69 442. So my Pertronix bit the dust the other day, in the middle of nowhere. Only had it in for half a year and yes, I had a full 12v going to it. Now I’m going back to points. My question is about the voltage on the + side of the coil. I have about 10-11v with engine running. Thought it should be about 9v. Resistance wire is intact and not cut. With the engine off and ignition in run, I have 6v.

 

What is the battery voltage with the battery charged and the car running? Is the charging system overcharging?

Yes 10-11VDC sounds high. Any chance of borrowing another meter to confirm accuracy?

There should be full battery voltage at the resistance wire with it disconnected from the coil and the key in run. The voltage will not drop unless amperage is drawn/flowing.

The resistance wire does fail once in a while.

Good luck!!!
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Your fine.

 

I think the resistance wire is suppose to cut voltage to 9 volts, that’s the number I always heard. The only drawback to 11 volts is accelerated point wear. Make sure the condenser is new, and check the dwell frequently. You might find out the dwell doesn’t need adjusted any more frequently than before, so no problem.

 

This is because at rest, the points just happen to be closed when you made that measurement. Had the engine stopped where the points would be open, you'd see the full battery voltage here (no current through the resistance wire, so no voltage drop). If the resistance wire didn't have any resistance, you'd see the full battery voltage whether the points are open or closed.

With the engine running, the voltage across the (points + coil) would be the average of (the battery voltage * duty cycle the points are open) and (the 6V you are seeing with the points closed * the duty cycle the points are closed), because your meter is averaging them. You may be seeing higher than 9V when the engine is running due to your dwell being too short (more time w/ the points open than nominally).

 

Not surprised with the Pertronix.... although yours lasted longer than mine (just over a month).
Thankfully Summit Racing was very helpful and obliging in letting me refund it!

 

Ok thanks for the info. One other question, this resistance value seems to change slightly with engine rpm. Is that normal?

 

How is it doing that? The voltage value changes with charging load based on RPM.

 

I need some clarification. Which resistance do you speak of? Resistance is usually expressed in ohms.

 

We’ve been talking about voltage here, C’mon man keep up!😉 Yeah I meant voltage value sorry

 

Remember, half of the ignition circuit (BATT >> Resistance Wire >> Points >> COIL >> GND) is a coil, whose impedance changes with frequency (RPM). So it is to be expected that the (average) voltage at the node between the resistance wire and points would vary with RPM.

 

What??

 

Resistance changes with temperature. And if you will open your textbooks to the chapter on Ohms Law, you with learn that if the voltage to the ignition coil changes (as it would with typical charging system voltage variance, the voltage at the coil will also change.

I have always heard the resistance wire is suppose to drop voltage to around 9 volts to help ignition point life. I have never verified it for myself, I also can’t recall ever seeing the voltage specified in the manual. Maybe it is in there, a d if it’s different that what the OP is seeing then it might be worth investigation.

if not, I wouldn’t sweat 11 volts. Drive it, occasionally check the dwell and ignition points for wear.

 

Pertronix modems really suck! You may just carry a spare or two in your glove box and switch it out when it dies not much different than throwing in a set of points. But like you I went back to points.. At least they let you know when they are getting ready to quit..... Tedd

 

Thats my plan thanks