Ignition coil problems

[Truckedup]

Ok,this is what's going on....The voltage fluctuates between about 7 and 14 volts as the points open and close.My Fluke digital meter "stabilizes" readings. And it stabilized on about 12 volts.So I checked it with engine off,points closed. Then opened the points with my finger .So my ballast is correct.No one picked up on the digital meter problem............................
Why did the coils fail? Bad luck I guess as there are no shorts and twice a replacement coil got it running with no changes.

[Warpspeed]

No your ballast is NOT correct.

If the ballast resistor is 1.8 ohms, in series with the 1.6 ohm ignition coil, there should be more than half of the battery voltage dropped across the ballast resistor.

In other words, the coil voltage cannot possibly be 12 volts if the ballast resistor is properly wired and working as it should.

[Truckedup]

No your ballast is NOT correct.

If the ballast resistor is 1.8 ohms, in series with the 1.6 ohm ignition coil, there should be more than half of the battery voltage dropped across the ballast resistor.

In other words, the coil voltage cannot possibly be 12 volts if the ballast resistor is properly wired and working as it should.

when the points are open,there is no load ,no resistance,you see close to battery voltage.
Take off off a points ignition distributor cap,rotate the engine so points are closed,turn on ignition,open the points with a finger nail and watch the meter..

[Warpspeed]

The voltage across the points when they are open, has absolutely nothing to do with the voltage measured directly across the ignition coil primary winding when the points are closed.

[af2]

The voltage across the points when they are open, has absolutely nothing to do with the voltage measured directly across the ignition coil primary winding when the points are closed.

The main thing is to have the 7 or so volts. never have 12 or 14 like you are saying....

[Truckedup]

Please reread my post,perhaps I'm not being clear. It's about 7 volts the points closed. There never was a problem with the operating voltage,it was the inability for my expensive Fluke meter to deal with rapid voltage fluctuations while the engine is running.
I probably should know better.......As an electrician checking voltage drop when a large electric motor starts.An analog meter is more responsive....Oh well,no one else noticed so I ain't alone

[bill jones]

-might be a good idea to install an amp meter inline in the power the coil circuit and see what sort of amperage is happening with the "key on---engine off---and points closed".

-and same thing when the engine is idling.

-anything under about 4 amps at idle is probably not much concern----but with the engine off and the key on and the points closed amperage probably shouldn't be much more than about 6 or 7 amps or so--if is well above 10amps---that is way too much---and will burn something.

[af2]

Please reread my post,perhaps I'm not being clear. It's about 7 volts the points closed. There never was a problem with the operating voltage,it was the inability for my expensive Fluke meter to deal with rapid voltage fluctuations while the engine is running.
I probably should know better.......As an electrician checking voltage drop when a large electric motor starts.An analog meter is more responsive....Oh well,no one else noticed so I ain't alone

An analog meter will never be as fast as a digital.

I will stick with UEI after using all 3 for voltage drop. Remember when a motor starts it is not the same as a point deal.

What Bill Jones wrote is what you need to do. Amperage kills windings.

I hope you will find the problem and maybe let us know.

[Truckedup]

Well,yesterday I put on a used 1.5 ohm coil. Drove the Jeep into town on errands about an hour of running time.Nothing failed and it ran perfectly. My only conclusion is the original coil failed,then the new Crane coil failed,and then a used coil failed.Nothing is different other than the coils......It is what it is.....bad luck

[af2]

Well,yesterday I put on a used 1.5 ohm coil. Drove the Jeep into town on errands about an hour of running time.Nothing failed and it ran perfectly. My only conclusion is the original coil failed,then the new Crane coil failed,and then a used coil failed.Nothing is different other than the coils......It is what it is.....bad luck

I hear you on the bad luck...
Glad you got it straight..

[Warpspeed]

From the way you tell this, there appears to be nothing wrong with the setup, just some faulty coils and sheer bad luck.
I guess kind of like getting three punctures on the same day.

Yeah, sometimes life can be like that...

[CharlieB53]

Well,yesterday I put on a used 1.5 ohm coil. Drove the Jeep into town on errands about an hour of running time.Nothing failed and it ran perfectly. My only conclusion is the original coil failed,then the new Crane coil failed,and then a used coil failed.Nothing is different other than the coils......It is what it is.....bad luck

I'm way late to this party, but.....

Good catch on using the fluke vs an analog. I have both and when things just don't seem to add up right I often grab the other meter to verify readings then it becomes clear watching the analog needle swing.

One thing no one else mentioned, on a points ignition there needs to be a ground cable between the movable point plate and the dist housing, otherwise you are depending on sliding metal to metal contact for a good electrical connection. Ain't always the best and when a circuit has an unreliable ground, strange things happen, like amps draw climb, arcing, etc.