Coil input information

[Kelly]

Just fishing for comments here.

I am in the population of people who have fried multiple coils with minimal use (two that I purchased plus one that was already on the engine when I bought it). I have just recently lined up my ducks by eliminating possibly mis-matched parts in the ignition circuit: new plugs and wires from Moyer Marine, new Pertronix Flamethrower coil (oil-filled; 40,000V; 3.0Ohm) to go with my Pertronix electronic ignition.

I made a few measurements today with my basic digital volt-meter. Positive was taken from the + on the coil and ground was a near-by head nut.

Results:

1)Everything off: 0.25V
2)Ignition switch on: 11.12V
3)Cranking engine: 9.3V
4)Engine started at idle, cold (no alternator): 11.7V
5)Engine idling at 1000RPM w/ alternator excited: fluctuating from 5.4V to 13.5V
6)Engine warm at 1400RPM w/ alternator : settled at 14.04V
7)Engine warm at 800RPM: 13.0V

5, 6 and 7 are with the engine in gear.

I am way over my head here so any comments? Missing information?

[hanleyclifford]

Oddly enough it seems that the members most diligent about ignition systems are the ones burning coils (right, Shawn?). I don't like #6, 14.04 volts but I'm not able to explain exactly why. I still run points and condenser with automotive type (cheapo) coils. Usually I test less than 10 volts at coil+ (no external resistor), BUT, I run my electric raw water pump and fuel pump on the same circuit. I'm afraid this thread could empty the barracks (again).

[Kelly]

Originally Posted by hanleyclifford

Oddly enough it seems that the members most diligent about ignition systems are the ones burning coils (right, Shawn?). I don't like #6, 14.04 volts but I'm not able to explain exactly why. I still run points and condenser with automotive type (cheapo) coils. Usually I test less than 10 volts at coil+ (no external resistor), BUT, I run my electric raw water pump and fuel pump on the same circuit. I'm afraid this thread could empty the barracks (again).

That's a virtual risk I'm willing to take in order to understand why I can't dial-in a consistent performer with my A4.

All hands on deck!

[Mark Millbauer]

From a WEB article on ignition systems:
"The coil is designed to operate on 9 volts. Battery voltage (12 volts) is reduced to 9 volts by the Ballast Resistor. When the ignition switch is in the run position, the coil is powered through the Ballast Resistor feeding it 9 volts; but when the ignition switch is turned to "start", the Ballast Resistor gets by-passed. This feeds full battery voltage to the coil for better starting. The starter motor is drawing battery voltage down to about 10 volts at this time."

We must either run a ballast resistor of the correct resistance for the volts our system is feeding it or, as Moyer states, a coil with internal resistance. It too must have the correct resistance for the voltage our system is trying to shove through it.

The type, operation and condition of the ignition switch is a key component here as well. As is the output of the charging system.


mark

[sastanley]

Hi Kelly, Just for grins, can you measure the static resistance of the coil before you turn on the key? How many hours do you have on the new Flamethrower?

My 'dead' Flamethrower was in the 3.3 ohm range (I have to check my notes to confirm) at rest (cold), and 4.2 or 4.3 ohms when it would fail 25 minutes later. However, the voltage at the coil as the engine sputtered to a slow death never faltered from 13.94volts. No real way that I can tell to measure the secondary output voltage while the coil is active...except for a visibly weak spark that wouldn't start the motor again when I cranked it.

I need to measure my new coil after I've run the engine, with the key off, to see if the resistance stays constant or is the same as it was cold..which I think it should. I think the resistance went up and caused the bad coil to fail...or rather, the higher resistance at failure is a symptom of a 'fried' coil...I am purely guessing here that the resistance gets high enough that the coil can no longer produce a reliable secondary spark (to the plugs) and it dies. I would expect a good coil's resistance to stay constant.

[hanleyclifford]

Originally Posted by Mark Millbauer

From a WEB article on ignition systems:
"The coil is designed to operate on 9 volts. Battery voltage (12 volts) is reduced to 9 volts by the Ballast Resistor. When the ignition switch is in the run position, the coil is powered through the Ballast Resistor feeding it 9 volts; but when the ignition switch is turned to "start", the Ballast Resistor gets by-passed. This feeds full battery voltage to the coil for better starting. The starter motor is drawing battery voltage down to about 10 volts at this time."

We must either run a ballast resistor of the correct resistance for the volts our system is feeding it or, as Moyer states, a coil with internal resistance. It too must have the correct resistance for the voltage our system is trying to shove through it.

The type, operation and condition of the ignition switch is a key component here as well. As is the output of the charging system.


mark

Thank you, Mark; your post represents the conventional wisdom and still merits our attention.

[Kelly]

Shawn,

I'll make the measurements the next time I can make it down to the boat- should be tonight or tomorrow at lunch at the latest.

My Flamethrower is less than an hour old. Measured Volts at the coil + seem to reflect yours (13-14V). Taking into account Mark's response, I would like to think that my internal resistance coil is the perfect match for my electronic ignition (both Pertronix). My installation is very basic...I've just "upgraded" to the electronic ignition in the hopes of having fewer parts to adjust.

[smosher]

I don't know what a coil is rated for in watts, but here's the calculations
based upon a 3.3 ohm coil.

14.2 volts / 3.3 ohms = 4 amps

4 x 4 x 3.3 = 61 watts

12 vdc / 3.3 ohms = 3.6 amps

3.6 x 3.6 x 3.3 = 47 watts

61 / 47 = 130 percent

We know heat kills coils and at 14.2 volts the coil has to sink 30% more heat.

To decrease the amps in a 14.2 system to the draw in a 12 volt system you would add a ballast resistor to the coil.

14.2 / 3.6 = 4 ohms - 3.3 coil = .7 ballast.

So to me this means that if we add a ballast resistor we can reduce the heat
in the coil by 30% and still provide the 14.2 to the battery.

knock on wood, as I have an electronic ignition and I have used both a pertronix and an autozone coil, both oil filled and for 5 years I haven't had a problem. My Alt charges at 14.2 volts. The pertronix coil moyer sells is epoxy which is for vibration area's, oil coils have better cooling.

The question is what coil and where are they mounted ?

Steve

[sastanley]

Kelly, you essentially have the same setup as I had which just failed, however, seems to work just fine for everybody else. To remedy the problem I had this summer of running from storms in 15 minute chunks until the coil would die, I've gone to a redundant coil system: I have a (identical to the recently failed one) 3 ohm oil filled Flamethrower as my backup, and I am currently running a 1.5ohm (Accel brand) oil filled coil with a 1.5 ohm resistor in front of it, as recommended by Pertronix. I figured after burning up the 3 ohm coil, why not?

Full disclosure - I've screwed up my 'testing grounds' too by dialing down the voltage a little bit..Those numbers reported above were in the "as failed" running conditions..I am seeing something in the 10v range at the externally resisted coil now. I'll have to do further testing (sorry, going cruising this weekend!) on the readings of the new 3 ohm coil to compare to my dead 3 ohm coil with the updated voltage settings. So, essentially, I've changed three things...a new externally resisted coil, an internally resisted coil as backup, and the voltage I am sending to the coil.

So much for following my own suggestions for a methodical approach.

[JOHN COOKSON]

But here goes anyway R\E electronic ignitions.

I don't think burned out coils are the problem. They are a symptom of a bigger problem.

To me burned out coils mean the electronic ignition is acting up. Why do some EIs work fine and others fry coils? (as others have noted)

Maybe some dwell readings would be helpful. Dwell with engine (and EI) at idle cold, and dwell with cold engine reved up. Then dwell with engine (and EI ) warmed up at idle and then dwell with a throughly warmed engine (and EI) reved up.

Just an idea. My $0.01 for the day.

TRUE GRIT

[hanleyclifford]

Originally Posted by JOHN COOKSON

But here goes anyway R\E electronic ignitions.

I don't think burned out coils are the problem. They are a symptom of a bigger problem.

To me burned out coils mean the electronic ignition is acting up. Why do some EIs work fine and others fry coils? (as others have noted)

Maybe some dwell readings would be helpful. Dwell with engine (and EI) at idle cold, and dwell with cold engine reved up. Then dwell with engine (and EI ) warmed up at idle and then dwell with a throughly warmed engine (and EI) reved up.

Just an idea. My $0.01 for the day.

TRUE GRIT

Interesting questions raised here. I would like to see some dwell data from the EI crowd. We know that the EI has greater dwell than the point ignition and that greater dwell imposes a greater heat burden on the coil. The fact that some EI systems work and others don't might be related to actual, effective, cruising voltage at coil+ which can reflect dozens of electrical system differences on our boats. Coil+ is where "the rubber meets the road", so to speak.

[smosher]

The ei does have a larger dwell than the points, larger dwell more heat in the coil.

All comes back to more heat in the coil.

Mine is installed on the engine in the original location. I wonder if someone
has remoted the coil and it had failed.

I think this we though I'll hook up a 1/2 ohm ballast to the 3.3 ohm coil and see if it works.

The primary side resistance is 3 ohms, while the secondary side is in the 1000's of ohms.

[sastanley]

I am guessing my regular run-of-the-mill multi-meter doesn't do dwell.

edit - steve, sorry I missed your post until now. Yes, my failed coil was remotely mounted, as shown in this picture taken earlier this spring. That is actually the dead coil, and the location where it lived the last 26 months since it was new in 2009. My original bracket rusted off, and the mounting bolts are solid in the block, so I just left them there. It would be a bear to remove them to re-mount a coil to the engine.

[JOHN COOKSON]

My theory is that it is a heat related problem with some EIs that is manifesting itself through the dwell angle.

By proving or disproving this theory hopefully some light will be shed on the final answer to the problem.

TRUE GRIT

[ndutton]

As part of my ongoing testing of another theory I have already measured EI dwell. My Pertronix dwell is 62 degrees and this is pretty much in line with an email exchange I recently had with Hot Spark, another Hall effect electronic ignition manufacturer who specifies a particular unit for the A-4. Theirs is 50 degrees.

[smosher]

Hi Shawn, was that a 3 ohm oil filled flamethrower ?

Steve

[Loki9]

Hey Shawn-

An off topic question: where can I find a raw water strainer like the one that you have? Who makes/sells it?

Thanks!

-Jeff Taylor

[ndutton]

Here is Pertronix's discussion on input voltage, primary resistance and acceptable levels:

What type of coil can I use with the Ignitor™? How do I check my coils resistance? (12V negative ground only)

To determine if your system's coil is compatible with the Ignitor, some measurements should be taken prior to installation of the Ignitor. Caution… While performing this test, never leave the ignition switch on for more than 30 seconds at a time.

Set your voltmeter to a 15 or 20-volt scale. Attach an 18 or 20 AWG jumper wire from the negative coil terminal to an engine ground. Attach positive (red) lead of your voltmeter to the positive side of the coil, and the negative (black) lead to an engine ground. Turn the ignition switch to the run position. Now read the voltage at the positive coil terminal. Turn the ignition switch off. If the voltage measured is approximately 12 volts, no resistance wire is present. A typical resistance wire will provide 9 - 6 volts.

The next step is to determine the resistance in the primary ignition. Label the wires attached to the coil terminals and note their appropriate location. Make sure that the ignition switch is off and disconnect all wires from the coil. Adjust your meter to the lowest ohm scale. If you are using an analog style meter make sure to zero the needle.

Measure from the negative terminal to the positive terminal. Write your measurement down.

Now the maximum system amperage can be determined, divide your voltage measurement by your coil resistance measurement. This will give you the system current or amperage.

Four and six cylinder engines should not exceed 4 amps. Eight cylinder engines should not exceed 8 amps. If the total amperage in your system is higher than the amount recommended for your application, you should install a ballast resistor.

If you have 14.2 volts at the coil terminal and a 3 ohm internal resistance coil, your amperage is 4.73, that's too much according to Pertronix.

My view on this is to avoid tweaking down the voltage regulator because of the negative resultant effect on battery charging. I believe a ballast resistor is the preferred method to maintain the 4 amp maximum and maybe a little less, remember 4 amps is a maximum.

[hanleyclifford]

Great research, Neil - I think you have nailed it down for us. BTW, I agree that for most members it is not wise to lower alternator output voltage below 14 v.

[Kelly]

I would like to run a few more tests as I try to get my head around all this.

The calculations are clear and would seem to point me in the direction of adding a ballast resister (1.5 ohm) in front of the coil+ in order to reduce incoming volts to the coil.

In my case we have:

14.04V / 3.0 ohms = 4.68 amps (or 13.0V / 3.0 ohms = 4.33 amps in the best case scenario).

Both of these values are outside of the acceptable range. Adding 1.5 ohms resistance would give us:

14.04V / 4.5 ohms = 3.12 amps

I assume this would also mean running a wire from the starter+ to the coil+ to have full battery volts while cranking?

And all this begs the question: why are the volts measured at the coil+ too high in my basic installation? Is this not the case for everyone?? If we reverse the formula for a circuit with 3.0 ohm resistance at the coil and 4 amps maximum desired at the coil+ we get 12V maximum. Any time you charge the battery you're going to exceed this value.

This would also mean that the condition has existed "forever"?

Are we chasing fireflies here?

[ndutton]

If we accept Pertronix's advisory as gospel, you are correct Kelly, anyone with an alternator that charges at more than 12 volts (that's all of us) and have a 3 ohm coil have trouble in our future.

So why the difference between those of us with and without overheating coils? I'm guessing there are variables from boat to boat:

1. Charging voltage - the higher the charging voltage the higher the amperage and the farther away from the specified maximum.
2. Ammeter or volt meter - those long ammeter wire runs that produce voltage drop while bad for the battery may be helping the coil.
3. Engine run time - the longer the run time the hotter the coil. Heat build up is cumulative. I believe heat related coil damage is also cumulative.
4. Oil or epoxy filled coil - Pertronix's own literature says oil filled coils are more heat tolerant.
5. Internal coil resistance - How accurate is the 3 ohm figure from coil to coil? 1/2 ohm either way can make a big difference.

I have the Pertronix ignition and their 3 ohm oil filled Flamethrower coil that is performing well. I'm adding a ballast resistor ASAP as a precaution and will measure coil temps as soon as it's done. I've already measured the temps on the current system so I'll have something to compare.

As far as what size resistor, I'm figuring the charging voltage from my fixed point alternator at a worst case scenario of 15 volts (no ammeter run), will measure the internal coil resistance and calculate the target system amperage at 3.75 amps (see edit) (1/4 amp margin of safety). Assuming the coil is at precisely 3 ohms (before actual measurement for the sake of this example only), I'll need a 1 ohm resistor.

Coil temperature measurements will be the acid test but I'm kind of excited that finally there's something solid to follow instead of grasping at clouds.

Anyone else interested in making coil temperature measurements, it would be best if the measurements were made both before and after the addition of a resistor for comparison.

edit:
Later on in the testing process I arbitrarily decided to lower the target amperage to 3.4 amps or 15% below the maximum for a wider margin of safety.

[sastanley]

Originally Posted by smosher

Hi Shawn, was that a 3 ohm oil filled flamethrower ?

Steve

Steve - Yes..it is oil filled..the only difference is it was just the chrome model (#40501). My new one is the boring black (#40511).

Originally Posted by Loki9

Hey Shawn-

An off topic question: where can I find a raw water strainer like the one that you have? Who makes/sells it?

Thanks!

-Jeff Taylor

Jeff - No problem - Neil turned me on to that cool simple strainer. Check out the "BoaterBits" store on ebay..they sell them for all types of different hose sizes..and cheap! Who needs a $200 bronze strainer? Also, here is a link to their website - http://www.boaterbits.ca/

and now back to our regularly scheduled programming:

Neil, Wow..this is interesting information to say the least. However, your theory is supported by some facts that a typical older installation (mine certainly met that criteria) with long runs and voltage drop between the alternator and the coil (& possibly undersized wire with old, or inferior terminations) could be helping the coil.

Remember this spring, the ONLY thing I did was remove my ammeter completely from the circuit and replace all the primary (4 gauge) cables in my electrical system with nice new wire & nice tinned copper lugs. The runs actually got longer, but I eliminated a lot of small wire sizes & inferior connections. So, the result, the first 1+ hour run on the coil, BAM!, failure.

As to your question about coil & ballast resistance as compared to what is on the packaging: My personal experience has been that the numbers run slightly high, meaning they are built with a tad more resistance than advertised...maybe providing a little bit of a safety net, but not when you jam it with too much voltage and fresh, big gauge wire runs like I did.

I did not measure voltage the way Pertronix recommends. I did my readings right on the two terminals of the coil. I can re-measure pretty easily.

So, with that, & working from memory (my notes are not with me at work):
My NAPA/Echlin 1.35 ohm ballast resistor = 1.6x ohms (part # ECH ICR11)
My Accel 1.5 ohm coil = 1.70 ohms.
Need to measure my new Pertronix 40511 oil filled (boring black) coil = x.x

currently in the spares bin -
My dead Pertronix 40501 oil filled chrome coil = 3.3 ohms
My NAPA/Echlin 1.82 ohm ballast resistor = 2.1x ohms (part # ECH ICR13)

When my charging voltage jumped with the new wires to near 15v (i know, too high) I was seeing 13.95-14.05 volts at my (now dead) coil. That puts the amps at 4.26. That sounds to me like it is over the threshold. When that coil was seeing 13.1-13.2v last year with old cabling, I was probably right at the edge. Actually, 13.2/3.3 = 4.00amps

Now, I have done the following:
Adjusted my charging voltage down to 14.1v
Currently running the 1.35ohm resistor ahead of the 1.5ohm coil. Using actual numbers measured above that is about ~3.3 ohms. Assuming we have a drop of 0.9 volts at the coil to 13.0v from the lowered charge voltage I am right on the edge at ~3.93 amps. I need to measure this to be sure, I think I mentioned somewhere else I was seeing lower voltage than this at the coil.

So..there's my numbers..Neil, I am thinking about maybe incorporating BOTH resistors into my system..maybe trying the 1.35 ohm in front of the 3 ohm coil and the 1.82 ohm in front of the 1.5 ohm coil and re-testing. It may also be interesting to try one of those resistors in front of the OLD coil and see how long it would last.

[joe_db]

See my notes:

Originally Posted by Kelly

Just fishing for comments here.

I am in the population of people who have fried multiple coils with minimal use (two that I purchased plus one that was already on the engine when I bought it). I have just recently lined up my ducks by eliminating possibly mis-matched parts in the ignition circuit: new plugs and wires from Moyer Marine, new Pertronix Flamethrower coil (oil-filled; 40,000V; 3.0Ohm) to go with my Pertronix electronic ignition.

I made a few measurements today with my basic digital volt-meter. Positive was taken from the + on the coil and ground was a near-by head nut.

Results:

1)Everything off: 0.25V BAD should be 0. Leaky switch someplace?
2)Ignition switch on: 11.12V LOW - either bad wiring or a really low battery
3)Cranking engine: 9.3V LOW see above
4)Engine started at idle, cold (no alternator): 11.7V A little low - my alternator will provide current at idle
5)Engine idling at 1000RPM w/ alternator excited: fluctuating from 5.4V to 13.5 Very odd - should be steady around 13.5
6)Engine warm at 1400RPM w/ alternator : settled at 14.04V Normal
7)Engine warm at 800RPM: 13.0V Low to normal, depending on the electrical system total load5, 6 and 7 are with the engine in gear.

I am way over my head here so any comments? Missing information?

[ndutton]

Before we start piling on a bunch of resistance on the input side of the coil we need to consider the output as well. Having a cool running coil that puts out a weak spark is not a solution. Accordingly, not any random resistor will do.

I can speak only to my system and how I intend to approach this new strategy:

• I'll do a visual spark check off the coil lead to the block before changing anything.
• I'll accurately measure internal coil resistance at rest and coil input voltage with the alternator under load, engine at 1500 RPM minimum.
• I'll do the calculation with a target amperage of 3.75 amps (see edit) and add a resistor to achieve that balance as close as possible.
• Repeat the coil wire spark to block test for comparison.
• Run the engine for 1/2 hour and read coil temps every 2 minutes (already did this with the current system) and compare.

Regarding coil spark output, as I recall the standard points type coils were 28K volt. The Pertronix Flamethrower I installed as part of the conversion to electronic ignition is a 40K volt coil so I'm thinking I could tolerate a 30% output reduction and still run as well as when I had the old points ignition and original coil.

Dang this is interesting.

edit:
To repeat, I eventually lowered the target amperage to 3.4 amps for a wider margin of safety.

[hanleyclifford]

This has turned out to be one of the more interesting and informative threads in a while thanks in large part to Neil and Mark and others. Good shot Kelly! Since the coil (automotive type) is designed to run on 9 volts it seems we have a large voltage cushion to work with. I will do the math as recommended by Neil to see where I fit in the equation. 40K volts? Are we headed back to the Drags?