WD coil

besides.. as coils age.. their spark potential tends to decline, due to insulation problems. My 8n came with it's oem 6v oil.. sure it -worked- but when hooked up and switched out side by side with a new 6v coil, everything else the same.. the new 6v coil had better looking sparks. That in itself would be a good reason to replace the coil.. that is.. re-fitting an older part with a more efficient one.. and while your at it.. if you are buying a coil anyway.. might as well get a new one... 15$ is not alot to pay during a regular tune up if it gets you better quality spark... and when you are dealing with points.. better spark is always nice, and never hurts..

Also.. not all ballast resistors were used with ignition bypass switch setups. Some used thermal coeficient properties.. I.e. when the ballast resistor is cold.. it's resistance is less.. thus more current inthe primary circuit. Only took about a minute to heat up and increase resistance / lower primary current.. Ford front mount distribuitors used this method.

Soundguy

Soundguy

The energy expended in either the ballasted 6 volt or the internally ballasted 12 volt system is the same. It is about 48 watts (4 amps x 12 volts). In the six volt system, some of the heat is dissapted in the ballast resistor. I believe almost all of the energy consumed ends up in heat in the coil or the ballast resistor and a small percentage is in the the spark. A little experiment is to run a spark plug at 1500 rpm outside of the cylinder. See how much it heats up. They don't heat up much.

Ford did a funny thing on the N series tractors. Even though they were six volt, they still had a ballast resistor. I'd sure like to know the reasoning there. Did you change any of the wiring when you put in the new coil? Is that ballast resistor an example of a thermistor (resistance changes with temperature)?

Denny

As for the ballast resistor on the ford front mounts.. it was mainly because of the square coil that sat on top of the distribuitor was a very marginal product at best, and was prone to overheating.. it didn't tolerate much more than about 3.5 volts.

And yes.. the resistance change in the ford ballast resistor was on purpose... it gave the same effect of the ignition bypass for max volts onthe coil during a cold start. then resistance came up as the ressitor warmed up and cut the current back to nominal levels..

Later side mount 6v units did not incorporate the ballast resistor.

For my test, I had already changed out the wire harness.. but had originally kept the OEM coil.. but changed it out when i saw haow the new coil performed side by side... Old coil was simply degraded and most likely was having insulation breakdown problems after 53 years of hard farm life.

Soundguy

I would say there's a LOT more to the construction and operation of a coil than just the "interuption of 4 amps of current" theory.

The quality of both the windings AND the coil's magnetic core will determine how well that "4 Amps" is converted into usable spark energy to be sent to the spark plugs! Not all coils drawing the same current will produce as "hot" of a spark.

After all, it is the STRENGTH of the core's magnetic field at the instant the points open that determines the amount of energy the coil's secondary kicks out.

I think that's probably safe to say that we are more on the 'agree' than the disagree side... just looking at the same answer from two different angles.

Soundguy

I've split open dead 'standard' and IH 12v coils... no resistor element found.. just copper... Maybee in the 70's you might have found an internal resistor coil.. or possibly vintage restoration quality specialty producers perhaps making 'as original' parts in some overseas factory.. but the run of the mill true 12v coil.. like the napa ic14sb is just copper windings. Remember... length of wire, and gauge effect resistance... not hard to make a 3 ohm 12v primary coil by manipulating length of primary winding, or gauge of wire used.. vs a 1.8 ohm 6v coil.. etc.

So.. yes.. it does make a difference... and not just in cleanliness of instalation.

( for the EE's and nitpickers.. yes.. I'm aware of the difference in dc resistance in a steady state circuit.. and inductive impeadance, and time as a factor.., IR circuits.. tuned and all. been there.. done that.. got my ticket..)

Soundguy

Regarding this current topic of discussion, I have a few thoughts/questions regarding the choice/benefit of EITHER the full 12 volt rated coil VERSUS using a 6 volt coil and a series ballast. Youre an ex engineer also right?? I LOVE these deep technical discussions, here goes, hope we dont bore the others.

Lets look at it in terms of ENERGY. Except for the inefficiencies and heat losses (a coils not a 100% perfect transfer device as we all know) the coils output energy, much of which eventually gets expended across the spark plug gap, corresponds to what energy enters it and can get stored when the points are closed and shes conducting current. Okay, if its a 12 volt coil and shes drawing 4 amps (typical) thats 48 watts of instataneous power input, while the output, of course, is less due to heat and inefficiency losses.

HOWEVER, if its a 6 volt coil (regardless if after a ballast or on a straight 6 volt tractor) and it, likewise draws 4 amps (still typical) thats only 24 watts of input power, correct???

THEREFORE, MY QUESTION FOR DISCUSSION IS

Wouldnt the energy stored in a 6 volt coil when its conducting current, and what eventually gets expended across the plug gap, be LESS THAN the energy stored and expended in a full 12 volt coil????? ????? ?????

HOWEVER AGAIN:::::: I believe (not dead sure on this) some 12 volt coils are "internally ballasted", meaning they have an internal pure non inductive/coil resistance and, therefore, the energy they store in their magnetic field and which gets expended across the plugs gap would be near the same as on a 6 volt coil.

As I understand it, the max curent the points can switch, and still last a reasonable time, is around 4 amps or so. Thats why a 6 volt coils primary resistance (measured between its lil + and - terminals) is only about half that of a 12 volt coil. That way, regardless of voltage and coil (so long as correct) the points still switch around 4 amps AND ITS THE POINTS CURRENT SWITCHING CAPACITY thats the limiting and design requirement factor.

Sooooo oooo QUESTION/DISCUSSION for yall, wouldnt you store more energy (and expend across the plug gap) when using a 12 volt coil then in a 6 volt coil????? ????? ????? ????? ????? ????? ????? ????? ????? ????? ????? ????? ????? ????? ????

I TOTALLY AGREE the 6 volt coil + ballast is pefectly acceptable (still whats on my D 15 lol) and works fine, I just wonder if one wouldnt store and impart more energy across the plug gap when using a 12 volt coil PROVIDED THE 12 VOLT COIL ISNT INTERNALLY STRAIGHT DC RESISTIVE BALLASTED !!!!! !!!!! !!!! i.e. if it has BOTH coil/transformer windings PLUS some straight NON INDUCTIVE resistor/ballast portion. Im just unsure if all its resistance is part of the actual coil/wire windings or if it has an internal pure resistive portion. Seems like some have a separate top portion where its ballast instead of coils, anyone know fer sure????? ???

ONE MORE THING The energy expended across the plug gap is NOT just volts x amps, but volts x amps x time. The firing voltage is a function of the plug gap and the medium (compresion and fuel), so for the same current, to expend more energy, that would just mean a longer arc duration. BUTTTTT TT what is it that ignites the fuel more efficiently n completely??? Is it the raw sudden release of "heat" (caused by current arc gap) or does it ignite better if the current arc is of less amperage (which would cause less heat) but lasts a longer time????? ? Still looks to me regardless, a 12 volt coil has more energy to expend then a 6 volt would????? ?

What ya think Denny and others??? Any good hearted cussin or discussin lol

John T

Now for the equation. The energy stored in an inductor which is put into the secondary and passed to the plug is related to dI/dT. It is the amount of current flowing at the moment of point opening that will determine the amount of energy that will hit the secondary. An inductor is a current device and doesn't give a hoot what the voltage is.

Certainly a new coil may work better that an old one but 6 or 12 volt won't make a difference. One other thing, if the coil was designed to double the spark by using the higher voltage, the designers would have had to build a bigger capacitor inside the distributor. That capacitor, usually called a condensor, would have to be twice as large to absorb that sudden stop of the current through the coil. I believe the designers reasoned correctly. They just modified the system so the capacitor could remain it's current size avoiding a distributor redesign. After all, the spark was hot enough to do the job.

That is my take on the subject.

And a sufficiently hot spark is better than a weak spark because it will fire every time. My studies of thermo dynamics and internal combustion engines says that once the spark ignites the mixture, it doesn't matter how big the spark is or how much energy is in it. What matters is that the spark jumps every time. And a hotter spark should insure that.

In the new electronic ignitions, they are designed to have less heat generated by having a higher voltage and lower current. Plugs now last 100,000 miles plus and they used to last about 10,000. They did improve the materials somewhat but material improvements don't account for much of the total improvement - I'd guess about 10%.

Denny

As I've mentioned a few times over on the "N" board, I've got a distributor machine ("synchrograph") and an ignition oscilloscope.

I've GOT to find some time this winter to test and document various coil and resistor combinations to see what voltage they REALLY put out!

Soundguy

Its the total energy expended across the plugs gap measured as Volts x Amps x Time Im concerned with and still believe a 12 volt coil PROVIDED ITS ALL INDUCTIVE COIL ABSENT ANY INTERNAL BALLAST WHICH I BELIEVE SOME HAVE should deliver more energy. Therefore, given the firing voltage is the same (6 or 12 volt coil) the 12 volt coil might pump more amps and more resultant heat across the plug gap to better ingite the fuel???

My biggest unknown is whether the 12 volt coil has more resistance cuz it has more inductive coil windings,,,,, ,,,OR,,,,, ,,,,, because the top portion of it has a straight resistor stuck in there????? If so, I see no difference in a 6 or internaly ballasted 12 volt coil as far as the available energy to discharge across the plug

WHERES A COIL MANUFACTURER WHEN WE NEED THEM???

John T

Well, nowadays, likely Taiwan or China!

We all know the ampere-turns rules for magnets, and the turns ratio's effects on transformers (not to mention inductance), but I've never been completely sure how all this plays out in a coil in a "Ketterling" igntion system.

Plus the effects of the inductance of the coil, and the capacitance of the condensor forming a "tank circuit" and extending spark duration time by extending the period the coil oscillates after the points open. It's intersting stuff to watch on the ignition 'scope.

I will DEFINITELY have to fire up the test equipment and check out some of this stuff this winter!

Or, perhaps someone can suggest a good textbook that "tells all"!

Isn't a tank circuit something that functions continuously? This is kind of an intermittant circuit. I've got to get out my Electrical Engineering handbook and do some studying. I thought I was done with that when I retired. I guess I need to get on my toes.

Thanks,

I will try n dig that data out n get it to you guys so you can explain it lol.

I agree with Denny that current flowing in an inductor DONT LIKE TO CHANGE, similar to how voltage on a capacitor dont like to change and the condesnor sitting there like an empty open reservoir bank hungry to accept electrons is what keeps them all from arcing across the points to burn them quicker. YOU CAN TAKE THAT TO THE BANK, TRUST ME LOL

We three nerds need to get together or e mail so we dotn bore the others. Mines [email protected] and I have Dennys, whats your Bob????

John T

Thanks for the help.

And as for the coils.. I'd also agree with what was said about a 12v coil that actually included a resistive element... no different than a 6v coil with an external resistive element. However the 12v coil with simply more turns / lower gauge..etc.. i think that is where the extra reserve come in.. again.. probably not useable as the spark jump ovccours as soom as the barrier is overcome. I think the addition of an inline spark gap might show more 'benefit' on the system that was able to generate a higher spark potential, vs one that was already just barely jumping the gap.. etc.

Soundguy

Most ballast resistors are around 1.5 to 1.85 ohms or so, whats yours???

Sooooo oo if youre gonna buy a new coil anyway, I also would use a full 12 volt rated coil and do away with that Ballast Resistor. Again, however, if you use a 6 volt coil YOU NEED THAT SERIES BALLAST.

John T

I'd suggest getting rid of the 6v coil and power resistor and get a real 12v coil.. like a 15$ napa IC14SB. Polarize it correctly... that is.. coil - terminal to the points.

Soundguy

Kent