Coil input information

[ndutton]

The reason for the cooked/overheated coils with the Pertronix 1146A (fixed dwell), is due to the internal resistor in the coils. If you have a 3-4 ohm resistor in the coil, the heat generated by that resistor heats up the coil and cooks it. Remove the resistor from the coil and the source of the heat is removed from the coil.

I just cut open a NAPA Echlin 905 coil (IC14), 3.5Ω measured resistance prior to the surgery. No such resistor inside.

Here are the innards as they came directly out of the canister



. . . and here are the primary windings alone (core removed), inside and out. No resistor anywhere.

Some continue to argue the minutiae of coils and ignition systems but they are arguing against that by applying the basic Ohm's Law statically to limit the system amperage to a maximum of 4 amps per Pertronix's published advisement we have had a 100% success rate in eliminating the previously common coil overheating and failures following the upgrade to electronic ignition. As of this post it has been 8 years of success.

[Dave9111]

Hi Dave, thanks for your explanation regarding the role of inductive resistance in the primary ignition circuit whenever the engine is running. I have a follow-up question regarding the way coil manufacturers add internal resistance. You seem to imply that they add a separate resistor inside the coil. It was my understanding that coil manufacturers vary internal primary resistance by simply using heavier or lighter gauge wire in the primary windings. Would this alter the heat buildup/distribution concern you described? Don

Hi Don,
I know that in years gone by that coil manufacturers added actual resistors in the coil cans to increase the overall resistance and limit the current. Its not hard to find info on those on the web.
Regarding what they do now.... I'm not entirely certain, but I suspect in most cases they are not using actual resistors in the coil, but that they are using resistance wire in the coil for the primary winding.

https://en.wikipedia.org/wiki/Resistance_wire

If you are a huge company like Bosch, its not a big deal to have your wire manufacturer run a batch of wire to your specification that results in X ohms per hundred feet, etc.
The Bosch Blue 00012 coil that I cut apart did not have a visible resistor in the primary winding, however the wire was not fine. It was probably 20-22 gauge wire. If it was pure copper wire it would have taken hundreds of feet of 20 gauge pure copper wire to get 3+ ohms of resistance.

http://hyperphysics.phy-astr.gsu.edu/hbase/Tables/wirega.html

The turns ratio between the primary and secondary is usually about 100:1, so that in itself puts a limit on the number of primary turns.

[Don Moyer]

Coil primary resistance

Thanks Dave, Don

[joe_db]

I will emphasize again the heat produced by a 4 ohm coil is EXACTLY THE SAME regardless of the resistance of the primary winding vs. any internal ballast.
Ohm's law applies

[Dave9111]

I will emphasize again the heat produced by a 4 ohm coil is EXACTLY THE SAME regardless of the resistance of the primary winding vs. any internal ballast.
Ohm's law applies

I agree. It really doesn't matter how the resistance is created, however using resistive wire would probably better spread the heat throughout the coil vs using a discrete carbon or ceramic resistor.

My point before was that the heat is best kept OUT of the coil entirely.




Note 3: The Moyer coil and other 4 ohm coils have been well proven to last on A4s. Empirical data is good here
Note 4: I think a 4 ohm coil produces higher voltage than a 1.4 ohm coil ballasted to 4 ohms.[/QUOTE]

That is really great that you were able to attach pictures of a scope trace!

As you can see this is nothing close to DC! DC would be flat lines that shift up and down as the points go open and closed. The inductance of the primary and secondary limit the current flow and create the "ringing" that you see in the scope trace.
Coil voltage output is determined by the turns ratio of the coil. You only need enough voltage to jump the spark gaps in the distributor and the plug. The other important part is the amount of energy that is released from the coil. However the Atomic 4 is no high performance, high rpm race engine, so its needs are pretty basic. Its more like a 1930's-50's tractor engine.

[Dave9111]

For reference; These are the picts from the internals of a failed Bosch PN 00012 "Blue Can" VW 4 cylinder coil. The Bosch blue coil is rather famous in VW circles. They are suppose to be ultra reliable and are rated at 3 ohms, although I have measured them to be slightly higher than 3 ohms.

This coil was on a Ford Tractor, but it is identical to another Bosch coil that I had fail on my Atomic 4. The tractor is exposed to rain and apparently some rainwater got into the coil.

This coils internals showed signs of water infiltration. It has a potted coil. Some say it is some type of epoxy but it seemed more like some type of stiff silicone rubber. The case itself is aluminum and the top was sealed (not well sealed apparently) by a rubber gasket. There was an iron or steel wrap around the core inside the aluminum case. You can see where rust has caused staining on the inside of the aluminum case from the corrosion of the

The Bosch coil I had on the Atomic 4 that failed worked for probably a couple of hours and then it would stop functioning and the engine would stop. If I let it cool off (it became very hot) it would work for a few minutes and then die again. I later tested this same coil on a bench top and it made a nice blue spark that would jump a 1/4" gap, so I have kept it, but it won't be used in the boat.

I wouldn't recommend using this coil on an Atomic 4 with the 1146 Pertronix ignition due to a heat build up issue.

[joe_db]

IThat is really great that you were able to attach pictures of a scope trace!

As you can see this is nothing close to DC! DC would be flat lines that shift up and down as the points go open and closed. The inductance of the primary and secondary limit the current flow and create the "ringing" that you see in the scope trace.

FYI - I used inductive coupling to the coil lead for the scope, so you are not seeing any DC components. Ringing is a good description of what happens, I think when I counted the divisions on the screen it seems to be in the RF range - 2 MHz maybe?

[roadnsky]

...we have had a 100% success rate in eliminating the previously common coil overheating and failures following the upgrade to electronic ignition. As of this post it has been 8 years of success.

I wonder if we should move this discussion to a new thread to avoid confusing future reader's?
Especially if they just jump to the last page...

[ndutton]

That is really great that you were able to attach pictures of a scope trace!

As you can see this is nothing close to DC! DC would be flat lines that shift up and down as the points go open and closed. The inductance of the primary and secondary limit the current flow and create the "ringing" that you see in the scope trace.

This is incorrect. The direct DC application of Ohm's Law certainly does apply and here's why: With the ignition points closed you have a simple DC circuit energizing - - and heating up - - the primary windings in the coil. There is nothing else going on other than direct current flow during that time (dwell). The resonance happens only when the points open to interrupt the circuit and the stored charge is dumped. Only when the points open does the resonance apply and Ohm's Law does not. It is a simple matter that with the points open there is no DC current flowing.

I wonder if we should move this discussion to a new thread to avoid confusing future reader's?
Especially if they just jump to the last page...

It's probably too late for that. As has been the case for years, we'll just have to let the results speak for themselves. It's too bad we have to keep reminding about those results.

[joe_db]

I wonder if we should move this discussion to a new thread to avoid confusing future reader's?
Especially if they just jump to the last page...

We need a sticky!
If you don't care how coils work and just want to buy one that won't burn out- READ THIS

[ndutton]

We need a sticky!
If you don't care how coils work and just want to buy one that won't burn out- READ THIS

I think we can manage time without knowing how to build a watch.

[Dave9111]

So my Accel Superstock 1.4 ohm coil and ballast resistor setup (part numbers mentioned before) is still working fine.

I recently altered my cooling system (homebuilt fresh water cooling) so I did a load test for 40 minutes and had the infrared thermometer out to check on the cooling system every 5 minutes. (Tied to the dock, boat in gear, churning up the water, engine definitely loaded) FWIW, all temperatures stabilized after about 15 minutes which was faster than I expected.

While I was at it I checked coil temp after running it moderately hard for 40 minutes. The side of the engine block was at about 160 degrees F and the coil registered about 200 degrees F.

Which seems pretty hot, but considering that its bolted next to the 160 engine block, that makes it a roughly 40 degree F temperature rise. Which is really not bad for anything like an electrical transformer.

I did some digging around and finally found some mention of coil design operating temperature as well as some interesting information on ignition coils in general that I thought I would share.

https://www.championpowersports.eu/assets/Beru/ti-07-ignition-coils-gb-2013-lowres-0.pdf

Page 5 mentions -40C to 180C which is a max temp of about 352 Degrees F. So my coil is not anything close to what they would consider hot for a modern ignition coil.

I had no idea who Beru was, but apparently they are big in Europe and they are owned by Federal Mogul.

[Dave9111]

This is incorrect. The direct DC application of Ohm's Law certainly does apply and here's why: With the ignition points closed you have a simple DC circuit energizing - - and heating up - - the primary windings in the coil. There is nothing else going on other than direct current flow during that time (dwell). The resonance happens only when the points open to interrupt the circuit and the stored charge is dumped. Only when the points open does the resonance apply and Ohm's Law does not. It is a simple matter that with the points open there is no DC current flowing.

Your correction is incorrect. :-)
An inductor/ignition coil resists changes in current. A good analogy is a heavy spinning object. It takes energy to get it to spin, and stopping it requires the release of energy. Once it starts spinning it doesn't want to change speed.

That Beru link I just added mentions that a typical coil has roughly 200 turns of primary windings. When the electronic ignition module first applies voltage to the coil primary, zero current flows and then the current flow ramps up until it is limited by the resistance of the coil and wire (if it ever hits max current in the available time). This takes time... milliseconds.

The inductors "natural desire" to maintain constant current is why a capacitor is required in a conventional points ignition. The capacitor absorbs the back emf from the primary coil when the points are opened. If there is no capacitor, a spark occurs at the points and that eats away at the contacts.

[Surcouf]

During this process I've learned or realized a few basic facts as they pertain to coil heat.


Example for Fact 7 or why our coil has run fine for years
Let's say your ignition wiring is deteriorated and/or Heaven forbid you have a Catalina 30 with 2 corroded rubber trailer plugs in the circuit all of which imparts enough voltage drop to reduce your 14VDC alternator output to deliver 11.3VDC to your 3 ohm coil. Using V=IR, V= 11.3, R=3 so the current (I) = 3.8 amps, well within the recommended maximum of 4 amps. Life is good.

Then one day you can't stand looking at all the spaghetti any longer. Perhaps you've been inspired by Msauntry's or Rust's or that PITA ndutton's pics and decide the time has come to clean the mess up. So you rip out the old and install all new wiring using the proper gauge, new corrosion free and tight terminations and no more butt splice repairs everywhere. There, she looks great and functions much better. So much better that the voltage drop is now reduced to a point where you're delivering 13.2VDC to your coil, the same 3 ohm coil that has worked fine for years.

Again, V=IR, V=13.2, R=3 so the current (I) is now 4.4 amps and there's trouble in your future.

Okay, I've blabbed long enough. Hope all this helps.

And here I am discovering that I should have left the ugly spaghetti mess... and probably should not sail anymore without a spare coil?
I am only on page 4 of the 12 and realized that by trying to be a good owner, I may have put myself into a lot of trouble... not even mentioning cleaning all connections on top of the coil from their previous oxydation etc...

I will be on the coil with a voltmeter first thing tomorrow

[roadnsky]

I am only on page 4 of the 12 and realized that by trying to be a good owner, I may have put myself into a lot of trouble...

Don't worry. It a very easy fix and there are a couple of easy answers.