Why not 6 or 50? What's the dealio?
Adrian
Home built Eaton M62 Supercharger with 9psi boost, "stock" high ratio rocker arms, 8:1 compression, Piper 270 cam, ported head, matched manifolds, CB Performance computerized ignition.
Edited 1 time(s). Last edit at 20170514 07:40 PM by pinkyponk.
MGB & GT Forum
Why are coils 3 ohms?
Posted by pinkyponk
pinkyponk
Adrian Page
Berwick, Nova Scotia, Canada

May 14, 2017 07:07 PM
Top Contributor
Joined 6 years ago
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Fred Winterburn
Fred W
Ripley, Ontario, Canada
1956 Morgan Plus 4 (+4)

May 14, 2017 09:49 PM
Joined 2 years ago
463 Posts

For points ignitions if the current exceeds 4 amps through the point contacts, they will burn exponentially faster. 3 ohms limits the current so that it is only briefly higher than 4 amps at low rpm. It also keeps the coil from cooking itself to death when the points are closed continuously such as with the ignition on and the engine not running and the points just happening to be closed. With points, the primary side resistance should be a minimum of 3 ohms which includes any separate ballast resistor for a lower ohms coil. The two should add up to a minimum of 3 ohms. Exceeding 3.5 ohms starts to reduce spark energy more than it should. Fred
'Anyone who likes liver, can't taste it'
'If you want to repair car electrical systems successfully, learn Ohm's Law'.
In reply to # 3511515 by pinkyponk
Why not 6 or 50? What's the dealio?
Adrian
Adrian
'Anyone who likes liver, can't taste it'
'If you want to repair car electrical systems successfully, learn Ohm's Law'.
benhutcherson
Ben Hutcherson
Louisville/Frankfort, Kentucky, USA
1970 MG MGB

May 14, 2017 10:01 PM
Joined 1 year ago
1,703 Posts

In reply to # 3511605 by Fred Winterburn
For points ignitions if the current exceeds 4 amps through the point contacts, they will burn exponentially faster. 3 ohms limits the current so that it is only briefly higher than 4 amps at low rpm.
To add to that, most of the modern high energy computerized systems I've worked with have very low primary resistance.
The last one I changed was on a '97 Geo Prizm(Toyota Corolla), which had a single coil and a distributor but used the ECM/CPS to trigger the coil. My friend reported that the car would crank but not start. When I went digging(Toyota wants you to replace the whole distributor, but my friend didn't want spend $250 on a car worth about that much) I found the coil open. The replacement checked out at around .75Ω, and the car is still more or less running with that coil.
I think the new COPs I've installed have been in that same ballpark.
May 14, 2017 10:11 PM
Top Contributor
Joined 7 years ago
5,467 Posts

The stock CEI coil was in the 0.8 ohm range.
“Where did the public good enter into all this maze of personal intrigue, this wilderness of stunted natures where no straight road is to be found, but only the tortuous and aimless travels of beasts and things that crawl?”
“If you are not paying for it, you're not the customer; you're the product being sold.”
“Yes, another great idea destroyed by a simple set of facts."
“All of us at one time or another have had a sense of déjà vu, a feeling that this has happened before, that this has happened before, that this has happened before."
TANSTAAFL !
In reply to # 3511609 by benhutcherson
To add to that, most of the modern high energy computerized systems I've worked with have very low primary resistance.
The last one I changed was on a '97 Geo Prizm(Toyota Corolla), which had a single coil and a distributor but used the ECM/CPS to trigger the coil. My friend reported that the car would crank but not start. When I went digging(Toyota wants you to replace the whole distributor, but my friend didn't want spend $250 on a car worth about that much) I found the coil open. The replacement checked out at around .75Ω, and the car is still more or less running with that coil.
I think the new COPs I've installed have been in that same ballpark.
In reply to # 3511605 by Fred Winterburn
For points ignitions if the current exceeds 4 amps through the point contacts, they will burn exponentially faster. 3 ohms limits the current so that it is only briefly higher than 4 amps at low rpm.
To add to that, most of the modern high energy computerized systems I've worked with have very low primary resistance.
The last one I changed was on a '97 Geo Prizm(Toyota Corolla), which had a single coil and a distributor but used the ECM/CPS to trigger the coil. My friend reported that the car would crank but not start. When I went digging(Toyota wants you to replace the whole distributor, but my friend didn't want spend $250 on a car worth about that much) I found the coil open. The replacement checked out at around .75Ω, and the car is still more or less running with that coil.
I think the new COPs I've installed have been in that same ballpark.
“Where did the public good enter into all this maze of personal intrigue, this wilderness of stunted natures where no straight road is to be found, but only the tortuous and aimless travels of beasts and things that crawl?”
“If you are not paying for it, you're not the customer; you're the product being sold.”
“Yes, another great idea destroyed by a simple set of facts."
“All of us at one time or another have had a sense of déjà vu, a feeling that this has happened before, that this has happened before, that this has happened before."
TANSTAAFL !
benhutcherson
Ben Hutcherson
Louisville/Frankfort, Kentucky, USA
1970 MG MGB

May 14, 2017 10:22 PM
Joined 1 year ago
1,703 Posts

course2kid
Jeffrey Johnson
Fountain Valley, CA, USA
1979 MG MGB "Lucy (Lucifer)"

May 14, 2017 10:52 PM
Joined 6 months ago
602 Posts

Deleted post as it was accidentally posted before complete (fatfinger typing error).
Edited 1 time(s). Last edit at 20170514 11:02 PM by course2kid.
Edited 1 time(s). Last edit at 20170514 11:02 PM by course2kid.
course2kid
Jeffrey Johnson
Fountain Valley, CA, USA
1979 MG MGB "Lucy (Lucifer)"

May 14, 2017 10:59 PM
Joined 6 months ago
602 Posts

EDIT: i had to make some corrections per Fred's comment that followed my original post.
A coil designer is probably needed to get a realworld practical answer, but, I can attempt an academic answer...
A coil is basically a transformer. Two coils, primary and secondary wrapped around a common magnetic path so that they are both coupled to the same magnetic field. The primary will have both resistance and inductance and will have a time constant of L/R. This time constant determines how quickly current builds up in the coil to it's maximum value of V/R. The magnetic field strength is generally proportional to the current in the primary (unless the soft magnetic materials get saturated, but, I wouldn't think the designers would push the flux that high simply because doing so makes the design process more challenging).
When the current path of the primary is interrupted by the points, the magnetic field collapses and induces a voltage on the secondary coil. That voltage is dependent on the number of turns on that coil and the rate of change in the magnetic field strength. The output voltage on the secondary must be plenty high enough to jump the gap between the rotor and distributer cap (at atmospheric pressure) and must also be high enough to jump the spark plug gap (at 150 psi or whatever compression your engine achieves). Also, the voltage cannot be so high that it can cause sparks along unintended paths (e.g. from the plug electrode to the top of the piston or from the rotor to the distributor body).
Additionally, the total energy stored in the magnetic field must be designed such that the energy in the spark at the plug is sufficient to properly ignite the A/F mixture. The ratio of turns between secondary and primary determines the peak secondary coil voltage and, I think that the total spark energy is related to the time constant of the secondary (L/R), the spark gap in the plug, the spark gap from rotor to cap, and the length of time that the current to the primary is interrupted.
Once the engine designers have defined how much spark energy they need for proper ignition of the A/F mixture at the designed compression and the engine rpm range (which determines the time period of a charge/discharge cycle), the distributor designers have to consider practicalities like the arc lengths of the rotor and cap, the range of desired vacuum advance, mechanical tolerances, and the number of cylinders to determine the actual minimum charge discharge period.
The coil designers would use that information along with the spark voltage requirements to determine what (L/R) ratios they need for the primary and secondary coils. Then they'd consider the currents they need to carry in each coil along with heat transfer considerations as well as size, weight, and packaging constraints to select appropriate wire gages.
Sorry, this explanation is getting pretty long and boring without much practical insight, so, I'll do my best at that ... If we tried to design a 6 ohm in place of a 3 ohm coil, we could either choose to use an equal length wire with half the cross section of the original wire or a double length wire of the same cross section (or other combination of wire length and cross section that yields 6 ohms resistance).
If we did the first, the time constant would be half that of the original coil because it would have the same number of turns, but twice the resistance (L stays the same, R doubles, and L/R is halved). In addition, the coil size and weight would be halved. On the downside, the steady state current V/R would be halved, so, the fullycharged energy stored in the magnetic field would be 1/4 of the original coil (magnetic energy is 1/2 L i squared) and the secondary coil might not be able to pull enough energy from this weakened field to provide adequate spark energy.
If we tried the second way (twice as many coils of the same gage wire), L would be quadrupled (L is proportional to number of turns squared), R would also be doubled, so (L/R) would be double that of the original coil. Unfortunately, the size and weight of the primary coil would be doubled. Since R is doubled the steady state current is halved, but, the magnetic field energy remains the same since there are twice as many turns on the primary coil (energy is 1/2 L i*i where L has been quadrupled, but i has been halved, so energy stays the same).
Since R is doubled and current is halved, and heat generation (i squared x R) is 1/2 that of the 3 ohm coil. So, this would probably work, but the coil would be larger, heavier, and more costly to produce).
Edited 2 time(s). Last edit at 20170515 09:29 PM by course2kid.
A coil designer is probably needed to get a realworld practical answer, but, I can attempt an academic answer...
A coil is basically a transformer. Two coils, primary and secondary wrapped around a common magnetic path so that they are both coupled to the same magnetic field. The primary will have both resistance and inductance and will have a time constant of L/R. This time constant determines how quickly current builds up in the coil to it's maximum value of V/R. The magnetic field strength is generally proportional to the current in the primary (unless the soft magnetic materials get saturated, but, I wouldn't think the designers would push the flux that high simply because doing so makes the design process more challenging).
When the current path of the primary is interrupted by the points, the magnetic field collapses and induces a voltage on the secondary coil. That voltage is dependent on the number of turns on that coil and the rate of change in the magnetic field strength. The output voltage on the secondary must be plenty high enough to jump the gap between the rotor and distributer cap (at atmospheric pressure) and must also be high enough to jump the spark plug gap (at 150 psi or whatever compression your engine achieves). Also, the voltage cannot be so high that it can cause sparks along unintended paths (e.g. from the plug electrode to the top of the piston or from the rotor to the distributor body).
Additionally, the total energy stored in the magnetic field must be designed such that the energy in the spark at the plug is sufficient to properly ignite the A/F mixture. The ratio of turns between secondary and primary determines the peak secondary coil voltage and, I think that the total spark energy is related to the time constant of the secondary (L/R), the spark gap in the plug, the spark gap from rotor to cap, and the length of time that the current to the primary is interrupted.
Once the engine designers have defined how much spark energy they need for proper ignition of the A/F mixture at the designed compression and the engine rpm range (which determines the time period of a charge/discharge cycle), the distributor designers have to consider practicalities like the arc lengths of the rotor and cap, the range of desired vacuum advance, mechanical tolerances, and the number of cylinders to determine the actual minimum charge discharge period.
The coil designers would use that information along with the spark voltage requirements to determine what (L/R) ratios they need for the primary and secondary coils. Then they'd consider the currents they need to carry in each coil along with heat transfer considerations as well as size, weight, and packaging constraints to select appropriate wire gages.
Sorry, this explanation is getting pretty long and boring without much practical insight, so, I'll do my best at that ... If we tried to design a 6 ohm in place of a 3 ohm coil, we could either choose to use an equal length wire with half the cross section of the original wire or a double length wire of the same cross section (or other combination of wire length and cross section that yields 6 ohms resistance).
If we did the first, the time constant would be half that of the original coil because it would have the same number of turns, but twice the resistance (L stays the same, R doubles, and L/R is halved). In addition, the coil size and weight would be halved. On the downside, the steady state current V/R would be halved, so, the fullycharged energy stored in the magnetic field would be 1/4 of the original coil (magnetic energy is 1/2 L i squared) and the secondary coil might not be able to pull enough energy from this weakened field to provide adequate spark energy.
If we tried the second way (twice as many coils of the same gage wire), L would be quadrupled (L is proportional to number of turns squared), R would also be doubled, so (L/R) would be double that of the original coil. Unfortunately, the size and weight of the primary coil would be doubled. Since R is doubled the steady state current is halved, but, the magnetic field energy remains the same since there are twice as many turns on the primary coil (energy is 1/2 L i*i where L has been quadrupled, but i has been halved, so energy stays the same).
Since R is doubled and current is halved, and heat generation (i squared x R) is 1/2 that of the 3 ohm coil. So, this would probably work, but the coil would be larger, heavier, and more costly to produce).
Edited 2 time(s). Last edit at 20170515 09:29 PM by course2kid.
glbishop
Gary Bishop
Spring Hill, FL, USA

May 15, 2017 05:30 AM
Top Contributor
Joined 6 years ago
1,951 Posts

In reply to # 3511625 by benhutcherson
I thought the Lucas CEI system on MGBs used a 1.5Ω coil thatin normal runningwas supplied power via a 1.5Ω resistance wire.
In reply to # 3511615 by rocannon
The stock CEI coil was in the 0.8 ohm range.
I thought the Lucas CEI system on MGBs used a 1.5Ω coil thatin normal runningwas supplied power via a 1.5Ω resistance wire.
Lucas did use a 1.5 ohm coil and resistor wire to 'externally' limit current for the Opus system. The CEI replacement Lucas box has the GM 4 pin module inside. It has internal current limiting capability and was designed to be used with coils as low as .6 ohm. No external current limiting devices are needed however considerable heat is generated when the module is doing all the limiting. I've run it that way without any problem but I did use a big heat sync on top of the Lucas box.
Right now I'm using a 1.5 ohm std coil and an external ballast resistor to prevent the module's current limiting circuit from activating. Much less heat for the module to deal with and the ignition works just as well.
Fred Winterburn
Fred W
Ripley, Ontario, Canada
1956 Morgan Plus 4 (+4)

May 15, 2017 06:24 AM
Joined 2 years ago
463 Posts

Actually, if you halve the current, you will make the energy storage 1/4 of what it was with double the current, since the energy stored in an inductor is proportional to the current squared times the inductance. I'll bet Charles Kettering experimented long enough to find out what worked and what didn't. Fred
'Anyone who likes liver, can't taste it'
'If you want to repair car electrical systems successfully, learn Ohm's Law'.
In reply to # 3511647 by course2kid
A coil designer is probably needed to get a realworld practical answer, but, I can attempt an academic answer...
A coil is basically a transformer. Two coils, primary and secondary wrapped around a common magnetic path so that they are both coupled to the same magnetic field. The primary will have both resistance and inductance and will have a time constant of L/R. This time constant determines how quickly current builds up in the coil to it's maximum value of V/R. The magnetic field strength is generally proportional to the current in the primary (unless the soft magnetic materials get saturated, but, I wouldn't think the designers would push the flux that high simply because doing so makes the design process more challenging).
When the current path of the primary is interrupted by the points, the magnetic field collapses and induces a voltage on the secondary coil. That voltage is dependent on the number of turns on that coil and the rate of change in the magnetic field strength. The output voltage on the secondary must be plenty high enough to jump the gap between the rotor and distributer cap (at atmospheric pressure) and must also be high enough to jump the spark plug gap (at 150 psi or whatever compression your engine achieves). Also, the voltage cannot be so high that it can cause sparks along unintended paths (e.g. from the plug electrode to the top of the piston or from the rotor to the distributor body).
Additionally, the total energy stored in the magnetic field must be designed such that the energy in the spark at the plug is sufficient to properly ignite the A/F mixture. The ratio of turns between secondary and primary determines the peak secondary coil voltage and, I think that the total spark energy is related to the time constant of the secondary (L/R), the spark gap in the plug, the spark gap from rotor to cap, and the length of time that the current to the primary is interrupted.
Once the engine designers have defined how much spark energy they need for proper ignition of the A/F mixture at the designed compression and the engine rpm range (which determines the time period of a charge/discharge cycle), the distributor designers have to consider practicalities like the arc lengths of the rotor and cap, the range of desired vacuum advance, mechanical tolerances, and the number of cylinders to determine the actual minimum charge discharge period.
The coil designers would use that information along with the spark voltage requirements to determine what (L/R) ratios they need for the primary and secondary coils. Then they'd consider the currents they need to carry in each coil along with heat transfer considerations as well as size, weight, and packaging constraints to select appropriate wire gages.
Sorry, this explanation is getting pretty long and boring without much practical insight, so, I'll do my best at that ... If we tried to design a 6 ohm in place of a 3 ohm coil, we could either choose to use an equal length wire with half the cross section of the original wire or a double length wire of the same cross section (or other combination of wire length and cross section that yields 6 ohms resistance).
If we did the first, the time constant would be half that of the original coil because it would have the same number of turns, but twice the resistance (L stays the same, R doubles, and L/R is halved). In addition, the coil size and weight would be halved. On the downside, the steady state current V/R would also be halved, so, the fullycharged energy stored in the magnetic field would also be halved and the secondary coil might not be able to pull enough energy from this weakened field to provide adequate spark energy.
If we tried the second way (twice as many coils of the same gage wire), L would be doubled, R would also be doubled, so (L/R) would remain unchanged. Unfortunately, the size and weight of the primary coil would be doubled. Also, snce R is doubled the steady state current is halved, but, the magnetic field energy remains the same since there are twice as many turns on the primary coil. Since R is doubled and current is halved, and heat generation (i squared x R) is 1/2 that of the 3 ohm coil. So, this would probably work, but the coil would be larger, heavier, and more costly to produce).
A coil is basically a transformer. Two coils, primary and secondary wrapped around a common magnetic path so that they are both coupled to the same magnetic field. The primary will have both resistance and inductance and will have a time constant of L/R. This time constant determines how quickly current builds up in the coil to it's maximum value of V/R. The magnetic field strength is generally proportional to the current in the primary (unless the soft magnetic materials get saturated, but, I wouldn't think the designers would push the flux that high simply because doing so makes the design process more challenging).
When the current path of the primary is interrupted by the points, the magnetic field collapses and induces a voltage on the secondary coil. That voltage is dependent on the number of turns on that coil and the rate of change in the magnetic field strength. The output voltage on the secondary must be plenty high enough to jump the gap between the rotor and distributer cap (at atmospheric pressure) and must also be high enough to jump the spark plug gap (at 150 psi or whatever compression your engine achieves). Also, the voltage cannot be so high that it can cause sparks along unintended paths (e.g. from the plug electrode to the top of the piston or from the rotor to the distributor body).
Additionally, the total energy stored in the magnetic field must be designed such that the energy in the spark at the plug is sufficient to properly ignite the A/F mixture. The ratio of turns between secondary and primary determines the peak secondary coil voltage and, I think that the total spark energy is related to the time constant of the secondary (L/R), the spark gap in the plug, the spark gap from rotor to cap, and the length of time that the current to the primary is interrupted.
Once the engine designers have defined how much spark energy they need for proper ignition of the A/F mixture at the designed compression and the engine rpm range (which determines the time period of a charge/discharge cycle), the distributor designers have to consider practicalities like the arc lengths of the rotor and cap, the range of desired vacuum advance, mechanical tolerances, and the number of cylinders to determine the actual minimum charge discharge period.
The coil designers would use that information along with the spark voltage requirements to determine what (L/R) ratios they need for the primary and secondary coils. Then they'd consider the currents they need to carry in each coil along with heat transfer considerations as well as size, weight, and packaging constraints to select appropriate wire gages.
Sorry, this explanation is getting pretty long and boring without much practical insight, so, I'll do my best at that ... If we tried to design a 6 ohm in place of a 3 ohm coil, we could either choose to use an equal length wire with half the cross section of the original wire or a double length wire of the same cross section (or other combination of wire length and cross section that yields 6 ohms resistance).
If we did the first, the time constant would be half that of the original coil because it would have the same number of turns, but twice the resistance (L stays the same, R doubles, and L/R is halved). In addition, the coil size and weight would be halved. On the downside, the steady state current V/R would also be halved, so, the fullycharged energy stored in the magnetic field would also be halved and the secondary coil might not be able to pull enough energy from this weakened field to provide adequate spark energy.
If we tried the second way (twice as many coils of the same gage wire), L would be doubled, R would also be doubled, so (L/R) would remain unchanged. Unfortunately, the size and weight of the primary coil would be doubled. Also, snce R is doubled the steady state current is halved, but, the magnetic field energy remains the same since there are twice as many turns on the primary coil. Since R is doubled and current is halved, and heat generation (i squared x R) is 1/2 that of the 3 ohm coil. So, this would probably work, but the coil would be larger, heavier, and more costly to produce).
'Anyone who likes liver, can't taste it'
'If you want to repair car electrical systems successfully, learn Ohm's Law'.
Steve S.
Stephen Strange
Harrisonburg, Virginia, USA
1972 MG MGB MkII "The Mouse Trap"

May 15, 2017 08:17 AM
Top Contributor
Joined 9 years ago
1,245 Posts

May 15, 2017 10:32 AM
Top Contributor
Joined 13 years ago
13,798 Posts

And, if you don't believe Fred, try running a ballasted coil setup without a ballast resistor  it doesn't take long for the points to burn. A common failure in the era of pointsbased ignition systems was for the ballast resistor to burn out. It would drive people crazy  the engine would start while they were cranking (the ballast resistor is bypassed) and die as soon as they released the key. The quick cure to get home was to put a piece of wire across the ballast resistor  which doubled the current through the points (and coil). However, you couldn't go far like that or you would fry the points (and possibly the coil).
I suppose the question might be, why didn't they manufacturers go to heftier points (or dual points)? I suspect it was a question of optimization. The 3 to 4 amp current provided enough energy to do the job and the benefits of higher current were small compared to the cost of a larger and more expensive breaker point system.
Of course, when semiconductors came into the picture, lower resistance (higher energy) coils became possible. Tighter emission requirements were also a driver to ensure that the cylinder fired on every turn (er, 2nd turn) of the crank.
Terry Ingoldsby
terry.ingoldsby@DCExperts.com
I suppose the question might be, why didn't they manufacturers go to heftier points (or dual points)? I suspect it was a question of optimization. The 3 to 4 amp current provided enough energy to do the job and the benefits of higher current were small compared to the cost of a larger and more expensive breaker point system.
Of course, when semiconductors came into the picture, lower resistance (higher energy) coils became possible. Tighter emission requirements were also a driver to ensure that the cylinder fired on every turn (er, 2nd turn) of the crank.
Terry Ingoldsby
terry.ingoldsby@DCExperts.com
May 15, 2017 10:57 AM
Top Contributor
Joined 7 years ago
10,703 Posts

OK, let's assume for a moment we are talking about a late model "B".
Fred is saying to measure the overall resistance of the circuit up to and through the coil. I'm thinking I may be fighting the same thing as some of the current discussions going on, so I'm curious.
Where would I measure from/to to measure overall resistance of this circuit? Can someone give me some wire connections and colors to research?
TIA as always.
Wayne Sanders
Rose Lodge, OR
(TD 4288)
"I don't care to belong to any club that accepts people like me"joined Willamette Valley Club in 2011
77 MGB  Four tone paint Pertronix  hood props  cheap tires  new springs all around  mixture of poly and rubber bushings fuzzy seatcovers  stereo out of old F150 pickup runs flawlessly and drives nice.
78 MGB  Done right by a good PO, and I only bought it. Tell Jim how nice it is. But I did put in a Datsun 5 speed.
53 TD Mark II  a work in progress.
79/65 MGB  Carmine V6  T5
This car is now very nearly completely done. Sure to find something else, but not now.........
Fred is saying to measure the overall resistance of the circuit up to and through the coil. I'm thinking I may be fighting the same thing as some of the current discussions going on, so I'm curious.
Where would I measure from/to to measure overall resistance of this circuit? Can someone give me some wire connections and colors to research?
TIA as always.
Wayne Sanders
Rose Lodge, OR
(TD 4288)
"I don't care to belong to any club that accepts people like me"joined Willamette Valley Club in 2011
77 MGB  Four tone paint Pertronix  hood props  cheap tires  new springs all around  mixture of poly and rubber bushings fuzzy seatcovers  stereo out of old F150 pickup runs flawlessly and drives nice.
78 MGB  Done right by a good PO, and I only bought it. Tell Jim how nice it is. But I did put in a Datsun 5 speed.
53 TD Mark II  a work in progress.
79/65 MGB  Carmine V6  T5
This car is now very nearly completely done. Sure to find something else, but not now.........
pinkyponk
Adrian Page
Berwick, Nova Scotia, Canada

May 15, 2017 11:06 AM
Top Contributor
Joined 6 years ago
9,189 Posts

In reply to # 3511605 by Fred Winterburn
For points ignitions if the current exceeds 4 amps through the point contacts, they will burn exponentially faster. 3 ohms limits the current so that it is only briefly higher than 4 amps at low rpm. It also keeps the coil from cooking itself to death when the points are closed continuously such as with the ignition on and the engine not running and the points just happening to be closed. With points, the primary side resistance should be a minimum of 3 ohms which includes any separate ballast resistor for a lower ohms coil. The two should add up to a minimum of 3 ohms. Exceeding 3.5 ohms starts to reduce spark energy more than it should. Fred
In reply to # 3511515 by pinkyponk
Why not 6 or 50? What's the dealio?
Adrian
Adrian
Thanks Fred. That's what I figured.
Adrian
Home built Eaton M62 Supercharger with 9psi boost, "stock" high ratio rocker arms, 8:1 compression, Piper 270 cam, ported head, matched manifolds, CB Performance computerized ignition.
May 15, 2017 04:03 PM
Top Contributor
Joined 2 years ago
5,811 Posts

CEI used the GM HEI transistor module, designed for 1.5 Ohms 4 cylinder, or .75 on V8s. No points to burn. Much better ignition. If the distributor had a decent curve, it would be an excellent system.
Points are limited to the 4 Amps. So, 3 Ohm coil ( or with the brilliant 1.5 Ohm/ballast resistor for starting boost) If we had not invented electronic ignitions, I would be wondering if iridium contacts would let us run 2 Ohms or less with a conventional system. Maybe some of the other tricks like bifurcated contacts.
As clever as the start boost system is, it does provide considerably less energy running as the primary inductance is a lot less. I would not run it on a 4cylinder. Of course, I prefer high energy electronic systems anyway.
Cogito ergo sum periculoso
Points are limited to the 4 Amps. So, 3 Ohm coil ( or with the brilliant 1.5 Ohm/ballast resistor for starting boost) If we had not invented electronic ignitions, I would be wondering if iridium contacts would let us run 2 Ohms or less with a conventional system. Maybe some of the other tricks like bifurcated contacts.
As clever as the start boost system is, it does provide considerably less energy running as the primary inductance is a lot less. I would not run it on a 4cylinder. Of course, I prefer high energy electronic systems anyway.
Cogito ergo sum periculoso
Steve S.
Stephen Strange
Harrisonburg, Virginia, USA
1972 MG MGB MkII "The Mouse Trap"

May 15, 2017 07:24 PM
Top Contributor
Joined 9 years ago
1,245 Posts

Scott
Although I'm not a specialist in ignitions systems as you are, I do know that that while unballasted ignition coils have the virtue of rapid charging times, they also release their stored energy faster, producing an ignition spark of shorter duration. For combustion to be triggered efficiently within the combustion chamber, the pressure wave that is produced by the squish (quench) of the fuelair charge between the piston and the edges of the combustion chamber must arrive in the vicinity of the spark plug either before or as the spark plug fires. However, due to the shorterduration ignition spark produced by an unballasted ignition coil, the accuracy of the ignition timing is of more critical importance. 6 Volt Ballasted ignition coils produce a longerduration ignition spark, therefore this is rarely a problem and the engine is less sensitive to small errors of ignition timing. Another advantageous factor of the 6 Volt ignition coil is that, having half the number of primary windings as a 12 Volt ignition coil, it also has half of the inductance of a 12 Volt ignition coil, but the condenser (capacitor) value is the same for both. This lower inductance that is inherent to the 6 Volt ignition coil means that it recharges more quickly when the contact breaker points close again (inductance in a component has the effect of causing the electrical current to build more slowly than in a pure resistance), therefore it can be used at higher engine speeds without a loss of High Tension (HT) output. So, why do you dislike that ballasted system? If it's energy that you like (and who doesn't on a cold winter's morning?), you can always install a Lucas Sport Coil for the ballasted system and get 40K Volts, no problem. This is what I run, and my compression ratio is 10:1. That's kinda high for today's 93Octane pump fuels. I do, of course, have to pay closer attention to the ignition timing and the carburetion, but I have no ignition shortcomings.
Edited 1 time(s). Last edit at 20170515 07:59 PM by Steve S..
Although I'm not a specialist in ignitions systems as you are, I do know that that while unballasted ignition coils have the virtue of rapid charging times, they also release their stored energy faster, producing an ignition spark of shorter duration. For combustion to be triggered efficiently within the combustion chamber, the pressure wave that is produced by the squish (quench) of the fuelair charge between the piston and the edges of the combustion chamber must arrive in the vicinity of the spark plug either before or as the spark plug fires. However, due to the shorterduration ignition spark produced by an unballasted ignition coil, the accuracy of the ignition timing is of more critical importance. 6 Volt Ballasted ignition coils produce a longerduration ignition spark, therefore this is rarely a problem and the engine is less sensitive to small errors of ignition timing. Another advantageous factor of the 6 Volt ignition coil is that, having half the number of primary windings as a 12 Volt ignition coil, it also has half of the inductance of a 12 Volt ignition coil, but the condenser (capacitor) value is the same for both. This lower inductance that is inherent to the 6 Volt ignition coil means that it recharges more quickly when the contact breaker points close again (inductance in a component has the effect of causing the electrical current to build more slowly than in a pure resistance), therefore it can be used at higher engine speeds without a loss of High Tension (HT) output. So, why do you dislike that ballasted system? If it's energy that you like (and who doesn't on a cold winter's morning?), you can always install a Lucas Sport Coil for the ballasted system and get 40K Volts, no problem. This is what I run, and my compression ratio is 10:1. That's kinda high for today's 93Octane pump fuels. I do, of course, have to pay closer attention to the ignition timing and the carburetion, but I have no ignition shortcomings.
Edited 1 time(s). Last edit at 20170515 07:59 PM by Steve S..
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