Which replacement factory style coil to buy? 6 or 12 Volt??

Hey,

I want to get one of the replacement coils that look identicle to the originals for my Super M. It has long since been converted to 12 volts using the original 6 volt coil with the resistor put in line.

On these newer coils,should I buy the 12 v or the 6 V ??? Does it even matter????(I do not know the level of resistance in either one of the new ones???)

Does the tractor have a ballast resistor in wire running from the ignition switch to the coil?

If yes, then 6V.

If no, then 12V, but MAKE SURE the "12V" coil you purchase says "no external ballast resistor required."

Most 12V coils are really just 6V coils, and need a ballast resistor. The reason for this is to prevent confusion at the parts counter...

"I need a coil for my 1969 Dodge Charger."
"Here is a coil."
"But, it's labeled 6V. My car is a 12V."
"Yes sir, that is because there is a ballast resistor on the firewall. All coils are 6V."
"But, my car is 12v. I need a 12V coil."
"Sir, trust me, it will work fine."
"But, my car is 12V. I must have a 12V coil."
"*sigh* Sir, there is no such thing as a 12V coil."
"But, there must be. My car is 12V and it has been running fine until the coil blew. I need a 12V coil."

It really does not matter which coil you use.

The 12V coil has an internal resistor, while the 6V coil needs a resistor added. Since you already have an external resistor, you can just replace the coil with a 6V one, or remove the resistor and use a 12V coil.

On a 12 volt tractor you can EITHER:

a) Use a 12 volt nominal rated coil (designed to operate at 12 volts nominal, but still produce a decent spark from like 9 or 10 (starting) to 14 volts and handle the current and sufficiently dissipate the heat and not overheat (around 2.5 to under 4 ohms primary, typical 3 ohms)

OR

b) Use 6 volt nominal rated coil PLUS an external series voltage dropping (12 to 6) Ballast Resistor which reduces the 12 battery volts down to 6 as the coil was designed to handle so it passes the current and dissipates the heat and still produces a decenT spark at starting (maybe 4.5 volts) and running (maybe 7 volts) Their primary winding (of many NOT every one mind you) is around 1.25 to under 2 ohms, around 1.5 typical.

NOTE many 6 or 12 volt tractors still use the same coil butttttttt if on a 12 volt tractor the ballast is in series ahead of them to drop 6 volts leaving 6 on a 6 volt coil AS ITS LABELED AND DESIGNED FOR

NOTE allllllll coils are NOT the same. If you go to NAPA they will ask if you want a 6 or 12 volt they will NOT say they are all the same. (although you can use a 6 on a 12 volt tractor with a ballast, i.e. same coil can still work on either)

NOTE a coil labeled "12 volts" or "12 volts NOT for use with external ballast resistor" is a 12 volt nominal coil HOWEVER a coil labeled "6 volts" or "12 volts for use with an external ballast" is in reality a 6 volt coil i.e. designed to produce a spark at 4.5 to 7 volts AND STILL HANDLE THE CURRENT AND NOTTTTTTT OVERHEAT

NOTE different manufacturers used differnt rated coils and ballast sizes so the above cant be true for alllllllllllllllllllll tractors and coils and Im talking original old farm tractor typical ignitions here NOT after market or high energy like Mallory and Accell etc etc race cars IM TALKIN MOST OLD 6 AND 12 VOLT TYPICAL FARM TRACTORS

Hope this helps

John T

Mike, I wouldn't mind getting on of these also, where are you getting yours? Do you know if it is made in the States?

The original style coils that I've seen lately for sale are listed as 6v and 12v, however all the ones I've seen require an external resistor on 12V.

Good morning Kirk, NOT to be argumentative (ONLY here to help) but try and educate some here who may be confused by the terms "internal ballast" "internal resistor" or "internally ballasted" , let me comment on your statement

"The 12V coil has an internal resistor"

Actually if you take "most" typical old farm tractor 12 volt coils and disect them and/or x ray to look inside, YOU WILL NOTTTTTTT FIND A DISCRETE STAND ALONE "RESISTOR" TUCKED AWAY SOMEWHERE INSIDE THE CAN... Their necessary (around 2.5 to under 4 ohms typical 3) primary coil winding resistance is achieved EITHER by more windings/length and/or higher resistance wire NOTTTTTTTTT by adding a stand alone discrete "resistor" in series with the primary windings in order to reduce current and/or reduce voltage across the actual primary coils of wire........

Its true some eaqly autos indeed did have a coil with a seperate porition of the can for a true stand alone discrete resistor and many had like a ring or seperation around the coil for the internal actual resistor

Allllll wire (NOT a prefect zero ohms conductor) contains "resistANCE" but wire is generally called WIRE NOT A RESISTOR at least in engineering and technical circles. Wire while it has some resistnce is very low resistance while a "resistor" is purposely designed for higher then straight normal low resistance wire i.e., it may be 1 to several thousand OHMS, its called a "resistor" NOT wire (although some resistors are wire wound with resistive wire and called wirewound resistors)

Sooooooo "most" typical old stock 12 volt farm tractor coils called internally ballasted DO NOT HAVE A STAND ALONE DISCRETE "RESISTOR" TUCKED AWAY SOMEWHERE INSIDE THE CAN. Their primary total resistance (made up of allllllll those windings/turns of "wire") is around 2.5 to under 4 ohms if a 12 volt rated coil and more like 1.25 to 2 or so if a 6 volt coil

Make sense?? Hope this helps God Bless n take care

John T

Yooper,

I am seeing them at Kuhn's Tractor in New York.They seem to have the best price.(You can get them about anywhere.I think Stiener's)

The ones I am seeing DC Snider have a separate part # for each the 6 and 12 volt. SO,I am thinking they both have a different resistance internally???

I guess If I could call someone knowledgeable who sells these.they could give me the technical data on each???

Or,I could buy either and just check it with an Ohm meter and add ballast accordingly???

Anyone know the ACTUSALL resistance of these new IH looking/ style replacement coils????

If your tractor already has a ballast resistor use a 6 volt coil.

I think 6 volt coils have 1.5 ohms of resistance across the primary terminals and use a high amp 1.5 ohm ballat resistor. Twelve volt coils have 3 ohm resistance across the primary coils. Measure the resistance of your old coil and buy one with the same resistance.

The advantage of a 6 volt coil and a ballast resistor is most vehicles add a starting circuit for a hotter spark when starting. An extra wire runs from the switched terminal on the starter solenoid to the hot terminal on the coil, (or the coil side of the ballast resistor). When the starter is engaged the extra wire sends full battery voltage to the coil for a hotter spark. Once the starter is disengaged the coils receives 6 volts from the ballast resistor for longer point and coil life.

The starting circuit helps most in cold weather or with a low battery.

If you use a 12 volt coil with a ballast resistor and starter circuit the engine starts well but as soon as the starter is released it runs poorly from lack of spark.

Kuhn's web site says theirs are American made.
I called Steiners, theirs are made in China.

I did verify with both Kuhn's and Steiners that both require an external resistor.

For clarification (no flame) the switched terminal on the solenoid or relay must be an isolated terminal from the starter. It will (usually be labeled "I". If wired to the starter connection, the ignition circuit will try to spin the starter, It will smoke. One way to do that on a solenoid or relay with no "I" terminal is to put a 6 amp diode in the line to allow current to go to the ignition, but not back to the starter motor. Jim

I prefer a 6V coil with ballast resistor and starting bypass. You will get a much hotter spark during cold weather starting.

I am glad you mentioned that Jim because I am going to do that "Bypass" on my 600 Ford tractor.It starts TOO hard because of the coil being reduced. I just know that is what is going on with it!!!

On MY Super M, Since the Starter has the saddle mounted start button bolted to it,I really cannot think of a good way of picking up the FULL 12 volts from there to run to the coil during start up???

Also,After talking to the guy at Stieners about the 12 volt Vs 6 volt coil,he is steering me towards the 12 volt.He is telling me that using these "6V" coils on a 12 volt system is "hard on them"???(even though we are reducing them via a ballast resistor.)???

Also,he actually checked BOTH with an ohm meter for me.Said the 6V model checks at 4 ohms and the 12V model checked at 5 ohms???? Something seems wrong to me here?????

Please advise.

No disrespect to the "guy" at Steiners, not sure if hes an enginner or electrician or lay person etc or where he got his info but Id have to question WHY his statement

"He is telling me that using these "6V" coils on a 12 volt system is "hard on them"???

A coil is a purely passive inductive/resistive device and has a rated voltage at which the resultant (V/R) current and heat can be sufficiently disspiated so if a ballast is used which makes its input voltage 6 volts same as if on a 6 volt tractor I see no engineerign reason why its "hard on them". If a start by pass is used on a 12 volt tractor theres indeed a short time at which the current may be higher then rated maybe thats what hes afraid of??? but thats so short and usually occurs at initial start up when the coil is cold???

Id have to see detailed specific engineering data and test results before Id make the final call.

John T

One among others, of the reasons primary current (coil + any ballast) is limited in Kettering points and condensor ignitions is to limit the current the points have to switch to around 4 amps and under otherwise they burn up too quickly. That would be like at least 1.5 ohms at 6 volt or 3 ohms at 12 volts HOWEVER the whole system (points, coil, condensor) comes into play engineerign wise so if properly designed (to handle current and heat etc) there no reason the figures approximated above have to be exact i.e many 6 volt coils are around 1.25 to under 2 ohms and many 12 volt are 2.5 to 4 but nottttttt alllllllll of them.

Also see my posts below

John T

THAt is what I was trying to get to the bottom of too John T.I hear what you are saying! I feel the same way about what you are saying here. But you have more technical detail.

I was tryng to get specs on both coils.I want to buy one,but DO NOT want to spend $60.00 on a P.O S. Coil!!!

If I could figure out who ACTUALLY manufactures them,it might help? I would talk tech with them

The reality is he is not informed.
Running a 12 volt coil with the 5 ohm value on the primary will let it run well, but not enhance the starting.
Run a 12 volt coil for use with a external resistor. It will be equivalent to a 6 volt coil (not an issue) Use a ballast resistor out of a mid 1960s Chevrolet Belair 6 cylinder. (it just works)
Connect the resistor to the coil positive side if it is negative ground, and the coil negetive side to the points. If positive ground, the resistor goes to the neg side and the points to the pos.

Next run a 12ga wire to the coil side of the ballast resistor from the area of the saddle switch or solenoid relay. Use a diode (Old diode from a scrapped out alternator is good, or one from Radio Shack (5 amp 100piv)
Make sure it is polarized so it conducts toward the ballast resistor when cranking, and blocks flow when just the ignition is on.
Top assure this: with the diode hooked to the 12ga wire only, use A test light from the open diode lead to the tractor frame. with the ignition on, the test light should not light up.
If it does. it is wired with the wrong polarity.
Reverse it.
This diode will prevent the back flow into the starter which just turns the resistor into a temporary light bulb. Jim

Buy the way John T and I agree on 99.99% of the electrical stuff. This included. Jim