JMOR, A resistor question.

[Jim.ME]

no matter if you have 6v or 12v square front mount coil you need the resistor that changes resistance with temperature , otherwise eventually you will need another new coil, .

Why would you need it if the 12 volt square coil has the proper resistance to use in a 12-volt system. You don't use a resistor with a true 12-volt "can" coil.

 

[Hobo,NC]

Why would you need it if the 12 volt square coil has the proper resistance to use in a 12-volt system. You don't use a resistor with a true 12-volt "can" coil.

Your true 12-volt "can" coil has a primary resistance of 3.15 to 3.48.
A so called 12V coil 2.5 so you tell me.
Its recommended to keep the amps in the 4.0 ohm range to get in the 4amp arange the OEM resistor is needed. When using a square can coil I use the OEM resistor on all front mount applications 6 are 12 points are EI. They have all lived a happy life.

I am advocate to ditch the square can coil all together, life will be good.

 

[Jim.ME]

Your true 12-volt "can" coil has a primary resistance of 3.15 to 3.48.
A so called 12V coil 2.5 so you tell me.
Its recommended to keep the amps in the 4.0 ohm range to get in the 4amp arange the OEM resistor is needed. When using a square can coil I use the OEM resistor on all front mount applications 6 are 12 points are EI. They have all lived a happy life.

I am advocate to ditch the square can coil all together, life will be good.

I agree with the resistor if the ohms aren't right. 2.5 ohms is low for 12-volt coil resistance. So, the real answer sounds like the most, if not all, square 12-volt coils are not up to spec resistance wise for stand alone12-volt use (as 12 volt "can" coils are), thus the standard has become you must leave the OEM resistor with either the 6 or 12-volt square coils.

 

[JMOR]

I agree with the resistor if the ohms aren't right. 2.5 ohms is low for 12-volt coil resistance. So, the real answer sounds like the most, if not all, square 12-volt coils are not up to spec resistance wise for stand alone12-volt use (as 12 volt "can" coils are), thus the standard has become you must leave the OEM resistor with either the 6 or 12-volt square coils.

You are catching on.

 

[Jim.ME]

You are catching on.

I thought this was the case, but wanted to see if someone would just come out and say that 12-volt square can coils, at least most, are not true stand-alone 12-volt coils, as they are designed with lower resistance so they need that resistor. I really liked Tim's answer of "So, the reason to leave the OEM resistor assembly in place when doing a 12-volt conversion, using a 12-volt coil, is because it is easier and best for a rookie."

 

[Jim.ME]

I thought this was the case, but wanted to see if someone would just come out and say that 12-volt square can coils, at least most, are not true stand-alone 12-volt coils, as they are designed with lower resistance so they need that resistor. I really liked Tim's answer of "So, the reason to leave the OEM resistor assembly in place when doing a 12-volt conversion, using a 12-volt coil, is because it is easier and best for a rookie."

And I can agree with Hobo saying ditch the square coil especially if totally rewiring as 12 volts and or EI.

 

[wore out]

I thought this was the case, but wanted to see if someone would just come out and say that 12-volt square can coils, at least most, are not true stand-alone 12-volt coils, as they are designed with lower resistance so they need that resistor. I really liked Tim's answer of "So, the reason to leave the OEM resistor assembly in place when doing a 12-volt conversion, using a 12-volt coil, is because it is easier and best for a rookie."

"but wanted to see if someone would just come out and say that 12-volt square can coils, at least most, are not true stand-alone 12-volt coils, as they are designed with lower resistance so they need that resistor"

With today's parts from "The Land of Almost Right" HOW could anyone come out and say that with certainty?

Even if one "batch' from one supplier was checked and turned out to have a certain resistance that isn't to say how the next batch would be.

Jim. you must have missed the good old days on here when (now deceased) "N" GURU/Sparky Meister "Dell" used to rant about the "weak sister" front-mount/square can coils and the need to keep the OEM resistor and, in some cases, even add an extra .5 Ohm resistor with the so-called 12 Volt versions! You would have gotten quite an "earful" buy now!

Those coils have never known to be very robust, there's a bit of copper and steel in there, surrounded by "pitch" inside a big "plastic" container and they sit in a hot location just behind the radiator and fan.

The theory here has always been that it's best to keep primary current and thus HEAT under control so the "pitch" doesn't melt.

Looking at this another way, with the OEM resistor left in place, if spark is adequate and the engine runs well, what is the "harm" in the resistor being there?

 

[Jim.ME]

With today's parts from "The Land of Almost Right" HOW could anyone come out and say that with certainty?

Even if one "batch' from one supplier was checked and turned out to have a certain resistance that isn't to say how the next batch would be.

Jim. you must have missed the good old days on here when (now deceased) "N" GURU/Sparky Meister "Dell" used to rant about the "weak sister" front-mount/square can coils and the need to keep the OEM resistor and, in some cases, even add an extra .5 Ohm resistor with the so-called 12 Volt versions! You would have gotten quite an "earful" buy now!

Those coils have never known to be very robust, there's a bit of copper and steel in there, surrounded by "pitch" inside a big "plastic" container and they sit in a hot location just behind the radiator and fan.

The theory here has always been that it's best to keep primary current and thus HEAT under control so the "pitch" doesn't melt.

Looking at this another way, with the OEM resistor left in place, if spark is adequate and the engine runs well, what is the "harm" in the resistor being there?

Yes, I missed the good old days when Dell was here, so didn't have this back story. To me the question arose after someone had a burnt-out OEM resistor, was doing a 12-volt conversion (with a square coil) and asked if the OEM resistor was needed. The answer is always it is required, which doesn't fit with telling folks, having or doing conversions on other systems, including the Fords with side mounts. to use a 12-volt coil to eliminate the need for a ballast resistor.

Being familiar with the can coil where a resistor is not needed when doing a conversion to a 12-volt coil, it would seem the resistor wouldn't be needed with a 12-volt square coil. Now this discussion has gotten to the real answer, they may be called 12-volt coils but most, and maybe all, actually are not if resistance is checked, thus they can pass more current, Therefore the resistor is needed. reduce current(heat) in the coils as well as it can prolong point life. This now sounds like using a ballast resistor between the OEM resistor and a 6-volt coil is as good as spending money on a new 12-volt coil. Or convert to a 12-volt can coil and eliminate all resistors.

I wasn't saying the PTC resistor wouldn't work, Low resistance when cold will have minimal affect (kind of like a resistor bypass setup) at startup but provide some protection for the coil as it warms and extra resistance won't affect the spark as much. I was just trying to get the base reason behind why it is said you have to have it with both 6- and 12-volt coils, or better yet it's easier for rookies. Hopefully, in the future someone going through a conversion will read this thread and get the reasoning behind the "it must be there" for both square coils. Trying to bring the old info to the top so the "rookies" can learn. To me that helps them more that "just do it because we said". That's why I have been trying to get an earful here.

 

[professorx]

The points get damaged if you run too many amps through them. About 4 amps is right for them. Less amperage and they survive better but the spark is weaker.

With the coil it is harder to give advice as coils are available in so many different resistances. On a tractor you can run the engine slowly and it does not have many cylinders so the points dwell time is longer. This all to the good for points ignition. The ballast resistor is important for easy starting because it can be briefly bypassed to put full system voltage to the coil( overvoltage ) for a big strong spark when it is most needed. So much current flows through the coil when starting that it will soon burn out if the current is not reduced to a safe level by the ballast resistor.

If the voltage for the coil is enough, you can start on reduced voltage with no ballast resistor but it is iffy. The above applies to either 6 or 12 volt systems. Do not confuse other resistors with ignition ballast resistors.

Now you are on your own. Some coils have internal ballast resistors which heat up and then reduce coil primary winding voltage. Other coils must have external ballast resistors. Coils are made in different ohm ratings The coil and ballast resistor are designed as a pair. Very low resistance coils are made only for high systems without breaker points. Although they look alike, they may not be alike.

For a tractor, a points ignition system is simple and reliable giving excellent starting.

 

[Jim.ME]

The points get damaged if you run too many amps through them. About 4 amps is right for them. Less amperage and they survive better but the spark is weaker.

With the coil it is harder to give advice as coils are available in so many different resistances. On a tractor you can run the engine slowly and it does not have many cylinders so the points dwell time is longer. This all to the good for points ignition. The ballast resistor is important for easy starting because it can be briefly bypassed to put full system voltage to the coil( overvoltage ) for a big strong spark when it is most needed. So much current flows through the coil when starting that it will soon burn out if the current is not reduced to a safe level by the ballast resistor.

If the voltage for the coil is enough, you can start on reduced voltage with no ballast resistor but it is iffy. The above applies to either 6 or 12 volt systems. Do not confuse other resistors with ignition ballast resistors.

Now you are on your own. Some coils have internal ballast resistors which heat up and then reduce coil primary winding voltage. Other coils must have external ballast resistors. Coils are made in different ohm ratings The coil and ballast resistor are designed as a pair. Very low resistance coils are made only for high systems without breaker points. Although they look alike, they may not be alike.

For a tractor, a points ignition system is simple and reliable giving excellent starting.

People regularly say a 12-volt coil has an internal resistor. Many years ago, there were a few coils with resistors mounted under a cap on the coil, however they are long out of production. As far as I know no 6- or 12-volt automotive type coils in production use internal resistors, they are wound to give the desired resistance for the operating voltage. You say some have internal resistors. Please provide the manufacturer, part number, and documentation for a coil in current production that has an internal ballast resistor.

 

[JMOR]

People regularly say a 12-volt coil has an internal resistor. Many years ago, there were a few coils with resistors mounted under a cap on the coil, however they are long out of production. As far as I know no 6- or 12-volt automotive type coils in production use internal resistors, they are wound to give the desired resistance for the operating voltage. You say some have internal resistors. Please provide the manufacturer, part number, and documentation for a coil in current production that has an internal ballast resistor.

Don't hold your breath waiting for that answer!

 

[Jim.ME]

Don't hold your breath waiting for that answer!

Ok, If you say so, I've been waiting for it.

 

[Eman85]

The ballast resistor is important for easy starting because it can be briefly bypassed to put full system voltage to the coil( overvoltage ) for a big strong spark when it is most needed. So much current flows through the coil when starting that it will soon burn out if the current is not reduced to a safe level by the ballast resistor.

N's don't have a bypass like autos do using the S terminal of the solenoid.

 

[JMOR]

N's don't have a bypass like autos do using the S terminal of the solenoid.

So many posters seem to think that every vehicle is the same as one that they knew a little about a long time ago, hence, such comments as you see here.

 

[wore out]

N's don't have a bypass like autos do using the S terminal of the solenoid.

Front-mount distributor "N's" have a PTC ballast resistor that has low resistance when first powered, making for better starting, then the resistance increases as the resistor heats up.

Many/most ignition systems that used a starting bypass used a FIXED VALUE ballast resistor.

 

[JMOR]

Front-mount distributor "N's" have a PTC ballast resistor that has low resistamce when for powered, making for better starting, then the resistance increases as the resistor heats up.

Many/most ignition systems that used a starting bypass used a FIXED VALUE ballast resistor.

https://imgur.com/XaaFeYj