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Someone educate me about resistor and non resistor spark plug caps


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  #1  
Old 11-05-2016, 12:21:27 AM
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Default Someone educate me about resistor and non resistor spark plug caps

Like my title question asks. What is the advantage, from an ignition standpoint, is having a resistor spark plug cap? I see them for motorcycles and such and know that it isn't for radio noise suppression on a motorcycle. Does a resistor cap give you a hotter spark? Does using a resistor cap work with both a DC battery type ignition and an AC magneto type?
Here is what I am looking at:
http://www.ebay.com/itm/162130191196...%3AMEBIDX%3AIT
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Old 11-05-2016, 02:03:03 AM
Thaumaturge Thaumaturge is offline
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Default Re: Someone educate me about resistor and non resistor spark plug caps

A resistor will not give you a hotter spark. By nature it limits current in circuit and drops the voltage to the plug. A lower voltage spark is cooler. But limiting current to plug will also limit current in coil or magneto. Thereby cushioning effect of spark on coil or magneto. (Current in series circuit same at any point.) Such effect same on AC or DC.
That's my read on it. Others may disagree.
Doc
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Old 11-05-2016, 02:24:23 AM
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Default Re: Someone educate me about resistor and non resistor spark plug caps

SO Doc, What would be the advantage or disadvantage to a cooler spark? I see that they are used on high RPM motorcycle engines. Is this same cooler spark achieved with resistance plug wires too? Some Onans had resistance wire on them. I like the NGK plug ends that I showed but want to make sure they can be used on maybe some of my generators and on my 1967 Triumph Tiger Cub 200cc single with Lucas' famous(famous for being a pain in the ass to tune right) Energy Transfer A/C ignition system with mechanical advance.
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Old 11-05-2016, 02:59:03 AM
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Default Re: Someone educate me about resistor and non resistor spark plug caps

Ok I am going to give my take on what resistor plugs and wires do. The energy stored in the coil will build up until it can overcome the resistance of the plug the wire and the airgap in the cylinder then it will fire. If additional resistance is introduced into the system the firing will be delayed until the threshold is met ie the voltage will be higher than it would if a normal plug or non resistor wire is used. This obviously only works to a point when the voltage in the secondary circuit is insufficient to fire the plug and finds some other path to discharge. The resistance of the plug and or wire is of a lower order of magnitude than the airgap in the cylinder I believe that plug wires are on the order of 10 -15K ohms or so and the plug maybe 5K , my memory is not perfect on this, I believe that the airgap in the cylinder is several Megohms or more though that goes down in the presence of ionized products of combustion. The benefit of resistor plugs and wires is that they reduce radio frequency interference which screws up electronic devices, they also will fire in somewhat adverse conditions like carbon deposits on the plug electrodes as long as they are able to overcome the threshold voltage needed . Pretty much the polar opposite of what Doc said but I am listening to any logical arguments and am open to correction by wiser minds. Learn me. Cheers Dan
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Old 11-05-2016, 03:03:41 AM
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Default Re: Someone educate me about resistor and non resistor spark plug caps

Ouch, put me on the spot.... In truth I can only conjecture (not being an ignition guru.)
1. Resistive wire probably same as resistive cap.
2. Spark temp will affect burn. I like to run a hotter plug on my gens because I'm at 5100 feet altitude and thus preset (non-adjustable) carbs tend to run rich.
3. A cooler spark may not necessarily be of value to the burn process, but rather contribute to the longevity of the coil or magneto.
That's about the end of my conjectures.
Doc
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Old 11-05-2016, 07:14:38 AM
Greg Mosley Greg Mosley is offline
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Default Re: Someone educate me about resistor and non resistor spark plug caps

Electrical Noise Suppression to reduce interference for nearby electronics etc. Enuf Said
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Old 11-05-2016, 08:12:01 AM
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Default Re: Someone educate me about resistor and non resistor spark plug caps

^ This.............
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Old 11-05-2016, 08:22:03 AM
PopsGarage PopsGarage is offline
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Default Re: Someone educate me about resistor and non resistor spark plug caps

Quote:
Originally Posted by BigBlockChev View Post
Ok I am going to give my take on what resistor plugs and wires do. The energy stored in the coil will build up until it can overcome the resistance of the plug the wire and the airgap in the cylinder then it will fire. If additional resistance is introduced into the system the firing will be delayed until the threshold is met ie the voltage will be higher than it would if a normal plug or non resistor wire is used. This obviously only works to a point when the voltage in the secondary circuit is insufficient to fire the plug and finds some other path to discharge. The resistance of the plug and or wire is of a lower order of magnitude than the airgap in the cylinder I believe that plug wires are on the order of 10 -15K ohms or so and the plug maybe 5K , my memory is not perfect on this, I believe that the airgap in the cylinder is several Megohms or more though that goes down in the presence of ionized products of combustion. The benefit of resistor plugs and wires is that they reduce radio frequency interference which screws up electronic devices, they also will fire in somewhat adverse conditions like carbon deposits on the plug electrodes as long as they are able to overcome the threshold voltage needed . Pretty much the polar opposite of what Doc said but I am listening to any logical arguments and am open to correction by wiser minds. Learn me. Cheers Dan
Pretty much what I learned when a SUN salesman said while demonstrating the advantage of using the scope to troubleshoot ignition problems back in the 60s. He claimed that it would pay for its self in no time. I saw it as a tool to identify problems in the high voltage circuit.

Bob
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Old 11-05-2016, 09:04:07 AM
Leon N. Leon N. is offline
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Default Re: Someone educate me about resistor and non resistor spark plug caps

My take on this. Resistor or no resistor, no spark, thus no current flow until the voltage over comes the series resistance of the circuit. When the current initially flows, that is the plug fires, the circuit rings at a hi frequency, thus the RFI in those older cars with radios. So, by adding resistance, the ringing is reduced markedly as the voltage will now decay quicker due to the added resistance. Wish I still had my oscilloscope to confirm. Does this make any sense?
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Old 11-05-2016, 10:04:37 AM
G.M.Johnson G.M.Johnson is offline
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Default Re: Someone educate me about resistor and non resistor spark plug caps

Greg has it right.. purely to eliminate electrical RFI noise. RFI = Radio Frequency Noise. For further information Google is your best friend.
WHAT IS RFI?
A: Radio frequency interference (RFI) or electrical "noise" is caused by ignition systems, alternators, wiper motors, etc., but the ignition system causes the strongest "noises" and they include a wide range of frequencies. This noise can cause interference with the operation of radios, electronic components, fuel injection systems, depth finders and other sensitive electronic equipment. Resistor plugs, wires and spark plug caps are used as an RFI suppression system to reduce this noise.
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Old 11-05-2016, 11:25:12 AM
Birken Vogt Birken Vogt is offline
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Default Re: Someone educate me about resistor and non resistor spark plug caps

Quote:
Originally Posted by Leon N. View Post
My take on this. Resistor or no resistor, no spark, thus no current flow until the voltage over comes the series resistance of the circuit. When the current initially flows, that is the plug fires, the circuit rings at a hi frequency, thus the RFI in those older cars with radios. So, by adding resistance, the ringing is reduced markedly as the voltage will now decay quicker due to the added resistance.
This is the correct "longer" explanation except I would change it to say:

"The ringing is reduced as the RINGING will now decay quicker..."

After the spark extinguishes, there is a wild oscillation that takes time to decay.

The resistance spoils the resonance of the circuit so that it decays much faster.

I grew up on a farm with machines from the 1940s and 50s and you could hear one coming a long way off with their solid core wires and non resistor plugs if you were listening to the radio.
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Old 11-05-2016, 11:34:53 AM
Andrew Mackey Andrew Mackey is offline
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Exclamation Re: Someone educate me about resistor and non resistor spark plug caps

Resistor wires are for radio suppression (noise). Resistor plugs raise the voltage necessary to jump the gap, thus raising the amount of energy imparted into the spark itself. With today's alcoholized gas and lean burn engines, you need higher energy to light the charge. Most of today's autos need at least a .040" gap, if not larger.

there IS a drawback to resistor plugs. It raises the voltage to the point that it can cause insulation failure in older coils. Today's coils are built to handle the extra resistance and higher voltage imparted by resistor wire and plugs. Today's auto ignition systems typically make over 60,000 to 100,000 volts! Most of our old engines made between 10 to 20,000 maximum. Older systems cannot overcome that resistance. Spark (electricity) will find the easiest path to ground. if resistance is too high, it will jump thru the old type shellac used on older mag and battery type coils, thus shorting out the secondary wiring. On some engines, this extra resistance will also short out on distributor caps, and if the resistor wiring is old, it will also break thru the insulation sleeve on the wire itself.

it is NOT recommended to use resistor secondary wiring on magneto fired engines built before the mid 1960s. it also is not recommended for multi-cylinder gas engines built before the early 1960s as the extra voltage built up could arc between distributor posts within the cap. This is especially true in aircraft and v-12 engines, as the posts are close together. With resistor wiring, the potential between posts may be less than the resistance between the post and the plug to be fired, so the spark will jump the air gap between posts and cause a cross fire. Case in point - the American La-France V-12. Using resistor wires will cause cross fire between cap terminals as the spark will jump to a short wire lead to ground rather than a long lead (resistance is greater as distance to end point increases). On the ALF V-12, the high tension leads can be as short as less than 2 feet to as long as nearly 5 feet long, each! With 24 plugs, you can see why resistance is critical. in actuality, there are about 125 feet of high tension wire for 1 engine!. The electricity will always take the shortest path. On the ALF engines, and on our old timers, you must use a wire core wire, like Packard 440 or an equivalent. You should not use modern carbon core resistor wire. Another magneto that is susceptible to resistance damage is the Maytag 72 D and DA. Putting resistor plugs and or resistor wire on them is a sure way to kill the already weak insulation in the coils on these engines. On most of our old engines, it also is not a good idea to pull the high tension wires to stop an engine. if you must pull wires, pull the low tension side ot short the high tension to ground, to stop an engine.

In short - resistor wiring and or plugs raise impedance - the ability for electricity to flow. This raises the voltage necessary to complete the circuit. higher voltage means higher energy at the spark plug gap, thus a hotter spark. Resistance lowers current flow. A special note is also needed here: YOU must not pull high tension wires off autos to test for spark! Too much resistance, such as an open circuit will damage computer controlled ignition systems, and can damage the coil. On older GM High energy systems (HEI), they can build to over 100,000 volts! When it first came out in the late 1960s, dealer mechanics were given notice that the HEI coils could kill you! A cross body shock from an HEI coil would stop your heart, much as an AED used to remedy heart attacks do today. There were several cases of serious injury and death associated with them, as older mechanics, used to pulling off wires, were getting severely shocked by the new system.
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Old 11-05-2016, 11:43:02 AM
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Default Re: Someone educate me about resistor and non resistor spark plug caps

Short answer: Resistor stops RF interference in radios and tv.

Here's what I read in RF interference magazine for electrical engineers:
Resistance is added to spark plug wires and spark plugs to greatly reduce RF radiated from spark plug wire. It does this by making an RF impedance mismatch between spark wire (antenna) and free air. (free air has a RF impedance of 377 ohms). Ham radio guys know this stuff , they even have VSWR (voltage standing wave ratio) tuners on their antenna lines to make the match as good as possible for max radiated power.).


My personal experience:
I suspect ideally resistance should be in spark wire since it's the longest "antenna". Historically I first saw it appear in spark plugs in the 70's. I suspect having it in the boot is just a patch attempt if your running copper wires, But it may also work by creating an impedance mismatch at the end of the wire. It likely has same effect as a resistor plug, and is not needed if plug has resistor..

As far as secondary ringing, yes it likely happens but as I recall everything that follows the 1-st hi-voltage pulse is so low voltage ( <10% ) that it is insignificant to restrike the arc ( highly damped, arc consumes most of energy on 1-st pulse/arc). I've seen this on my hi-voltage car tune up scope

BTW motorcycles DO need resistors because otherwise they can easily interfere with radios in nearby cars. FCC legal issue.
In the beginning of radio the first Marconi radio transmitter was a spark gap type and morse code.

I strongly believe in your ebay ad cap means boot , not capacitor.

Last edited by len k; 11-05-2016 at 02:26:05 PM.
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Old 11-05-2016, 12:23:06 PM
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Default Re: Someone educate me about resistor and non resistor spark plug caps

Greg has it right. I remember in the 60s and 70s how noisy cars could be... some of our neighbors, well, you could tell they were on their way down the road from the buzzing/popping in the radio.

It was on the test (as I remember) when I got my Amateur radio ticket in 80, and the advice for any mobile installation was to make sure you ran resistive wires or plugs to cut down on RFI. Basically what a resistor does is increase the rise time of the spark - the rise time needed for igniting fuel is far longer than the rise time that causes RFI. Adding resistance or inductance has little effect on the running of the engine, while helping to eliminate radio frequency noise. (According the the ARRL Handbook.)
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Old 11-05-2016, 01:42:19 PM
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Default Re: Someone educate me about resistor and non resistor spark plug caps

AM Radios in vehicular traffic. If your motorcycle was idling at a stoplight, you were interfering with someone's reception.

If your Onan was powering a two-way radio facility, resistor plugs and/or wires would be mandatory.

When FM Radio became popular, then resistor plugs were still there as a $$$$ profit center to sell more stuff!

Back when I was heating up a 426 hemi, we did not use resistor plugs or wires! ALL of the current went to the spark plug!

Today, resistors might make your plugs last longer.
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Old 11-05-2016, 03:34:44 PM
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Default Re: Someone educate me about resistor and non resistor spark plug caps

Quote:
Originally Posted by Harry View Post
When FM Radio became popular, then resistor plugs were still there as a $$$$ profit center to sell more stuff!
Solid wires and plugs do a very good job of interfering with FM radio as well. Noise is noise.
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Old 11-05-2016, 04:24:18 PM
Leon N. Leon N. is offline
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Default Re: Someone educate me about resistor and non resistor spark plug caps

I do know from theory, the faster the rise time, the higher the harmonic frequencies that are produced. Also, the ringing occurs only when the current flows through the spark. I do not believe there is a restrike condition because the energy would have been expended at that point. I had some trouble but finally was able to obtain replacement solid core spark plug wires for my JB which was built in 1966.
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Old 11-05-2016, 05:42:49 PM
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Default Re: Someone educate me about resistor and non resistor spark plug caps

When I was a kid that was how we could tell the school bus was coming....
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Last edited by Fred Van Hook; 11-05-2016 at 10:00:16 PM.
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Old 11-05-2016, 07:16:41 PM
Leon N. Leon N. is offline
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Default Re: Someone educate me about resistor and non resistor spark plug caps

My JB sat in a shed 125 feet behind the house. And, the ignition wires are behind a metal enclosure. No problems with RFI in the house.
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Old 11-05-2016, 08:17:41 PM
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Default Re: Someone educate me about resistor and non resistor spark plug caps

When I was a kid spark RFI from cars didn't seem to travel very far, but it was just a casual observation, a long time ago.
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