Coil input information

[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]

Hmmmm.....

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).

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:

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]

A word of caution

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?

[sastanley]

40K volts? Are we headed back to the Drags?

Yup....flying down the creek at 2,000 RPM!

[ndutton]

I will do the math as recommended by Neil to see where I fit in the equation

As I recall you're still running with a points system. If so, this discussion doesn't really apply. Although, I wonder what increasing your dwell would do to coil temperature.

I think but as yet cannot prove a big part of what is aggravating our coils is the dwell common in electronic ignition. What's our A-4 specified dwell, 31 degrees? Well, my Pertronix measured at 62 degrees and there ain't nuthin' I can do about it.

I can't see any other difference between the two (points and EI) but this difference is significant.

[smosher]

More dwell means more amps is flowing through the coil, generating more heat.

If we knew the minimum amps needed to create the spark needed then we can calculate the total resistance needed to stay below the 4 amps

The other solution is maybe there's another coil that can take the higher amps

Steve

[jpian0923]

This is an excerpt from Wikipedia on Resistors:

"The term also refers to an automobile engine component that lowers the supply voltage to the ignition system after the engine has been started. Because cranking the engine causes a very heavy load on the battery, the system voltage can drop quite low during cranking. To allow the engine to start, the ignition system must be designed to operate on this lower voltage. But once cranking is completed, the normal operating voltage is regained; this voltage would overload the ignition system. To avoid this problem, a ballast resistor is inserted in series with the supply voltage feeding the ignition system. Occasionally, this ballast resistor will fail and the classic symptom of this failure is that the engine runs while being cranked (while the resistor is bypassed) but stalls immediately when cranking ceases (and the resistor is re-connected in the circuit)."

I thought it was interesting as to "why" our coils are designed to operate at the lower voltage.

[sastanley]

Jim...my understanding is that coils were originally built at 6 volts & they supplied sufficient voltage for spark plugs to work. the coil technology hasn't kept up with the shift to 12v apparently..This is an entirely layman's answer and I don't really know...just my own personal theory. You'd think a slight change in the number of wraps on one side or the other of the coil would fix the issue.