coils

I asked about a 12 volt coil that needs a resister,I guess I asked worng,What I meant was do they sell 3 different coils? a true 12 volt,a true 6 volt and a 12 volt that needs a resister?

Yeah, that's about right.

'Cept the coil sold as a "12 Volt needs external resistor" is more or less a relabeled 6 Volt coil.

There IS a reason for the "12 Volt needs external resistor" coil. The use of an external resistor makes it possible to use a bypass setup to take the resistor out of the circuit during cranking to compensate for the low battery voltage available to the ignition system while the starter is hogging current.

Also, there's 2 types of ignition resistors used, a fixed resistor is often used with the bypass starting scheme, a "PTC" (positive temperature coefficient) resistor MAY be used in systems WITHOUT a starting bypass. It's resistance starts out low to allow for a HOT spark if the engine is cranked right away, (as soon as the ignition is switched "ON"), then it's resistance drops as it heats up to limit primary current for long point life and less coil heating.

Thanks for the info,

NOTE, theres a bit of "semantics" going on with this whole coil voltage thing, myself and Bob and JD have discused this ad nauseaum lol heres the real deal from a long retired electrical engineers perspective:


1) They design amd manufacture Kettering Ignition System Coils designed to operate at 6 volts nominal across the primary which can handle the current, dissipate the heat, and still provide the sufficient voltage and energy for a suitable spark when the voltage is reduced while cranking, yet raised (maybe to 7 volts) at fast RPM when the battery is charging.

I CALL THEM 6 VOLT COILS AND STAND BY THAT


2) They design amd manufacture Kettering Ignition System Coils designed to operate at 12 volts nominal across the primary which can handle the current, dissipate the heat, and still provide the sufficient voltage and energy for a suitable spark when the voltage is reduced while cranking yet raised (maybe to 14 volts) at fast RPM when the battery is charging.

I CALL THEM 12 VOLT COILS AND STAND BY THAT and have, like others, referred to them as true 12 volt coils as they are for 12 volts nominal across their primary NOT 6 NOT 8 but 12, and they will still handle the current, dissipate the heat and provide sufficient voltage and energy for a spark even at reduced cranking voltages or increased charging voltages. They are labeled 12 volt. I guess one could call them a 9 to 15 volt coil??????? as they can provide a spark while cranking or charging, but I prefer to call them a 12 volt coil or a true 12 volt coil NOT a 9 to 15 lol THATS A SEMANTICS ISSUE


BUTTTTTTTTTTTTTTTT NOW GET THIS WHICH CONCERNS LABELLING ON THE COIL AND WHERE THE RUB COMES IN

A) Some coils are labeled "12 volts"
OR
"12 volts NOT for use with Ballast Resistor"

I CALL AND CONSIDER THEM AS 12 VOLT COILS and some folks (semantics issue) refer to them as "Internally Ballasted" BUTTTTTTTTTTTTTTTTT they are still designed to operate and handle the current and dissipate the heat and provide a spark (at reduced cranking voltage or increased charging voltage) at 12 volts nominal across the primary. THEY ARE INDEED 12 NOTTTTTTTT 6 VOLT COILS

B) HOWEVER AND NOTE THIS CAUSES MORE CONFUSION TO SOME, some coils are labeled "12 volts to be used with external ballast resistor" or "12 volts requires external ballast" etc

SOOOOOOOOOOO these mean EXACTLY what they say, if you want to use them on a 12 volt tractor YOU MUST USE THE EXTERNAL SERIES VOLTAGE DROPPING (12 to 6) BALLAST RESISTOR otherwise they can overheat and be ruined. They are in one view in reality 6 volt coils since they are designed to operate WITH ONLY 6 VOLTS ACROSS THEIR PRIMARY as the 12 battery volts is reduced down to 6 by a 6 volt drop acros the external ballast. They can be used on a 12 volt tractor but "require an external voltage dropping (12 to 6) ballast JUST LIKE THEY SAY.

SOOOOOOOOO they can make a common (what I'd consider (semantics) as a 6 volt) coil that can be used on EITHER a 6 or a 12 volt tractor understand???????? Its just that if used on a 12 volt tractor they require the external series voltage dropping (12 to 6) ballast resistor buttttttttttttt if used on a 6 volt tractor NO BALLAST IS USED.

ALMOST FINALLY: If you go to a parts store and ask for an ignition coil for your old tractor IM CONFIDENT THEY WILL ASK IF YOU WANT A 6 OR 12 VOLT COIL AND THEY WILLLLLLLLLL NOTTTTTTTTTT SAY THEY ARE ALL THE SAME. NOTE However as above, you can use a 6 volt coil on EITHER a 6 or 12 volt tractor provided if on a 12 you add the series voltage dropping (12 to 6) ballast resistor in which case the coil only sees 6 volts which is why I still consider it a 6 NOT a 12 volt coil.

FINALLY: Could they design and manufacture a coil that can actually be used on EITHER a 6 or 12 volt tractor, AS AN ENGINEER IM SURE THEY COULD and would expect its primary resistance to be well over 2 ohms and its design parameters would be that if EITHER 6 or 12 volts were applied (NO BALLST MIND YOU) they can still handle the current, dissipate the heat and provide sufficient voltage and spark energy if used on a 6 volt or a 12 volt tractor unballasted. HOWEVER the more normal typical situation is EITHER 6 or 12 volt coils NOTTTTTT a one size fits all common generic coil.

HEAT DISSIPATION AND SPARK ENERGY:

a) If you use a 6 volt coil on a 12 volt tractor and dont use a series voltage dropping (12 to 6) ballast resistior THEY CAN OVERHEAT BADLY AND BE RUINED

b) If you use a 12 volt coil on a 6 volt tractor, they sure dont overheat buttttttttttt the spark energy will be very weak

THATS WHY THEY DESIGN AND MANUFACTURE 6 AND 12 VOLT COILS WELLLLLLL DUHHHHHHHHHHHHHHH yet you can still use a 6 volt coil on a 12 volt tractor with the series voltage dropping (12 to 6) ballast

THATS MY STORY AND IMA STICKIN TO IT UNTIL PROVEN OTHERWISE LOL

Hope this helps, God Bless yall

John T

Thanks you and Bob,I understand it better now. I had a 2 years old coil on my 6 volt B that said it was a 12 volt and it needed a resister , I had a weak spark and it run at times and not at other times, I now have a ture 6 volt coil and it runs great,just like it did all last year,Thanks again to you both

Slightly off topic but seeking your expert input.

For the third year in a row, our JD 70 (gas 12V) stopped dead in the furrow during our club plow day. There's a lot of heat coming off that block and it gets the coil really hot.

Last year we replaced the coil with the "Real McCoy," a $73.00 genuine JD coil! So last Saturday, same old thing happens.

Any suggestions? Maybe mount the coil one the left side of the dash, away from the heat?

Any input from you is appreciated.

Thanks,
Dave 2N

1. Did you check to be SURE it lost spark and was not a fuel flow/vapor lock issue?

2. Was there still power TO the coil (ruling out and ignition switch or wiring issue?

3. Put a test light on the points side of the coil and see if the points are actually making contact when closed and not shorted when open.

4. Check the primary current (engine stopped, points closed).Much over 4 Amps WILL overheat the average coil.

I had a gas 70 that used to do that and it turned out the tank wasnt being vented and she died from gas starvation until she could suck/leak air back in the tank again. If I left the cap loose it didnt happen, of course.

I cant say sitting here if she died form gas starvation or the ignition stopped working??

There can indeed be heat related problems causing ignition failure which can often be attributed to a bad coil or a bad condensor but from what you say it may NOT be the coil, maybe try a new condensor (as much cheaper) n see what happens.

One way to tell is right when she dies pull the coil or a plug wire to see if shes still firing?????????? If so Id be looking to see if the carb bowl has gas or if its dry and determine the cause of starvation such as the sediment bowl or fuel line or the tank isnt venting.

If its an ignition problem instead Id immediately hang a test lamp on the coils input (NOT to distributor) terminal and see if its hot as it MUST BE when the switch is on. If not suspect the ign switch so maybe hot wire the coil n see if she fires then?????? If the coils input is hot (or shes hot wired) yet still no fire hang the lamp on the coils output to distributor and crank her over and it should flash on (when poins open) and flash off when they are closed. If its never on suspect a shorted condensor or a short to the points or wiring IT MUST FLASH ON AND OFF AS SHES CRANKED

I dont think that tractor uses a 6 volt coil plus an external series ballast butttttttttt if it does the ballast resistor may have a problem or be by passed or shorted which would cause a 6 volt coil to overheat badlyyyyyyyyy and fail. The coil should run hot but NOT so hot you cant keep your hand on it, if so I wonder if its the wrong coil or a ballast problem IFFFFFFFF it even has one that is.

It wouldnt hurt to mount the coil where it gets less engine heat but Im not sure thats your problem.

heres my ignition troubleshooting if needed

http://www.ytmag.com/cgi-bin/viewit.cgi?bd=farmall&th=5745



John T
John Ts Ignition Troubleshooting

internal ballast?? Does that mean there is an internal resistor?

For 12 volt systems,I have noticed that the combined resistance of coil resistance plus its needed external resistor seem to be equal to the coil resistance of a none external resistor coil. Both about 3 ohms.
Does combined resistance of a 6 volt coil and resistor used on 12 volt have about the same 3 ohms?

"internal ballast?? Does that mean there is an internal resistor?"

With a typical modern coil, NO, simply more turns/length of primary winding.

"Does combined resistance of a 6 volt coil and resistor used on 12 volt have about the same 3 ohms? "

Yes, the combo is typically a bit over 3 Ohms.

The bottom line... (In round figures) 13 Volts (nominal) battery/3.5 Ohms = about 3.75 Amps primary current (engine OFF, points CLOSED).

Typically, points and common coils don't like to see a whole lot more current than that or the smoke begins to be let out.

I don't know who "they" is, but there's probably over 100 different coils available that can be use in a 6 volt or 12 volt systems. Slight differences for all. To be technical, a coil in a "12 volt" system needs to make good spark voltage at 9 volts when cranking, and up to 15 system volts when running. There is no such things as one type of "true" 12 volt coil.
The term "12 volt system" means just that - a system of various matched components.

The vast majority of coils used in "12 volt systems" since 1960 with breaker-points are what others are NOT calling "true 12 volt."

Id agree "basically" many (NOT all) older 6 volt tractor coils (Im NOT talking high performance or after market or electronic ignition stuff) had in the vicinity of 1.25 to 2 or a bit over ohms (good average may be 1.5) while many (NOT all) older 12 volt coils had more like 2.5 to 3.5 or so ohms (good average may be 3 ohms). That way the current that had to flow through and be switched by the points was in the neighborhod of 4 amps AND IF YOU SWITCH TOO MUCH MORE CURRENT THE POINTS WILL BURN UP PREMATURELY. (6/1.5 = 4 points amps on a 6 volt system,,, 12/3 = 4 points amps on a 12 volt system)

THEREFORE YES the ignition primary series circuit combination of COIL PLUS BALLAST was in the neighborhood of say 2.5 to 3.5 or so ohms on 12 volt systems which limited points current to the 4 amps range.

As usual Bob and I agree, most older tractor coils that some refer to as "internally ballasted" didnt actually contain an internal discrete resistor, but the higher primary resistance was made up of either higher resistive wire or simply more wire length. HOWEVER they indeed made some coils (those were truly internally ballasted) that had a seperate internal compartment with stand alone resistor but I view that more on older cars then our 40 and 50 vintage tractors

Hope this helps, we have pretty much beat this to death lol

John T

John T...I am Dave"s son, have had the pleasure of being towed out of the firld on the 70 for this reason. Up until last week i was sure it was a coil issue as A)it has always been getting gas whenever this has happened. B)Often times after sufficieant cool down it ran well again.
The coil is mounted directly above and behind the manifold and does get unbearably hot, but thinking it was a coil overheating has always bothered me because i know lots of the old 70s spent time in the South and the South West, and if that had been an issue, it would be well known by 2010...BUT...the next option being condenser and this would be the 1st time I have ever seen a condensed quit then work again...so i discounted that idea.
I was ready this year: wired up a 2nd coil with a switch, all we had to do was connect the coil wire to the distributer, flip the switch and go...worked great in the shop. Whwn it died this time...no spark at all with either system...I am going to replace the points condenser, plug wires...and see what happens again...I guess the ignition switch could be questionable...but it works 99% of the time...would that or the wires maybe be suceptible to heat? TY Pete

I really doubt the switch but thats sooooooo easyyyyyyyyyto run a temporary hot wire to the coil to find out. If the coil is located such that it gets so hot you couldnt stand to keep your hand on it then yes I reckon its overheating may be an issue. Maybe relocate it,,,,,install a new condensor,,,,,,,insure its NOT gas starvation and give her a try, let us know

John T

I get to it this weekend...ty

John T, does the coil have to be mounted to metal, grounded, on the tractor or engine or will it work if just hanging in midair like tied up with a string as in working on things and too hard to continue mount, take off and remount? Or to be remounted to a handier place but possibly mounted to like a piece of plastic that would not be a conductor?

(quoted from post at 20:19:16 05/04/10) John T, does the coil have to be mounted to metal, grounded, on the tractor or engine or will it work if just hanging in midair like tied up with a string as in working on things and too hard to continue mount, take off and remount? Or to be remounted to a handier place but possibly mounted to like a piece of plastic that would not be a conductor?

Click to expand...

'm not John, Leroy, but no your coil does not need to be mounted to metal, all electrical windings inside are isolated from the housing. If it is heat that you are concerned with, not to worry, as when run hard on a warm day there isn't anything around the engine or attached to it that you can hold your hand on (unless your superman, 140 to 150 degrees is about all you can stay on). Set your coil on the work bench, connect to a power supply, set current to 3 amps and come back in 3 hours and pick up your coil,,,,it won't take you long to "feel" of the 200 degree can! Between the coil generated heat & the engine heat/surrounding heat, close to 200 is where it normally runs. It is designed for it, stop worrying.