Ignition Coil 12 volt

I wanted a little hotter spark for my Farmall H .. (plus my 12 standard coil went bad).
I pull this tractor some so wanted to get a "hotter" coil ..

I thought of putting an electronic ignition with a hotter coil but the store had to order it so didn't - and not sure that is what I needed anyway.

I am a little confused about what I need for maximum spark.

One person told me to make sure my coil was a 3 ohm coil -- another recommended an "Accel Super Stock 8104 12 volt" coil
The "more power" Accel coil says it's "Primary resistance is 1.4 ohms and secondary resistance is 9.2 kilo ohms" .. (not sure what this means).

Again ... I am not sure about this "resistance" thing .. the one I had on it said "12 volt use without external resister" ...

So - those of you who know about this type of things .. what do I really need to get maximum spark?
I understand vaguely - about an internal resister and "use without resister" but not sure which does WHAT ...

Just wanted some opinions or help in this matter .. thanks a lot !!

Gary (gdtractor)

The use of a coil with 1.4 ohms will draw more than 8 amps on 12v. (let alone 14.2 running volts) that coil with a ballast resistor will still draw lots of amps. The points in a conventional distributor will burn up quickly either way. The coil can work with a resistor, and electronic ignition. Voltage is a function of a fully saturated coil primary (dwell) and spark gap/wire resistance. The wider the plug gap the higher voltage it takes to jump it. I would use a coil with 3.5 to 4 ohms W/O resistor, and 2.5 ohms with a resistor. If electronic, go with the recommended coil from the supplier. THere are no internal resistors in coils, just enough windings to operate at a specific run voltage. The confusion comes from the words "external resistor required", which implies that some have an internal resistor. they do not. Jim

I don t even know if they are still available, but I used to use a Blue Streak coil,it was a heavy duty coil listed for a 1963 Chevy 36,000# truck. What I liked about them is they fit in the factory mount, and my 350 perked right up.(you will need a resistor with) it.)

(quoted from post at 20:28:58 07/09/16) The use of a coil with 1.4 ohms will draw more than 8 amps on 12v. (let alone 14.2 running volts) that coil with a ballast resistor will still draw lots of amps. The points in a conventional distributor will burn up quickly either way. The coil can work with a resistor, and electronic ignition. Voltage is a function of a fully saturated coil primary (dwell) and spark gap/wire resistance. The wider the plug gap the higher voltage it takes to jump it. I would use a coil with 3.5 to 4 ohms W/O resistor, and 2.5 ohms with a resistor. If electronic, go with the recommended coil from the supplier. THere are no internal resistors in coils, just enough windings to operate at a specific run voltage. The confusion comes from the words "external resistor required", which implies that some have an internal resistor. they do not. Jim

Click to expand...

Jim is correct.

Especially want to hit the "hot coil" thing here. If your plugs fire at say 6K volts and you put a hotter coil on it they will still spark at 6K volts. When they advertise those things they are giving you what the coil will put at maximum resistance that the coil will overcome. Couple of different ways to increase the voltage to the plugs. As Jim pointed out a wider than stock gap is one way. The other way is to increase the pressure in the combustion chamber. The higher the compression is the higher the voltage has to be to make the spark jump the gap. The downside there is the higher the compression the higher the octane rating has to be to prevent ignition ping. So basically the "hot coil" is a rip off if you are running a stock engine. In a simple form what happens is when the points close the coil gets electricity. When they open the coil very quickly build voltage until it has enough voltage to jump the gap. But when that jump voltage is reached the coil discharges to create that spark. So it starts at low voltage and bulds until it can overcome resistance up to the max the coil can produce.

As far as electronic ignition is concerned I love it. Lets face it even what has been considered the better brands of points are getting cheaper. For years I've use Echlin, Standard and Blue Streak. The last set I bought was defective right out of the box. They are a pretty simple item to install too.

Rick

I like my magnentos

You will gain more in the way of consistent, reliable spark with the electronic conversion than with a performance coil.

If you have ever watched points operating on a scope, you will see the points "bounce" each time they close. That is wasted saturation time, and the points are arcing during the bounce cycle. Add to that any wear in the distributor shaft bushing and the gap will vary, which will affect dwell time and ignition timing.

When viewing an electronic switch, the pattern is a nice, square wave pattern. It is all off, all on, nothing in between.

A coil's resistance determines the amperage it pulls. Too low resistance and the amps are more than the points or electronic switch can handle. The coil is only going to make as much voltage as it takes to jump the gap to ground.

There are higher power coils, but they are designed to jump a wide gap plug, intended to better light a lean mixture for better fuel economy, not necessarily for better performance. There is a down side to the high powered ignitions, they are hard on plug wires, and they tend to find other places to go to ground, like through the center of the rotor, or follow any trace of moisture.

There are extreme performance ignition systems. But they are more for high RPM applications, which has no benefit for a tractor engine, unless you have done some serious modifications. The only advantage they have is some have a programmable rev limiter.

Thanks so much .. I think I will go the electronic ignition route!!

If I do go witht he E. I. what coil do you recommend? Please.

Thanks much

Gary

Thx much !! Sounds good (and reasonable too)

Any 12 volt external resistor not required coil. I prefer the better brands like Echlin from Napa or Standard. The reasoning behind that is the external resistor is just something else to go wrong in the system.

Rick

Makes sense .. thanks Rick !!

Most likely, the &#%* thing has been running just fine all these years with the coil and breaker points it left the factory with.
UNLESS you have built up a high-reving 12,000 RPM motor just for the drama of it all your tractor will darned near live up it's maximum potntial as it left the factory.

From what I have learned from Youtube ... etc .. it appears that the electronic ignitions are fairly easily installed as well .
Not really sure how to do it .. but it looks too simple ..... but I am wondering if I am missing something .. LOL !!

Thanks again ..
Gary

Thanks much !! Makes sense ....

Gary

The thing to understand is that to truly have a "hotter" spark, you need more energy. The amount of energy in a conventional ignition system is determined by the primary inductance of the coil and the current through the coil. Coil current is limited by primary resistance, and in a 12 volt system resistance has to be added to keep the points from burning out. If you replace your original coil with anything other than a "12V no external resistor" coil, you'll need to add an external resistor. Looking at the specs for the Accel 8140, they don't publish the primary inductance, which tells me it's probably the same as stock. So the claims of a hotter spark are probably bogus, since current is fixed by the external resistor and inductance is the same as stock.

There are aftermarket coils with higher-than-stock inductance. But these are really intended for use with aftermarket dual-point distributors. (Do they even make those anymore?)

The fact of the matter is the stock ignition system is totally adequate for the slow speeds at which your H operates. Just install another "12 volt no external resistor" coil and fuhgetaboutit. (The only downside of the "no external resistor" coils is they seem to have a high failure rate, possibly due to heat from the internal resistance and small wire gauge on the primary side.)

My take:

Energy in the coil is ? LI exp2 where L is the inductance of the coil winding and I is the current running through the primary winding circuit at the instance the points open (as Mark said). Energy is measured in watt seconds (Joules)....volts x amps x time it takes to dissipate the VA.

The voltage breakdown is determined by the characteristics of the plug. Once the plug and it's environment determine the voltage breakdown point (on it's way to 18,000V or thereabouts), you have established the V of the VIT energy dissipation equation and the fired plug clamps the voltage across the coil to that value. Since the voltage is now clamped, and the current is determined by the fixed resistance of the circuit (and that clamped voltage value which is less than 100v), the only variable left is "how long will it take" to dump the energy in the coil? The longer it flows, the better chance you have of getting your fuel mixture to explode.

On the question of high resistance in the secondary, the turns ratio of the coil is 6 to 18,000 (or 12-18,000 for 12v circuits) meaning you have 3000 turns of wire in the secondary for every turn in the primary circuit which is where the points opening control the amount of initial current....or thereabouts, depending on how much of the charging current is across the wire and how much is across the current limiting resistor.

On the current limiting resistor, I prefer it external too as the heat of it does not add to the heat developed by the wiring inside the coil and heat kills! The external resistor is built to take what's fed to it for many 10's of years. Also I don't like the "convenience" of mounting the coil to the side of the engine block where a lot of OEMs liked to mount it...if you want to talk about reliability improvement measures, regardless of how many million have been built like that for how many billion hours of usage. Just my preference not to have it there.

(quoted from post at 22:51:31 07/09/16) Most likely, the &#%* thing has been running just fine all these years with the coil and breaker points it left the factory with.
UNLESS you have built up a high-reving 12,000 RPM motor just for the drama of it all your tractor will darned near live up it's maximum potntial as it left the factory.

Click to expand...

Bob the fact of the matter is that as time goes by even the better brands of points are dropping in quality. It's like the voltage regulators currently available. I've seen it a couple of times with people I know where they are bad right out of the box. So for a working tractor electronic ignition and an alternator is making more and more sense just for reliability. Then add that some new battery chargers don't even have a 6 volt setting on them plus the price of a 6 volt battery anymore and the 12 volt EI conversions are a no-brainer. Inexpensive over the long run and LOW maintenance! Heck I even switched my old pony start D4 7U Cat over to 12 volt!

Rick

Great question, good info below, I will try and give a short sweet not too technical explanation, but that's hard for me being an attorney and engineer lol.


1) When you read all the hype about HIGH VOLTAGE COILS MAYBE 50,000 VOLTS BLAH BLAH BLAH remember that at the same (within coils capacity) conditions the stock coil will fire at "near" the SAME VOLTAGE as "Super High Voltage Coil" as the voltage only rises high enough so current will arc jump the gap and that necessary voltage (maybe 10,000 volts) is a function of THE GAP DISTANCE AND THE MEDIUM (fuel and compression) IN WHICH IT FIRES.

2) However, an after market "high voltage" coil has the "capacity" to achieve a higher (then stock) firing voltage if necessary due to say use of a much wider plug gap, say 0.035 to even 0.060 or so.

3) A High Energy after market coil CAN INDEED CAN DELIVER A HIGHER "ENERGY" SPARK then a stock coil but they dont work well with old points ignition because they "can" draw more current then points can handle and you get premature burning THEREFORE USE OF AN ELEC SWITCH IS THE ANSWER AS THEY "CAN TYPICALLY" HANDLE MORE CURRENT THEN POINTS.

4) Even with a stock coil an elec switch delivers fast more positive current switching then bouncing ringing points so it can help, HOWEVER to get the most bang for the buck afforded by an elec switch, couple it with a high energy high voltage coil and run a wider plug gap AND YOU END UP WITH A HIGHER ENERGY DISCHARGE ACROSS A WIDER PLUG GAP.

5) Unless youre running exotic fuels and super high compression and an extra wide plug gap theres "less need' for an elec system but hey that's your choice, they have advantages as well as disadvantages. But if you invest in an elec switch Id go ahead and opt for a high energy high voltage coil so you get a higher energy spark.

CAUTION be careful of using a high energy coil with old points as if its LV primary resistance is to much less then 3 ohms on a 12 volt system and you draw more then 4 amps of coil current, THE POINTS CAN BURN PREMATURELY.

CAUTION if you start running wider plug gaps and high energy high voltage coils you need good quality cap and rotor and plug wires to withstand higher voltage and current


TO YOUR SPECIFIC QUESTIONS:

a) I am a little confused about what I need for maximum spark.

For more spark energy you need a higher energy coil and a switch that can handle high enough coil current.


b) One person told me to make sure my coil was a 3 ohm coil

If its a 12 volt tractor with points THATS GOOD ADVICE because current is 4 amps which points can handle

c) another recommended an "Accel Super Stock 8104 12 volt" coil, The "more power" Accel coil says it's "Primary resistance is 1.4 ohms and secondary resistance is 9.2 kilo ohms" .. (not sure what this means).

1.4 ohms LV primary resistance is a tad less then Id recommend for points but it will "work"

d) Again ... I am not sure about this "resistance" thing .. the one I had on it said "12 volt use without external resister" ...

Primary ignition resistance is the total of the coils LV primary PLUS any external series ballast resistance.

A coil labeled "12 Volts" or "12 Volts NOT for use with ballast" or "12 Volts NO ballast required" IS JUST WHAT IT SAYS you can use it on a 12 volt tractor as is with no need for an external ballast resistor, its a full true 12 volt coil

CONTRARY to Old Wives tales or what Bubba told you, the typical old farm tractor coil (Not talkin a very few old 30's car coil) DOES NOTTTTTTTTTT HAVE ANY INTERNAL DISCRETE STAND ALONE RESISTOR TUCKED AWAY INSIDE THE CAN. It DOES NOT have an internal "ballast resistor". Its primary resistance is a function of the wires resistance and length.


NO WARRANTY I'm long retired as an engineer and rusty on this and cant cover every imaginable situation nor explain in a paragraph what takes books and years to understand so the above is only a rough short approximate answer TAKE OR LEAVE IT.


THIS IS NOTTTTTTTT TO START NOR ENGAGE IN A POINTS VERSUS ELEC IGNITION AS THAT WASNT YOUR SPECIFIC QUESTION, that's a whole other topic and debate I'm not addressing here.

Hope this helps, post back any questions.

John T

OOOPS my bad, Before anyone or some Troll has a calf or jumps out of the woodwork yelling GOTCHA I was in a hurry (ITs Sunday morning you know) and made a mistake below

For a 12 volt tractor a 1.4 ohms LV primary coil IS TOO LOW and points would burn up prematurely, an elec switch can handle more coil current. I was hurriedly thinking about a 6 volt system where 1.5 ohms could work. If you used such a coil with an external series voltage dropping (12 to 6) current limiting BALLAST RESISTOR the points wont burn up prematurely but lower current wont yield as much energy either !!!!!!!!!!!!

Sorry about that, so many questions so little time but I try my best to help

John T

John T;
In spite of what the first wife may tell you it is possible you didn't make a mistake. LOL Way back when GM actually made a coil like that. Cold resistance was 1.5 and increased to 3 as it heated up. It was basically a bypass starting system built in to the coil instead of the wiring circuit. Don't have a clue how they did it or why they didn't stick with it but it worked. I still have one on one of my M's.

Yep, mid-50s, early 12v Mopars had them also. Temp variable resistor in the bottom of the coil can.

Yep I have heard of those, I call them THERMISTORS which change resistance upon a temp rise and I think a few later tractors may have even used that system but NOT these old ones. That way they didn't need any ballast by pass when starting system. I was thinking of 12 volts when I made my mistake below so I hurried and corrected it before the Trolls who love nothing better then jumping out of the woodwork yelling I GOTCHA could get their jollies lol

best wishes, nice chattin with ya M Man

John T

(quoted from post at 10:20:29 07/10/16) John T;
In spite of what the first wife may tell you it is possible you didn't make a mistake. LOL Way back when GM actually made a coil like that. Cold resistance was 1.5 and increased to 3 as it heated up. It was basically a bypass starting system built in to the coil instead of the wiring circuit. Don't have a clue how they did it or why they didn't stick with it but it worked. I still have one on one of my M's.

Click to expand...

Because hot re-starting was lousy,

(quoted from post at 05:36:11 07/10/16)

(quoted from post at 22:51:31 07/09/16) Most likely, the &#%* thing has been running just fine all these years with the coil and breaker points it left the factory with.
UNLESS you have built up a high-reving 12,000 RPM motor just for the drama of it all your tractor will darned near live up it's maximum potntial as it left the factory.

Click to expand...

Bob the fact of the matter is that as time goes by even the better brands of points are dropping in quality. It's like the voltage regulators currently available. I've seen it a couple of times with people I know where they are bad right out of the box. So for a working tractor electronic ignition and an alternator is making more and more sense just for reliability. Then add that some new battery chargers don't even have a 6 volt setting on them plus the price of a 6 volt battery anymore and the 12 volt EI conversions are a no-brainer. Inexpensive over the long run and LOW maintenance! Heck I even switched my old pony start D4 7U Cat over to 12 volt!

Rick

Click to expand...

I run everything 12v with a resistor and never change points. I take the points out to file them but rarely have to do that. I think I have six tractors on points that I use regularly, the others have magnetos.

Mid '60's MF 35 gasser, service manual, 5 amps max.