Spark Coil Polarity

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Guest

Spark Coil Polarity

#1

Post by Guest » Mon Nov 26, 2007 11:09 am

Hello......I'am about to replace my 6v coil on my Panhead. The replacement coil wiring instruction appears to show the connections to timer and ign. feed the opposite way round to stock...but the wiring diagram is not that clear.....so, is the polarity connection important ?...and if so, is there a way of checking which is the correct way. Thanks all.



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#2

Post by King » Mon Nov 26, 2007 3:32 pm

Guest

It really doesn't make any difference which wire goes to which post. For convenience I run the wire from the timer to the left post (as viewed facing the coil) and the hot wire to the right one.

King

Guest

#3

Post by Guest » Mon Nov 26, 2007 4:25 pm

Thanks guys....good news, as it won't do any damage if I wire it the wrong way !...In my search for an answer, I found that there is a lot of info relating to the polarity of the spark cable itself, which is influenced by the way the coil is wired..i.e. it is best to have it negative polarity. I found this info. for anyone interested .... . http://www.chicagolandmgclub.com/techti ... l/574.html

It may help on those cold, damp mornings !

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#4

Post by King » Tue Nov 27, 2007 6:37 pm

Guest

Very interesting discussion, thanks for posting it. I'll have to check it out. Anything one can do to get more spark in the old Pan is worth doing.

King

Guest

#5

Post by Guest » Wed Nov 28, 2007 1:42 pm

Wiring the coil the 'opposite' way to the design causes the tip electrode to wear away rather than the centre electrode, this happens more rapidly than the normal wear, reducing spark plug life.

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#6

Post by Panacea » Fri Nov 30, 2007 3:55 am

Guest, The link you posted describes a test useing a voltmeter connected to the plug and grounded to the head and gives a result to look for when cranking the motor. They describe testing a vehicle with a pos. ground system, so should we be looking for the opposite result? (negative value). Thanks! Mike

Guest

#7

Post by Guest » Fri Nov 30, 2007 9:10 am

Hi Mike.....its in the detail ....You test for correct polarity by hooking up a voltmeter with the negative lead to the plug terminal (which should be of negative polarity) and the positive lead to the block (which should be of positive polarity). Set the meter on the highest volt range. These connections remain the same whether you have a positive ground or negative ground electrical system. The secondary winding's polarity which we are testing is determined by the combined hookup of the battery and primary windings, so it may or may not match the battery's ground.

I shall be checking my set up later.

Guest

#8

Post by Guest » Fri Nov 30, 2007 4:49 pm

OK....I just tested my coil and the result was obvious really !
Changing the polarity of the coil does change the polarity of the spark leads....however, because the two leads are part of the same circuit, the spark effectively travels from the coil, down one lead, through the plug to the motor, then back up the other lead....so one plug electrode will always be the opposite polarity to the other.

For info, when I checked my coil as wired as per the markings on the spark coil body, the front spark plug centre electrode is negative.

So it's true that whichever way it is connected does not matter, as I was told at the beginning (thanks King), but it is also nice to understand the science of why it is true.
Oh well, it was worth a try I suppose.

Of course....did the factory think it desirable to have the front spark lead as negative ?.. :?
Rich.

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#9

Post by ozwick86 » Fri Nov 30, 2007 5:07 pm

What will happen when the Earth's poles reverse?

:roll:

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#10

Post by FlatHeadSix » Fri Nov 30, 2007 10:20 pm

Rich,

WHAT???, now I'm confused.

On a dual-fire wasted-spark coil both the leads should discharge simultaneously and arc across the plug gaps to the engine block at exactly the same time. How or why would the charge find its way back up the opposite lead and reverse its polarity?

And, front or back should not make any difference either, you can connect the spark plug leads either way and it doesn't change a thing.

Ozwick,

I heard a psychic has predicted that the earth's poles will reverse at precisely the same time that Hillary is elected president. All magnetic compasses will then point south and all the British people will have to move their steering wheels to the left side of the vehicle. I'm not sure why they will have to move the steering wheels but I believe the other stuff could actually happen and I, for one, am scared.

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#11

Post by john HD » Fri Nov 30, 2007 11:22 pm

now lets see if one of you einstiens can tell me if the coil has an additive or subractive polarity!

john :D

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#12

Post by FlatHeadSix » Sat Dec 01, 2007 2:20 am

John, don't get me started, you know how long I can stand on a soap box!, but since you asked......

The additive and subtractive properties really only apply to big transformers when you start hooking them up in parallel. If you don't connect them correctly (line the insulators up the right way) they will induce current which offsets the intended direction of flow; subtractive.

But, guess what, a motorcycle coil is essentially a transformer and Faraday's Law of Induction applies here too. Its a step-up transformer, the high voltage (20,000 volts or higher) is produced when the magnetic field produced by the primary circuit collapses (the points open) and makes the park jump across the plug gap. Transformers are really the first "solid state" electronic devices, they produce high potential electricity without any moving parts. The motion is just magnetic fields building and collapsing next to each other.

I don't know if you would consider it additive or subractive but one of the bad side effects in motorcycle ignitions is the momentary voltage spike induced in the primary circuit when the plug fires and the magnetic field in the secondary circuit collapses. I guess this is additive because it causes the voltage to jump higher than battery voltage and try to go backwards through the points. This is why there is a condensor or capacitor in the ignition circuit, it soaks up the voltage surge after a plug fires and prevents a secondary spark from trying to jump the points. If you have no condensor, or a bad condensor, the points will quickly weld themselves together.

Back to the original topic, I'm definitely going to hook up the analog voltmeter to a few bikes in the morning and check for polarity at the plugs. The original advice is still correct, it won't matter how you hook the coil up, it works any way you connect it and it won't damage anything. The real question is if it will work better if you connect it so that the center electrode of the plug is negative. Theoretically it should. Direct current, by definition, only, and always, flows in one direction. The electron direction of travel is from negative to positive, so if you put the higher potential on the negative side its only natural that it wants to jump across the plug gap to complete the circuit.

I always wondered why none of those OEM 6 volt coil terminals were ever marked. There is no + or - on the primary connections and no "front" or "back" marked on the plug wire towers. Maybe because it really does not make any difference, it works the same no matter how you hook it up.

John, you're the professional here, what's your take on the whole polarity issue?

motormouth mike

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#13

Post by john HD » Sat Dec 01, 2007 3:56 am

my take?

i haven't seen anything in this tread that is incorrect so far!

i wonder if someone would apply an AC voltage accross the coil as pictured in this test http://www.kilowattclassroom.com/Archive/TransfPol.pdf page two.

will you get a higher or lower voltage? it would be interesting to find out! if it turns out to be an additive transformer one could assume the right hand low voltage terminal on a harley coil would be the negative one.

now one just needs to find a low voltage AC source, doorbell transformer perhaps...

john

Guest

#14

Post by Guest » Sat Dec 01, 2007 5:46 pm

John HD....its good that I've got it right so-far. In my simple mind, I have an understanding of how it works. I don't claim to understand it any more than what I've found !....

Rich (GB)

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Re: Spark Coil Polarity

#15

Post by DeltaMike » Tue Aug 24, 2010 10:47 am

Anyone any idea why Bruce Palmer 111, in 'How to Restore Your Harley Gavidson', says the plug lead to the front cylinder must connect to the rear HT outlet on the coil please?
Page 401 in my book.

BUT only on original coils.

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