12 volt coil with resistor

[f balsiger]

will a 12v coil with resistor send 12v to the points? I don't understand if the resistor lowers voltage or ohms

[rotorwrench]

The ballast resistor is more for current control than dropping the voltage even though it does both (basic OHM's Law). The coil doesn't need to draw as many amps with the higher voltage. Some coils are designed with higher primary coil resistance so that they can be run direct off 12-volt but there are still plenty of 1.5 ohm primary coils out there. The 3.0 ohm primary coil is more for a 12-volt system.

[redmodelt]

When cold it will send 12 volts to the points, as the resistor warms up it creates more resistance dropping the voltage to points. That is why many cars have a bypass for starting, so even if the resistor is warm the system sends full voltage for hotter spark for starting.

[rotorwrench]

Brand X (GM) actually had a bypass circuit to bypass the resistor or resistance wire so that it would have a full 12-volt while the starter was turning. Ford did that later to some extent but they had a different type solenoid than GM. The resistor will heat up as soon as the points are closed so they warm up almost instantaneously but it certainly controls the current by bleeding off what it doesn't need to function. The old Ford/Mallory coils only needed around 3 or 4 volts to function normally. Much more than that would burn them up. Can type coils can take a lot more heat so most never needed a ballast running on 6-volts. Modern insulating materials allow coils to take a lot more heat than they ever could before.

[Purdy Swoft]

I use the three OHM Pertronix flamethrower coil on my 12 volt converted 31 roadster . No resister is used or needed when a three OHM coil is used on a twelve volt system . No wires will need to be changed or reversed as long as it remains positive ground . . If a person feels that they need or must use a negative ground setup , reverse the wires at the coil and ammeter . The battery must be connected negative ground and you will be hooked up negative ground . I don't know what voltage is sent to the distributor but it works and I have had no problems with it .

If a 1.5 Ohm coil is used on 12 volts it will be necessary to use a resistor . Coils are rated in OHMs . In other words three Ohm for twelve volt will make a cleaner more ioriginal look without a resister .

There can be confusion between a six volt and twelve volt coil . When buying at a local parts house , I find it is best to ask for a coil in OHMs rather than volts Some counter people still won't know the difference and there will be NO telling what coil that you may end up with . Usually they will ask what year and model vehicle the coil is for . If you tell them the coil will be used on a model A Ford , they will usually tell you that they don't have one . This is why The OHM rating is sio important . I mostly order my coils from Pertronix and ask for three OHM for twelve volts or one point five OHM for six volts . .

[30 Closed Cab PU]

Sponsored Links (Register now to hide all advertisements)

I've read that some like running 6v coils with the external resistor on 12 V systems.
Power dissipation of teh coil is substantially reduced since the power in the circuit is shared by the resistor. The benefit is the coil runs cooler and extends the coils life.

[Patrick L.]

Originally Posted by f balsiger

will a 12v coil with resistor send 12v to the points? I don't understand if the resistor lowers voltage or ohms

The easy and fast answer is no. Points don't like or live long on anything greater than 8v. The lower the voltage the better, to a point. [ pun intended]

[30 Closed Cab PU]

On a 12v system if you measure across open points it measures 12V. When points are closed it drops to 0V since one side is ground. This is for all combinations. Since there is no current flow, voltage is not dropped across the components of the system.


You do not use an external resistor on 12 V coils in 12 volt systems, The 6 V coil has an internal resistor of 1.5 ohms., so when used in 12 systems an external 1.5 ohm resister is added. The 12v coil has a 3 ohm internal resistor.


The external 1.5 ohm resistor is only used if you have a 12v system with a 6v coil.


It is mostly the current that causes points issues if a resistor is not used with the 6 v coil.


Additionally if the resistor is not used in 12v systems/6 volt coil - the coil has to dissipate a lot more heat/power than it was designed for.

[rotorwrench]

When the points are closed and the ignition switch is on then the coil is in effect an electromagnet so it does drop some current to maintain the electromagnetic field. This is why some folks end up with a burnt up coil if they forget to turn off the ignition and the points just happen to be closed. The primary will generate a lot of heat and some coils just can't take it.

When Ford changed over to 12-volt in 1956, they added a ballast resister to the system so they could use the same coil but keep the current in check. They did that for a long time. In the modern era, there are a lot better materials for manufacturing ignition coils than there were back when they changed over to 12-volts.

The breaker points can take whatever the system is designed for as long as they have a good condenser to make & break the circuit with. The condenser protects the points and slows the collapse of the magnetic field in the coil core just a bit. This makes for an efficient high tension induction force to the secondary winding and on to the spark plug. Bad condenser equals burnt points and poor or no spark.

[redmodelt]

Don't many 12 volt coils have a built in resistor?

[Patrick L.]

Originally Posted by redmodelt

Don't many 12 volt coils have a built in resistor?

Many/most do, but, many don't. Thats why the ohm rating is important to know. Most with a resistor installed will state it on the case, but, then again, some don't.

[Patrick L.]

I won't get into the voltage at the points discussion, only to say points will not stand 12v for very long.

[Bob Bidonde]

In 12V electrical systems with breaker point ignitions, ignition coils start the vehicle on 12V through the coil, and the resistor drops the coil to 6V to 8V once the engine is running.

[rotorwrench]

All ignition coils have a built in resistor. It's called a primary winding. More turns, more resistance.

[Tacoma Bob]

My head hurts.

[30 Closed Cab PU]

Originally Posted by rotorwrench

When the points are closed and the ignition switch is on then the coil is in effect an electromagnet so it does drop some current to maintain the electromagnetic field. This is why some folks end up with a burnt up coil if they forget to turn off the ignition and the points just happen to be closed. The primary will generate a lot of heat and some coils just can't take it.

When Ford changed over to 12-volt in 1956, they added a ballast resister to the system so they could use the same coil but keep the current in check. They did that for a long time. In the modern era, there are a lot better materials for manufacturing ignition coils than there were back when they changed over to 12-volts.

The breaker points can take whatever the system is designed for as long as they have a good condenser to make & break the circuit with. The condenser protects the points and slows the collapse of the magnetic field in the coil core just a bit. This makes for an efficient high tension induction force to the secondary winding and on to the spark plug. Bad condenser equals burnt points and poor or no spark.

This is one of the best/thorough explanations I've seen. You have to read/understand every word, every word is important. - Thanks

[Gold Digger]

I'm not too technological on electronics and electrical. That being said I have done real well keeping trucks and cars running up till all of this new computer age. Here's one for you, I bought a 30 model A a few years back with a 12 volt modern Motorcraft coil on it. I noticed this as soon as I raised the hood but didn't get around to changing it and it ran so good I never have changed it because I am still running 6-volt. Never had a problem yet after 4 years driving.

[Purdy Swoft]

Originally Posted by 30 Closed Cab PU

I've read that some like running 6v coils with the external resistor on 12 V systems.
Power dissipation of teh coil is substantially reduced since the power in the circuit is shared by the resistor. The benefit is the coil runs cooler and extends the coils life.

Some may want to run an original Ford script coil , Others may just not want to spend the money for a new coil . If running a six volt coil on twelve volts a resistor mounted at the coil connection will be needed or the coil will burn out . The three Ohm coil will give hotter spark than the six volt coil being used on twelve volts with a resister . I run a three Ohm coil on twelve volts and my coil doesn't get hot . I use the Pertronix three Ohm Flamethrower coil . The Flame thrower coil is a performance coil that will add power that can be felt . The spark comes from the coil . I'm not saying that a performance coil must be used . its just a matter of choice . The model A needs all the help it can get !!!

[30 Closed Cab PU]

Originally Posted by Purdy Swoft

Some may want to run an original Ford script coil , Others may just not want to spend the money for a new coil . If running a six volt coil on twelve volts a resistor mounted at the coil connection will be needed or the coil will burn out . The three Ohm coil will give hotter spark than the six volt coil being used on twelve volts with a resister . I run a three Ohm coil on twelve volts and my coil doesn't get hot . I use the Pertronix three Ohm Flamethrower coil . The Flame thrower coil is a performance coil that will add power that can be felt . The spark comes from the coil . I'm not saying that a performance coil must be used . its just a matter of choice . The model A needs all the help it can get !!!

Am just trying to understand.



Why does the 12 V coil give a hotter spark than a 6 Volt coil with resistor? Both draw the same current, and both use the same spark plug gap/points gap. What am I missing? Does the 12v Coil Store more energy for the discharge? If so wouldn't that be hard on the points?

[rotorwrench]

The coil doesn't store any energy. It's just an inductor. Induction coils generally don't work on direct current (DC) power but they will work for alternating current (AC) power and are used a lot in electronics to step voltages up. They work for an automotive ignition due to the pulsating direct current provided by the breaker points since it is half wave alternating current.

A hotter spark is a product of more modern technology. The systems only need to create a spark hot enough to light off the flame front in the cylinder. If a designer wanted a hotter or higher voltage spark back in the day, it would cost them in lower reliability of the system components. After the advent of modern electronic ignitions, there was a lot less worry about reliability with breaker points and condensers since they no longer had them. Coils were designed with materials that can take a lot more heat so reliability was no longer a problem with them and they could add a lot more windings to increase voltage step up. They can generate a spark that can actually be heard snapping while the engines running on some designs. I could always hear the spark on the GM HEI set ups while the engine was idling. They had to have a lot wider gaps for the spark plugs as well. A DC points ignition would never be able to do this for very long.

The model T uses four trembler coils for its ignition (one for each cylinder). They put out a shower of sparks instead of just one spark per ignition event. That makes them hotter than any 6-volt coils but they were powered off a magneto set up on the flywheel.

The model A went to a can type coil that had an oil inside for an insulator so it could take some heat and not need a ballast to control current.

When the Ford V8 came out, they changed the coil to a different design that evolved with several different configurations but they had to have a ballast to control the current (heat) or they would lose reliability. They would put out just as hot a spark as the model A but they only used about half the voltage of a 6-volt system to do it.

When Ford went back to the can type coils for the 8BA in 1948, they did away with the ballast resistor and it didn't come back till they changed over to 12-volt systems. The ballast resistor is all about reliability in the old systems.

[jrelliott]

If you were to measure the voltage of the open points on a 12V system with a 6V coil and a ballast resistor, You would see 12V at the points as the volt meter is a very high resistance and draws VERY little current to make the reading. As soon as you close the points the reading of the voltage at the points would be 0 Volts. If you had the coil and the ballast resistor arranged so the wire from the ignitions switch went to the ballast resistor first then to the coil, you would see 12 Volts to the input of the ballast resistor and 6 Volts at the input to the coil and zero at the closed points. The 12Volts should be dropped equally across the two devices.

[redmodelt]

RE;The model T uses four trembler coils for its ignition (one for each cylinder). They put out a shower of sparks instead of just one spark per ignition event. That makes them hotter than any 6-volt coils but they were powered off a magneto set up on the flywheel.

Very true if running on battery, the coils will continue to fire as long as the roller is in contact with a segment in the timer. On magneto different thing. Because of the spacing of the 16 coils on the ring 16 magnets and length of segments in timer, they can get 2 and maybe 3 separate sparks from the coils at each firing of the cylinder. The magneto is an AC device and can put out as much as 35+ volts AC depending on engine speed.

[30 Closed Cab PU]

Originally Posted by rotorwrench

The coil doesn't store any energy. It's just an inductor. Induction coils generally don't work on direct current (DC) power but they will work for alternating current (AC) power and are used a lot in electronics to step voltages up. They work for an automotive ignition due to the pulsating direct current provided by the breaker points since it is half wave alternating current.

A hotter spark is a product of more modern technology. The systems only need to create a spark hot enough to light off the flame front in the cylinder. If a designer wanted a hotter or higher voltage spark back in the day, it would cost them in lower reliability of the system components. After the advent of modern electronic ignitions, there was a lot less worry about reliability with breaker points and condensers since they no longer had them. Coils were designed with materials that can take a lot more heat so reliability was no longer a problem with them and they could add a lot more windings to increase voltage step up. They can generate a spark that can actually be heard snapping while the engines running on some designs. I could always hear the spark on the GM HEI set ups while the engine was idling. They had to have a lot wider gaps for the spark plugs as well. A DC points ignition would never be able to do this for very long.

The model T uses four trembler coils for its ignition (one for each cylinder). They put out a shower of sparks instead of just one spark per ignition event. That makes them hotter than any 6-volt coils but they were powered off a magneto set up on the flywheel.

The model A went to a can type coil that had an oil inside for an insulator so it could take some heat and not need a ballast to control current.

When the Ford V8 came out, they changed the coil to a different design that evolved with several different configurations but they had to have a ballast to control the current (heat) or they would lose reliability. They would put out just as hot a spark as the model A but they only used about half the voltage of a 6-volt system to do it.

When Ford went back to the can type coils for the 8BA in 1948, they did away with the ballast resistor and it didn't come back till they changed over to 12-volt systems. The ballast resistor is all about reliability in the old systems.

Now my brain hurts. Will have to let this sink in, reread multiple times, and let it digest in my brain. You are too good/smart and I am at the limits of trying to fully comprehend this. Not complaining, just feel like I am back in electronics school, and learning how it applies to the A.

[Purdy Swoft]

Originally Posted by rotorwrench

The coil doesn't store any energy. It's just an inductor. Induction coils generally don't work on direct current (DC) power but they will work for alternating current (AC) power and are used a lot in electronics to step voltages up. They work for an automotive ignition due to the pulsating direct current provided by the breaker points since it is half wave alternating current.

A hotter spark is a product of more modern technology. The systems only need to create a spark hot enough to light off the flame front in the cylinder. If a designer wanted a hotter or higher voltage spark back in the day, it would cost them in lower reliability of the system components. After the advent of modern electronic ignitions, there was a lot less worry about reliability with breaker points and condensers since they no longer had them. Coils were designed with materials that can take a lot more heat so reliability was no longer a problem with them and they could add a lot more windings to increase voltage step up. They can generate a spark that can actually be heard snapping while the engines running on some designs. I could always hear the spark on the GM HEI set ups while the engine was idling. They had to have a lot wider gaps for the spark plugs as well. A DC points ignition would never be able to do this for very long.

The model T uses four trembler coils for its ignition (one for each cylinder). They put out a shower of sparks instead of just one spark per ignition event. That makes them hotter than any 6-volt coils but they were powered off a magneto set up on the flywheel.

The model A went to a can type coil that had an oil inside for an insulator so it could take some heat and not need a ballast to control current.

When the Ford V8 came out, they changed the coil to a different design that evolved with several different configurations but they had to have a ballast to control the current (heat) or they would lose reliability. They would put out just as hot a spark as the model A but they only used about half the voltage of a 6-volt system to do it.

When Ford went back to the can type coils for the 8BA in 1948, they did away with the ballast resistor and it didn't come back till they changed over to 12-volt systems. The ballast resistor is all about reliability in the old systems.

The original model A coil was TAR filled , not oil Filled . Many times it makes NO difference what the original designer wanted !!! Modifications have always been the choice of the owner of the vehicle . I don't need electronic ignition for hotter spark or reliability of original system components . I use original distributor with points and have never had a problem with burned points with my 12 volt setup . Again , when a three ohm coil is used , No resistor will be required to run twelve volts . The system can be made to run with a six volt coil and resistor on twelve volts but you will be using the weaker one point five OHM coil . The resistor will be in full view and will get too hot to touch . The resistor needs to be in the open because of heat . I don't need a resistor with my 12 volt system and the coil doesn't get hot . The coil gets warm but I can grab the coil with my hand without getting burned and I use a forty thousand volt coil . I know that it doesn't put out forty thousand volts at all times and probably no time on a low RPM model A engine without other mods . Most Model A people probably don't use electronic ignition . there are many ways to warm up the original ignition for quicker starts and better performance , anybody that doesn't want it certainly doesn't have too bother

[rotorwrench]

I remember when the first ACCEL super coils came out. A friend of mine just had to have one for his 1970 Chevelle SS with the 454. He swore up and down that it had more power with that big yellow hunk of crap in there but he got really tired of replacing points & condensers every other weekend.

You can put a ballast resistor from a 1948 Ford with the rabbit ear distributor and hook it up with a can type 6-volt coil and it will still put out a good spark even though it doesn't need one. Ford elected not to use it since it worked reliably without it.

They did use a tar in the old coils clear back to the model T era. It's like type III roofing tar. If you ever see an old coil that overheats and breaks open then you'll see that it pours right out of the can when it's hot. It only takes about 140 degrees F to start it to liquefy. Coils can get pretty warm in service. Modern coils are generally filled with epoxy resin of a sort that can take a lot of heat. This is how they can work well with a 3 Ohm primary winding and not get hot. Generally they will work with point & condenser since they won't draw any more current than a standard can type 1.5 Ohm coil with a ballast. You will find though that high energy coils with more windings are hard on condensers which in turn will be hard on points. They are designed for breakerless ignition systems.

Most folks that convert to electronic ignitions now days don't care if it's a high energy system. They just want to get away from points & condensers for a long and trouble free operation.

[30 Closed Cab PU]

Sponsored Links (Register now to hide all advertisements)

Know we are delving deep into theory, I apologize. My personality latches onto things like a dog with a bone, just will not let go. Sometimes lay awake at night not able to sleep, trying to make sense of things.


Have been thinking about this, this morning. And realized I do not know what a "Hotter Spark" actually is, and what makes a hotter spark. Just that it seems to be desirable sometimes, and seems to improve combustion (a good thing), but can be hard on other system components if they are not designed for hotter spark.


Rotorwrench - "The model T uses four trembler coils for its ignition (one for each cylinder). They put out a shower of sparks instead of just one spark per ignition event. That makes them hotter than any 6-volt coils but they were powered off a magneto set up on the flywheel."


I get that multiple sparks increase combustion, same concept as multiple spark plugs per cylinder. Which I believe some cars have, and also on motorcycles.


On Ts - So the individual sparks are not hotter, but since there are multiple sparks that makes the total ignition event hotter?


One of the areas that confuses me is that in order to take advantage of a hotter coil, do you have to increase plug gap? I am unclear of the voltage/current relationship and how it affects Gapping in the ignition circuit.


Was an electronic repair tech 1st 20 working years, know enough theory to be dangerous, but not enough theory to design/engineer.


Please comment.

[Purdy Swoft]

Just because a performance coil is used doesn't mean that points and condensers will fail on a weekly basis or at all . If points and condensers are failing on a regular basis there are other problems . I'm pretty sure that ACCEL super coil did give your friends car more power .

In a nut shell , the use of a performance coil is WAY over yours and closed cabs heads !!! Your ignorance speaks for its self and really doesn't help anybody .. There is a lot of people that are interested in a twelve volt upgrade and YES I did say upgrade . I only posted information on how I did mine for others that may be interested in the same . I suggest that you don't read any of my posts because they are likely more than you can grasp !!!!!!!

[30 Closed Cab PU]

Originally Posted by Purdy Swoft

Just because a performance coil is used doesn't mean that points and condensers will fail on a weekly basis or at all . If points and condensers are failing on a regular basis there are other problems . I'm pretty sure that ACCEL super coil did give your friends car more power .

In a nut shell , the use of a performance coil is WAY over yours and closed cabs heads !!! Your ignorance speaks for its self and really doesn't help anybody .. There is a lot of people that are interested in a twelve volt upgrade and YES I did say upgrade . I only posted information on how I did mine for others that may be interested in the same . I suggest that you don't read any of my posts because it is likely more than you can grasp !!!!!!!

No need to be rude/name calling, excuse me for asking and trying to learn. Thought learning was part of what this forum is for. I do not believe I have disagreed with you, if yes and I was rude I apologize.

[Purdy Swoft]

Originally Posted by 30 Closed Cab PU

No need to be rude/name calling, excuse me for asking and trying to learn. Thought learning was part of what this forum is for. I do not believe I have disagreed with you, if yes and I was rude I apologize.

.


Maybe I was quick to anger . I thought I explained every detail of how I did my 12 volt setup . It just seemed to me that you and rotowrench were trying to say that what I did would result in burned points and condensers on a weekly basis .

I do try to give helpful information with every minute detail of what I have did with my model A's that has worked well for me .

No modifications are necessary unless a person drives the model A a lot and wants .to make improvements . Just about everything about the model A can be improved . Brakes and more power for hills is probably the most popular mods.

I only try to give back some of the things that I have lerarned about the model A over the past sixty years . Otherwise I get nothing from posting here . I should probably quit wasting my time.

I really don't care what modifications that others make to their model A.

[Patrick L.]

Purdy, don't leave again. The info you give is good, always has been. Don't worry about this.

[Patrick L.]

The burnt points on the Chevelle was just caused by the wrong coil, in that it needed a ballast resistor. Been thru this more times than I care to think about.

Sometimes a different condenser is needed depending on how the points are 'burning'.

Ballast resistors have been used by just about every manufacturer at one time. Some were included into the start circuit, some not.

[30 Closed Cab PU]

Originally Posted by Purdy Swoft

.


Maybe I was quick to anger . I thought I explained every detail of how I did my 12 volt setup . It just seemed to me that you and rotowrench were trying to say that what I did would result in burned points and condensers on a weekly basis .

I do try to give helpful information with every minute detail of what I have did with my model A's that has worked well for me .

No modifications are necessary unless a person drives the model A a lot and wants .to make improvements . Just about everything about the model A can be improved . Brakes and more power for hills is probably the most popular mods.

I only try to give back some of the things that I have lerarned about the model A over the past sixty years . Otherwise I get nothing from posting here . I should probably quit wasting my time.

I really don't care what modifications that others make to their model A.

As said in the previous post - please do not leave, the info you post I find helpful and appreciated. Sometimes I am a little thin skinned. I was concerned/confused as to what happened. Hopefully this straightens things out. I know I can be a PIA when I do not understand things. Like a dog with a bone, just will not let things go. I apologize for this.


No Worries - After reading your last post and re-reading mine, seems my post could be taken as I was posting the info as facts, and that was not the intention. I could have done a better job of prefacing the post as "this is how I understand things, please correct me". Email/forums can lead to a lot of miscommunications/misunderstandings.


To tell you the truth, I still do not understand why systems with hotter spark do not affect life of the other ignition components. Will chaulk it up as beyond my comprehension and let it go. Additional discussion not needed.


Also I agree that updates/upgrades are worthwhile if you have the desire/cash/time/ability to do them.


Happy Thanksgiving, hope you have a good one.

[Purdy Swoft]

Thanks Pat I'm probably not going anywhere unless it gets worse . Sometimes I just get agrivated when I try to give what I feel may be helpful info and it seems that some will jump right on it . I agree that a resistor was needed or the wrong resister was used . A twelve volt conversion isn't a crime . Nether is a performance coil . Most have never tried a performance coil because they just didn't know how much it could help . The people that used a performance 12 volt coil probably knew about resistors and which one to use . I was only trying to tell how I did mine for those who may be interested .

[Purdy Swoft]

Originally Posted by 30 Closed Cab PU

As said in the previous post - please do not leave, the info you post I find helpful and appreciated. Sometimes I am a little thin skinned. I was concerned/confused as to what happened. Hopefully this straightens things out. I know I can be a PIA when I do not understand things. Like a dog with a bone, just will not let things go. I apologize for this.


No Worries - After reading your last post and re-reading mine, seems my post could be taken as I was posting the info as facts, and that was not the intention. I could have done a better job of prefacing the post as "this is how I understand things, please correct me". Email/forums can lead to a lot of miscommunications/misunderstandings.


To tell you the truth, I still do not understand why systems with hotter spark do not affect life of the other ignition components. Will chaulk it up as beyond my comprehension and let it go. Additional discussion not needed.


Also I agree that updates/upgrades are worthwhile if you have the desire/cash/time/ability to do them.


Happy Thanksgiving, hope you have a good one.

I'm very sorry if I took things wrong . No hard feelings, just my bad . I'm sorry that I was Rude . Please forgive . Happy thanksgiving .

[Mike V. Florida]

Originally Posted by f balsiger

will a 12v coil with resistor send 12v to the points? I don't understand if the resistor lowers voltage or ohms

I'm going to try this without formulas and such.


A coil without a resistor with 6 volts in will give 6 volts out.
The same coil with 12 volts will give 12 volts out and would be too much for the points to last a long time. So we add a resistor equal to the resistance of the coil. Now with 12 volts in the voltage is split in two (because the resistance is the same) and the voltage to the points is 6 volts.


The resistor can be internal to the coil or external to the coil.

[rotorwrench]

As I mentioned before, an ignition coil is an inductor. Inductor coils step up voltage. The amount the coil steps the voltage up depends on the number of turns in the primary windings versus the number of turns in the secondary windings. The primary has larger gauge wire with fewer number of turns and the secondary has a very fine gauge wire with a very large number of turns. There is a laminated iron core in there that acts as the electromagnet to build a field. Both primary and secondary coils are wound around the laminated iron core. The primary coil winding is connected to one of the terminals at one end and the other terminal at the other end. The secondary winding is only connected to one of the terminals and the other end is connected to the tower where the coil wire terminal to the distibutor is. This internal connection of the secondary is what sets the polarity of the coil. It is generally connected at the negative terminal but now days it's muddier water than it was back in the day. They labeled a lot of coil terminals as dist & ign so a mechanic would know where to connect but that was with positive ground systems.

The average ignition coil has a 100:1 turn ratio for a step up from say 150 to 250 peak primary voltage to 15,000 to 25,000 volts in the secondary. Now that's still a hot enough high tension voltage to jump a pretty good gap. When aftermarket manufacturers try to increase the turn ratio with a higher secondary winding rate then the output high tension voltage can go as high as 50,000 volts but at some point, if the ratio is too high, the voltage starts to drop off so this is limited on how much the voltage can be stepped up. This also puts a heavier load on the condenser which is just a simple capacitor so it can only build so much charge and can get more feed back from the coil during the induction process. Dwell time for coil core saturation is also limited by rpm with a single ignition coil.

A lot of manufacturers of aftermarket coils want to sell products so they can have some pretty outrageous claims about their products. Since most folks would never have the capability to put their claims to a test then they would never know if they are true. An oscilloscope can tell but you don't even see those around much anymore.

Modern cars generally have one coil per cylinder so dwell time is not even a consideration since its all electronically controlled. They would operate at rpms that the engines could never reach.

The term hotter is all about the output high tension voltage. The higher the voltage the hotter the spark.

[katy]

When aftermarket manufacturers try to increase the turn ratio with a higher primary winding rate then the output high tension voltage can go as high as 50,000 volts

Methinks you mean a higher secondary winding rate , not higher primary. It's all a matter of ratio.

Sometimes a different condenser is needed

That's correct, the condenser needs to be matched to the coil.

[rotorwrench]

My bad. I've corrected my error. But primary coil windings can also be involved at the same time. It's really about the ratio though.

The condenser has to be able absorb the counter EMF that's generated when the points open in the primary circuit so it does have to be matched to the coil design. The resonance depends on that.

[Ranchero50]

I always thought the resistor was more for having the ignition on and the points closed to dissipate the current through heat that would otherwise be dissipated through the coil. It's interesting that Ford in the late '60's used a 6' long resistor wire that was taped inside the main harness behind the dash for that purpose. The firewall connection tee'd and also went to a "start" lug on the solenoid to apply full voltage to the coil when the starter was turning over.

I'm about to the point of wiring the ignition on m speedster and trying to come up with a strategy. I have a new distributor but don't know what guts are in it. It did have a 12v GM alternator so maybe it's already set up for 12vdc.

[30 Closed Cab PU]

Not so on a Points system. If points and ignition are on for a length of time, the coil becomes extremely hot, think I have heard stories of things melting, points going bad, etc. That's one reason why every time you leave an A, check your ammeter to make sure everything 0s.


Mathematically - 12v/3ohm coil - 4amps, Power generated if ignition on and points closed 4amps x 12 volts = 48 watts. So the coil has to be able to dissipate 48 watts in a hot engine bay in the middle of the summer. For a 6 volt 1.5 ohm coil is 24 watts.


By using a 6 v 1.5 ohm coil with a 1.5 ballast resistor on 12v, the heat is shared , and the coil only has to dissipate 24 watts.


Other reasons for checking your ammeter are driving during the day with your headlights on and forgetting to turn them off, bad shorted stop switch ( or misadjusted or worn brake link a components), a malfunctioning cuttoff, and other various wiring issues.


If above is incorrect or you disagree, am open to learning new stuff and/or being corrected.

[rotorwrench]

The math looks close enough for me per Ohms law.

For Ranchero50
The resistor wires were used by all the big 3 and probably others too. The heat was dissipated over the length of the resistor wire so it wasn't all in one spot. I'm not sure what the coil specs were for those systems either. The mounted ballast is usually 1.3 to 1.5 Ohms and are easy to work with for a 1.5 Ohm coil. I prefer to use the components I know for building a system from scratch. On a GM engine, I'd use an HEI type system with 12-volt. On a Ford engine, I'd use what ever came with that engine unless it has an old Load-O-Matic. Those systems were tied to the carburetor and don't work well without the original carb. The type of vacuum advance signal also has to be considered. Many conventional breaker types can be changed to electronic systems if a person doesn't want points & condenser.

A person always has to keep in mind that a 6-volt system runs at around 7.1 to 7.6-volts in operation. The 12-volt systems are closer to 14-volts in operation with the generator or alternator on line.

[Purdy Swoft]

If the ignition switch is left on without the engine running , if the points are closed the coil will get hot whether a resistor is used or not . When a resistor is used with a six volt 1.5 ohm coil , the resistor prevents full voltage from entering the coil . If full 12 volt voltage was connected to a six volt coil it would burn out the coil unless it had the proper resistor to protect it .