of that), it just drops the voltage. The "ripple" you might be thinking of is the on/off/on/off signal seen at the negative side of the coil.

Correct. In my wold I call that AC ripple. If you look on a scope you have a DC component with the AC riding on top of it based on the on/off/on/off firing pattern.

In addition to saving the points I also believe that the ballast resistor drops the voltage to the coil while the points (or electronic ignition closed transistor) are closed. If you don't drop the voltage to the coil while running the coil would overheat and burn out the coil.

Years ago I had a 340 69 Dart. Going to work lost the ballast resistor so bypassed it. Coil went about 10 minutes before it burned up - just got me to work.

A capacitive discharge like a MSD doesn't need a ballast because they saturate the coil not by current but by high voltage. By putting a high voltage across the coil for a very short duration the coil does not have time to get hot. In a conventional ignition the winding needs dwell time to build the magnetic field which can cause the coil to overheat if voltage is too high.

During starting the ballast resistor is bypassed in order to get a hotter spark during starting.

So above is the answer that I came up with and then I called Pertronix. Guess we are both right!

What he said is that if the primary resistance of the coil (negative to positive) is 1.5 ohms or more you can eliminate the ballast resistor. If it is less don't eliminate the ballast as it can hurt the coil and the ignitor (Pertronix). If less than 1.5 ohms then hook up the power lead to the ignition side of the ballast.

My caution is that if you do measure the coil resistance make sure you have good leads on your ohmmeter and better yet use the relative mode.

Make sense?

[Avenger]

If you keep the balast though you can keep a set of points in the glovebox incase of failure..which im doing just incase since i drive to carlisle haha