is there a decrease of avalable spark at the electrodes by using a resistor type spark plug vesus a non resistor type? i want maximum spark!! is there a preffered brand of spark plug for a briggs flathead application? (champion,ngk,autolite).
resistor spark plugs
- Thread starter james1950
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IIRC, the resistor is to minimize RF interference, so you can listen to your tunes while you mow. O don't think the resistor has anything to do with how bright the spark is.
I was always under the impression that as resistance in the secondary circuit increases,so does the voltage output of the coil...pushing up voltage to the plug.So,more resistance should increase spark energy.Solid metal wires and little resistance...not so much.
There's something related to ohm's law that makes spark plug & wire resistance largely irrelevant at 30k volts. As said, it's there for the RF interference reduction. You're also forgetting the incredible resistance of .030 inches of air with a little atomized fuel thrown in.
If OP is having spark issues he should check his magneto gap, general coil quality, and condensor if he has one.
All three brands listed are good; if you want ultimate performance look for one of those fine wire small engine plugs.
If OP is having spark issues he should check his magneto gap, general coil quality, and condensor if he has one.
All three brands listed are good; if you want ultimate performance look for one of those fine wire small engine plugs.
Voltage = Current x Resistance
IIRC, the coil/magneto puts out a constant voltage, so if you reduce the resistance in the circuit you'll be increasing the current proportionally. Yes that will get you a hotter spark, but might also burn up ignition components.
Power = Current x Voltage
So as you increase current, you increase power proportionally, but the wiring in the system will only handle so much... Once, before I knew better, I burned up a brand new distributor cap by installing low resistance wires and non-resistor plugs... you need some resistance in the system.
IIRC, the coil/magneto puts out a constant voltage, so if you reduce the resistance in the circuit you'll be increasing the current proportionally. Yes that will get you a hotter spark, but might also burn up ignition components.
Power = Current x Voltage
So as you increase current, you increase power proportionally, but the wiring in the system will only handle so much... Once, before I knew better, I burned up a brand new distributor cap by installing low resistance wires and non-resistor plugs... you need some resistance in the system.
MolaKule
Staff member
The resistor plugs reduce Radio Frequency interference by damping the oscillating wave at the gap.
The average current through a spark plug at 1 mS is approx. 250 mA or 0.250 Amps.
A resistor spark pug has a resistance of less than 10,000 ohms.
The voltage drop across the resistance cylinder (slug) in the spark plug is therefore 2,500 volts.
For an ignition system with a coil secondary voltage of 25,000 volts, this drop represents a 10% drop in voltage, or a drop in the bucket compared to the coil voltage.
I prefer Champions for Outdoor Equipment (OE) and replace them every two or three years. Resistance plugs can increase their resistances slightly over time.
For OE such as chainsaws and weedeaters, the heat range of the plug is very important.
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i want maximum spark!!
As shown above, there isn't a lot of voltage difference between the resistance type vs the non-resistance type at the gap.
The average current through a spark plug at 1 mS is approx. 250 mA or 0.250 Amps.
A resistor spark pug has a resistance of less than 10,000 ohms.
The voltage drop across the resistance cylinder (slug) in the spark plug is therefore 2,500 volts.
For an ignition system with a coil secondary voltage of 25,000 volts, this drop represents a 10% drop in voltage, or a drop in the bucket compared to the coil voltage.
I prefer Champions for Outdoor Equipment (OE) and replace them every two or three years. Resistance plugs can increase their resistances slightly over time.
For OE such as chainsaws and weedeaters, the heat range of the plug is very important.
Quote:
i want maximum spark!!
As shown above, there isn't a lot of voltage difference between the resistance type vs the non-resistance type at the gap.
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An ignition coil creates just enough voltage to overcome the resistance. A coil may be capable of putting out 40,000 volts but if it only 20,000 is needed to jump the gap that's all it charges up to.
You are getting maximum spark regardless of resistor or non-resistor.
You are getting maximum spark regardless of resistor or non-resistor.
You should use a resistor plug if you have electronic ignition (everything made in the last 20-30 years) . I have read that RFI can damage certain ignition modules and non resistor plugs will void the warranty on some equipment.
If you have a points style ignition, then use the old non resistor plug if you want.
Like already said, the hotter spark you seek is pointless.
I use NGK plugs. The NGK BR2LM is the correct plug for flat head briggs engines.
If you have a points style ignition, then use the old non resistor plug if you want.
Like already said, the hotter spark you seek is pointless.
I use NGK plugs. The NGK BR2LM is the correct plug for flat head briggs engines.
MolaKule
Staff member
There's another factor at work here that hasn't come up yet in this discussion. That's the issue of rate of rise of the spark voltage. The slower the rise, the higher the strike voltage in a gas discharge. An air or other gas gap can sustain a much higher open circuit voltage if the voltage rises slowly - big friction belt generators in science fairs demonstrate this point quite well. A sudden rise will trigger an arc at a much lower voltage than a slow-rising voltage.
So what's this got to do with resistor wires and plugs? Well, when you put a resistor in series with the capacitance of the wires and plug gap, it lowers the rate of rise of the voltage across the plug gap, causing it to arc at a higher voltage. The higher arc voltage contains more energy (proportional to the voltage squared), so you get a hotter spark with the higher voltage. In other words, resistor plugs give you a hotter spark than non-resistor plugs. Non-resistor plug systems, like the ones Mercedes-Benz used to use, used resistor connectors for the same purpose. Less RF noise and a hotter spark.
So what's this got to do with resistor wires and plugs? Well, when you put a resistor in series with the capacitance of the wires and plug gap, it lowers the rate of rise of the voltage across the plug gap, causing it to arc at a higher voltage. The higher arc voltage contains more energy (proportional to the voltage squared), so you get a hotter spark with the higher voltage. In other words, resistor plugs give you a hotter spark than non-resistor plugs. Non-resistor plug systems, like the ones Mercedes-Benz used to use, used resistor connectors for the same purpose. Less RF noise and a hotter spark.
MolaKule
Staff member
MolaKule
Staff member
Quote:
A sudden rise will trigger an arc at a much lower voltage than a slow-rising voltage.
And that is exactly what you want, a fast rise time high voltage spark so the ionization channel can be established.
I don't see any analogy between the science fair friction belt and the physics of the spark plug gap.
A sudden rise will trigger an arc at a much lower voltage than a slow-rising voltage.
And that is exactly what you want, a fast rise time high voltage spark so the ionization channel can be established.
I don't see any analogy between the science fair friction belt and the physics of the spark plug gap.
Originally Posted By: MolaKule
And that is exactly what you want, a fast rise time high voltage spark so the ionization channel can be established.
I don't see any analogy between the science fair friction belt and the physics of the spark plug gap.
Actually, you don't want a fast rise-time. To transfer the maximum energy to the gas column, you want the initial phase to be as energetic as possible - that means start at the highest voltage you can engineer, not the lowest. If you allow it to establish the arc channel at the lowest possible voltage, then more of the energy of the spark is wasted in the second and third phases.
And that is exactly what you want, a fast rise time high voltage spark so the ionization channel can be established.
I don't see any analogy between the science fair friction belt and the physics of the spark plug gap.
Actually, you don't want a fast rise-time. To transfer the maximum energy to the gas column, you want the initial phase to be as energetic as possible - that means start at the highest voltage you can engineer, not the lowest. If you allow it to establish the arc channel at the lowest possible voltage, then more of the energy of the spark is wasted in the second and third phases.
MolaKule
Staff member
Did you red the link in #3092078. I describe the timing, voltage, and energy for the spark gap.
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To transfer the maximum energy to the gas column, you want the initial phase to be as energetic as possible - that means start at the highest voltage you can engineer, not the lowest. If you allow it to establish the arc channel at the lowest possible voltage, then more of the energy of the spark is wasted in the second and third phases.
No one is arguing low energy or low voltage spark initiation but you.
How much energy is delivered per phase is determined by the ionization physics of the plasma channel.
When the ECU commands a current pulse to the ignition coil's primary, you want as fast a drop in current as possible in order to create a high voltage at the coil's secondary.
You want the highest voltage available in the shortest amount of time at the SP gap to ignite the plasma. The overall rise time of the voltage on the coil's secondary is a function of the coil's leakage inductance, resistance of wiring and plug, capacitance of external circuit, gap width and cylinder pressure, and gas species. That rise time is designed into the ignition system.
Too much ignition system delay wrt piston position affects combustion efficiency, which in turn affects engine performance and mpg.
When I am speaking of the SP gap rise time, I am speaking of the initial curve showing the leading edge of the SP gap current as the voltage rises to about 35,000 volts and just before current flows. Upon ignition of the plasma, the current rises to about 200 Amps but only sustains this level for about 10 (10^-9) seconds or 10 nanoseconds.
And please explain your comment:
Quote:
- big friction belt generators in science fairs demonstrate this point quite well. A sudden rise will trigger an arc at a much lower voltage than a slow-rising voltage.
Quote:
To transfer the maximum energy to the gas column, you want the initial phase to be as energetic as possible - that means start at the highest voltage you can engineer, not the lowest. If you allow it to establish the arc channel at the lowest possible voltage, then more of the energy of the spark is wasted in the second and third phases.
No one is arguing low energy or low voltage spark initiation but you.
How much energy is delivered per phase is determined by the ionization physics of the plasma channel.
When the ECU commands a current pulse to the ignition coil's primary, you want as fast a drop in current as possible in order to create a high voltage at the coil's secondary.
You want the highest voltage available in the shortest amount of time at the SP gap to ignite the plasma. The overall rise time of the voltage on the coil's secondary is a function of the coil's leakage inductance, resistance of wiring and plug, capacitance of external circuit, gap width and cylinder pressure, and gas species. That rise time is designed into the ignition system.
Too much ignition system delay wrt piston position affects combustion efficiency, which in turn affects engine performance and mpg.
When I am speaking of the SP gap rise time, I am speaking of the initial curve showing the leading edge of the SP gap current as the voltage rises to about 35,000 volts and just before current flows. Upon ignition of the plasma, the current rises to about 200 Amps but only sustains this level for about 10 (10^-9) seconds or 10 nanoseconds.
And please explain your comment:
Quote:
- big friction belt generators in science fairs demonstrate this point quite well. A sudden rise will trigger an arc at a much lower voltage than a slow-rising voltage.
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The big friction belt generators develop a very high voltage very slowly, and the demonstration of hair flying up from the field and other phenomena like that works because of the slow build-up of the field. My point was that the static display of a static field was the case that demonstrates how high voltages can be developed and sustained without arcing if the voltage rises slow enough - kind of a polar opposite to a spark plug. The opposite end of the spectrum is the ignition spark, where, as you correctly point out, the whole system is engineered to deliver the max energy during the phase of the arc that creates the most benefit. All of the time constants we're talking about are in the microsecond or nanosecond range.
I got buried in the technology of "how to strike an arc in a gas mixture" back in the 1980's when I was developing electronic controls for fluorescent and HID lamps. I didn't have the luxury of being able to rely on the external "starter" that regular inductive ballasts use to strike an arc. I had to research how arcs form so I could design an integrated ignitor that would initiate an arc but that wouldn't trash my control circuit in the process. The faster the rate-of-rise (kv per us) the lower the strike voltage - that's where my research stopped, because once I had an arc, the rest was what the core technology was about.
I got buried in the technology of "how to strike an arc in a gas mixture" back in the 1980's when I was developing electronic controls for fluorescent and HID lamps. I didn't have the luxury of being able to rely on the external "starter" that regular inductive ballasts use to strike an arc. I had to research how arcs form so I could design an integrated ignitor that would initiate an arc but that wouldn't trash my control circuit in the process. The faster the rate-of-rise (kv per us) the lower the strike voltage - that's where my research stopped, because once I had an arc, the rest was what the core technology was about.
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