Ignition Coil Overheating

[67Dart273]

Well it's a "circle." Increasing duty cycle at the points changes the current through the system, and this changes the heat in the ballast. That's why it's called a ballast. It changes resistance with heat.

The thing is there is multiple reasons

Damage to the points is one aspect

The other thing is, the fact that there is a resistor, means, that if you bypass the resistor during start, then you maintain a fairly hot spark for starting. The coil COULD have been designed to eliminate the ballast, but then you would have a weaker spark during cranking

So far as I know, the "big change" was with GM HEI. It incorporates internal dwell control, and so far as I know was the first system without a ballast.

In the 70's my cousin had a Jeep with the ? Prestolite factory system that AMC used. One day he came into the store and bought an ECU. He asked me if I knew why the thing "ate" brain boxes. I asked "HIM" if any of the kids left the key on sometimes. "Just to listen to the radio." I said "You mean they turn the key ON?" Turns out he himself was guilty........did not know the difference between accessory and "run." I guess that thing "ate" about 3 ECUs before he got wise.

The point? These systems were sometimes not very well engineered. Breaker points systems are not the only one that can be damaged by carelessness.

 

[nm9stheham]

See what I mean? I agree with some of this, it is a gray area. How would a resistor change its value just because the engine is operating at a high RPM? I get how it changes value as it warms up.

When the RPM's go up high enough:
- There is certain amount of time needed for the coil current to rise to its full value each spark cycle. This is determined by what is called the circuit's time constant, which is set by the coil inductance and the total resistance. (Internal coil resistance plus ballast resistance.)
- When the dwell time gets shortened at high enough RPM's, the coil current each cycle does not have time to reach full current like it does at lower it mid RPM's. So the average coil current drops.
- The ballast resistor's resistance is effected by its temperature, which is set by average current; when the average coil current drops, the temperature of the ballast drops. The ballast resistance then goes down and allows more current to flow. It does not fully compensate for the small dwell times at high RPM's, but it helps.

Not grey.....just applied circuit theory stuff. Now back to your regularly scheduled program......

 

[Mopar Tim]

When the RPM's go up high enough:
- There is certain amount of time needed for the coil current to rise to its full value each spark cycle. This is determined by what is called the circuit's time constant, which is set by the coil inductance and the total resistance. (Internal coil resistance plus ballast resistance.)
- When the dwell time gets shortened at high enough RPM's, the coil current each cycle does not have time to reach full current like it does at lower it mid RPM's. So the average coil current drops.
- The ballast resistor's resistance is effected by its temperature, which is set by average current; when the average coil current drops, the temperature of the ballast drops. The ballast resistance then goes down and allows more current to flow. It does not fully compensate for the small dwell times at high RPM's, but it helps.

Not grey.....just applied circuit theory stuff. Now back to your regularly scheduled program......

Got it thanks.

 

[CheeseWheel]

I fixed the wiring and the car is back to running fine. Thanks for all the help guys.

 

[nm9stheham]

Very good to hear!

 

[BillGrissom]

... So far as I know, the "big change" was with GM HEI. It incorporates internal dwell control, and so far as I know was the first system without a ballast. ...

I agree the biggest improvement was in electronic dwell control. I expect all the auto companies were working on that the same time. I expect the "spark computer" box in my 1982 Aries (similar to V-8 "lean burn" box) probably didn't have a ballast resistor and had similar dwell control. But, you can't separate the ECU easily like you can w/ the GM HEI modules to retrofit older cars. Don't know about Ford, other than their later ECU was termed "TFI". Surprisingly, I heard that Honda still used points and carburetors into the 1990's. The public assumed the Jap cars were more modern, but their controls tended to lag the U.S., as did many Euro cars. But not always bad since GM has pushed many innovations to the public that weren't ready for prime-time and the buyer was stuck with the issues.