Another Coil Question

When I started the restoration on my Fathers 1948 Super A it had been converted to 12V and already had a coil and resistor. The coil went out on one of our 140's so I took the coil off the SA and purchased a new Flame Thrower coil, 3.0 ohm, Carb E.O. # D-57-10 for the Super A. Works for all 12 V. systems, standard ignitor, 40,000 volts.

Purchased it two years ago and I threw the box away along with the instructions.

I went back to the place where I purchased it and he didnt know if I needed the resistor or not and didnt know if it had an internal resistor. This is the same coil they sell here at YT but they dont give any information.

I want to know if I can do away with the resistor?

If you buy a "tractor" coil the balest resister is built into the coil. That is why you never see external resisters from the factory.

The factory coil was only 25,000 volts.


When you add a high voltage coil [ automotive] the balest resister is "not" built in . You can run with out it but the coil will get very hot. If you happen to pull the ign switch on and not start it, it will start burning parts up [ points , cond ]

I learned this the hard way !!!!

I use a MSD blaster 2 coil with a balest resister i bought at the auto parts store.
Just make sure it is for a 12 volt system [car] and you will be fine.

I got one for a Dodge, all older Mopars used them.

All it does is drop the votage from the coil to the dist.

Napa has a coil with the builtin ballast resistor
P/N IC14SB for about $18.00. Hal

My 450 and 560 gassers both have factory resistors. In fact, using a resistor setup lets the tractor start with 12V to the coil and 6V when running, just the way IH wired it.

I walked into my Case/IH dealer the other day and he pulled an OEM resistor unit off the shelf. Pricey, but it bolts up to the coil bracket and looks pretty good.

Just about any coil I've ever seen has printed on it whether to use a resistor or not.

Chris B.

Yep, that's the way the Mopar resistors were set up -- ceramic (or resin) block with a flat strap on one side and a coil on the other.

Are you burning points? A vibrating set of points are designed to cary no more than 2 amps.anything more than that will arc and pit the points. If your coil is allowing more than 2 amps to the points add a resistor.

No resistor required. Read this link. David.....http://www.ytmag.com/articles/artint131.htm

Read the IGNITION section. David............

TX, if that coil inded has 3 ohms of primary winding resistance as measured between its lil + and - terminals, its suitable for 12 volts NO EXTERNAL BALLAST IS REQUIRED. If you use a 3 ohm (12 volt) coil PLUS a Ballast the coil current is reduced and the spark will be weaker !!!!!!!!!!!

A 12 volt coil has typically around 2.5 to 3.5 ohms of primary winding resistance while a typical 6 volt coil is more like 1.25 to 1.75 ohms. This limits the amount of current the points have to switch to around 4 amps and that points switching current is the limiting factor (to reduce premature points burn up) and why the coil resistance or the sum series of a coil plus any external ballast is such that 4 amps is around the max points current. Ohms law makes that equate to the 3 primary resistance ohms on 12 volt coils or 1.5 ohms on 6 volt coils.

The alternative is to use a 6 volt coil (say 1.5 ohms) PLUS an external series voltage dropping (12 to 6) Balalst Resistor also around 1.5 ohms so again on a 12 volt tractor the points current is around 4 amps I = E/R = 12/3 = 4 amps. NOTE one advantage of a 6 volt coil plus an external balalst on a 12 volt tractor is the ballast can be by passed while starting/cranking for a hotter startign spark, such cant be accomplished if theres no external ballast which can be temporarily by passed.

NOTE just cuz that coil is rated and is capable of rising to 40,000 volts DONT MEAN IT FIRES THE PLUG AT ANY SUCH VOLTAGE. The necessary voltage which the coil must rise to in order to arc jump current across its gap is a function of 1) The plug gap 2) The medium (compression and fuel) in which it fires. All else (compression and fuel and plug gap) being equal that HV coil wont fire at any higher voltage then the stock coil!!!

This high energy high voltage coils are more for when you use an elec ignition and run a wider plug gap in which case it indeed requires a higher voltage to fire. That coil dont hurt nuttin when used with points (if its 3 ohms) and if its more efficient due to better magnetic materials and improved mutual inductive coupling you can have less heat losses and discharge slightly more energy across the plug gap then with the stock coil but to get the most bang for the buck if you couple up a HV high energy coil with a faster more positive elec switch (replaces points) and run a wider plug gap you get a higher energy ignition.........

BOTTOM LINE if the coil is indeed 3 ohms (like a stock true 12 volt coil) primary resistance NO BALLAST IS REQUIRED AND USE OF ONE WILL MAKE A WEAKER SPARK. If it were a 6 volt (1.5 ohms) coil on a 12 volt tractor then YES a ballast is required.

John T in Indiana, retired Electrical Engineer

Thanks,

John, your info along with the link GA Dave (thanks) posted told me everything I needed to know.

Reason I asked was I wanted to put the wire on the opposite side of the tractor and there isnt a place to mount the resistor. Plus that thing is kind of stuck out there and I just didnt like it. Im kind of picky when it comes to my tractor.

May have to wait til it cools off, over 100 every day and even hotter in that metal building.

Thanks everyone!

John T

Sounds like you know what your talking about ! You might want to go to MSD s website. A ballest resister doesn't effect spark performance in anyway, it is for lack of better wording a inline fuse.

I "not" douting you know what your talking about. If it made for a weaker spark then what would the point of it be?

Hotter coils are used to burn fuel better.
Yes we open gaps on plugs bigger with hotter spark but not with out a CDI.

[CDI] the red box MSD sells. Under high rpm compression puts spark "out", CDI won't let that happen so a bigger gap can be used. [fact]

If a ballest resister made for a weaker spark why the hell did they put them on every HEMI car or wedge car i have ever driven or seen.

Automotive coils with out a ballest resister on tractors can cause problems ! It cost me a eletronic ign , it burned the eletronic pick up right out of the dist. Petronics told me to put a ballest resister in next time due to the auto coil.

There is no doubting you know the theory on how it all works, but not in this case.

I have a brand new wireing harness in the tractor as well so that there wasn't any chance of there being a unseen problem.

I have sence installed the MSD 6al CDI box and openeed up the plug gap to .050 and it runs great. And guess what MSD wants that ballest resister in place.


I only spin this motor around 1800 rpm with 240 psi cylinder presure , this by no means is a big harry pulling motor. Good clean spark helps these old tractor motors out alot.

The cylinder combustion chamber design on 60 year old tractors is very poor , so anything you can do to make for a better burn can only help .

John i'm not taking a shot at you , i'm just passing on what i have learned and been told from the companys that sell the products.

Remember when Chrysler tried out there first computers on the cars" lean burn" in the late 70s. WOW was that a flop

James, Thanks for the great post, Funnnnnnnnnn discussion, I love electrical chat, I will try n address your questions. At the end I will cover where you with the MSD info may be comparing apples to oranges i.e. just because Im right dont mean your wrong cuz use of an elec switch and a coil designed for such isnt the same thing as the old convention points ignition which the poster is using and upon which my answer stands correct based on the laws of physics..


QUESTION:
I "not" douting you know what your talking about. If it made for a weaker spark then what would the point of it be?

ANSWER: The purpose of a ballast resistor is to reduce the amount of current flow in order that in a conventional points ignition the points dont burn up prematurely. In a points ignition where the coil itself already has 3 ohms of ignition circuit primary resistance the coil draws the 3 amps it was designed for but if you lower the current you lower the amount of stored energy the coil can achieve during its conduction cycle and less energy in = less energy stored and therefore less energy discharged across the spark plug gap. The coil is a passive energy storage device and the more energy in the more out soooooooo if you cut the current in half (approx what a ballast would do) theres less input energy n less output. If a coil is designed for 12 volts that allows x amount of current flow which a ballast resistor will reduce THEREFORE the laws of physics and conservation of energy dictates less energy in = less out i.e. use of a ballast (in this 6/12 situation) MUST equate to less energy in the coil = less energy stored = less energy discharged across the plug gap

QUESTION:
If a ballest resister made for a weaker spark why the hell did they put them on every HEMI car or wedge car i have ever driven or seen.

ANSWER: Because in those systems use of a ballast accomplished a dual purpose. 1) If a ballast is external to the coil its possible to by pass it ONLY during cranking to get a hotter starting spark sice cranking drops battery voltage down. 2) If a ballast is used that again reduces the current throught the coil MAKING THE CURRENT THAT WHICH THE COIL AND THE SWITCHING DEVICE WAS DESIGNED FOR. In that case the current is correct WITH THE BALLAST IN PLACE BUT NOTTTTTTTT WITHOUT IT. That system was designed for x amount of coil current and for what current the elec switch could handle PLUS if needed (not all used it) an external balalst is able to be by passed for a hotter starting spark.....A BALLAST IS USED THERE CUZ THE SYSTEM WAS DESIGNED FOR THAT AMOUNT OF CURRENT AND IF THE BALLST WERE REMOVED THE COIL WOULD OVERHEAT PLUS THE SWITCHING DEVICE MAY BE DAMAGED. Howeverrrrrrrrrrr if you added yet another ballast, again same as my original answer, the spark will be of less energy

QUESTION:
Automotive coils with out a ballest resister on tractors can cause problems ! It cost me a eletronic ign , it burned the eletronic pick up right out of the dist. Petronics told me to put a ballest resister in next time due to the auto coil.

ANSWER: Thats cuz the elec switch you used wasnt rated to switch the amount of current flow that coil was drawing buttttttttttt if the primary ignition was of more resistance (like if you added a ballast) then the current is reduced and the switch or coil dont overheat.....They have different current rated switches for different coil and/or coil and ballast combinations and in our case YES INDEED THE COIL NEEDED BALALST CUZ WITHOUT IT THERES TOO MUCH CURRENT WHICH CAN BE HIGHER THEN THE SWITCH WAS RATED FOR Fried switch grrrrrrrrrr Soooooooo if the elec switch vendor says you need a ballast then in that case yessssssss its needed so the switch dont fry due to too much current

QUESTION:There is no doubting you know the theory on how it all works, but not in this case.

ANSWER; Youre entitled to your opinion and I respect that butttttttt the laws of physics and conservation of energy in my opinion win out making me RIGHT in this case. Less energy into a coil (from less current) means less energy stored during conduction means less energy available to be dischaged across the plug gap

QUESTION:
John i'm not taking a shot at you , i'm just passing on what i have learned and been told from the companys that sell the products.

ANSWER: Nor me at you, what you were told can still be correct buttttttttttt remember the use of an elec switch that was designed for x amount of current DICTATES the total primary resistasnce and if the coil isnt enough Then a ballast may be needed.

CLOSING: heres the deal, his question was for a points ignition system NOT an elec switch remember......The points can handle around 4 amps of current sooooooooo if his coil was 3 ohms THEN HE DONT NEED ANY EXTRA BALLAST BUTTTTTTTTTTTTTTTTTTTTTTTT IF HE WAS USING AN ELEC SWITCH that couldnt handle but say 2 or 3 amps YESSSSSSSSSSSSSS he needs a ballst or the switch will fry. What Im saying is you (MSD) can be right but Im also still right cuz we cant comparer an elec switch ignition to A POINTS system........They sell different current rated switches designed for diffetnt coil and/or coil + ballast soooooooo if they say a ballast is needed it is buttttttttttt if his points can switch 4 amps they can handle his coil UN BALLASTED. Yet if pertronix sells him an elec switch that cant handle 4 amps yessssssssss he needs a ballast

FINALLY Its IMPOSSIBLE to cover and explain all here in a few paragraphs that takes yearsssssssss of study to understand soooooooooo I just cant possibly cover and explain everything here to a non engineering or technical general group of people I JUST DO MY BEST TO HELP. If you study the physics of ketterign coil ignition systems n how coils work and understand the concept of conservation of energy you will understand why less energy pumped into a coil = less energy stored during its conduction cycle = less energy discharghed across the plug gap PERIOD and if you add an external ballast that means less energy i.e. weaker spark butttttttttttttt remember if the overall system is designed for a ballast then yes its needed otherwise the switching device overheats soooooo thats NOT the same situation as his example where points that can handle 4 amps is used and his coil resistane is such that 4 amps is available WITHOUT A BALLAST therefore if one were used the laws of physic dictates less spark energy. NOT the same as a situation where the coil and/or ballast was designed for x lesser amount of current which does require a ballast

AGAIN its IMPOSSIBLE to explain ALL THIS COMPLICATED STUFF to lay persosn but hey I do my best lol

Yall take care now n God Bless

John T retired electrical engineer

Youre most welcome, Glad I was of help. PS if you used an elec switch that was current rated for like 2 or 3 maps or so then yessssssssssssss you may need a ballast but if your coil is 3 ohms thats sufficient unballasted as is.

John T

When you say "elec switch" are you talking about the ignition switch located on the guage panel? If that is the case then I have no idea what it is rated. I guess it is the one that came on the SA so was more than likely for 6v.

Maybe I better just leave well enough alone. It starts and runs perfect so maybe its like the old saying, "dont fix it if it aint broke".

NO, by elec switch I was referring to an electronic ignition switch used to replace a set of old fashioned contact points. As you say if it aint broke dont fix it and that 12 volt coil (if its indeed 3 ohms primary resistance) ought to be fine without any ballast.

best wishes

John T

John,

I admire how you are able to diplomatically respond to all these different ignition scenarios. I pretty much understand what you are saying (and what you say IS correct) even though my electronics education (BSEE) and work was in radio and radio related stuff, AM and FM broadcast, TV broadcast, professional 2 way radio (HF, VHF, UHF and 800 MHZ) and cellular phone, not ignition stuff. Also worked a lot with Navy radar in my military service. As you say, the electric principles are the same though, all based on the same laws of physics. By the way, physics wasn"t my best subject in college!!!

I bought 3 of those from this site and used them without resistors. Work fine. Open your plug gap to 0.040 to 0.045 inches.

Used them on a SA? If I remember correctly you have a SA.

Ron,
With due respect to John T. you may or may not know but he is also a lawyer well trained in the use of our language.
I can remember in my electronics days that the term 'Ballast resister' was used but I can't find it in my newer books. They use 'current limiting' or 'voltage dropping' and there are subtle difference in the use and calculation.

Sam, Right on, the term "Ballast" is used somewhat loosely lol. In engineering terms the function it indeed accomplishes is to reduce or lessen or limit current and it does so by dropping the voltage ahead of the load. As I sure you and Sam are aware, the energy dissipated in the form of heat prior to the remaining energy available to store in the coil when its conducting all reduces the energy that can be transferred eventually in the form of the spark plug gap discharge. IN ENGINEERING AND ENERGY THERES NO FREE LUNCH LOL

Yep I retired from engineering BEFORE going back to law school so I had a "real life" first in engineering n farming and I have no regrets.

Thanks, fun chat,

John T retired engineer now country lawyer

Two 140's and a cub, C123's and a C60. 12V.
You're good to go.

Thanks for the kind words Ron, yep a techy or engineering type can understand and appreciate this energy n physics stuff, even if its boringggggggg or Greek to many others....Similar, however, whatever field others are trained and experienced in would be likewise Greek to me.

The energy dissipated in the form of heat in any "ballast" indeed lessens the energy imparted into and stored in any downstream passive device such as a coil which then reduces the energy dissipated across the spark plug gap when it fires. The thing is (as Im sure youre aware) is the total picture and design and circuit of the ignition system which involves a coil (with its voltage and design parameters) PLUS a device to switch its current on and off which also has design limitations such as current and voltage. If the system is designed for an external ballast due to the current rating of the switching device thats all well n good, but take a design (12 volt coil or 6 volt coil + ballast) if you then further reduce the input energy by the addition of more external ballast, the energy dissipated in it reduces the remaining energy for the rest of the circuit. GUYS WAY SMARTER THEN US PROVED ALL THAT YEARSSSSSS AGO LOL

tHANKS AGAIN, BEST WISHES

John T

Good deal John, i to like this kind of forum.

I will admit you learned me some new things i never knew.

Thank You.

James Rumph

John T

I got to thinking ! When i replaced the harness i put a new switch in at that time, it is rated for 40 amps.

Semco is a switch company that happens to be right around the corner from me so i was able to get the correct parts .

So with a new harness and switch on 12v generator [ new ] as well as voltage regulator [new].

Why did it melt the eletronic pickup coil out with the ign on but not running ?

You can throw the tech talk this way , i do understand most of it. I build automation tooling for a living.

You got me woundering now !

Yup that is it!!!!
Electronic Ignition (when on not running) supplies full rated running voltage to the coil 100% of the time. This compares to about 30 % of the time (or so) when the engine runs. This is not an operational situation for the heat load of the coil, ballast resistor (if any) or the electronics of the electronic ignition. Duty cycle is important, and often ignored. Points could handle the issue a bit better, but still often got hot.
Coils are also heat affected in the same way.
Shutting off the ignition when not running is imperative. As normal, John you are great to be around. Even if only digitally. Jim