Positive and Negative ground spark output..

[BUBBAS IGNITION]

Lots of stuff happening at the shop lately as we have been more than a little busy. I have some good people helping me catch up and we all hear the shop sounds every day , some are pleasing others are not! Even my office manager complains if the sound we make with testers is off from time to time!!
I noticed last week while final testing a distributor that not only was the sound different but the spark display on the spark load tester was different as well. This was a customers unit and it just happened to be positive ground.
Customer had supplied his own ignition coil for testing and it was a new aftermarket coil with proper resistance etc.
Shot a couple videos for comparsion today and this ought to open up some discussion ( or at least i think it should). One is (first one) is negative ground and the other one is positive . I used the same coil for each example and realize i need to test with the proper coils and will later. The way i tested is often the way each of you are in fact running your cars.

http://s103.photobucket.com/albums/m...t=100_7442.mp4


http://s103.photobucket.com/albums/m...t=100_7443.mp4

Now its my opinion ( may or may not be correct) that in a negative ground system ( using electron theory) the spark jumps from the outside to the electrode . In the positive ground the spark jumps from the center to the outside .
Also spark always goes to the coolest spot each time ..

[Ken Crans]

Looks like the 12 volt is always at the cool spot with a fine spark compared to the 6 volt with a nice solid blue. How about a spark plug with a triangle electrode set up for a real hot spark in the chamber? Ken

[Frank Miller]

Try this. To test polarity put a pencil lead between the high tension lead and the spark plug. If there is a flare from the pencil to the spark plug, the polarity is correct. If the flare is between the lead wire and the pencil the polarity is wrong. Got that off another site but I have heard it done to make sure coil connections are correct.

[Jack E/NJ]

Frank Miller>>>If there is a flare from the pencil to the spark plug, the polarity is correct. If the flare is between the lead wire and the pencil the polarity is wrong.>>>

What's correct for negative ground cars might be wrong for positive ground cars. Or vice versa. 8^)

Jack E/NJ

[Frank Miller]

I think this just wants to route the electrons from the top of the plug across the gap to ground, whether it be positive or negative.

[40 Deluxe]

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A lot of modern vehicles use a "waste spark" system where one coil fires two cylinders (one plug is fired on the power stroke and the other fires on the exhaust stroke, thus it is "wasted"). There are two high voltage plug wires on each coil. When the computer fires that coil the high voltage travels out one plug wire, jumps the plug gap, travels through the head/block to the companion cylinder, jumps that gap and travels back to the coil to complete the circuit (the secondary windings are not grounded to the coil case; one of the plug wires is the "ground". Ford saved some money by using single platinum plugs; the plug that had the spark jumping from the center electrode to ground had only the side electrode platinum plated and the plug that had the spark jumping to the center electrode only had the center electrode tip platinum plated (double platinums were recommeded for replacement to prevent mixups). So these systems always have half the plugs firing "backwards" but coil output is high enough to prevent misfires.

[Mike51Merc]

Now I may be wrong, and I can't explain this in terms of electrical theory, but my understanding is that primary (battery) polarity is separate from secondary (ignition spark) polarity. My best guess is because of the induction that creates the secondary voltage.
In other words, battery polarity only determines how you wire the primary coil. If the primary coil is properly wired, then the spark from the secondary will always jump from the center electrode to the side. If you reverse the primary wiring, the spark goes from outside to center.

After thinking more about this: The primary coil polarity probably controls the direction of the magnetic field collapse, thereby determining the polarity of the secondary field. For example, if the primary coil field collapses directionally from top to bottom as opposed to bottom to top, it may (best guess) change the polarity of the secondary charge.

[jimTN]

Ouch on the late Fords, I am about 25K away from a plug job on my 2002 Bird and understand it is a real pain just to get the plugs in and out. Bubba, what breed of machines are you using for the early Ford dist.

[Juergen]

It doesn't matter if it is positive ground or negative ground, for proper polarity, the spark plug is negative with respect to the engine ground. That is why the pencil test is used on either system to determine the proper polarity. If the test fails, you have the wrong type coil which are would differently for positive or negative grounded systems.

Remember the coil is just a transformer with the primary wire in and the other end grounded. The secondary also has two wires with the positive end grounded so that the voltage out of the secondary is negative with respect to ground. In reality there is only one wire with it grounded between the two ends and the turn of the windings determining polarity. Which is why you can't interchange 6 volt Chevy and Ford coils.

[rotorwrench]

You can buy a polarity checker that plugs in between the high tension lead & the coil and has a little window to watch the spark and which way it goes. In the old days they always marked one little primary terminal bat and other one dis. On later coils and after market coils they were + & - and many were not marked at all so you just had to wire it up & check it to see polarity with one of those little checker tools. You can still get them from a few of the parts suppliers.

Kerby

[BUBBAS IGNITION]

Some good discussion and i couldnt disagree with any of it so far. Makes ya think doesnt it.
A couple notes for further thought.

There are two types of coils concerning the secoundary windings.
1-A tapped transformer where the secoundary is tapped to the actual primary and the other end goes to the output. Issue here is that the inductive kick is fed back thru the primary windings. No problem on the older non electronic cars as a 300-400 volt kick wouldnt hurt anything.
2-Isolated transformer where the secoundary winding is not hooked (or tapped) to the primary and usually the secondary winding is grounded somewhere. Lessens the primary inductive kick for electronics but raises holey hell if the ground is left loose of not grounded.

Someone mentioned the difference between Ford and Chevy coils . The difference is the positioning of the primary and secondary windings . The chevrolet unit has the secondary inside the primary and the Ford has the primary inside the secondary. Makes some differences in operation and a huge difference if you are making test equipment to check like a lab scope etc . The coils would have two very different signatures....

[BUBBAS IGNITION]

Originally Posted by jimTN

Ouch on the late Fords, I am about 25K away from a plug job on my 2002 Bird and understand it is a real pain just to get the plugs in and out. Bubba, what breed of machines are you using for the early Ford dist.

I have a couple Allen Syncographs ( the caddy of all machines) and a couple
Sun 500s and a couple adapters for the flathead....

[BillM]

Here is a link to a web page with a good explanation of coil polarity and why the spark plug likes to see a negative voltage:
http://mgaguru.com/mgtech/ignition/ig104.htm