Coil Polarity

Reading Roy's post below about coil polarity got me to thinking, then tractorguy pointed out it makes very little difference...

Just what difference does it make? Both terminals connect to the primary coil, so nothing polarity sensitive there. Only difference I see in the diagrams is the secondary grounds to the + end of the primary coil. Still don't see what difference that would make.

Any theories?

(quoted from post at 20:41:28 07/02/15) Reading Roy's post below about coil polarity got me to thinking, then tractorguy pointed out it makes very little difference...

Just what difference does it make? Both terminals connect to the primary coil, so nothing polarity sensitive there. Only difference I see in the diagrams is the secondary grounds to the + end of the primary coil. Still don't see what difference that would make.

Any theories?

Click to expand...

The way I remember the explanation 'back in the day' the reversing of the primary results in reversal of the secondary which results in a less-intense spark since d.c. current 'naturally' flows from positive to negative ....... at least that's the way I remember it :roll:

Same as I posted below:

You say....."it makes very little difference. They will work either way."

YES it will work either way BUT it (correct polarity) DOES MAKE A DIFFERENCE. (If not ever wonder why the coil manufacturer bothers with placing those + and - labels on the coils????? HMMMMMMMMMMM why have those + and - labels anyway lol

If connected at the correct polarity as designed for and labeled you get more spark energy (less wasted heat loss) and the coil operates more efficiently.

Hope this helps

John T Retired Electrical Engineer in Indiana

You state: "current 'naturally' flows from positive to negative"

When I studied electronics of solids and solid state physics (included Quantum Mechanics yukkkkkkkk lol) at Purdue University we learned that electrons, and what's referred to as "Conventional" Current, flow is + to -. HOWEVER when an electron is knocked out of its outer orbit (good conductors like copper have readily available free outer orbit electrons which is why they are indeed good conductors) A HOLE IS CREATED and the holes flow in the opposite direction and that was defined as "Electron" Current. The electrons flow one way while the voids/holes flow in the opposite. Conventional current + to - but Electron Current - to +.

The coil makers have a reason for labeling their coils with + and - you know. I've NEVER seen a coil with no labels or directions that say hook it as you like, it makes NO difference YEAH RIGHT

John T Retired Electrical Engineer

A rep from Impco propane carbs told me that a coil produces 40% less spark if installed with the polarity wrong . Folks were complaining that their engine ran good on gas , but ran poorly when converted to propane. In almost all cases this was the cause . I doubt that is an exact number , but he convinced me to always check ...

Thanks for your post

I didn't think it produced that much less energy if wired at the wrong polarity BUT INDEED IT PRODUCES LESS SPARK ENERGY IF WIRED INCORRECT. (Yes Billy Bob and Bubba, I know it can still "work" if wired wrong BUT NOT AS WELL)

The coil makers have a reason for labeling their coils with + and - you know. I've NEVER seen a coil with no labels or directions that say hook it as you like, it makes NO difference YEAH RIGHT

John T

IMHO, coil/spark polarity makes NO difference in the starting of a cold engine.

But once the engine is running and warms up, the center spark plug electrode is HOTTER than the ground electrode, making it a better emitter of electrons (thermionic emission).

For this to work, the center electrode must be "fired" with a negative-going pulse.

Which is exactly what happens when the coil primary polarity is "correct".

In my experience, having the coil polarity correct CAN help prevent miss-fire under lean conditions, or full-load conditions, when the throttle is wide open and compression pressures are at their max.

On the other hand, many modern engines have a "waste spark" setup that fires two sparkplugs at the same time, one with a negative-going pulse, and the other with a positive-going pulse, and those engines run just fine. (I guess 'cuz they simply have a HOT spark to begin with!)

Also, typical old tractor magnetos fire every other plug with the opposite polarity. I wonder hoe many of my fellow tractor "GURUS" realize that?

John T , I would think that the way the coils are wound would be why polarity IS important. A coil is a Transformer of sorts.

joe

There's a "tractor guru" under my name, but it's not appropriate.

I did not realize that. But given the magnetic armature, it makes sense. Maybe that helps explain why I prefer a battery ignition.

Yes indeed they are wound a certain direction for a reason and yes indeed polarity does make a difference which is why they are designed and manufactured with that + and - post labels.

John T

From SM-2093-(Jul-73)[Service Manual for JD 140 lawn tractor]

Wrong polarity of the coil is not a serious problem, but it can cause damage over a long period of time. A coil that is connected incorrectly will require an extra 4000 to 8000 volts to create a spark.

A coil that is wired correctly will have the same polarity as the battery, figure 12.If the battery has a negative ground, the coil negative terminal should be connected to the breaker point lead. If the battery has a positive ground, the coil's positive terminal should be connected to the breaker point lead.

The wrong coil polarity makes the center electrode of the spark plug have the wrong polarity. This can cause misfiring as voltage requirements increase.

One method of checking polarity is to connect the negative lead of a volt meter to the spark plug terminal. With the engine running, momentarily touch positive voltmeter lead to a ground. The coil polarity is correct if the meter reads up scale.

Another method is to hold the spark plug wire terminal about 1/4 inch from the spark plug. Insert the lead point of a wooden pencil between lead [plug wire "lead", I think they mean-Z.B.] and spark plug,figure 13. Spark should flare and turn orange on the plug side of a pencil lead if polarity is correct. [you'll want some insulation between the pencil and your fingers-Z.B.]

A loss of engine power is also evidenced if coil polarity is reversed.

[End quotation]

Comments? I'm guessing the meter test should be done with a robust analog meter...

Zeke B.

(quoted from post at 19:54:03 07/02/15) Same as I posted below:

You say....."it makes very little difference. They will work either way."

YES it will work either way BUT it (correct polarity) DOES MAKE A DIFFERENCE. (If not ever wonder why the coil manufacturer bothers with placing those + and - labels on the coils????? HMMMMMMMMMMM why have those + and - labels anyway lol

If connected at the correct polarity as designed for and labeled you get more spark energy (less wasted heat loss) and the coil operates more efficiently.

Hope this helps

John T Retired Electrical Engineer in Indiana

Click to expand...

Question: Yes - I understand the reason for following the polarity as the coil was designed for. What I don't understand is why you get more spark energy when connected correctly?

It is my understanding the spark energy is determined by the plug gap. Increasing the gap requires a higher voltage "to jump" resulting in a higher energy spark. In a simlar manner, incorrect polarity requires higher voltage for the spark to jump from the ground eletrode to center electrode. It would seem more acurate to say; incorrect polarity results in a higher energy spark however, mis-fire can result if the coil is not able to deliver the extra voltage.

Not arguing - just trying to understand....

Thanks Ken, see my post above for a more detailed explanation. If at the incorrect polarity and therefore voltage has to rise higher to fire the plug, the coil has to work harder and produce more heat which is wasted I Squared R Energy (heat loss) as opposed to discharging more energy across the plug gap?? Make sense lol

best wishes, I wire mine at the labeled polarity but have no problem if others choose to wire them opposite

John T