6v Coil - Pos or Neg Ground?

[Don Boshara #594]

I have a Delco 6v coil numbered 1115401. The post that connects to the side of the distributor is marked negative. Is this a neg. or pos. ground coil?

[Dave Shepherd]

Neg. ground.

[Wayne Womble 12210]

You should be able to use it either way.  For positive ground, just connect the positive post to the distributor.

[Dave Shepherd]

Reversed polarity will reduce the coils out put, under max load.

[Don Boshara #594]

Thanks for the replies. I was afraid it would be a negative ground.

[Wayne Womble 12210]

Reversed polarity will reduce the coils out put, under max load.

I dont know if his coil is model specific or not, but typical GM coils of the 50s to early 70s will operate just fine in either direction. I have run 12V negative ground coils on 6V positive ground systems with no problems what so ever, and the spark is plenty hot. 

[Doug Houston #2257]

The intensity of the spark will be the same, regardless of whether the coil is connected positive or negative ground. As  far as the distributor breaker points and condenser being proper, you'll get a good hot spark. No question there.

HOWEVER, the comprssed charge in the cylinder does care what the polarity of the spark at the plug center terminal is. You have to have that polarity NEGATIVE, in order for the cylinder to fire properly, and efficiently. This is something that was established many years before any of us got our first pat on the butt, and it hasn't changed yet, and never will.

I'm sure that the reason for this phenomenon is known, but I've never seen it (nor have ever tried to find out).  I have tried a coil of wrong polarity on a couple cars, and they run poorly with that hookup.

If there is still doubt about this, I suggest running a combustion efficiency test on the car, analyzing the exhaust gases. I'd expect a very different result from one coil polarity to the other.

[Wayne Womble 12210]

But Doug, The coil doesnt care.  The spark plug wants to see a negative pulse at the center electrode.  If that pulse is not negative, you just change the primary wires around. The theory has to do with ionizing the mixture to start the spark propagation. It is easier to jump form the hot center to the cooler tip with a negative charge.  It will run either way, but it looses about 15% under heavy load if hooked up wrong. But, with the compression ratios of most 6V cars, it really wont make much difference.

[Glen]

Guys, check the attached drawing.  Normally when the points are closed battery current flows through the primary side of the coil building up the magnetic field.  When the points open the current stops and the magnetic field collapses creating a high voltage pulse in the secondary side of the coil.  Meanwhile the primary windings and the capacitor oscillate boosting the secondary output and the spark.

If you reverse the polarity of the battery you also reverse the polarity at the spark plug.  Otherwise the operation is normal.  Except the spark does not ignite the fuel as well. 

If you also reverse the coil leads, you then exchange the battery and points in the circuit.  How does that work? 

Glen

[Wayne Womble 12210]

Glen, Someone went to great lengths to confuse the issue didnt they?  In the upper set of drawings the far right drawing is the same circuit as the far left, except the points are located on the opposite leg. This circuit would act the same as the first, and be the same polarity.

[Jose Gomez]

Folks,

Not to add more wood to the fire..!

The basic theory of the ignition coil as an induction coil (aka spark coil) is the interruption (make and brake) of the DC voltage at the primary creates an induction at the secondary winding, also called electromagnetic induction.

The voltage at the secondary is a pulsating voltage that goes from zero to positive and from zero to negative mimicking an AC voltage. During the duration of the contacts “brake” and “make” at the primary, the storage cycle, the capacitor/condenser charge/discharged, etc the induced AC voltage at the “output” (secondary) will have a higher positive voltage spikes and a lower negative voltage spikes. This concept depends on how the coil primary windings are reference to the secondary windings to induce the opposite potential at the secondary.

If the coil is connected accordingly the spark will fire at the higher end of the pulse, and thus utilizing the higher end of the spike, and thus maximum voltage. If the coil is reversed the spark would fire at the lower end of the spike which would be at a lower voltage.

So just as a basic example, the spark could have 20K volts with the correct connections, or 15K volts or less with the incorrect setup.

Traditionally the” neg” side of the coil represents the breaker points or distributor side regardless if the system is positive or negative ground. The coil is design and built accordingly to provide the maximum output voltage with the correct connections.   

[Dave Shepherd]

Folks,

Not to add more wood to the fire..!

The basic theory of the ignition coil as an induction coil (aka spark coil) is the interruption (make and brake) of the DC voltage at the primary creates an induction at the secondary winding, also called electromagnetic induction.

The voltage at the secondary is a pulsating voltage that goes from zero to positive and from zero to negative mimicking an AC voltage. During the duration of the contacts “brake” and “make” at the primary, the storage cycle, the capacitor/condenser charge/discharged, etc the induced AC voltage at the “output” (secondary) will have a higher positive voltage spikes and a lower negative voltage spikes. This concept depends on how the coil primary windings are reference to the secondary windings to induce the opposite potential at the secondary.

If the coil is connected accordingly the spark will fire at the higher end of the pulse, and thus utilizing the higher end of the spike, and thus maximum voltage. If the coil is reversed the spark would fire at the lower end of the spike which would be at a lower voltage.

So just as a basic example, the spark could have 20K volts with the correct connections, or 15K volts or less with the incorrect setup.

Traditionally the” neg” side of the coil represents the breaker points or distributor side regardless if the system is positive or negative ground. The coil is design and built accordingly to provide the maximum output voltage with the correct connections.   

Hmm sounds familiar, but more thoroughly explained, if you put the car on an ocilloscope and check sec. voltage at the plug, disconnect a plug wire and look at the max voltage with the coil installed properly vs reversed as stated nicely above, the voltages are about 25% less.

[Glen]

Glen, Someone went to great lengths to confuse the issue didnt they?  In the upper set of drawings the far right drawing is the same circuit as the far left, except the points are located on the opposite leg. This circuit would act the same as the first, and be the same polarity.

Maybe the problem with the drawing is it uses ground symbols instead of showing the current path through ground with a line like the other conductors. 

The return path for the current that flows through the spark plug is designed to go through ground then through the battery to the secondary of the coil.  If you reverse the coil leads that puts the points and capacitor in the return path with the battery and primary coil in parallel to the distributor points.  There is a potential for some of the spark to be wasted at the distributor points.  If there is no arching at the points then you still have the coil primary in the return path.  There is no way the right diagram is the same as the left one. 

Glen

[TJ Hopland]

So the short answer is that as long as you have the + to + and - to - (on a + ground car that would mean the points are +) you will get the maximum performance from the coil ?

[Wayne Womble 12210]

Maybe the problem with the drawing is it uses ground symbols instead of showing the current path through ground with a line like the other conductors. 

The return path for the current that flows through the spark plug is designed to go through ground then through the battery to the secondary of the coil.  If you reverse the coil leads that puts the points and capacitor in the return path with the battery and primary coil in parallel to the distributor points.  There is a potential for some of the spark to be wasted at the distributor points.  If there is no arching at the points then you still have the coil primary in the return path.  There is no way the right diagram is the same as the left one. 

Glen

Glen,  If you connect the grounds and close the points, you will see that the potential is in the same order on the left and the right diagrams.   Thats what I was saying. You are correct that the ground on the plug is reversed.          

[Jose Gomez]

So the short answer is that as long as you have the + to + and - to - (on a + ground car that would mean the points are +) you will get the maximum performance from the coil ?

TJ

Maybe the correct way would be, as long as you connect the "-" to the distributor and the "+" to the ignition you will get the maximum performance on the coil, assuming the coil is the correct one for the type and make of the vehicle.

[Glen]

Glen,  If you connect the grounds and close the points, you will see that the potential is in the same order on the left and the right diagrams.   Thats what I was saying. You are correct that the ground on the plug is reversed.          

I will agree current flow through the primary is the same in both diagrams.  But the discharge phase is the important part and the circuitry is wrong for that. 

The difference between coils used on positive ground and negative ground systems is the primary or secondary winding is wound in the opposite direction. 

Glen

[TJ Hopland]

Maybe the correct way would be, as long as you connect the "-" to the distributor and the "+" to the ignition you will get the maximum performance on the coil, assuming the coil is the correct one for the type and make of the vehicle.

If that is how they marked them then I can see why its so dang confusing.  I can grasp them labeling the coil that way because that is the polarity of the discharge but if they were going to be that picky about the terms then why did they call a capacitor a condenser?  It would have made more sense to mark the coil with a B for battery or I for ignition and a D for distributor.

[Jose Gomez]

If that is how they marked them then I can see why its so dang confusing.  I can grasp them labeling the coil that way because that is the polarity of the discharge but if they were going to be that picky about the terms then why did they call a capacitor a condenser?  It would have made more sense to mark the coil with a B for battery or I for ignition and a D for distributor.

TJ,

I totally agree with you…!
 
Since the positive ground was a common setup for 6V or 12V, it could be assumed that everyone knew then the proper way to connect the coils since it was the standard.  But after industry changes and 60 plus years things tend to get lost if they are not properly documented. 

That is why a repair manual is so critical on these cars to decipher the correct setup.

When the auto industry transition to the standard negative ground, it became obvious the “negative” is always ground, so distributor “breaker points”=ground, ground=“negative” then coil “negative” goes to distributor.

One thing the British cars have is they stenciled “SW” and “CB” on the old positive coils to avoid confusion, “SW”=switch, “CB”=contact breaker. 

I have been working on positive and negative ground equipment for 30 plus years, and even today every time I switch between them I have to <Ctrl><Alt><Del> my brain..! 

[TJ Hopland]

So pre WW2 in the USA all coils were marked + and - and everyone knew that - went to the distributor?   

When the + ground and 12V stuff came out were those coils clearly marked as such or was it just a manufacturer part number?