Spark plug voltage

[Fred W]

Wow. This thread went into a technical tailspin...

Everything in MCA's posts are correct as is the usual. My prior answer was to the inferred question of (paraphrasing here): Will the new "Coil On Plug" (COP) design result in a spark with more ignition energy? The answer to which is: Yes! Having the COP allows the designers to spec a wider gap plug, which will result in a higher voltage beforer arcing over, which means a bigger spark and better ignition source.

Plus the voltage will always be negative at the plug's center electrode in reference to the grounded side electrode, so the arc will always occur from center to side. The reason this matters is that the center electrode can be made from platinum or iridium, which does not erode as quickly as conventional metals. The side electrodes on plugs are typically not made of such metals.

Fred, you have confused me again. The side electrode is grounded as you said because it is on the part of the plug that is physically touching the engine. The engine is linked to the - or negative side of the battery. If the center electrode or core also has a negative voltage??? I am confused. I don't think the coil can create a more negative voltage, I would expect to see a positive voltage. Educate me please.

The polarity of any voltage is always relative, not absolute. The positive side of the battery is 12V positive only as compared to the negative side. Since the negative battery terminal is directly attached to the bike's chassis (sometimes inaccurately called ground), that means that the positive battery terminal will be 12V positive in reference to the chassis.

[tangent]

The reason I said inaccurately above is that nowhere is the above electrical system referenced to earth ground. The entire motorcycle is insulated from the earth by the rubber tires, so its voltage is "floating" compared to ground. If you stuck a ground rod into the earth and connected a meter between the rod and the positive battery terminal you would read no difference in potential (voltage).

[/tangent]

An ignition coil is really just a high ratio step-up transformer, where a relatively small voltage input pulse on the primary side (~12V) gets stepped up to a high voltage on the secondary (10's of thousands of volts). The transformer provides DC isolation between the primary and secondary so, although one side of the primary may be referenced to chassis common, both sides of the secondary output can be isolated from it (floating). This is the case on the 1st and second gen FJRs. During each ignition pulse, on the two secondary leads one is always positive ~X0,000 volts and the other is negative X0,000 volts, but only in reference to each other.

The only place where a chassis ground reference comes in on the coil secondary is when you screw the spark plugs into the head. If you pulled both spark plug leads off and measured between the plug lead and the chassis, or the plug lead and the positive battery terminal there would be no voltage, even when being pulsed.

So how does this all work when the plug wires are attached? The fact that the side electrodes happen to be screwed into the head which is at chassis ground potential is of no significance to the ignition coil. The head just forms an electrical conductor between the two plugs' side electrodes to complete the secondary circuit. So on an ignition pulse the current will flow from the negative coil secondary terminal to the center electrode of the first plug, arc to the side electrode, through the head to the side electrode of the 2nd plug, then arc from the side to the center of the second plug, and finally back to the positive side of the ignition coil. It doesn't give a damn what the voltage between the battery and chassis ground is, except in as much as that will be involved in creating the input pulse to the coil in the first place.

I don't know if that was helpful or made things even more confusing. Hopefully the former.

It shouldn't make much difference if a platinum plug is firing from center to side, or vice versa. Both the center and side electrode have a small pad coated with platinum that keep them from eroding for a long time. That is, unless you gap them with a metal gapper and scrape the platinum off, then they don't last nearly as long.

Au contraire, mon amie. Some, not all, platinum plugs are of the "double platinum" design you showed. My old V8 Ford Exploder required them because it too was of a wasted spark design which results in half of the plugs firing "backwards", and the designers wanted to spec 100k mile plug changes.

But the stock NGK CR8E plugs on the FJR are not platinum plugs at all. And the CR8EIX iridium plugs (iridium is just a high faluten platinum) that many FJR owners are wont to use are only iridium on the center electrodes. This seems to be the case with all of the iridium plugs that I can find.

I've made that point before in the past, that iridium plug users are only getting the iridium benefit on half of their plugs, and (joking) that they should rotate their plugs at regular intervals.

 

[ionbeam]

... the gas within the gap ionises,...the rise-time up to the ionisation voltage and allows sufficient voltage with a lower coil primary voltage,,,

I just love it when he talks like this :wubsmiley: (only here in the US we uze the Z, ionization)

 

[Redfish Hunter]

OK Fred, I won't lie. I had to read and re-read to fully get it. IF I really got it.

The center (core) voltage of the spark plug could be either positive or negative and still create a spark because of the tremendous multi-thousand volt difference in potential between the core and the electrode.

The one thing I am not sure I agree with is your statement that the positive terminal of my battery to a ground rod would read 0.0 volts. I don't think that is correct. If the battery has a stored energy of 12+volts and I test it to an earth ground I would expect to see a difference of potential equal to the charge of the battery. I understand that the 12+ volts of a battery is the difference between the positive and negative terminals, not the earth ground. I would still expect to see a difference of potential. I am almost willing to carry my lazy behind out in the cold to test this. Almost.

Thank you for taking the time to give such an in depth and well thought out response. I really appreciate it. I think you are secretly just showing off though! I am OK with that though. If I were that smart I would want everyone to know it also.

 

[ionbeam]

...The center (core) voltage of the spark plug could be either positive or negative and still create a spark because of the tremendous multi-thousand volt difference in potential between the core and the electrode.

...statement that the positive terminal of my battery to a ground rod would read 0.0 volts. I don't think that is correct...

Thank you for taking the time to give such an in depth and well thought out response...

True that anytime there is a huge potential difference that an arc will jump the gap, regardless of polarity. It may jump from the center electrode to ground or from ground tab to the center electrode if the center electrode is negative enough, like negative 5 kilo-volts. It happens in 2 cylinders of our FJRs, all the time.

Fred is correct about there being different ground references. Reading between the battery and a ground rod you will not measure 12 volts, you *may* read some floating voltage but it will be floating noise and not a real reading. This often befuddles rookie electronic techs when their O'scopes give them bizarre readings because they have different ground references.

Ya Fred, thanks for the the well though out response!

 

[mcatrophy]

... the gas within the gap ionises,...the rise-time up to the ionisation voltage and allows sufficient voltage with a lower coil primary voltage,,,

I just love it when he talks like this :wubsmiley: (only here in the US we uze the Z, ionization)

My English English spell checker throws a hizzy fit if I put "ionization"

.

 

[Fred W]

The one thing I am not sure I agree with is your statement that the positive terminal of my battery to a ground rod would read 0.0 volts. I don't think that is correct. If the battery has a stored energy of 12+volts and I test it to an earth ground I would expect to see a difference of potential equal to the charge of the battery. I understand that the 12+ volts of a battery is the difference between the positive and negative terminals, not the earth ground. I would still expect to see a difference of potential. I am almost willing to carry my lazy behind out in the cold to test this. Almost.

Nope. It's real, man. Like I said, voltage is only voltage in reference to something else. In most electrical applications we use earth ground as a reference. Since most things in the world are already grounded, this makes voltage fairly universally in reference to ground. That's why a bird can land on a high voltage power line and not get zapped. They aren't touching ground (or another phase wire), so there is no reference for the voltage. It could be a 30 zillion volt potential to ground, but if you are adequately insulated from ground you could grab hold of it with no problem.

 

[ionbeam]

Continuing the minor thread hijack...

... the gas within the gap ionises,...the rise-time up to the ionisation voltage and allows sufficient voltage with a lower coil primary voltage,,,

I just love it when he talks like this :wubsmiley: (only here in the US we uze the Z, ionization)

My English English spell checker throws a hizzy fit if I put "ionization"

.

That's because your computer speaks proper Queen's English. My computer speaks 'Merican English.

 

[johnny80s]

You guys need to ride more.

 

[Redfish Hunter]

The one thing I am not sure I agree with is your statement that the positive terminal of my battery to a ground rod would read 0.0 volts. I don't think that is correct. If the battery has a stored energy of 12+volts and I test it to an earth ground I would expect to see a difference of potential equal to the charge of the battery. I understand that the 12+ volts of a battery is the difference between the positive and negative terminals, not the earth ground. I would still expect to see a difference of potential. I am almost willing to carry my lazy behind out in the cold to test this. Almost.

Nope. It's real, man. Like I said, voltage is only voltage in reference to something else. In most electrical applications we use earth ground as a reference. Since most things in the world are already grounded, this makes voltage fairly universally in reference to ground. That's why a bird can land on a high voltage power line and not get zapped. They aren't touching ground (or another phase wire), so there is no reference for the voltage. It could be a 30 zillion volt potential to ground, but if you are adequately insulated from ground you could grab hold of it with no problem.

OK Fred, I am just as hard headed as you are. Not as smart maybe...

I understand fully about the bird on the wire. As long as he is only touching that wire, there is no difference in potential, he is safe. But, that is AC voltage, not the DC we are discussing here.

According to what you are saying a 12 volt battery has no difference in potential to an earth ground. I disagree. If a battery has a charge, there is energy stored within. That energy can and will discharge from that battery if you were to run a wire from the positive terminal to an earth ground. This is because there is in fact a difference in potential. Don't believe me? Go hook your jumper cables to a battery and the ground rod for your house.

I work with voltages ranging from the millivoltage produced by a thermocouple all the way up to 13,800 volts AC. I am most frequently involved with 24 volt DC systems and I have no problem using an earth ground to troubleshoot. I thought about this for a while and realized that those systems are not battery powered but are instead powered by a DC power supply and are therefore earth grounded. Given the respect I have for your knowledge, I had to know. Therefore I fired up the Yamaha Big Bear, rode it to the side of the house and hooked my Fluke from the positive of the battery to the ground wire running up the wall. I chose not to use an outside receptacle because of bonded neutral issues. With the 4-wheeler running, I read 14.55 volts positive from the battery to an earth ground. Please know this is a reflection of my respect for you, not an effort to prove you are incorrect. But, I think you are.

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[Redfish Hunter]

You guys need to ride more.

You know, I absolutely agree with you. And the weather here was so nice today. But I spent my day with the wife and son. And thinking of ways to outsmart FredW.

 

[odot]

You guys are reminding me of the smart kid pushing in on the "out" door.

 

[Fred W]

The one thing I am not sure I agree with is your statement that the positive terminal of my battery to a ground rod would read 0.0 volts. I don't think that is correct. If the battery has a stored energy of 12+volts and I test it to an earth ground I would expect to see a difference of potential equal to the charge of the battery. I understand that the 12+ volts of a battery is the difference between the positive and negative terminals, not the earth ground. I would still expect to see a difference of potential. I am almost willing to carry my lazy behind out in the cold to test this. Almost.

Nope. It's real, man. Like I said, voltage is only voltage in reference to something else. In most electrical applications we use earth ground as a reference. Since most things in the world are already grounded, this makes voltage fairly universally in reference to ground. That's why a bird can land on a high voltage power line and not get zapped. They aren't touching ground (or another phase wire), so there is no reference for the voltage. It could be a 30 zillion volt potential to ground, but if you are adequately insulated from ground you could grab hold of it with no problem.

OK Fred, I am just as hard headed as you are. Not as smart maybe...

I understand fully about the bird on the wire. As long as he is only touching that wire, there is no difference in potential, he is safe. But, that is AC voltage, not the DC we are discussing here.

According to what you are saying a 12 volt battery has no difference in potential to an earth ground. I disagree. If a battery has a charge, there is energy stored within. That energy can and will discharge from that battery if you were to run a wire from the positive terminal to an earth ground. This is because there is in fact a difference in potential. Don't believe me? Go hook your jumper cables to a battery and the ground rod for your house.

I work with voltages ranging from the millivoltage produced by a thermocouple all the way up to 13,800 volts AC. I am most frequently involved with 24 volt DC systems and I have no problem using an earth ground to troubleshoot. I thought about this for a while and realized that those systems are not battery powered but are instead powered by a DC power supply and are therefore earth grounded. Given the respect I have for your knowledge, I had to know. Therefore I fired up the Yamaha Big Bear, rode it to the side of the house and hooked my Fluke from the positive of the battery to the ground wire running up the wall. I chose not to use an outside receptacle because of bonded neutral issues. With the 4-wheeler running, I read 14.55 volts positive from the battery to an earth ground. Please know this is a reflection of my respect for you, not an effort to prove you are incorrect. But, I think you are.

">

Wow. You really have stumped me here. That is just not how it works.

The only way that your meter should have registered the battery voltage is if the chassis of the bike was some how grounded to earth.

What is really perplexing is how you managed to get a ground reference from a plastic (non-conductive) conduit. Perhaps you made a measurement with your DVM and then forgot to clear the "hold" feature? Or maybe the black meter lead shown disappearing behind the camo bodywork doesn't really go to the plastic conduit, but to the frame of the bike?

And FWIW, it doesn't make a bit of difference if we are talking AC or DC. AC is just DC that is constantly changing and alternating polarity. Voltage is voltage. And there is no voltage of any kind without a reference.

I must admit this thread is taking on all of the "character" of the "An airplane can take off from a conveyor belt" thread.

 

[ionbeam]

Wow. You really have stumped me here. That is just not how it works. The only way that your meter should have registered the battery voltage is if the chassis of the bike was some how grounded to earth...

Well, I have to continue to back Fred on this one, he is correct. If you are really measuring battery voltage to either the PVC or brick wall there is something else going on. There is a large amount of carbon in tires and carbon is not a pure insulator, it is the stuff that resistors are made from but unless water or something else is present it shouldn't allow you to read voltage that way.

Electrical circuits have to have a pathway between the positive post and the negative post for the electrons to flow WTF am I doing.... Err, um, I have to vote with Fred on this.

 

[Redfish Hunter]

Fred, the lead is NOT hooked to the PVC conduit, it is attached to the #4 solid copper wire running up the wall behind the conduit. I could not get the flashlight, the 4-wheeler, the meter and the camera all lined up. Explaining to my wife that I needed her to leave the fireplace and go out in the cold to take pic was counter productive. Please tell me you did not think I was dumb enough to hook to a PVC conduit. :dribble:

I think that this is how it works. You have voltage at the battery. You have no voltage at the earth ground. That makes a difference of potential. If you are still worried about it, carry a battery over to a receptacle and put your voltmeter on it.

If we got this far off on spark plug voltage, I don't want to know anything about the "airplane taking a dump on a conveyor belt thread."

 

[Fred W]

Nope. It doesn't work that way. Not at all.

My 38 years of electrical & electronics experience says you can't do that. If you change all of the rules on me now, well I may as well switch professions to something else. Maybe knitting humorous cummerbunds, or some cutting edge basket-weaving would be apropos. :blink:

PS - A quick search shows the "airplanes and conveyor belts" thread didn' t make it through the last server -reformat, so you will be spared that NEPRT. Either that or my Google search skillz suck. Many an old timer still references that thread now and again. It was pretty classic. People arguing against physics is always entertaining.

 

[ionbeam]

I started and canceled several replies. I not going to bother to present my electrical/electronic credentials 'cause it probably won't matter. When dealing with the public sometimes ya just have to know when to pick a fight and when it's just not worth it. It's hard to fill a glass when it has a lid on.

So, is there a germane take-away from this tangent thread that will benefit the Forum and add useful motorcycle electrical system knowledge? If not, stick a fork in it and go back to worrying about the big things in life like the change in spark plug gap.

It won't take long for this path to lead to that big red X and a lock on the thread.

 

[Fred W]

So.. how do you feel about humorous cummerbunds? Once you get past all the humor of course.

 

[RadioHowie]

I can't wait to see how this one turns out....

mcatrophy is gathering up ammo as we speak, redfish hunter JUST discovered the "hold" feature on his DVM, ionbeam is looking for an earth-ground on his house to test RH's theory, and FredW just cracked the seal on a bottle of Maker's Mark.

Personally, I'm with Fred on the Maker's Mark!

 

[Fred W]

Hah!! Shows what you know.

It's martinis tonight. Only made with Gordons, since it's dirt cheap at the NHSLS and way more gooder than all the hoitey toitey boutique stuff they bend you over for.

But clearly you are on the right track, Howie. The Bourbon Manhattans start tomorrow in early preparation for the Meleagris gustatory festivities. It's just like "no white shoes after Labor Day"; No more Martinis after Turkey Day here!

I mean. doesn't everyone observe these traditions?

:drinks:

 

[Redfish Hunter]

I started and canceled several replies. I not going to bother to present my electrical/electronic credentials 'cause it probably won't matter. When dealing with the public sometimes ya just have to know when to pick a fight and when it's just not worth it. It's hard to fill a glass when it has a lid on.

It won't take long for this path to lead to that big red X and a lock on the thread.

Well, up to this point I was trying to find out the truth. I had enough respect for FredW and for you to go out and do a very simple experiment. Do you have enough respect for me to even check to see if I am right or not? Or are you so convinced that your electrical theory is superior to the real world truth?

If my glass had a lid on it, I would not have bothered to go hook my meter to a ground wire and a battery. Apparently your glass has the lid on it.